Thank you, I'm sure I've watched and like other videos of yours. I was struggling with a milling machine control box I'm building not being a electrition etc at 55 year old, including 2x VFDs, coolant, 2x electric power drawbars etc and wanting every safety factor a factory would put into it, and couldn't find anything online regarding 24vac NVR wiring. I was wanting to use 24vac for a NVR as space is at a premium and you solved my problem in your 3 phase diagram as I have 2 spare contacts using single 3 phase contactor on 240v here in Australia. Thank you for taking the time to do the video.
if only school! teachers explained things so consise and clear like you JW. I'm enjoying learning from you even though I don't practice electronics. thanks
Unfortunately school teachers are employed by people who do not CARE if they can teach or not, but are only interested in them having the correct qualifications.
In many "small" tools like table saws or belt sanders there's no separate switch for start but the start button mechanically actuates the contactor witch then latches on through one of it's contacts.
John,Greetings from the other side of the pond. I find it funny how we use different mains voltages but the control circuits are both 24v (normally). Great vids. Keep 'em coming.
That's a very nice explanation. and quite informative. I've got to figure out how to wire the e-stop when I've got a variable frequency drive involved. I know I want to break the power to the contactor, but all that is internal to the VFD. I'll have to do some more research.
Many VFDs have emergency stop functionality built into them, and you can control whether it's a free wheel stop (cutting power and letting it coast to a standstill) or whether the VFD actively tries to brake the motor to stop it as quickly as possible. Some of them require special resistors to be attached in order to achieve fast braking so there is somewhere to dump the excess power to (since braking a motor works by turning it into a generator, and the more power you can pull out of the "generator" and dump somewhere, the faster the motor will stop turning).
John ive often seen the electric organ piano in the background corner of your office, is this another hidden talent of yours and would you at all do a video showing your favorite music
I have put latching relays with push on, and off buttons in my CNC engraver, and a table saw. I like them. If I ever find more relays, and buttons I might install them in other machines I have too.
Things have changed a lot with E-stops, machines are risk classified which specifies the required protection, devices I work on even pillaar drills have pilz saftey relays and safety contactors, which of course have dual circuit monitored e-stop switches.
hi there good informative video, but what do you do if you have 5th wire coming from a motor (overload protection) i think and your NVR only has 4 connections?
Brilliant video. Really appreciate the effort and time you've put into this. Keep up the good work John. However, I must say that I was looking to see if any of your videos demonstrate (calculating resistivity), but I didn't. If possible could please demonstrate a lil video or if it's not possible, please could you send us a lil calculation- say: for example: a piece of material measuring 100metre in length, CSA1.5, for copper?! Formula (17.5* 10-9). Thank you Lincoln
I have a friend who has a crane lorry and when is operating the crane the emergency stop buttons are 3 of these none of these stops the crane. Inside the pannel is a contactor easy512-dc-rcx, could it be this one faulty?
Hi john, this video will help in my project, however i am wanting to do something more complex but keep ending in a loop, i intend to power a geyser until boiled, as soon as its boiled it will not attempt to boil again until the circuit is manually closed, i am stuck on 2 requirements though that i am hoping to find a solution to, the switch will be a smart switch that cannot handle the 25 amps the geyser needs and i am attempting to not add another load to the circuit as its an attempt for both convenience and saving electricity. At this stage i could use your video to build a meet one or the other but not both, another would've been a momentary switch that energizes a coil that holds the switch in place until the geyser turns off, this again does not allow the smart switch, any ideas would be greatly appreciated
Interesting video, John. Thanks! In case of the three phase motor controlled by a 24V signal, you'd have to make sure that the motor and the control transformer/circuit were on the same breaker, right? Otherwise if the motor tripped the breaker, on switching that breaker back on the motor would immediately start spinning instead of requiring a manual start.
Yes, the 24 volt supply would be from the same breaker. For larger machines it's usually provided from a transformer inside the machine or it's control cabinet.
If the contactor is not latching type, when the power returns after a power failure, it will not start the motor as the contactor's own NO contact will be used to keep the contactor latched in ON position (which would have opened the contactor in the event of a power failure). Hope that clears the point.
