In the wild, you will very rarely find an ungrounded system that reads 0VAC to ground/earth. Modern multimeters are sensitive enough, with high enough impedance that the uA of capacitive leakage is often enough to provide a reference for the meter, and it will usually read in the 50% (60 VAC) range on either pole of the 'ungrounded' system. The minute current would still not be enough to even be perceptable as a 'shock' so this isn't a problem - but it has thrown a number of electricians for a loop when they THINK it should be 0 (as indicated in this video), when in fact it can be and range of voltages between 0 and 120 (depending on how even the leakage current is from each leg).
I’m confused. You read 60v on each leg because ungrounded systems are typically three phase and each ungrounded conductor is about 68 volts 1.732 out of phase with each other in order to get 120V. Or at least that’s how it is on boats. Is that not how it works in healthcare facilities?
When I was an electrician in the Navy, we ran all our electrical systems as ungrounded. This wasn't for safety but for reliability during battle. The idea was, if a conductor got grounded due to 'battle damage', you didn't lose power to vital equipment because there was no complete circuit. Standing watch, we had a device (called simply, 'ground detector') that measured insulation resistance to ground while system was energized. If it went below about 1 Mohm, we had to go through a process to isolate the faulty equipment. And because the entire ship is metal, and cabling running everywhere, the 'leakage capacitance' was pretty high and we couldn't do much about it. So it was NOT SAFE to touch a live wire as the leakage current was enough to kill you. And of course, we had an old safety film that was required training for Electrician's Mates "The Deadly Shipmate".
You said at the very end that if you have one of the ungrounded conductors go to ground that it would be a short circuit. Ground is isolated though so maybe I’m misunderstanding something but doesn’t look like a short circuit. Some current will flow but not very much. Again not a complete circuit.
It's topics such as this that make me extremely grateful for my path into theory and for my early teachers. Immersed into electronics theory first has given me the thousand foot view
Learn quite a bit here, and I'm a journeyman currently working on getting my masters license next year, but I've never seen this system and didn't realize it existed, but I do mostly residential and occasionally commercial. I understand the concept, much like the ungrounded delta systems that you sometimes see in older manufacturing facilities, not a system commonly used nowadays but nonetheless very useful in a situation where unexpected shutdown of equipment caused by a ground fault could result in damage or injury.
Thank you for that explanation. I am not an electrician nor an engineer, but retired from a power plant and dealt with lots of transformers. I had a pool installed last spring, and I just couldn't figure out how the isolation transformer protected me from a fault on the underwater light. After watching this video, I looked at the schematic drawing inside transformer again. The ground shown is not for either coil. (draw a lit light bulb over my head).
I came across one of these awhile back and when I put my meter leads on either L1 or L2 to ground I was showing 60 volts. No matter what wouldn't it find away back to the source? You make the statement at the end if the live wire were to touch the metal plate it would trip the breaker. The only way for that to happen is if there's a path back to the source.
yes, it's like a split phase system, but there's no grounded service conductor, aka "neutral". So it's a floating system. If you take earth as your reference, there is still a potential, you can still get shocked. I bet the operating table is very well insulated, and for wet conditions.
@@wim0104 Just the opposite, operating tables are quite often steel, and grounded via the EGC. 'back to source' just means back to the secondary of the isolation transformer. The reason you read 60VAC is that there is no such thing as a perfect 'open'. Air conducts electricity. Wire insulation conducts electricity. The plastic used to construct the receptacles conducts electricity. None of this is a lot of conductivity, but it is never 'zero'. This means that the ungrounded system IS ever so lightly connected to 'ground' from both legs. If this conductance is near equal, which is likely as the wiring is all parallel, then your high impedance sensitive multimeter will still measure JUST enough current to read the 60VAC you are seeing.
Question... would tying the ground of the isolated system with the ground of the "SUPPLY" To said isolated system would that clear ground faults if they were to occur?
I've never seen a system like this before, thanks for explaining it in a way I can understand. My insructor back in 2010 mentioned something about to 60v legs being the safest electrical system, and I did google it at the time, but never really go to the meat of what he mentioned. today its case closed on that memory
At the large hospital that I retired from at a meeting with so called LIM engineer and two other from the company that we purchased over twenty replacement LIM panels during OR remodeling asked them where is the label that provides the fault current. No e of the three know what I was asking and never provided information after I asked for it several times. If I was in charge they would not get final payment until they installed NEC required labels. Had the same problem with two JCI 1,750 HP chillers. They were each feed from 13.2 KV from switchgear room to inside a 18' long panel that had a transformer reducing 13.2 to 4,160 bolts that feed a 4,160 VFD. Asked for over a year for required arc fault labels and kept telling me they are working on it.
What's the purpose of ground in this picture? Why don't residential houses have isolated systems with an isolation transformer going into the house at the service drop?
probably a dumb question but why then do we not have these in our houses? it seems like the safer of systems to be ungrounded - i assume cost is one reason but is there more obvious reasons too?
A great explanation, Ryan! One question: In this Isolated Power System, are there any polarity COORDINATION considerations BETWEEN the grounded and ungrounded PRIMARY supply AND the two ungrounded SECONDARY conductors to the LOADS (receptacle and lampholders, in your example)? If the SECONDARY conductors are protected by a 2-pole breaker and there’s no grounded (neutral) conductor, why would it matter to POLARIZE by a ORANGE-STRIPED to the receptacle “WHITE” screw and to the lampholder shell AND by a BROWN-STRIPED to the receptacle “BLACK” screw and to the lampholder base center contact??
