The Jaw-Dropping Difference Between AC & DC Isolators!
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- Опубликовано: 30 май 2024
- Ever wondered about the puzzling differences between AC and DC isolation switches? Electricians will see them used as part of solar panel and inverter installations. They stand out, being coloured grey and black instead of red and yellow. But is that all? Our very own Joe Robinson is on a thrilling mission to uncover the distinctions between the two. Prepare to be electrified by his startling findings!
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00:00 DC & AC Isolators
00:44 What is the difference between AC & DC current?
01:50 Disconnecting AC current
02:23 Disconnecting DC current
03:04 What is the difference between AC & DC isolators
04:26 Voltage, current and load ratings
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How to Choose and Install a DC Isolator
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How to Specify & Install a DC Isolator
👉ruclips.net/video/Q3I6RL0pPso/видео.html
Slightly off topic, but could you do a clip demonstrating why using 10amp 240v house wire in a vehicle is a very bad idea?
I've been working as an "Automotive Engineer" (a fancy title for an accessory fitter on 4x4's 😑) for 2 years now, and I've noticed a LOT people are doing this!
They think of 240v as "bigger power so it must be ok!".....they don't realise that while it takes 240v and the vehicle only puts out 12/24 , the amps are different!
Cars can regularly put out 60 amps in places!
Six times the rated 10amps for house wire!
Very dangerous!
I am an aerospace engineer who has spent the last 30+ years in industrial control systems and automation as an EI&C engineer.
YOU MUST REVISIT THIS as parts are very easy to misinterpret. You can't just do the AC/DC thing in 5 minutes. You are not even taking into account the nature of inductive and capacitive loads which can dramatically alter the rating of contacts in isolators, contactors and relays.
You need to stress that ELECTRICIANS and ELCTRICAL ENGINEERS have to pay attention to the application and the nature of the load they are disconnecting and the ratings of the disconnect or switching device.
@@tonywilson4713 you would be amazed at some of the things that come into the workshop!
Just noticing people are doing all sorts of weird modifications to their vehicles, and a lot of people don't seem to understand that trying to home wire up a heavy duty winch for example with 240v wire is a bad idea!
@@kurdaitcha3509 Buddy after 30+ years of watching stupid people do stupid things for stupid reasons *NOTHING* surprises me anymore.
If you just even use basic high school science and math you can freak some people out.
As I said I started in aerospace and if I didn't care squat about making a difference and just wanted money I'd be at Space-X or Blue Origin or Boeing. If I wanted prestige I'd be and cared less about money I'd be at NASA or ESA.
Either way none of them are going anywhere fast. They just have really good PR that spins it that way.
On electrical power for our societies its barely believable how stupid governments and the media are and how easily people are sucked in by the insanity people are spinning.
*AND DO I MEAN EVERY COUNTRY*
The American film _"Idiocracy"_ is now a documentary.
I was expecting to see arc suppression blades inside the DC switch. Seems that printing a lower rating on the outside is actually the cheaper option. 😀
More than likely the blades would be used on higher rated ones.
Lower rating AND putting 3 contacts in series.
I served as a junior electrican for one trip when I was an engineer in the merchant navy. We used DC back then (45 years ago) for motor control, it was very good for it, pumps could be easily controlled for pressure and flow just by altering resistances. But the worst burn I ever saw while I was away was when (another junior electrician) told the senior electrician that he had isolated the main engine cooling pump. He had actually isolated the main engine oil pump. Due to the construction and access to the knife isolators, when he pulled the knife isolator it arced across and basically evaporated the skin off the back of his hand, 250 amps at 220 volts is really not good for you. Due to the pump stopping, the engine lost cooling water pressure and also stopped, so the engine room was full of people to assist in less than a minute.
Wow - power lessons
Actually DC isn't particularly good for motor control, PWM is. But you can argue that PWM is still DC but that's not really the point. DC control in this context is simply changing the magnitude of the current, which is what you said.
@@deang5622 You have to remember that although this was 45 years ago, the ships I was sailing on were 20-25 years old. There is nothing as conservative as an old style British ship owner, so the tech would have been another generation older again. So back 80 years ago it would have been cutting edge. Very robust as well.
