# Lost phase on step up transformer



## Pacific81 (Feb 19, 2010)

Hi I have a 120v/480 step up transformer in a commercial establishment supplying a panel board, When the circuit breaker in the panel board for a pump is turned on (newly installed over a week ago, and has been working fine) I loose the orange phase on the secondary side of the transformer, the circuit breaker is only turned on the control circuit that brings the coil in is off so there is no load on the motor pump!! Any ideas on what could be causing the phase to be lost would be great.


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## ponyboy (Nov 18, 2012)

what did you do to verify you are actually loosing a phase


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## wildleg (Apr 12, 2009)

sounds like you have a blown fuse, and you think there is phase voltage, but really not. of course, with the limited info you gave, that's just a wag


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## Pacific81 (Feb 19, 2010)

I tested the phase with an approved voltage tester. The 3 fuses in the disconnect to the transformer are working. I am getting voltage on the primary & secondary side of the transformer then when I turn the pump circuit breaker on I loose voltage on the secondary side of the transformer only.


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## Big John (May 23, 2010)

Did you test phase to phase and phase to ground? What make and model is an "approved voltage tester"? What were your numbers?

You're either reading backfeed, induced voltage, or else you have an extremely poor connection somewhere that's allowing just enough bleed-through for your tester to read.


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## xlink (Mar 12, 2012)

Pacific81 said:


> I tested the phase with an approved voltage tester. The 3 fuses in the disconnect to the transformer are working. I am getting voltage on the primary & secondary side of the transformer then when I turn the pump circuit breaker on I loose voltage on the secondary side of the transformer only.


That's also the symptom of a blown fuse. Turn the power off and test the fuses.


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## Pacific81 (Feb 19, 2010)

Hi, thank you for the replies. I used a fluke t1000 to confirm the voltage. I turned the power off and tested the continuity of all 3 fuses they are all fine. I am getting voltage to the orange phase but as soon as I turn on the pump circuit breaker the phase reads 0 volts. Never seen anything like it! As for readings I am getting 277 phase to ground and 480V between phases.


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## xlink (Mar 12, 2012)

I can't think of anything besides phase loss on the line side.

I'm confused about the 120/480 transformer. Typo?

For the little it may be worth, are there a lot of motors running off the service where the transformer is fed? That can simulate a phase, but the voltages would vary. When you find the problem, please post it here.


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## Big John (May 23, 2010)

I'm thinking he meant 208:480.

Are you testing directly at the transformer terminals? What's the configuration on this transformer? When you say you lose voltage, I assume you mean you get zero volts to ground, what're your L-L voltages at that point?


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## kevink1955 (Apr 25, 2012)

Like Big John said you need to provide more info.

The secondary could be ungrounded and you are reading phantom voltage to ground till you load it, is there a neutral run with the phase conductors.

Get all the readings, L to L, L to ground and L to N (if you have 1) and check back


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## Aussielec (Apr 1, 2012)

Pacific81 said:


> When the circuit breaker in the panel board for a pump is turned on (newly installed over a week ago, and has been working fine) I loose the orange phase on the secondary side of the transformer, the circuit breaker is only turned on the control circuit that brings the coil in is off so there is no load on the motor pump!!


So your saying that the control breaker for the pump control circuit is left off and your only switching on the breaker for the pump itself? 

So the power essentially only goes a far as the contactor?

If so check the load and line side of the pump circuit breaker with it switched on. Sounds like you may having a faulty breaker.


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## Pacific81 (Feb 19, 2010)

Sorry yes the transformer in question is a 480/120-208v 135 kva transformer. It is a three phase transformer with the neutral/ground from the panel connected to the mid point of the transformer. Yes Aussielec that is exactly whats happening, I will carry out further tests tomorrow morning. I am reading 480 v phase to phase then or 277 phase to ground, then as soon as I turn the pump circuit breaker on, with the control circuit turned off I loose the voltage. I will carry out further inspection tomorrow and post my findings. Thanks for all your input


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## Ultrafault (Dec 16, 2012)

Remove the contactor, fuses, and breaker from the circuit before you test their continuity. Does the motor hum when you try to turn it on?


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## brian john (Mar 11, 2007)

I assume in your lack of stating clearly the type of transformer, this is a 208 Delta Primary to 480/277 Wye Secondary or 208 Delta Primary to 480 delta Secondary? I would guess the first one 208 Delta Primary to 480/277 Wye.

If you were loosing primary input (208), the secondary voltages would not be just a loose of one phase, the secondary voltages would be low on two phases. I believe never powered up a 280 to 480/277 with a phase missing.