Electrically it doesn't matter - I honestly think the strict adherence to color matching the legs is more about ensuring every single bit of the highly protective system is built perfectly - so don't leave anything to chance of the whims of a lazy electrician.
@@RyanJacksonElectrical Here's a scenario it prevents: Take two devices which both expose the operator to voltage in the exact same manner. Say two tools or lights which both have a part which is "live" from the brown wire, but is not contacting ground. If everything is wired the same nothing happens when someone touches both lights at that point. However, if the second light was plugged into an outlet which was wired with the opposite polarity, that person would be electrocuted. A defect could mean that all lights manufactured within a certain period of time are defective in the exact same way. Bulk purchasing means having two from the same batch is extremely likely. It's not likely, but it's a "free" risk mitigation.
I don’t work in such facilities. You lost me at the two pole breaker. I guess I’d have to see the installation to understand it. Other than that, all good.
I have an adblocker, but I turn it off on your videos and watching them till the end, so at least your work can be supported somehow by myself. Keep up the good work, sir.
Thanks for your informative video Ryan, for a time this "balanced power" was installed in recording studios and other AV applications to avoid ground induced noise. I have also seen this onboard steel hull ships to avoid electrolysis at hull joints.
I believe that both the common marine galvanic isolator and the uncommon marine isolation transformer both retain a bonded connection of the secondary neutral wire and boat ground wire. The neutral bond is inside the secondary wiring of the transformer, and the shore ground is there but completely isolated from the secondary boat ground. In a marine isolation transformer the difference is that shore ground is completely separate from boat ground, and in a galvanic isolator the two grounds are connected but separated by a set of parallel, opposite polarity diodes with a 1.4V forward drop either way. So, the marine setup is fundamentally different than the isolation described here in operating rooms, where ground and neutral are separate when testing with a multimeter.
When you measure voltage on a ungrounded conductor (L1 or L2) to grounded source in a installed live system in a OR you will measure roughly 60v volts (it vary's between 50v-60v) Source: I have Safety tested 15 OR's for 9 years as a maintenance electrician. Another interesting fact our non monitored isolation transformers (1500va) have lower leakage current circuits than our systems with LIM (line Isolation Monitor) No LIM usually less than 20uA, LIM ranges 150uA-270uA. Enjoyed your video and appreciate the knowledge sharing.
Yes, I service quarterly a Marine Well Containment platform, and it has an ungrounded system. It thru me for a loop the 1st time I opened the service panel to throw the breaker for a fire alarm panel and found it to be 20A double pole. I was installing a Surge Protection Device on the fire panel's primary 120Vac power. When measuring across safety ground and either line conductor I also read somewhere around 50 - 60 volts.
I work in a shipyard and onboard shore power fed vessels I read about 60v on each leg to ground. When looking for ground faults with a 3 light ground detector installed at the panel, it has been pretty easy to isolate by shutting of breakers until the ground fault disappears. However, I have ran into a ground fault on a breaker connected to an audio system with back up power and hit a wall going further with isolation. I heard that it is not necessarily a fault in the equipment but a lack of capacitive balance between the three phases. It's new to me and I'm learning about it as I post this.
If you're wondering why the text on the receptacle is upside down, it's because receptacles are installed ground side up in healthcare spaces. (you can tell it's a healthcare receptacle by the green dot.)
@@mrpotatohead161 Not always. I've seen thousands of receptacles in health care facilities that are installed with the ground down. Proposals to mandate an orientation in the NEC have been rejected many times.
Excellent video. I was an electrician who changed careers and now works in ORs. Isolated OR systems is actually taught in Anesthesiology Residencies and tested on, Nursing has annual education on the subject. All equipment in the OR is routinely tested for proper grounding. Most common occurrence is when a "bad" piece of equipment is plugged in, the "isolation monitor" will alarm. At any other time, when it alarms, procedure is to unplug equipment in reverse order of how it was plugged in, IE Last piece plugged in is the first to be unplugged and repeated till the alarm clears. That equipment is then tagged out for evaluation and repair.
As a kid, I'd see the TV repairman insert an isolation transformer(1:1) between receptacle and TV before working on it. Yea, there were TV repair folk back in the day and TVs did break and people did fix them. The isolation XFMR in that case served the same purpose...no earth reference....for his /her safety.
this is similar to using an old school light bulb with a filament in stead of a safety fuse: the resistance of the filament goes up when current goes up. This helps with diagnosing an overcurrent inside the equipment.
Your question assumes it is grounded but it is not. There is 120 V between the legs. Each leg is 0 V to the ground. Think about a 1.5 V battery. It would make no sense to say each pole is 0.75 V? Voltage is always relative. There is no absolute voltage. This rather confusing. We can say that a leg is 120 V (for example) only because we have grounded the system. That is we have deliberately connected the system to the ground with a ground rod. Note that a system can also become accidentally grounded. An isolated system in that case stops being isolated but it still works. Likely you do not have 240 V equipment there or if you do, you have a separate system for them. . At surface one might ask why do we ground as isolated seems to be safer. Well you are not the first one to think so. In fact before 1899 grounding was banned (do not confuse this with the ground prong on the socket, this has absolutely nothing to do with it). However, it did cause problems so in 1901 it was recommenced and in 1913 mandated. Ungrounded systems can get over-voltage which causes arbitrary voltage to the ground because of lightnings, accidental touching of high voltage lines etc. The ground prong was later added to reduce the risk of shock that grounded systems have. Isolated systems are typically used in things like hospitals and ships. Norway is the only country where they are widely used to my knowledge and they typically have a high impedance connection to the earth for over-voltage. They do not distribute the neutral, just three phases 230 V between each two.