Very nice video. I am wondering if it can be applied to a three-button box. In fact I have a motor which I want to connect to the start/stop/e-stop box. Which is the wiring diagram for this? Many thanks in advance for your reply.
Hi John, thanks for the video. I tried to build a NVR panel and it failed miserably! I suspect the low voltage switches that I've been supplied with are incorrect, should one or both of the switches be latching? I need to provide a NVR for a 40amp 240v circuit, I have a 24v transformer and NC and NO switches along with a single phase 40amp contactor, can you please advise? I need this to protect a heat pump from restarting after a power cut.
Wire the push button switches like in the link, on the first circuit (line). Have all the load (40 amps) coming through the contactor. You need an auxiliary normally open contact (most contactors have them or you can add them, they clip on) for controlling the latching of the coil. The push button switches only will need to carry the current of the coil (very small amperage) at 24v. The main contacts on the coil will do the heavy lifting at 240 volts. It is simpler than it looks once you wrap your head around it. machineryequipmentonline.com/hvac-machinery/wp-content/uploads/2016/01/Control-Circuits-0278.jpg
What happens if one phase goes out? One building I worked in lost the Black (labled as Yellow) phase a few times. If the 24V supply is powered from one of the other phases then it would seem to keep the contactor in the on position with potentially bad results.
If you lost a phase has in johns circuit the overload relay for the motor or whatever is powered would shut the circuit down doesn't matter if the 24v is present the circuit has been opened. ..
Assuming we're talking three phase here, on many medium to high horsepower applications (10 or 15 hp+) a phase loss monitoring relay has become standard. You can't necessarily rely on an overload catching a phase loss before there's damage to the motor or the contactor. It's wired up in series with the overload on the coil control circuit. So if either device sees a problem, it cuts voltage to the coil and shuts off the device.
Thank you John for enlighten me.My daily activity is basic service and repair boilers within plant rooms.Would you be kind and explain how to read wiring diagrams for control panels?Also are you aware of any projects for beginners - building a control panel or automation control.thank you very much indeed
JOHN is there anyway you could do a quick video to explain the Schneider double pole 25A contactor, I know it’s not a two minute job to make a video but it would be hugely appreciated!!!!
A contactor power has to be continuous applied for the contacts to close a latching relay will latch on with a pulse of power and reverse the polarity to unlatch it
there are 2 types of latching relays dc ones which are basically a switch with a moved by a solenoid and a ac latching relay which is the circuit that john showed us the ac one will unlatch when power is cut
So a contactor is basically an AC latching relay then? On this cricuit you could basically use a N/O foot pedal as a dead man switch if the contactor was driving a lathe or drill press. Probably not so practical outside educational settings though.
DeKempster: I'm not sure how you can make a safe Deadmans-Switch (foot pedal) if you are using a NC contact. If you are using the NC contact then you have a 24v signal when the pedal is resting and no signal when the pedal is activated. Which is perfect for an ESTOP, but seems a bit odd for a Hold-To-Run function. What am I missing?
Technically you're supposed to wireless top button before the start button. It is safer that way, there are less wires and connections for power shut off to the circuit. In reality, I've seen it done both ways.
Even though wired correctly, your first drawing is wrong. When energized, your electromagnetic coil is pulling (and holding) the switch open. You should have drawn it so the coil, when energized, would pull the switch (and hold it) closed. Either move the coil to the left of the switch or move the switch to the right of the coil. Again, it's wired correctly, but it is visually wrong and confusing.
used the feed back method on contactors for ind gear for years,and customers who "knew better" would try and sort there machines only to realise they couldn't re-wire the feed back path.
Sorry to be picky but this circuit is unacceptable in a industrial environment, and was made illegal some years ago. All emergency stop circuits had to be made dual channel , with an emergency stop monitors to check both contact of the emergency stop buttons are working plus an additional contact to ensure all motor contactors had opened on the last stop command. Where Inverters are used there has to be isolation contactors fitted in the output circuit to the ac motor. Inverter being electronic are not classed as fail safe as are PLC's
I dont think you are correct when it comes to inverters have to be disconnected by dual contactors. A lot of new inverters I've seen lately have a Safe-Torque-Off function and the manufacturers says it can perform up to Performance Level d (Category 3).