@@deang5622 PWM is rarely the best, but it's far cheaper to make than efficiently synthesizing the fractional voltage approximated by a PWM.
Thanks for the story Bill. It sucks that so many decades-worth of electricians had to learn this lesson the hard way before the necessary PPE was developed and put in common use. I come at all this from a computer engineering background, and it is scary how much power goes into a data center to guarantee that 99.999% up-time. Multiple power companies supplying AC for failover and/or load balancing, batteries and flywheels for holdover, and big diesel engines all mean one hell of a steep learning curve, so the newbies working the high voltage side have to get used to suiting up like bomb disposal techs before going near anything. I was lucky: I had my "safety first" re-affirmation when poking at 3-phase manufacturing facilities' wiring.
One day I was probing some lighting circuits of all things when I got to experience my first arc flash. Some jackass had nicked a wire on install and left it in place rather than fixing the thing, and one of my probe tips got between it and the screw terminal I was trying to get a read on. BAM! Instantly vaporized my probe tip. I was wearing gloves and using a Fluke, so nothing else got damaged. Still, staring right at an arc flash puts out enough UV to give the back of your eyeballs an instant sunburn. I felt that for weeks!
Now I know better: I make the last guy who worked on a panel stand in front of me the first time I crack it open. It's AMAZING how many people will offer to take over a task for you when they know they did a bad job! :)
Another critically important factor is the actuator (knob on the front panel) of the switch. Most dc ones I see have an impulse mechanism (like engine magnetos) to rapidly snap the contacts apart to their maximum distance. Do not mix and match switch components.
All modern switches have that feature
Worked on a 1940’s cargo ship that had massive DC contactors. They made and broke the connection via a sacrificial carbon brush before the main contacts opened or
Closed. There were arc diverters and suppressors. It was pretty epic testing those circuits and pushing in contactors with broom sticks when needed...
I misread that as "pushing in contractors" at first. 🤣🤣🤣
@@chrisbrooking Well, that’ll teach them!
@@chrisbrooking If the contractors were electricians I presume they'd be trained & up for the task !
Fast DC breakers used in trains and trams running off DC overhead wires are enormous. Some are even preloaded with compressed air and have arc quenching chambers. With modern approach and in HVDC you typically have thyristor based breaker (to bring down the current) and physical disconnect in series
how does a thyristor breaker work, I thought they could only make and not break
@@thewhitefalcon8539 there are gate-turnoff-thyristors as well (GTO)
I've been in a few substations for UK southern railway and tramlink and the arc quenchers on those 750VDC breakers are pretty impressive
Compressed air? Don't think so. It's either gonna be vacuum or SF6 gas.
@@thewhitefalcon8539 Thyristors will break a circuit when the forward current flow drops below the latching (holding) current.
It's preferable in AC circuits because current across the thyristor will naturally drop below the holding current every time the AC crosses 0V.
In DC operation, a SCR isn't going to have its holding current drop by itself without intervention, so you need to reverse-bias the SCR so that its current is commutated. There's a bunch of methods, like placing a capacitor with reverse voltage in parallel with the SCR, using a LC resonator, etc. At the end of the day, you just need to reverse bias a 1V drop across the SCR and have whatever you used withstand the source voltage afterwards.
Excellent demonstration. There was quite a difficulty in obtaining DC switchgear (isolators and contactors) in the 1980s. Power stations use a lot of DC supplies, 240V and 110V for HV switchgear operating solenoids (hence highly inductive) and also emergency lighting and power supplies, but with the original suppliers defunct, obtaining equipment for a new workshop test facility was problematic. One of my colleagues eventually sourced some contactors after speaking with the manufacturers and they were wired as per your isolator with multiple contacts in series.
Back in the 90s In South africa, the DC switches and breakers, weren't always available. We used to take a 3phase contactors, and wire the contacts in series(to increase the switch gap), and de-rate the current rating for DC. We sometimes used 3pole switches wired in series aswell. I remember experimenting with small permanent magnets to blow out the arc. I tried fitting magnets to 2pole circuit breakers, to 'blow' the arc into the arc splitter/shoot. DC deserves a lot of respect, but it's not as dangerous as people make it out to be.
i once ran a hot air gun directly of 230v dc from solar panels. Worked just fine, worked so good it even worked when I tried to turn it off :P
Also you will find a lot of DC isolators are very much directional, in that you must mount them so current flow is according to the direction of flow marked on the switch, so for things like a battery disconnector you need to have 2 poles doing the switching action, as current can flow into and out of a battery.