This is a nice introduction but there are many more significant details to cover that need to be looked at hopefully in future series. While you can use an ungrounded system we must always remember in the operating room ground always exists even for an ungrounded electrical system. This means an ungrounded system is much more than the isolation low kvA transformer, line isolation monitor, XHHW wire, receptacles, breakers, heck power cords including all conductor in them need to be insulated. There are issues around insulation failure of electrical surgical equipment, monitors etc creating more dangerous leakage currents. Here testing and maintenance of those individual pieces of equipment should be regularly undertaken thats other standards beyond NFPA70. There should be a higher bar also on maintenance and monitoring of isolated ungrounded power systems that need to be understood not just by maintenance electricians but also medical staff in the operating room. Also you could make more of a connection between ungrounded system and emergency backup systems in the NFPA70. I am not surprised this area is not well understood the more you can do on this series using the hospital example and scenarios of faults in equipment or system components the better people will understand ungrounded systems. There was a good article in the IAEI magazine in 2007 on this worth looking over. iaeimagazine.org/2007/july2007/isolated-power-systems-in-health-care-facilities/
Many generators, and dc-ac power inverters, are also ungrounded systems. They usually call these "floating neutral". Like your example, if you measure either line to the case of the generator/inverter you frequently get 0 volts. This is why many generators do not have GFCI protected outlets. This is also a factor that helps make it possible to parallel the inverter type generators.
Please allow me to ask in earnest, is there a way to synchronize the phase and frequency of these inverter generator systems or is it done automatically looking at cumulative voltage considering summing vs subtractive interference?
@@jeffreystroman2811 Yes. Automatic synchronization is done by every grid connected solar inverter. What's more interesting are AC generators. In that case, the hard part is determining when they line up to connect them. Once that happens, the electrical coupling forces both systems to spin at exactly the same speed.* So as long as you use timing lights, or an automated equivalent, you can manually synchronize AC generators and tie them together into a larger system. Note that doing this at home using home-made timing lights might be an interesting project, but it is dangerous and almost certainly violates the NEC. Connect them at the wrong time and things will go bang. * Simplifying
You mentioned that one of the wires has to be colored brown, and the other one has to be colored orange. I know that the NEC doesn't require colors for each leg of a three phase system, but generally people use black red blue and brown orange yellow to distinguish between phases. Does the same practice apply to ungrounded systems? Are there three phase ungrounded systems like this? Or only single phase?
For an ungrounded delta, usually people just use the normal black, red, blue or brown, orange, yellow. If it was in a hospital, however, 517.160 specifies the colors.
The specific bits this is talking about is for hospital use, and is only really for equipment likely to come into contact with a patient during a wet procedure - which is all 120V. As such, I have never seen a medical isolated power system that was anything but 120V single phase. There are a number of ungrounded three-phase systems out there - but most are military and marine systems, and as such, not subject to NEC rules anyway.
This was a great video. I’ve personally never experienced working with this type of system but it was cool to see what it’s all about and the application. Thank you.
Used this to help me figure out current flow on a home generator (bonded vs un-bonded system. At the generator). My belief is that you would (float / break) the ground and neutral at the generator, so that in a fault (in the home circuit), current would flow thru the ground, to the ground bar passing it to the neutral ( in the load center) back to the generator coil (shortest path). So that current would not flow out to the generator receptacle plug (energizing it, being grounded to the frame) and then energizing the generator frame back to the neutral (if it remained bonded and not floating). I think.
Great instructor. Your way of teaching is clear, human and straight to the point. 👏 So, trying to understand the theory myself. There’s no difference of potential between the secondary coil and the metal box, although this one is connected to the earth/dirt, because there’s no circuit through the induction between the secondary and primarily coils. it would be such a voltage between the primarily coil and the metal box if it was grounded. Am I close or way far off?
Correct, the primary is a grounded system. The enclosure of the transformer (metal parts) would be connected to the equipment grounding conductor of the supply circuit (the primary), so there would be a voltage there.
In a system with no faults, would you not see voltage on both L1 to G and L2 to G? And then in the event one of the lines were to have a fault, voltage would drop to zero and then full voltage on the other line?
No, there is no voltage from L to G in normal condition. Under a fault you would get 0V from G to the faulted line, 120V to G on the line that isn't faulted. The faulted conductor really just becomes a grounded conductor at that point.
Since they can only reference each other(there are no grounded conductors), the only potential is between each other...120V. Otherwise is undefined/don't care or zero(Static charge only). It does make trouble shooting a bit more difficult since for voltages measurements, earth means nothing. For industrial controls, I always 'ground' a leg of a power supply. It is a real pain to diagnose circuits(control circuits especially) when there is no ground reference(floating system). 'Floating' systems are a tricky thing to diagnose.
I wonder if a modern GFCI circuit wouldn't work just as well, but without all the extra difficulty and cost that goes into building this system, not to mention the need to deal with hazard current.
the main feature of this "ungrounded" system, is that the breaker won't trip for a ground fault. GFCI or AFCI trips would be just as bad for the patient.
The locations that require these ungrounded systems ('wet' operating and procedure rooms), can be served by either ungrounded isolated power systems OR GFCI's. The decision is left to the facility on whether to use ungrounded systems (which stay energized with a ground), or GFCI's, which will turn off when grounded. Sometimes the complication of the ungrounded system offsets the risk of vital equipment turning off during a procedure.