ANDREW MICAS your use of "illegal" (as opposed to "against regulations") is almost certainly untrue - for one thing, there's more than one country out there, and for another, in most countries' regulations there are multiple categories of risk. Did you also notice that John was mostly talking about consumer shop tools, and not about "industry"? But feel free to post a video showing how it should really be done for ultimate reliability, and if you give us the link I'll watch it with interest.
Owh, love your channel but that first diagram is very very bad, slow acting start button in parallel with the power contacts, so everything has to be M rated for the locked rotor amps, that’s just stupid. Always use auxiliary contacts. To make it worse, it was the first and only full voltage example, so now you will have people hooking up direct acting, “pilot duty” start buttons on their 3Hp CSCR air compressors and welding fuk out of them. Never use the first example people it is wrong on so many levels, the second example is perfect, just use a 240 volt coil and forget the transformer.
He explicitly states the first example is for low consumption equipment. There are tons of things wired that way. He's showing people what they're going to see in their own equipment. Not everything comes from the factory using an aux contact.
you may have done this video a while ago but it is still helping numpties like me, thank you.
Thank you, I'm sure I've watched and like other videos of yours.
I was struggling with a milling machine control box I'm building not being a electrition etc at 55 year old, including 2x VFDs, coolant, 2x electric power drawbars etc and wanting every safety factor a factory would put into it, and couldn't find anything online regarding 24vac NVR wiring.
I was wanting to use 24vac for a NVR as space is at a premium and you solved my problem in your 3 phase diagram as I have 2 spare contacts using single 3 phase contactor on 240v here in Australia.
Thank you for taking the time to do the video.
if only school! teachers explained things so consise and clear like you JW. I'm enjoying learning from you even though I don't practice electronics. thanks
Unfortunately school teachers are employed by people who do not CARE if they can teach or not, but are only interested in them having the correct qualifications.
In many "small" tools like table saws or belt sanders there's no separate switch for start but the start button mechanically actuates the contactor witch then latches on through one of it's contacts.
John,Greetings from the other side of the pond. I find it funny how we use different mains voltages but the control circuits are both 24v (normally). Great vids. Keep 'em coming.
That's a very nice explanation. and quite informative. I've got to figure out how to wire the e-stop when I've got a variable frequency drive involved. I know I want to break the power to the contactor, but all that is internal to the VFD. I'll have to do some more research.
Many VFDs have emergency stop functionality built into them, and you can control whether it's a free wheel stop (cutting power and letting it coast to a standstill) or whether the VFD actively tries to brake the motor to stop it as quickly as possible. Some of them require special resistors to be attached in order to achieve fast braking so there is somewhere to dump the excess power to (since braking a motor works by turning it into a generator, and the more power you can pull out of the "generator" and dump somewhere, the faster the motor will stop turning).
John ive often seen the electric organ piano in the background corner of your office, is this another hidden talent of yours and would you at all do a video showing your favorite music
A great explanation and I wasn't aware of the No Volt Release on home workshop machines. Many Thanks
Thank you John. Finally I understand why operating my scroll saw with an on/off foot switch did not work as I had intended.
I have put latching relays with push on, and off buttons in my CNC engraver, and a table saw. I like them. If I ever find more relays, and buttons I might install them in other machines I have too.
Paul Frederick Does it act like a generator?
Things have changed a lot with E-stops, machines are risk classified which specifies the required protection, devices I work on even pillaar drills have pilz saftey relays and safety contactors, which of course have dual circuit monitored e-stop switches.
hi there good informative video, but what do you do if you have 5th wire coming from a motor (overload protection) i think and your NVR only has 4 connections?