Something else is wonky, like a ungrounded secondary that is grounded when you power up the controls.


What would be helpful

As noted transformer type

Grounding configuration

Primary Voltage

Phase to phase A-B, B-C, C-A

Secondary Voltage A-B, B-C, C-A, A-Gnd, B-Gnd, C-Gnd and if available A-N, B-N, C-N


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## Aussielec (Apr 1, 2012)

If it helps anyone I doubt this guy is from the UK, despite his profile. I'd say he's in the US....

My first thought was why being in the UK does he need a transformer to convert voltages considering the UK does not have mixed voltages (I think) like you guys do. It's a standared 400/230 volt system. Unless there using foreign motors of course, but thats highly unlikely.


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## xlink (Mar 12, 2012)

I think he moved to the US and didn't change his profile.


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## Pacific81 (Feb 19, 2010)

Hi all, Yes I am living in California now (san Diego) I am state CA certified but I still have a lot to learn in regards to the terminology and regulations. I have found the problem, there was a cable connected to the supply side on the top of the contactor (orange phase) connected a COM connector at the bottom of the contactor i think it was an auxiliary connector supposed to be used for a stop/start button. As to the reason to why it was loosing the phase is still unknown any ideas would be great? I tested all phases when the phase was out and was getting 480v between phases 277v phase to ground apart from the orange phase. I will try to post some pics.... Thanks


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## Pacific81 (Feb 19, 2010)

Photos


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## Pacific81 (Feb 19, 2010)

This is where the red cable was connected to, the connection was labeled common.


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## glen1971 (Oct 10, 2012)

Pacific81 said:


> This is where the red cable was connected to, the connection was labeled common.


I believe that is the common terminal for the overload relay.. N.C. for your control logic and if there is a N.O. set, that would be for an indicating light (i.e. "Overload Trip".)... Taking this out of the control would leave your control circuit energized in the event of one or more overloads tripping, which could result in single phasing the motor...


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## Ultrafault (Dec 16, 2012)

..... I'm walking away from this trainwreck catch you guys on the other side.


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## xlink (Mar 12, 2012)

I feel so smart.


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## brian john (Mar 11, 2007)

If you read my post and applied what I noted it might give us some insight to what is/was going on.


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## hoggieturk (Feb 19, 2013)

your control voltage shuold run thru those contacts in case of overload


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## Big John (May 23, 2010)

Clarify something for me: Were you always, under every circumstance getting 480V between all phases?

I'm starting to suspect you weren't actually losing a phase at all.


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## l0sts0ul (May 7, 2011)

ok, you are a journeyman electrician right? If you removed the red wire off the terminal below (as you have already been asked) you would have bypassed the overload relays. IF you are metering on L1, L2, L3 and not getting your required voltage, then yes, you have a power input problem. If you are metering from the T1, T2, T3 side, and missing a phase, I would believe you have a blown overload and that is your missing phase.

sorry,I broke the 3 sentence, or Haiku rule.


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## xlink (Mar 12, 2012)

Blow the pics up real big and note the red wire under the screw with the white wire. Why do you suppose the neutral has two wires?


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## Big John (May 23, 2010)

l0sts0ul said:


> ...Sorry,I broke the 3 sentence, or Haiku rule.


 :blink: I had no idea we had a Haiku rule. Now I gotta try it:

All phases are there.
Seems like a control problem.
Troubleshoot some more.


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## l0sts0ul (May 7, 2011)

or call us to fix it...

bottom line, you're control wiring is screwed.... 

remove all wires, draw out the start stop stn and wiring, and start again.

no haikus here.


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## SHADOW (Feb 24, 2009)

Press the contactor manualy and check if the motor start,it may be the
contactor coil that is wrong or a carbonized contact.


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## Peewee0413 (Oct 18, 2012)

Is it the reset?


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## hardworkingstiff (Jan 22, 2007)

I still want to know if this is a step down transformer fed in reverse or is it a designed step up transformer, plus is it Delta/Delta, Delta/Wye ? (yes, I understand the OP said it was a step up transformer, but I think this is a valid question based on the presentation of information so far)

I think you are reading a ghost voltage and it goes away when you turn on that breaker.

What kind of OCP is on/after the transformer?


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## xlink (Mar 12, 2012)

The motor is 480 volts and the starter was pre-wired to the 120 volt coil. The control neutral is probably the only ground on the transformer.


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## xlink (Mar 12, 2012)

Ultrafault said:


> ..... I'm walking away from this trainwreck catch you guys on the other side.