However for things like a solar panel or inverter they will havv a defined direction of current flow, and if the inverter has a battery charger there will be a separate isolator for the battery charger output. This because they use a magnet to direct the arc into an arc breaker, so that the arc itself can be cooled down to the point the ionised air no longer conducts.
Thus another difference between SELV and PELV DC and higher voltage, in that SELV and PELV DC circuits are so much less likely to have the energy to draw an arc, and the separation to disconnect can be less rigorous.
Incidentally that breaker shown is no longer recommended for new installations in certain countries, like Australia, as they have had a good number of them that have failed in use, and there have been recalls to install upgraded isolators with higher specification, and larger separation, plus also having magnetic arc diverters to more effectively break the circuit when operated under load.
Everything you have said is true, but how much simpler, AND safer, would it be to:
1. Disconnect the DC load
electronically
2. THEN isolate mechanically
???
ZERO need for much more complex mechanical features such as arc diverters (there would be ZERO arc/s anywhere)
Zero need to have had expensive recalls
Zero risk from arcing causing flashover, explosion and fire, when attempting to isolate due to say a gas leak !!!
MUCH safer and quieter operation due to zero arc, zero arc deflectors.
Much lower cost for domestic environments.
Several other advantages too potentially.
@@boblewis5558 Problem is you will need to still provide arc fault capacity, because the electronics are the item most likely to fail shorted. DC breakers with arc chutes, and a magnetic driver, are the preferred item, or you need to have active arc cooling that blows it out.
@@SeanBZA I guarantee mechanical features will fail LONG before modern electronic devices. Otherwise, why is DC welding with over 200Amps SO reliable, and TIG just as reliable ... No arc diverters CAN be used there.
In addition you speak as though the ONLY failure mode of electronic devices is "short"! ... NOT true! An open circuit failure mode CAN be designed in.
On top of all that, complicated DC isolators with arc deflection are not used in domestic settings ... The isolators are, as shown in the video, the same as AC types just wired and rated separately!
Whomever said that it's "impossible" for contact welding to occur in a DC isolator is as deluded as someone who believes semiconductors only ever fail short circuit!
In the case of welded contacts you are now left in a WORSE situation than if, in your perceived scenario, the series electronic disconnect were to short ... You have ZERO means of either isolating OR disconnecting the supply!
With ZERO arcing, ZERO overload current (easily covered in other reliable electronic ways) BOTH the isolator AND the electronic disconnect protect each other.
It's NOT that an AC isolator CAN'T disconnect DC, it's that it is definitely NOT something to do regularly because of the continual arcing. Isolating under zero current conditions is a no brainer for ANY set of contacts designed to handle the rated load ... There is NO load current at the isolation point!
DC arcs can be beautiful to watch.
Brilliant demonstration, two bits of food for thought,
1 as the two switches are identical could th AC switch have the two link wires installed there by making it a DC switch? And take them out of the DC switch there by making that into an AC switch , after all some room stats can be modified to work with different boiler systems by adding or removing a link wire.
Point 2 could you not use that wood switch to try and prove once and for all AFDDs work or not? As you know there is a long running debate weather theses things work at in a domestic installation.
Brilliant video as always Joe 👍👍👍
Come on Joe
They are both the same, BS EN IEC 60947-3 applies to switches, disconnectors, switch-disconnectors, fuse combination units, and their dedicated accessories to be used in, distribution circuits and motor circuits where the rated voltage does not exceed 1000 V AC or 1500 V DC.
It's refreshing to see a company's channel that that actually educates with their products as examples instead of just faffing about how great their products are. This is better than any advertisement, really.
Very well explained Joe. An AC current is much easier to interrupt than a DC one because the current flow is zero every half cycle or 100 times every second.
I've heard stories of having side resonance due to short lines & loads that oscillate at a high enough frequency that the contacts don't quench and burn out the switch.