@@CraziFuzzy I totally agree. The one goal that was not discussed, was the prevention of a ground fault on one of the two inputs of a vital (i.e. life support) equipment from becoming a show stopper. Naval Combat Ships have above ground electrical systems with isolation monitors. The grounding of one phase during combat will not become a show stopper. I worked with a retired Navy Electrician Chief who shared with me about searching through out the ship, the better part a day for the location of a ground on a phase when its Isolation Monitor went in alarm.
Retired from a large 560 bed hospital that had two LIM panels in each if the 20 plus OR'S . A GFCI should work off a LIM panel because they use a torrid coil to only measure current imbalance between the black ( energized ) & white grounded conductor ( no such thing called a neutral anymore in the NEC. LIM panels NEVER disconnects power on the circuits. It rings an alarm around 4.7 to 4.8 milliamps. Most times the heating pad on OR table is the cause of leakage current.
my question is then, if this is so much safer, then why aren't all power systems isolated? maybe because of cost and that it actually takes some intelligence to keep it tested and safe?
They were used. Grounding was banned before 1899. It was mandated in 1913 - just 30 years into the commercial electricity and decades before equipment grounding was adopted to protect from shocks. There must have been really good reasons to ground. Essentially in an ungrounded system one can have arbitrary high voltages because of for example lightnings. Accidental grounding is also a problem. Lets say you implemented the split phase system ungrounded and one of the legs grounded accidentally. Now the other leg would have 240 V to the ground - something it never has on a mid point grounded system.
The problem is that "Faults Happen." GFCI (or variations that measure the center tap voltage to earth) can detect these faults and cut off the circuit. Usually, an isolated system will be provided by center tapped transformer secondary's with 60 volts on each side. The center tap will have a resistive connection to ground. This leaks off any static charge but the resistance is high enough to keep life threatening currents from flowing via the earth. Some equipment used in surgeries uses a lot of power and regardless of some current leaking the equipment must continue to operate. That's why there is a monitoring circuit so that someone can address problems before something important is cut off. The reduced voltage to "earth" provides some protection also. Most hospital important equipment has built in battery backup so that even if a circuit trips the equipment will continue to operate.
@@mathman0101 -- Well, I think you etc. for the complement. I gathered my knowledge from a combination of an old NEC book I picked up from the library sale, some observations of family folks in the hospitals, and just plain common sense. The folks that write the rules are just trying to make things safer without making it impossible to do business. Personally (& with support from an old electrician friend) I believe that sometimes they go way, Way, WAY to far. The "arc fault" CBs are an example. Even the GFCI are a potential problem. These can "fail un-safe." Personally, I would like to see more "balanced" circuits in households with balanced outlets at 120 and 240 volts. The 120 volt outlets would have a lot less danger from shock. The 240 volt outlets would provide no more shock risk than existing 120 outlets but could be protected at lower current levels for the same power or provide better features. (E.g.: a dishwasher could deliver "bone dry" dishes.)
I'm trying to keep it simple. I agree that, if the conductors lengths are the same, you'll read equal voltage between them when measured to ground (in this case, 60V). But that is strictly capacitance and charging current, and for the purposes of this discussion I'm comfortable saying zero.
@@RyanJacksonElectrical Saying that the voltage is zero because it is not zero and may cause electrocution. The system capacitance will be the complete circuit that will cause elecrrocution if ungrounded conductor will be touched.
@@RyanJacksonElectrical Check voltage to ground. It is not zero. Touch potential is not zero. Never touch a hot conductor. The main reason for using ungrounded is continuity of service on a line to ground fault
![4 of 7 Grounded Versus Ungrounded System, NEC 2014 - [100], (35min:35sec)](http://i.ytimg.com/vi/y6KV6SJMMNA/mqdefault.jpg)
In the wild, you will very rarely find an ungrounded system that reads 0VAC to ground/earth. Modern multimeters are sensitive enough, with high enough impedance that the uA of capacitive leakage is often enough to provide a reference for the meter, and it will usually read in the 50% (60 VAC) range on either pole of the 'ungrounded' system. The minute current would still not be enough to even be perceptable as a 'shock' so this isn't a problem - but it has thrown a number of electricians for a loop when they THINK it should be 0 (as indicated in this video), when in fact it can be and range of voltages between 0 and 120 (depending on how even the leakage current is from each leg).
As an example, the "safe" 0.54mA in his picture is well more than enough to excite the multimeter and show a voltage.
If we used a voltage meter with "low impedance function" like the Fluke 117, do you think the measurement would finally be 0v?
I’m confused. You read 60v on each leg because ungrounded systems are typically three phase and each ungrounded conductor is about 68 volts 1.732 out of phase with each other in order to get 120V. Or at least that’s how it is on boats. Is that not how it works in healthcare facilities?
You are very well informed for this not being your career. I've installed one of these and this was a great refresher for me to learn again.
Hi Ryan, would you be able to kind of explain the difference between the earthing, grounding and bonding?
When I was an electrician in the Navy, we ran all our electrical systems as ungrounded. This wasn't for safety but for reliability during battle. The idea was, if a conductor got grounded due to 'battle damage', you didn't lose power to vital equipment because there was no complete circuit. Standing watch, we had a device (called simply, 'ground detector') that measured insulation resistance to ground while system was energized. If it went below about 1 Mohm, we had to go through a process to isolate the faulty equipment.
And because the entire ship is metal, and cabling running everywhere, the 'leakage capacitance' was pretty high and we couldn't do much about it. So it was NOT SAFE to touch a live wire as the leakage current was enough to kill you. And of course, we had an old safety film that was required training for Electrician's Mates "The Deadly Shipmate".