Brilliant video. Really appreciate the effort and time you've put into this. Keep up the good work John. However, I must say that I was looking to see if any of your videos demonstrate (calculating resistivity), but I didn't. If possible could please demonstrate a lil video or if it's not possible, please could you send us a lil calculation- say: for example: a piece of material measuring 100metre in length, CSA1.5, for copper?! Formula (17.5* 10-9). Thank you
Lincoln
I have a friend who has a crane lorry and when is operating the crane the emergency stop buttons are 3 of these none of these stops the crane. Inside the pannel is a contactor easy512-dc-rcx, could it be this one faulty?
Hi john, this video will help in my project, however i am wanting to do something more complex but keep ending in a loop, i intend to power a geyser until boiled, as soon as its boiled it will not attempt to boil again until the circuit is manually closed, i am stuck on 2 requirements though that i am hoping to find a solution to, the switch will be a smart switch that cannot handle the 25 amps the geyser needs and i am attempting to not add another load to the circuit as its an attempt for both convenience and saving electricity. At this stage i could use your video to build a meet one or the other but not both, another would've been a momentary switch that energizes a coil that holds the switch in place until the geyser turns off, this again does not allow the smart switch, any ideas would be greatly appreciated
How do you wire in the micro switch on a piller drill ie micro switch in belt casing to incorporate it into an nvr switch kjd12
Thanks John can you do a video on how safety relays work and are meant to be wired?
Interesting video, John. Thanks!
In case of the three phase motor controlled by a 24V signal, you'd have to make sure that the motor and the control transformer/circuit were on the same breaker, right?
Otherwise if the motor tripped the breaker, on switching that breaker back on the motor would immediately start spinning instead of requiring a manual start.
psh
Koffi Banan could you show us inside a start stop with coil?
Yes, the 24 volt supply would be from the same breaker. For larger machines it's usually provided from a transformer inside the machine or it's control cabinet.
If the contactor is not latching type, when the power returns after a power failure, it will not start the motor as the contactor's own NO contact will be used to keep the contactor latched in ON position (which would have opened the contactor in the event of a power failure). Hope that clears the point.
Very nice video. I am wondering if it can be applied to a three-button box. In fact I have a motor which I want to connect to the start/stop/e-stop box. Which is the wiring diagram for this? Many thanks in advance for your reply.
Great explanations jw
Thank you. This helped A LOT!
Regards,
Willem
It may have helped to use the actual schematic symbols for the NO and NC push-button switch. That way they wouldn't look like the contactor contacts.
Hi John, thanks for the video. I tried to build a NVR panel and it failed miserably! I suspect the low voltage switches that I've been supplied with are incorrect, should one or both of the switches be latching? I need to provide a NVR for a 40amp 240v circuit, I have a 24v transformer and NC and NO switches along with a single phase 40amp contactor, can you please advise? I need this to protect a heat pump from restarting after a power cut.
Wire the push button switches like in the link, on the first circuit (line). Have all the load (40 amps) coming through the contactor. You need an auxiliary normally open contact (most contactors have them or you can add them, they clip on) for controlling the latching of the coil. The push button switches only will need to carry the current of the coil (very small amperage) at 24v. The main contacts on the coil will do the heavy lifting at 240 volts. It is simpler than it looks once you wrap your head around it.
machineryequipmentonline.com/hvac-machinery/wp-content/uploads/2016/01/Control-Circuits-0278.jpg
What happens if one phase goes out?
One building I worked in lost the Black (labled as Yellow) phase a few times.
If the 24V supply is powered from one of the other phases then it would seem to keep the contactor in the on position with potentially bad results.
If you lost a phase has in johns circuit the overload relay for the motor or whatever is powered would shut the circuit down doesn't matter if the 24v is present the circuit has been opened. ..
Assuming we're talking three phase here, on many medium to high horsepower applications (10 or 15 hp+) a phase loss monitoring relay has become standard. You can't necessarily rely on an overload catching a phase loss before there's damage to the motor or the contactor. It's wired up in series with the overload on the coil control circuit. So if either device sees a problem, it cuts voltage to the coil and shuts off the device.
Thank you John for enlighten me.My daily activity is basic service and repair boilers within plant rooms.Would you be kind and explain how to read wiring diagrams for control panels?Also are you aware of any projects for beginners - building a control panel or automation control.thank you very much indeed
So so generous John, Thank you again.