That first demonstration of the arc was really graphic showing the difference between ac and dc. Colleges should do that demo. Though perhaps with a slightly less ‘Heath Robinson’ apparatus 😮
Having been brought up on diet of DC mains supplies I was very aware of the difference berween switching DC as opposed to AC. Even in domestic installations 'quick make and break' switches were generally employed to overcome the problem until AC became more generally used, I think GEC brought in the 'Mutac' switch early on to avoid the massive 'clunk of the QMAB switch when DC had long gone. Magnetic blowing is often used today even on AC circuits.
another great question answered. great video
Thanks very much. 😊
This was also a legitimate question/concern 150 years ago in the 1870s when household electricity was being introduced in the electrical format war between Thomas Edison's DC system and Nikola Tesla's AC system.
Great explainer. Some of the nastiest isolator burnouts I’ve dealt with have been 4 pole AC with links made from 4mm DC solar cable.
Made teaching media for lectures very well.
With out the sufficient amount of knowledge about DC switching, lives could be lost. A friend of mine had such a problem with the PV breaker. The electric arc set fire to the PV BREAKER.
luckily no one was hurt.
Excellent video Jo. I have learn’t something very important there… not to cut corners with DC and just use an AC isolator instead as i may happen to have one in the van. 👍
Excellent demonstration!
As always Joe, very well explained 👊😎👍💙
Ah, cheers Eddie, means a lot coming from you matey. 👍
I placed an AC isolator in my PV DC circuit, purely because of cost. It was a factor 5 cheaper. (10 years ago). Six months later we smelled something burning, and it turned out to be the AC isolator, completely burned inside. We were lucky to find out in time, while being home. Don't ever go cheap on isolators!
Expertly explained, as always, eFIXX.
Great demo!
An excellent demo and simple explanation of the basics. One vital factor you did not mention is that with dc switching you have to ensure (I.e. check, do not guess) that the time constant (L/R ratio usually expressed in milliseconds) of the load is also less than that for which the switching device is rated for. Also watch the number of switching cycles that the dc power device is rated for when breaking current (the on load rating). The dc number is significantly (multiples) less than that for ac where a device has a dual rating and a lower voltage rating will often be applied too. Whoa betide you if you exceed the number of cycles; it’s crucial that maintenance and replacement are carried out accordingly. On dedicated dc circuit breakers you can get blow out coils, arc splitters and runners within an arc chute. Orientation of the device can be critical in some cases, as is the clearances on the exit side of the arc chute. This so the arc is, stretched, cooled and quenched as the device designer intended (same for dc contactors too) My guidance is do not play with dc power unless you thoroughly know what you are doing and qualified/ supervised accordingly. As your demo if you contact dc your muscles will go into spasm and it’s difficult to let go as no current zeros, I have never got caught on that one, this after a long career in dc and ac drives, be extra careful! Hope helps Stephen
Very good information Robinson.,
Just in case it's not obvious, that arc is 'plasma', which is a fourth type of material after solid, liquid, gas, and importantly, while it's doing its thing (so 'hot' that the electrons and the nucleus of the atoms separate), it is a very good conductor, which has a great similarity (for those who like their physics) with the 'conduction band' in metals where all the electrons can go for a wander rather than staying with their nucleus as happens in non conducting insulators.
Lovely visual effect. There is plenty more interesting arcs and sparks stuff. Just beware those arc flashes!
Excellent explanation ! 👍
I worked for over 30 years on the power systems of the London Underground. We had equipment from the 1930s as well as modern when i started. The sound of a DC CB coming out at 8000A wakes you up. Old CBs had magnetic suppression of arc. Later, smaller form factors combined magnetic and air puffers which stretched the plasma and thus reduced the arc. Typically the contacts needed occasional light redressing depending on the section of track they served.
Your demonstration rig was not greatly dissimilar to the 22kV isolators on the old equipment. Opened with a pole and a hook, but of course not under load. The first couple of times of doing it was a buzz in more than one sense.
Great demonstration video... but @ 2:29 there is a lovely hum during the DC break-arc and its DC? since when does DC Hum?