You said at the very end that if you have one of the ungrounded conductors go to ground that it would be a short circuit. Ground is isolated though so maybe I’m misunderstanding something but doesn’t look like a short circuit. Some current will flow but not very much. Again not a complete circuit.
at that point, he was talking about if the OTHER leg ALSO went to ground while the original ground was still in place.
It's topics such as this that make me extremely grateful for my path into theory and for my early teachers. Immersed into electronics theory first has given me the thousand foot view
Can you elaborate?
Thank you Ryan for the simplified explanation, very helpful and appreciated! I wasn't aware of ungrounded systems in the OR setting.
Learn quite a bit here, and I'm a journeyman currently working on getting my masters license next year, but I've never seen this system and didn't realize it existed, but I do mostly residential and occasionally commercial. I understand the concept, much like the ungrounded delta systems that you sometimes see in older manufacturing facilities, not a system commonly used nowadays but nonetheless very useful in a situation where unexpected shutdown of equipment caused by a ground fault could result in damage or injury.
Ryan is my go-to for electrical education. Let's go!!
Thanks!
Thank you for that explanation. I am not an electrician nor an engineer, but retired from a power plant and dealt with lots of transformers. I had a pool installed last spring, and I just couldn't figure out how the isolation transformer protected me from a fault on the underwater light. After watching this video, I looked at the schematic drawing inside transformer again. The ground shown is not for either coil. (draw a lit light bulb over my head).
I came across one of these awhile back and when I put my meter leads on either L1 or L2 to ground I was showing 60 volts. No matter what wouldn't it find away back to the source? You make the statement at the end if the live wire were to touch the metal plate it would trip the breaker. The only way for that to happen is if there's a path back to the source.
yes, it's like a split phase system, but there's no grounded service conductor, aka "neutral". So it's a floating system. If you take earth as your reference, there is still a potential, you can still get shocked. I bet the operating table is very well insulated, and for wet conditions.
@@wim0104 Just the opposite, operating tables are quite often steel, and grounded via the EGC. 'back to source' just means back to the secondary of the isolation transformer. The reason you read 60VAC is that there is no such thing as a perfect 'open'. Air conducts electricity. Wire insulation conducts electricity. The plastic used to construct the receptacles conducts electricity. None of this is a lot of conductivity, but it is never 'zero'. This means that the ungrounded system IS ever so lightly connected to 'ground' from both legs. If this conductance is near equal, which is likely as the wiring is all parallel, then your high impedance sensitive multimeter will still measure JUST enough current to read the 60VAC you are seeing.
@@CraziFuzzy Thanks for the explanation.
Question... would tying the ground of the isolated system with the ground of the "SUPPLY" To said isolated system would that clear ground faults if they were to occur?
I've never seen a system like this before, thanks for explaining it in a way I can understand. My insructor back in 2010 mentioned something about to 60v legs being the safest electrical system, and I did google it at the time, but never really go to the meat of what he mentioned. today its case closed on that memory
At the large hospital that I retired from at a meeting with so called LIM engineer and two other from the company that we purchased over twenty replacement LIM panels during OR remodeling asked them where is the label that provides the fault current. No e of the three know what I was asking and never provided information after I asked for it several times. If I was in charge they would not get final payment until they installed NEC required labels. Had the same problem with two JCI 1,750 HP chillers. They were each feed from 13.2 KV from switchgear room to inside a 18' long panel that had a transformer reducing 13.2 to 4,160 bolts that feed a 4,160 VFD. Asked for over a year for required arc fault labels and kept telling me they are working on it.
What's the purpose of ground in this picture? Why don't residential houses have isolated systems with an isolation transformer going into the house at the service drop?
probably a dumb question but why then do we not have these in our houses? it seems like the safer of systems to be ungrounded - i assume cost is one reason but is there more obvious reasons too?
A great explanation, Ryan! One question: In this Isolated Power System, are there any polarity COORDINATION considerations BETWEEN the grounded and ungrounded PRIMARY supply AND the two ungrounded SECONDARY conductors to the LOADS (receptacle and lampholders, in your example)? If the SECONDARY conductors are protected by a 2-pole breaker and there’s no grounded (neutral) conductor, why would it matter to POLARIZE by a ORANGE-STRIPED to the receptacle “WHITE” screw and to the lampholder shell
AND by a BROWN-STRIPED to the receptacle “BLACK” screw and to the lampholder base center contact??
Thanks Brian! I can't think of a reason why it would matter.
Electrically it doesn't matter - I honestly think the strict adherence to color matching the legs is more about ensuring every single bit of the highly protective system is built perfectly - so don't leave anything to chance of the whims of a lazy electrician.
@@RyanJacksonElectrical Here's a scenario it prevents:
Take two devices which both expose the operator to voltage in the exact same manner. Say two tools or lights which both have a part which is "live" from the brown wire, but is not contacting ground. If everything is wired the same nothing happens when someone touches both lights at that point. However, if the second light was plugged into an outlet which was wired with the opposite polarity, that person would be electrocuted.
A defect could mean that all lights manufactured within a certain period of time are defective in the exact same way. Bulk purchasing means having two from the same batch is extremely likely.
It's not likely, but it's a "free" risk mitigation.
I don’t work in such facilities. You lost me at the two pole breaker. I guess I’d have to see the installation to understand it. Other than that, all good.
On ships ungrounded system fed from a shore power and pier to hull, each leg reads about 62 volts.
I have an adblocker, but I turn it off on your videos and watching them till the end, so at least your work can be supported somehow by myself.
Keep up the good work, sir.