Aww come on. You can't not watch a train wreck.


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## Peewee0413 (Oct 18, 2012)

Sissy lol. Its easy find where this is power and where there isn't power where it needs to be. Troubleshoot 101 lol


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## Pacific81 (Feb 19, 2010)

Hi all, 

Brian John, the transformer is a step up transformer 480/120-208v 135 kva transformer, with a delta configuration, I was not loosing the primary phase I was loosing the secondary phase (orange) , the grounding configuration was via an earth rod, primary voltage readings were 120v to ground/208 between phases, secondary voltage readings were 277v to ground/480 between phases, these readings were consistent apart from when I turned the motor circuit on and I would loose the voltage reading between B (orange) phase and ground but still got phase to phase readings on the secondary conductors. 

Big John, yes under every circumstance’s I was always getting 480V between the secondary phases. 

L0sts0ul, yes I am a journeyman electrician  well I have only had the Journeyman status for 4 weeks, previous to that I was an electrician in the UK. From my understanding the cable connected to the common is an option for an auxiliary switch used with a stop/start or emergency stop button (I may be wrong, excuse me if I am). 

Hopefully this answers all the questions, with the red wire removed I no longer seem to have lost a phase, I put my amp meter on the conductors at the transformer under load while the (phase was down) and it was pulling amps each secondary conductor was about 33A each with only a compressor running in the factory, I actually don’t think I was loosing a phase but for some reason when this (red) wire was connected to the supply side of the contactor to the COM as in the pics it was causing some sort of back feed enabling me not to read voltage on the orange phase to ground, I am not to sure hence asking you kind informative chaps for information 


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## Ultrafault (Dec 16, 2012)

bonding you do lack,
an electrician needs called,
someone you will kill.


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## Ultrafault (Dec 16, 2012)

ok so you guys had to lure me back with haikus.


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## brian john (Mar 11, 2007)

Is the secondary a delta? or a Wye

How is the secondary grounded and a ground rod is NOT THE CORRECT answer.

If it is a delta did you bond one phase to ground?

If is is a wye did you bond the neutral to ground?

The last two questions are criticial because I suspect you have a ungrounded system and when you pull the contactor in you have a short on the orange phase and the system is now grounded. 

Just a guess.


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## Aussielec (Apr 1, 2012)

Just a guess, but have a look at the bottom left picture. See that other red wire in the photo. It looks as though it comes out of the top terminal then shoots down behind the back of the contactor. I'd say who ever screwed that contactor back trapped the wire in behind. Thats possibly where your fault is.

The wire you disconnected looks as if goes through the overload NC terminal at the bottom and then exits at the top. Hence when disconnected the fault dissapeared. That wire is most likely shorted to the enclosure as is passes behind the contactor. In your picture I can see a protective earth conductor connected to the enclosure, which means if that is indeed the fault your breaker should of tripped.

So I'm kind of thinking that the entire enclosure was most likely energised and you were probably extremely lucky you or someone else wasn't electrocuted. Though this is just all a guess going off the information and the pictures provided.

As Brian mentioned how have you bonded your protective earth conductors back at the transformer? Because it's sounds like your protective earthing is non existant. Is the secondary star or delta connected?

These two questions need answering because something is not right here.


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## xlink (Mar 12, 2012)

I've often wondered why the factory pre-wires a 3 phase circuit to a 120 volt coil. It just has to be changed if you use a control xfrmr or a higher voltage.

That wire isn't faulted to ground. It's factory.

I assume the OP used 120 volts on the 120 volt coil, but I wonder if he knows that In North America we don't switch the neutral.


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## hardworkingstiff (Jan 22, 2007)

brian john said:


> The last two questions are criticial because I suspect you have a ungrounded system and when you pull the contactor in you have a short on the orange phase and the system is now grounded.
> 
> Just a guess.


I'm with Brian. Ungrounded secondary that gets grounded through the starter controls. Lift that "red wire" and you aren't grounded anymore.

To the OP, you need to slow down a little and try to understand what Brian is saying. Drop your preconceived ideas about what is wrong, and look at the facts as if it is a brand new problem.


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## BBQ (Nov 16, 2010)

hardworkingstiff said:


> To the OP, you need to slow down a little and try to understand what Brian is saying. Drop your preconceived ideas about what is wrong, and look at the facts as if it is a brand new problem.


Ditto what hard' said.

Brain is very sharp can teach many of us things.


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## hardworkingstiff (Jan 22, 2007)

BBQ said:


> Brain is very sharp can teach many of us things.