It was probably the variac buzzing. 👍
Good stuff Joe.
Ah yes. The forbidden arc welder.
It is not just switches (which means relays and breakers as well of course), but you can get the same issue with fuses. Now I don't suppose the everyday sparky is going to be designing circuits at this level, but it's interesting to not that some fuses have different voltage ratings for AC than for DC (the current ratings are the same).
The reason for this is that, when a fuse blows, there will briefly be an arc set up which is caused by ionised air providing a low-resistance path for current to flow. That ionised low resistance route will last as long as a lot of current flows as it self-generates. With AC, the current drops to zero twice every cycle, and that will normally be enough to kill the arc. With DC, it's different as the current will continue to flow through the ionised gas, and that very current will sustain the ionised gas (called a plasma). If the gap is fairly small, and the voltage is high enough, that process can be entirely self-sustaining, which is highly dangerous, especially in a fuse, which is there purely to break the circuit in the case of a gross overload. So, whatever anybody might say, many fuses do have different voltage ratings for AC and DC.
There is another issue with breaking DC into inductive loads. There can be a vicious reverse voltage spike when cutting off the current, and that can cause very large sparks or even weld contacts together. Often flyback diodes are installed to conduct those reverse voltage spikes which could otherwise cause a low of contact damage. This can happen in very low voltage circuits as what matters is the energy stored in the inductive component's magnetic field, not whatever voltage it is working at.
Excellent demo ... I never knew DC could generate such a 2 inch plasma arc, incredible!
Pretty sure the sparks that did my PV back in 2013 just stuck an AC isolator in as I suspect they knew no better - fortunately it’s on SolarEdge optimisers so the likelihood of the isolator ever having full whack going through it if it needed isolation is highly unlikely - I did make the installer return to add a separate RCD rather than leaving it piggy backed onto the existing one which feeds the rings 🤦♂️🙄
Clearly this is something I will try at home while showering.
Pls don't.
I've just got a course on this, really neat,
My DC weder is also making big arcs at 30 Ish volts 😊
2:57 - I assume that DC arc is supplied from a transformer and hence the 50hz hum in the background.
Last time I saw a DC arc, it hissed and was almost silent.
Yeah, there's a variac connected to control the voltage, this nknit was on the limits of what it could handle to be fair. 😃
Would a circuit breaker technically work as a DC isolation supply, just asking as it has the grill that can dissipate arcs in it, or would the arc be too strong for it then?
What happened to the old fashioned arc shields that used to be fitted to DC switches.
Back in the latest designs, along with ferrite magnets to force the arc through the shields and cool the arc down and break it. They also make them directional, so you need to have 2 in series for use with batteries that can feed or sink current, along also with having DC rated HRC fuses as well.
Have to say whilst this was an interesting video I am worried you could have inadvertently done more harm than good. Looking at the comments a lot of people will be under the impression that all you have to do to convert a AC switch to DC is series the contacts and derate the current and voltage. I am not at all impressed with the build up of the dc isolator you have shown, would be interesting to see how it performs under its rated loads.
I undetstand switch designed for AC can be problem with DC, but is there similar/other issue using a switch designed for DC with AC?
Do car relays work for 30amp DC for safe rapid switching?
Why is the D.C. arc at 2:33 making the classic 50-60hrz sound of A.C.? D.C. arc's don't sound like that. How many volts. How many amps. I feel like there is something amiss here.
It was probably the gumming of the variac I used to control the AC voltage in to the rectifier. It was straining at its limits I think! 😃
As a railway enthusiast who lives in an area where DC conductor rail (750v= ca. 50KA) is in use, I am trying to think just how *beefy* DC traction supply isolation gear must look like. Perhaps arching is the _real_ reason why DCCR electrification enforces a painfully slow speed limit of just 100mph? 🚄💨⚡😉
Besides the ultimate gap length, the other features affecting arc quenching (at same voltage and current) are at least a speed of the contact opening and added quenching means (cooling and magnetic blow). The opening speed is inadvertently affected by applying a freewheeling diode across the coil of the device! That relates to DC operated coils, of course. But it can be clearly seen on ordinary 24 V DC coil relays...