I was wondering what those orange receptacles were. Thanks OG Ryan
How does this work, when the plugs in the surgery or critical power are red, meaning connected to generator?
Thanks for your informative video Ryan, for a time this "balanced power" was installed in recording studios and other AV applications to avoid ground induced noise. I have also seen this onboard steel hull ships to avoid electrolysis at hull joints.
For recording studios it is very similar (60/120V), but it is a grounded system.
I believe that both the common marine galvanic isolator and the uncommon marine isolation transformer both retain a bonded connection of the secondary neutral wire and boat ground wire. The neutral bond is inside the secondary wiring of the transformer, and the shore ground is there but completely isolated from the secondary boat ground. In a marine isolation transformer the difference is that shore ground is completely separate from boat ground, and in a galvanic isolator the two grounds are connected but separated by a set of parallel, opposite polarity diodes with a 1.4V forward drop either way. So, the marine setup is fundamentally different than the isolation described here in operating rooms, where ground and neutral are separate when testing with a multimeter.
424.22. Why are water heaters limited to 48A?
When you measure voltage on a ungrounded conductor (L1 or L2) to grounded source in a installed live system in a OR you will measure roughly 60v volts (it vary's between 50v-60v) Source: I have Safety tested 15 OR's for 9 years as a maintenance electrician. Another interesting fact our non monitored isolation transformers (1500va) have lower leakage current circuits than our systems with LIM (line Isolation Monitor) No LIM usually less than 20uA, LIM ranges 150uA-270uA. Enjoyed your video and appreciate the knowledge sharing.
Yes, I service quarterly a Marine Well Containment platform, and it has an ungrounded system. It thru me for a loop the 1st time I opened the service panel to throw the breaker for a fire alarm panel and found it to be 20A double pole. I was installing a Surge Protection Device on the fire panel's primary 120Vac power. When measuring across safety ground and either line conductor I also read somewhere around 50 - 60 volts.
I work in a shipyard and onboard shore power fed vessels I read about 60v on each leg to ground. When looking for ground faults with a 3 light ground detector installed at the panel, it has been pretty easy to isolate by shutting of breakers until the ground fault disappears. However, I have ran into a ground fault on a breaker connected to an audio system with back up power and hit a wall going further with isolation. I heard that it is not necessarily a fault in the equipment but a lack of capacitive balance between the three phases. It's new to me and I'm learning about it as I post this.
Man great video appreciate it
now do one explaining why can't we have it at the house
If you're wondering why the text on the receptacle is upside down, it's because receptacles are installed ground side up in healthcare spaces. (you can tell it's a healthcare receptacle by the green dot.)
@@mrpotatohead161 Not always. I've seen thousands of receptacles in health care facilities that are installed with the ground down.
Proposals to mandate an orientation in the NEC have been rejected many times.
Excellent video. I was an electrician who changed careers and now works in ORs. Isolated OR systems is actually taught in Anesthesiology Residencies and tested on, Nursing has annual education on the subject. All equipment in the OR is routinely tested for proper grounding. Most common occurrence is when a "bad" piece of equipment is plugged in, the "isolation monitor" will alarm. At any other time, when it alarms, procedure is to unplug equipment in reverse order of how it was plugged in, IE Last piece plugged in is the first to be unplugged and repeated till the alarm clears. That equipment is then tagged out for evaluation and repair.
Great info, thank you!
Exactly understanding and monitoring ungrounded systems in an OR is also the responsibility of medical staff beyond just maintenance electricians.
As a kid, I'd see the TV repairman insert an isolation transformer(1:1) between receptacle and TV before working on it. Yea, there were TV repair folk back in the day and TVs did break and people did fix them. The isolation XFMR in that case served the same purpose...no earth reference....for his /her safety.
I've never heard that before. Interesting!
I think the main benefit there is for diagnosing faults; i.e. keep the system running even though it has a ground fault.
this is similar to using an old school light bulb with a filament in stead of a safety fuse: the resistance of the filament goes up when current goes up. This helps with diagnosing an overcurrent inside the equipment.
Great video! Thank you
What is the function of the equipment grounding conductor at the receptacle in this setting? Purely for the ground fault indicator?
yes. it's all about avoiding breakers tripping for ground faults and interrupting the operation.
Each leg is 60V I assume? I wonder what happens if they need a 240V piece of equipment in the operating room?
Your question assumes it is grounded but it is not. There is 120 V between the legs. Each leg is 0 V to the ground. Think about a 1.5 V battery. It would make no sense to say each pole is 0.75 V? Voltage is always relative. There is no absolute voltage. This rather confusing. We can say that a leg is 120 V (for example) only because we have grounded the system. That is we have deliberately connected the system to the ground with a ground rod. Note that a system can also become accidentally grounded. An isolated system in that case stops being isolated but it still works.
Likely you do not have 240 V equipment there or if you do, you have a separate system for them. .
At surface one might ask why do we ground as isolated seems to be safer. Well you are not the first one to think so. In fact before 1899 grounding was banned (do not confuse this with the ground prong on the socket, this has absolutely nothing to do with it). However, it did cause problems so in 1901 it was recommenced and in 1913 mandated. Ungrounded systems can get over-voltage which causes arbitrary voltage to the ground because of lightnings, accidental touching of high voltage lines etc. The ground prong was later added to reduce the risk of shock that grounded systems have.
Isolated systems are typically used in things like hospitals and ships. Norway is the only country where they are widely used to my knowledge and they typically have a high impedance connection to the earth for over-voltage. They do not distribute the neutral, just three phases 230 V between each two.