I like that, "Brain" :laughing:

I also am happy he is back posting. :thumbsup:


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## brian john (Mar 11, 2007)

Aussielec said:


> J
> 
> So I'm kind of thinking that the entire enclosure was* most likely energised* and you were probably extremely lucky you or someone else wasn't electrocuted. Though this is just all a guess going off the information and the pictures provided.
> 
> ...


If this is an ungrounded system and the control wire grounded it, the enclosure is grounded not energized. NOT SURE if that is what you are elluding to in your comment.


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## Big John (May 23, 2010)

brian john said:


> ...I suspect you have a ungrounded system and when you pull the contactor in you have a short on the orange phase and the system is now grounded....


 Agreed.


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## xlink (Mar 12, 2012)

Okay, here is my opinion of the fix.

The wire that came loose: remove it.

The wire on the auxiliary contacts at the top of the starter. Remove it.

Take your red control wire from the left coil screw and put in on the overload contact at the very bottom of the starter (circled in your picture).

You will have one red wire on the coil that comes from the other auxiliary contact at the bottom of the starter. The white, neutral, should be on the other coil screw.

You should not have two wires on any screws and no control wires should be connected to the 480 volt supply.

On your control circuit, make sure you are switching the hot. The white wire doesn't need to be switched, but if it is, you must also switch the red wire at the same time. In any case, you need to switch the red wire.

I'll leave it to the NEC electricians to guide you on grounding requirements for the transformer.


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## JRaef (Mar 23, 2009)

OK, here is MY theory.
The starter was originally set up for a line voltage coil, where the coil circuit would be powered by tapping off of two of the phases. Someone changed the coil to be 120V, but the OL side of the control circuit was not changed, hence the wire going to "Common", which was connected to the Neutral, which is now grounded. When the breaker was closed, the phase that was connected to that was now going directly to ground, but through a very small wire and contact elements. So it was heating up, but not enough to take out the primary fuses on the transformer yet. When he measured from that phase to ground he saw zero volts, because IT WAS ALREADY GROUNDED! Had he left it on long enough, the wire would have melted and the fault would be more obvious.


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## Big John (May 23, 2010)

JRaef, sounds possible, but my money is on that there actually wasn't a short-circuit: I think the ground he had that was zeroing his voltage was probably the only ground point on the secondary of that transformer. 

This would explain the failure of any protection to operate, and seems especially plausible when you consider it's probably a reverse fed Δ:Y. I bet whoever dropped it in wasn't sure how to ground the delta and left it floating. Also makes me wonder if the primary isn't double-bonded.


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## xlink (Mar 12, 2012)

Big John said:


> I bet whoever dropped it in wasn't sure how to ground the delta and left it floating. Also makes me wonder if the primary isn't double-bonded.


How do you ground a 480 delta?


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## BBQ (Nov 16, 2010)

xlink said:


> How do you ground a 480 delta?


Pick a phase, 'B' is often chosen, bond it to ground like you would XO on a wye transformer.


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## brian john (Mar 11, 2007)

xlink said:


> How do you ground a 480 delta?


Same way you ground a wye, A Delta is corner grounded, one phase is grounded then voltage on the secondary/load, asuming you grounded the "C" phase.

A-B-480
B-C-480
C-A-480

A-Gnd-480
B-Gnd-480
C-Gnd-0 (ZERO VOLTS)


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## xlink (Mar 12, 2012)

We have to ground to the service ground with a wire sized for the secondary. You?


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## Aussielec (Apr 1, 2012)

Pacific81 said:


> Brian John, the transformer is a step up transformer 480/120-208v 135 kva transformer, with a delta configuration, I was not loosing the primary phase I was loosing the secondary phase (orange) , the grounding configuration was via an earth rod





brian john said:


> If this is an ungrounded system and the control wire grounded it, the enclosure is grounded not energized. NOT SURE if that is what you are elluding to in your comment.


Not sure if Pacific means the primary or secondary but it sounds like the secondary is grounded via an earthing rod. This leads me to assume that it's not a floating voltage and something was probably energised. But as I said it's just a guess.

If he was getting 208/120 volts on the primary and 480/277 volts on the secondary that sounds like the transformer could be connected Y/Y, I'm not sure where Pacific got the idea he had a delta configuration from the readings he was getting. But again just a guess.

But yeah I agree something get's grounded when that part of the control circuit is energised.