JOHN is there anyway you could do a quick video to explain the Schneider double pole 25A contactor, I know it’s not a two minute job to make a video but it would be hugely appreciated!!!!
Great info and very clear explanation !!
excellent video info
John, great vid again. Can you please do a video on Storage Heaters and how they operate¿ Thanks!
Good video John.....now i know a lot people are wondering this when are you going play the old Hammond in the corner ? :)
Thank you so much.
Great video. Thank you.
What is the difference between a contactor and a latching relay?
A contactor power has to be continuous applied for the contacts to close a latching relay will latch on with a pulse of power and reverse the polarity to unlatch it
Thanks its a subtle difference but a difference all the same. SO a latching relay won't unlatch even if power is cut?
there are 2 types of latching relays dc ones which are basically a switch with a moved by a solenoid and a ac latching relay which is the circuit that john showed us the ac one will unlatch when power is cut
So a contactor is basically an AC latching relay then? On this cricuit you could basically use a N/O foot pedal as a dead man switch if the contactor was driving a lathe or drill press. Probably not so practical outside educational settings though.
DeKempster:
I'm not sure how you can make a safe Deadmans-Switch (foot pedal) if you are using a NC contact.
If you are using the NC contact then you have a 24v signal when the pedal is resting and no signal when the pedal is activated. Which is perfect for an ESTOP, but seems a bit odd for a Hold-To-Run function. What am I missing?
It may be different from here in america but we wire the stop button before the start button.
Technically you're supposed to wireless top button before the start button. It is safer that way, there are less wires and connections for power shut off to the circuit. In reality, I've seen it done both ways.
thanks for the informative video
Interesting vid John, clear and concise. Any chance of vids on motor starting? ie. Star-Delta, Part wind, Rotor resistance etc?
Superb sir.
Great Video Thanks
Even though wired correctly, your first drawing is wrong. When energized, your electromagnetic coil is pulling (and holding) the switch open. You should have drawn it so the coil, when energized, would pull the switch (and hold it) closed. Either move the coil to the left of the switch or move the switch to the right of the coil. Again, it's wired correctly, but it is visually wrong and confusing.
used the feed back method on contactors for ind gear for years,and customers who "knew better" would try and sort there machines only to realise they couldn't re-wire the feed back path.
Sorry to be picky but this circuit is unacceptable in a industrial environment, and was made illegal some years ago. All emergency stop circuits had to be made dual channel , with an emergency stop monitors to check both contact of the emergency stop buttons are working plus an additional contact to ensure all motor contactors had opened on the last stop command. Where Inverters are used there has to be isolation contactors fitted in the output circuit to the ac motor. Inverter being electronic are not classed as fail safe as are PLC's
I dont think you are correct when it comes to inverters have to be disconnected by dual contactors.
A lot of new inverters I've seen lately have a Safe-Torque-Off function and the manufacturers says it can perform up to Performance Level d (Category 3).
ANDREW MICAS your use of "illegal" (as opposed to "against regulations") is almost certainly untrue - for one thing, there's more than one country out there, and for another, in most countries' regulations there are multiple categories of risk. Did you also notice that John was mostly talking about consumer shop tools, and not about "industry"?
But feel free to post a video showing how it should really be done for ultimate reliability, and if you give us the link I'll watch it with interest.
this looks like whats called relays
Yes, same method of operation, contactors are just designed for switching much larger loads.
Owh, love your channel but that first diagram is very very bad, slow acting start button in parallel with the power contacts, so everything has to be M rated for the locked rotor amps, that’s just stupid. Always use auxiliary contacts.
To make it worse, it was the first and only full voltage example, so now you will have people hooking up direct acting, “pilot duty” start buttons on their 3Hp CSCR air compressors and welding fuk out of them.
Never use the first example people it is wrong on so many levels, the second example is perfect, just use a 240 volt coil and forget the transformer.
He explicitly states the first example is for low consumption equipment. There are tons of things wired that way. He's showing people what they're going to see in their own equipment. Not everything comes from the factory using an aux contact.