This is a nice introduction but there are many more significant details to cover that need to be looked at hopefully in future series. While you can use an ungrounded system we must always remember in the operating room ground always exists even for an ungrounded electrical system. This means an ungrounded system is much more than the isolation low kvA transformer, line isolation monitor, XHHW wire, receptacles, breakers, heck power cords including all conductor in them need to be insulated.
There are issues around insulation failure of electrical surgical equipment, monitors etc creating more dangerous leakage currents. Here testing and maintenance of those individual pieces of equipment should be regularly undertaken thats other standards beyond NFPA70. There should be a higher bar also on maintenance and monitoring of isolated ungrounded power systems that need to be understood not just by maintenance electricians but also medical staff in the operating room. Also you could make more of a connection between ungrounded system and emergency backup systems in the NFPA70.
I am not surprised this area is not well understood the more you can do on this series using the hospital example and scenarios of faults in equipment or system components the better people will understand ungrounded systems. There was a good article in the IAEI magazine in 2007 on this worth looking over.
iaeimagazine.org/2007/july2007/isolated-power-systems-in-health-care-facilities/
Is this isolation transformer something specific to a OR? are all isolation transformers ungrounded?
Most isolation transformers are just a 1:1 transformer. This type of setup is pretty specific to ORs.
very kool info Thanks Ryan..
T U well done---Jim
Many generators, and dc-ac power inverters, are also ungrounded systems. They usually call these "floating neutral".
Like your example, if you measure either line to the case of the generator/inverter you frequently get 0 volts. This is why many generators do not have GFCI protected outlets. This is also a factor that helps make it possible to parallel the inverter type generators.
Please allow me to ask in earnest, is there a way to synchronize the phase and frequency of these inverter generator systems or is it done automatically looking at cumulative voltage considering summing vs subtractive interference?
@@jeffreystroman2811 Yes. Automatic synchronization is done by every grid connected solar inverter. What's more interesting are AC generators. In that case, the hard part is determining when they line up to connect them. Once that happens, the electrical coupling forces both systems to spin at exactly the same speed.* So as long as you use timing lights, or an automated equivalent, you can manually synchronize AC generators and tie them together into a larger system.
Note that doing this at home using home-made timing lights might be an interesting project, but it is dangerous and almost certainly violates the NEC. Connect them at the wrong time and things will go bang.
* Simplifying
Please post your email so we can send questions with illustration
RyanJackson618 at Gmail dot com
You mentioned that one of the wires has to be colored brown, and the other one has to be colored orange. I know that the NEC doesn't require colors for each leg of a three phase system, but generally people use black red blue and brown orange yellow to distinguish between phases. Does the same practice apply to ungrounded systems? Are there three phase ungrounded systems like this? Or only single phase?
For an ungrounded delta, usually people just use the normal black, red, blue or brown, orange, yellow. If it was in a hospital, however, 517.160 specifies the colors.
The specific bits this is talking about is for hospital use, and is only really for equipment likely to come into contact with a patient during a wet procedure - which is all 120V. As such, I have never seen a medical isolated power system that was anything but 120V single phase.
There are a number of ungrounded three-phase systems out there - but most are military and marine systems, and as such, not subject to NEC rules anyway.
I have a question on ungrounded 480 delta system why do we measure 277V on each leg to ground if it’s ungrounded ??
same reason you will read 60VAC on the video's ungrounded system - sensitive meters and capacitive coupling between the isolated system and ground.
Thank you
Awesome Ryan !!!! Informative and educational . Thank You
Big Shout out to Mr Jackson! In my journey of doing electrical work, I can say this is the best explanation of what Isolated Power is. Thank you.
Another great video from the great Ryan Jackson...!
Thanks!
This was a great video. I’ve personally never experienced working with this type of system but it was cool to see what it’s all about and the application. Thank you.
Used this to help me figure out current flow on a home generator (bonded vs un-bonded system. At the generator).
My belief is that you would (float / break) the ground and neutral at the generator, so that in a fault (in the home circuit), current would flow thru the ground, to the ground bar passing it to the neutral ( in the load center) back to the generator coil (shortest path).
So that current would not flow out to the generator receptacle plug (energizing it, being grounded to the frame) and then energizing the generator frame back to the neutral (if it remained bonded and not floating).
I think.
Can you use HRG instead of ungrounded?
No.
👍👍👍👍👍👍👍
And what is the recommended way to clear a capacitive charge on this system? Thanks in advance.
👍
Very educational video, Ryan! Never seen one of these before. Loved learning this!
best explanation ever about isolated system panel
Thanks for the explanayion.
Great! Info Rayan thank you sir
Interesting, thank you
Great instructor. Your way of teaching is clear, human and straight to the point. 👏
So, trying to understand the theory myself. There’s no difference of potential between the secondary coil and the metal box, although this one is connected to the earth/dirt, because there’s no circuit through the induction between the secondary and primarily coils. it would be such a voltage between the primarily coil and the metal box if it was grounded. Am I close or way far off?
Correct, the primary is a grounded system. The enclosure of the transformer (metal parts) would be connected to the equipment grounding conductor of the supply circuit (the primary), so there would be a voltage there.
I really appreciate this, love the detail .
Great Job
In a system with no faults, would you not see voltage on both L1 to G and L2 to G? And then in the event one of the lines were to have a fault, voltage would drop to zero and then full voltage on the other line?
No, there is no voltage from L to G in normal condition. Under a fault you would get 0V from G to the faulted line, 120V to G on the line that isn't faulted. The faulted conductor really just becomes a grounded conductor at that point.