I've used high voltage DC relays in the past that had a strong permanent magnet adjacent to the contacts to blow out the arc. I'm surprised the SCARME DC isolator doesn't include this, as it works so well.
Boats make extensive use of DC circuits, 12V or 24V for house loads, depending.
Electric propulsion is becoming more popular, which is often 48V DC.
Good to know thanks, we've yet to delve into boat electrics. 🛥️😃
@@efixx Salt water makes everything more interesting...
I'm courious about the shape of the arc.
Seemed to be wider at the top, was that from direction of gravity or direction of current.
Could be the heat ionised the air above the arc causing the arc to bend up into the ionised air - that's how a Jacob's ladder works.
Why seperate DC isolators are still needed, modern string inverters do have those Dc isolator inside those ???
Then Can a DC one be used for AC isolation given we are under the spec for amperage and peak voltage?
I was wondering that too, or not so much can we as it has not been officially rated for both AC and DC, but what would happen if we did providing we did not exceed the current ratting of the DC isolator?
@@ElliottVeares Any mechanical switch designed for DC will in practice work for AC and generally be even less of a risk. But any professional fitting one would be asking for liability issues due to it being "inappropriate" as per the stated rating.
Looks like a clever way for manufacturers to re purpose some double pole AC switchgear into single pole DC switcher by just putting terminals in series to increase the air gap! 🔥
Well as long as it conforms and tests out OK. 😃
The noise of a DC arch reminds me of photonicinduction.. 😔
I popped it.
Why does the DC arc have a 50hz ish buzz to it? Just a consequence of rectifying AC to DC?
Not so much the rectification as the variac used to control the input voltage buzzing away in the background. ⚡
You should make video about C loads and the gear required to switch that.
So pretty much exactly the same switch just rated differently... And given that at CEF a 20A 3P AC is £30.79 and the DC Variant is £81.10, SCAM is the right name for this company, yes, I know I dropped the E off the end 😇
Exactly, they both conform to BS EN IEC 60947-3 applies to switches, disconnectors, switch-disconnectors, fuse combination units, and their dedicated accessories to be used in, distribution circuits and motor circuits where the rated voltage does not exceed 1000 V AC or 1500 V DC.
DC is not to be laughed at. When adding two 12V Car batteries to make a 24V system, and then accidentally shorting the opposite poles, it melted an inch of length off of a 1/4 inch threaded steel rod in seconds. I sat on top of that with just a padded seat between, and that was the most brown alert moment in my life still almost 30 years later. Solar roofs when connected the wrong way can be 1500V and capable of delivering about the same current as a car starter battery...there is a reason there are so many electrical house-fires after cheapest contractor with east-state labor have been on site assembling.
“Don’t try this at home”. Hold my beer 🙄
You didn't actually explain how the DC isolator prevents or suppresses the arc.
My rule of thumb is to half the current and then only use an average of 60% of that, and to keep the voltage well below 75% of the rated voltage when using DC on an AC switch (many will even have their DC equivalent ratings o the switches to give guidance for dual-use).
The other differences usually include a little bit of silvered coating on the contacts.
So far, so good.
Also, I expect the lifespan of a DC switch to be shorter than the AC equivalent.
of course, there's more to it than I mention, but the ball-park works, just make sure to not use AC isolators as a main DC-bus switch as technically it's a safety device, not just an isolator.
Hm, think I'd always just go for whatever ratings were on the kit really. 🤔
@@efixx Usually safer that way of course.
That's a thicc arc alright😍
I always see that happening here in the USA, people use AC disconnects for DC and will burn out quite quickly. Never use AC disconnects for DC loads! 😁👍
That's some Ark, even Noah would have been proud of that one. Thanks for sharing Joe.
Thanks Brian 👍🏻
If I need a DC circuit breaker of 20 Amps, but I only have AC circuit breakers, what formula must I use to know what amperage AC circuit breaker to use
The MCB must comply with BS EN IEC 60947-3, dedicated AC MCBs don't, but most MCCBs do.
Also please see my other comment regarding impulse switch (knob on the front) actuators. There are more differences than covered in the vid. Stay safe!
If you follow the logic of this manufacturer, connect every pole twice in series and lover the voltage and current rating by 25% aprox. (do not try this at home)
What is safer DC or AC?