I thought about it a little longer and figured it out in my head haha! Thanks for the vid!
what is the voltage of each ungrounded conductor ? 60 v ?+/-
Since they can only reference each other(there are no grounded conductors), the only potential is between each other...120V. Otherwise is undefined/don't care or zero(Static charge only). It does make trouble shooting a bit more difficult since for voltages measurements, earth means nothing. For industrial controls, I always 'ground' a leg of a power supply. It is a real pain to diagnose circuits(control circuits especially) when there is no ground reference(floating system). 'Floating' systems are a tricky thing to diagnose.
@@nhzxboi Well said.
Hi im from Poland watch Your chanel is spot on 👌👌
Thank you! Good luck to Poland against France this weekend.
@@RyanJacksonElectrical thanks , and also keep finger cros for US
I wonder if a modern GFCI circuit wouldn't work just as well, but without all the extra difficulty and cost that goes into building this system, not to mention the need to deal with hazard current.
the main feature of this "ungrounded" system, is that the breaker won't trip for a ground fault. GFCI or AFCI trips would be just as bad for the patient.
The locations that require these ungrounded systems ('wet' operating and procedure rooms), can be served by either ungrounded isolated power systems OR GFCI's. The decision is left to the facility on whether to use ungrounded systems (which stay energized with a ground), or GFCI's, which will turn off when grounded. Sometimes the complication of the ungrounded system offsets the risk of vital equipment turning off during a procedure.
@@CraziFuzzy I totally agree. The one goal that was not discussed, was the prevention of a ground fault on one of the two inputs of a vital (i.e. life support) equipment from becoming a show stopper. Naval Combat Ships have above ground electrical systems with isolation monitors. The grounding of one phase during combat will not become a show stopper. I worked with a retired Navy Electrician Chief who shared with me about searching through out the ship, the better part a day for the location of a ground on a phase when its Isolation Monitor went in alarm.
Retired from a large 560 bed hospital that had two LIM panels in each if the 20 plus OR'S . A GFCI should work off a LIM panel because they use a torrid coil to only measure current imbalance between the black ( energized ) & white grounded conductor ( no such thing called a neutral anymore in the NEC. LIM panels NEVER disconnects power on the circuits. It rings an alarm around 4.7 to 4.8 milliamps. Most times the heating pad on OR table is the cause of leakage current.
my question is then, if this is so much safer, then why aren't all power systems isolated? maybe because of cost and that it actually takes some intelligence to keep it tested and safe?
They were used. Grounding was banned before 1899. It was mandated in 1913 - just 30 years into the commercial electricity and decades before equipment grounding was adopted to protect from shocks. There must have been really good reasons to ground.
Essentially in an ungrounded system one can have arbitrary high voltages because of for example lightnings. Accidental grounding is also a problem. Lets say you implemented the split phase system ungrounded and one of the legs grounded accidentally. Now the other leg would have 240 V to the ground - something it never has on a mid point grounded system.
Why don’t we use ungrounded systems more? Seems very safe
The problem is that "Faults Happen." GFCI (or variations that measure the center tap voltage to earth) can detect these faults and cut off the circuit. Usually, an isolated system will be provided by center tapped transformer secondary's with 60 volts on each side. The center tap will have a resistive connection to ground. This leaks off any static charge but the resistance is high enough to keep life threatening currents from flowing via the earth. Some equipment used in surgeries uses a lot of power and regardless of some current leaking the equipment must continue to operate. That's why there is a monitoring circuit so that someone can address problems before something important is cut off. The reduced voltage to "earth" provides some protection also. Most hospital important equipment has built in battery backup so that even if a circuit trips the equipment will continue to operate.
@@GilmerJohn Well said.
@@GilmerJohn well done nicely explained 👏🏾
@@mathman0101 -- Well, I think you etc. for the complement. I gathered my knowledge from a combination of an old NEC book I picked up from the library sale, some observations of family folks in the hospitals, and just plain common sense.
The folks that write the rules are just trying to make things safer without making it impossible to do business.
Personally (& with support from an old electrician friend) I believe that sometimes they go way, Way, WAY to far. The "arc fault" CBs are an example. Even the GFCI are a potential problem. These can "fail un-safe." Personally, I would like to see more "balanced" circuits in households with balanced outlets at 120 and 240 volts. The 120 volt outlets would have a lot less danger from shock. The 240 volt outlets would provide no more shock risk than existing 120 outlets but could be protected at lower current levels for the same power or provide better features. (E.g.: a dishwasher could deliver "bone dry" dishes.)
If the center tap is connected to ground, then it is not an isolation transformer? Each leg is then referenced to ground? @@GilmerJohn
Please read IEEE 3003.1 System Grounding. Line to ground voltage in an ungrounded system is not zero
I'm trying to keep it simple. I agree that, if the conductors lengths are the same, you'll read equal voltage between them when measured to ground (in this case, 60V). But that is strictly capacitance and charging current, and for the purposes of this discussion I'm comfortable saying zero.
@@RyanJacksonElectrical
Saying that the voltage is zero because it is not zero and may cause electrocution. The system capacitance will be the complete circuit that will cause elecrrocution if ungrounded conductor will be touched.
@@bobcocampo No. You're not getting electrocuted from a single ground fault on an ungrounded system. That is the entire point of an ungrounded system.
@@RyanJacksonElectrical
Check voltage to ground. It is not zero. Touch potential is not zero. Never touch a hot conductor.
The main reason for using ungrounded is continuity of service on a line to ground fault
@@RyanJacksonElectrical
This is the reason why single phase 2 wire where one line is grounded and only one hot wire