Great video Jo, Could you just remove the links from the DC switch to have it act the same as a AC switch
Yes. But the wording on the switch would be misleading.
The question ultimately is, who is isolating a DC supply when its under load? That's where the problem occurs. Little bit misleading in that if you did a comparison with the heater off load, that arc wouldn't pose a risk because it wouldn't be there. Also, you wouldn't use an resistive load on such a high DC voltage, which was intended for use in AC supply only, because once the power is applied you're in a no return situation. It would have been a laugh to see the thermostat kick out when up to temperature and see the amazing arc within the casing of that heater.
The best way to explain this is just a good old welder. Because that is the effect trying to be avoided.
😊imo for dc or scame the only ones i use in solar 😮
Does pulsed DC behave differently?
Good question, I'd guess so but would imagine it depends on the nature of the pulsing. 🤔
Breaking a DC load is Big Boy's stuff versus an AC load
Before anybody thinks of doing this (despite the warning not to!) that D.C. arc is hotter than the surface of the sun.
You have a welder in DC
The logic behind using two switch contacts in series for DC switching is that one set of contacts will randomly open slightly before the other and be subject to the arc's thermal and electromagnetic effects so that (in theory anyway) the switch will have a greater operational life with the two (rather than just the one) set of contacts.
You know ya'll zap alike!
Some rotary DC isolation switches have opposed terminals...
eg: T1 is top left but switches T2 bottom RIGHT (not bottom left as people wrongly assume)
This can result result in a major DC short across say two strings in an incorrectly wired 4 pole DC switch isolating 2 PV strings, kinda surprised this wasn't mentioned that certain DC isolator switch terminals can have the contacts arranged DIAGONALLY than regular vertical arrangement.
Of course, it goes without saying RTFM & also wise to double/triple check the arrangement is correct/continuity across the poles to avoid risk of high voltage shorts or even reversing the polarity at the inverter etc...
But it has been known for people to wrongly assume the pinout is obviously the same standard, only to find out on some DC isolation switches they are crossed over & rotary terminals are stepped/layered/stacked
Some may already know this about DC switches, but others may not & there has been some costly lessons learnt when using different/unfamiliar DC isolation switches, not RTFM & assumption being the mother of all...
Double check all your wiring, but maybe closely triple check your DC wiring to avoid a DC short or reversing the polarity of MC4 connectors as they connect to the inverter
Great advice - sounds like we need to make a follow up - the advanced course 👍
Been there done that. And the paper that comes in the switch shows the poles opposite of eachother. Thankfully the inverter I wired had polarity protection
4:25 - no magnets in the DC breaker? Can you please poke around with a steel screwdriver or similar, to discern if there are hidden magnets near the electrodes in the DC-breaker?
"The Jaw-Dropping Difference Between AC & DC Isolators"
-> Proceeds to show no difference between them...
Did you actually watch the video?
I would assume that the DC switches, for the *same current load,* would have wider gaps between switch points. The switches shown in the vid are _identical,_ as shown by Joe, so they frigged the switch by dropping the current load for the DC version and using two switches in series. Personally I would rather have a DC switch with one switch with a larger gap between the points. Something tells me the 1st switching points in the two series switches may wear out quite quick.
*_Very informative... Great Video.. Learned New Information..._*
I have a question... Is 200 volts DC actually used in Residential Houses? I live in the States. We have 120 and 240 VAC. We use 480 VAC in Commercial Buildings. Solar is being installed everywhere now in different configurations; 12, 24, 48 VDC to Batteries then Inverter. It is converted to 120 or 240 VAC there and then into Household wiring.
I have a 16 KW Propane Fueled Generac Emergency Generator. There is an auto transfer switch preventing my lethal AC voltages from leaking back on Public Power Lines. Switch over is less than a few seconds. UPS's on critical computers, servers, and communications don't need to be very large. At most they run 5 seconds before generator is at full power. I bought my UPS's before getting generator. They were sized to run critical equipment for 1 hour. Outages rarely exceed 15 - 30 minutes.
*_Saw an article recently about newer Solar Panels that have their own builtin Inverters._*
You might find it on solar PV installations where there's a few panels connected in series.
I am disappointed that the series connection of the DC contacts are joined by what looks to be field removable jumpers. It is just a matter of time before the jumper wires are removed, allowing the switch to be used as individual contacts (up to 4PST) with a much inferior performance.
Thats exactly what I though. I wonder what the inside of a Krause and neimer ( apologies for the spelling) look like. They have been making high spec isolators for many years.
From my college electrical but mainly electronic training and working with dc circuits and batteries of over 30 years It’s all about RMS ac = dc but dc does not fluctuate like ac 50 full 360 degree cycles a second. What multi meters read when you measure ac is the RMS value of the peak not peak - peak. High power DC circuits are getting more common with solar battery banks so things can be gone in a flash lol 😂 just wait and see with the DIY market growing…
Well that's quite an unfortunate brand name right there
It's an Italian business, probably doesn't have the same connotations over there.
I will have have expected a better isolation in the DC switch, with a physical disconnect, like something that break the ark for sure
Hm seems as they just use a jumper to connect two contacts in series and call it a day. Changed the markings on the AC one, seems like it anyways.
I would imagine it's been through different testing processes.
So exactly the same hardware just wired up differently and derated.
Seems like the exact same product with the same specs that are obviously different for AC and DC voltage
So in reality we could use an ac isolator if we use double the contacts and half the current? Also I'd ad that I think that the reason the arc if so much bigger on the dc is because the ac value is only at its peak for that short interval, the rest of the time its decresing or increasing, or at zero!
Good video 👍
I wonder if a large capacitor in paralell with the isolator would do the trick?
Once the isolator is made open circuit, the capacitor charges, effectively meaning that the breaker disconnects at 0v.
After a second or two, another isolator in series with the capacitor could be opened to completely seperate the circuit.
why dont we just make all switched dc ???
I'm at that great point where I know enough to be dangerous, so thanks for this. I plan on putting some solar on my garage next year.
4:23 idk why they didn't just print AC and DC data on same device and sold it as one unit.... less packaging, less hassle in warehouse
switches are marked this way....example
12V DC 20A / 24V DC 16A / 125V AC 20A / 250V AC 16A
wait hold on why would a company put scam in their name? all they did is add an e at the end.
It's an Italian company, probably doesn't have the same connotation.
You didn't explain the physics. You only talked about rating, and the fact AC and DC are very different, but you did not say why.!
On AC, when the contacts start to break, the small spark occurs because the AC sinewave drops briefly to ZERO stopping the spark from arcing.
On DC the voltage never goes to zero, it always stays the same, so the spark never gets broken, the ionisation continues freely, till the gap is big enough.
I used a 10amp double pole relay in a 10amp DC power supply, by utilising both poles in parallel, the spark is halved, and the rating is also halved by using both poles to switch.
Electricians need to study the background physics behind DC switching, now that we have an ever growing amount of equipment running on DC.
Solid State switching might be a good way around this arcing problem. THOUGHTS.??
David G1ZQC.
Electricians don't need to study it though. It's the difference between electricians and electronics engineers. The engineers need to study electronic engineering - the electricians need to study big books full of rules to be followed without question or exception.
@@vylbird8014 Incorrect DC switching is a fire risk, so because there is far more now than before, they need to know why the ratings are different.
Out of ignorance, someone is going to cause a burn out through not checking with full knowledge of what they are installing.
Always good to debate.
@@G1ZQCArtwork That's what the big book of rules is for. It's not enough to just do things safely: The electrician needs to do things up to code, because that means no lawsuits and no rejected fire insurance claims.
omfGAWD 👽 💥
Off topic , but it should be mentioned that the convector heater you use , having almost no moving parts will last for DECADES ! .. ( unlike fan assisted heaters that get " fluff " in the bearings ... and .... the AWFUL cheap ( modern ) radiant heaters that burn FAR TOO HOT and burn out in a few months use ) ... the old ( 1960's ) style radiant heaters are no longer sold ( ? ) but last many years ......... DAVE™ ...............
DC is just 0 hz AC
The DC uded on the wooden switch still makes a 50Hz sound, so it's not even clean battery DC, which would be much worse.