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## Ultrafault (Dec 16, 2012)

Aussielec said:


> Not sure if Pacific means the primary or secondary but it sounds like the secondary is grounded via an earthing rod. This leads me to assume that it's not a floating voltage and something was probably energised. But as I said it's just a guess.
> 
> If he was getting 208/120 volts on the primary and 480/277 volts on the secondary that sounds like the transformer could be connected Y/Y, I'm not sure where Pacific got the idea he had a delta configuration from the readings he was getting. But again just a guess.
> 
> But yeah I agree something get's grounded when that part of the control circuit is energised.


You can not ground anything with a ground rod. Ground rods are only for lightning protection. EVerything must be bonded to the transformer netural or throungh a ground detector. You can however make great boobie traps with a ground rod and a unbonded grounding conductor.


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## Pacific81 (Feb 19, 2010)

Hello all, excuse my lack of information in regards to the transformer, I am from the UK we don’t work with a lot of trannys over there. I believe Its 3 phase as a phase is not bonded to ground the neutral is bonded to ground on the X0 bar. I did not install the transformer or coil or pump motor, I was only fault finding to see what the problem was. I know you guy’s don’t switch neutral in the US we do not switch neutral in the UK unless it is a double/triple pole switch. The primary and secondary supply/load are both bonded, the earth rod is just there for extra protection. 

I Think JRaef hit the nail on the head. 

OK, here is MY theory.
The starter was originally set up for a line voltage coil, where the coil circuit would be powered by tapping off of two of the phases. Someone changed the coil to be 120V, but the OL side of the control circuit was not changed, hence the wire going to "Common", which was connected to the Neutral, which is now grounded. When the breaker was closed, the phase that was connected to that was now going directly to ground, but through a very small wire and contact elements. So it was heating up, but not enough to take out the primary fuses on the transformer yet. When he measured from that phase to ground he saw zero volts, because IT WAS ALREADY GROUNDED! Had he left it on long enough, the wire would have melted and the fault would be more obvious.

I will further investigate when I return to the job next week, Since removing the red cable connected to the common there has not been a problem. Thank you for all the comments.


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## frenchelectrican (Mar 15, 2007)

Bonjour Pacific 81.,

Before you do anything more with that motour contractor unit due you mention you have 480 volts line to line ( phase to phase ) and the red conductor behind the orange conductor that should be removed when you use the 120 volt contractor coil otherwise you will burn the coil up. 

I will post the Americian verison which I do understand you are famuair with IEC format but not excatally with NEMA format which the NEMA's are pretty much standardized.

So let me post it so you can see the link http://static.schneider-electric.us/docs/Machine Control/0140CT9201.pdf

( this is one of my most common used item for wiring diagram on Sq D items ) 

I will find something simple with clear diagram for this type of starter.

For the rest of the guys in here go ahead and book mark that link I posted above that will just cover almost all the Sq D starter/contractors.

Merci,
Marc


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## hardworkingstiff (Jan 22, 2007)

Pacific81 said:


> I believe Its 3 phase as a phase is not bonded to ground the neutral is bonded to ground on the X0 bar.


That does not make sense to me. If the secondary is grounded, then when that phase conductor went to ground (through the neutral on the coil), smoke would have come out at the contactor and you would not "lose a phase", you would burn something up very quickly or trip an OCP device.

If you have the means to post pictures, when you get back there, please take a picture of the transformer data plate, the wiring in the transformer, and don't forget to post the voltages between phases and phases to ground.


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## brian john (Mar 11, 2007)

First if you really want help

1. Can you post a picture of the name plate?
2. If this is a step up I am assuming X1,X2,X3,X0 are on the 208/120 primary/input/supply? If so then XO should not be bonded/connected to ground or a supply neutral.
3. If the secondary/output/load is H1, H2, H3 then on of those would be grounded or you should have ground detection installed.
4. Is there an H)?
B-XO

I think your idea of the wire being to small is off base, and I still believe based on the limited information you provided you have an ungrounded system. 

SO lastly

FIll in the blanks
primary/input/supply
A-B_____________VAC
B-C_____________VAC
C-A_____________VAC
A-XO____________VAC
B-XO____________VAC
C-XO____________VAC

secondary/output/load 
A-B_____________VAC
B-C_____________VAC
C-A_____________VAC
A-Gnd____________VAC
B-Gnd____________VAC
C-Gnd____________VAC


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## Pacific81 (Feb 19, 2010)

Hi all, just an update I have still not been back to this job yet! When I do I will gather the above info. 

Chris


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## Ultrafault (Dec 16, 2012)

Thats good I was sure you had electrocuted yourself.


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## l0sts0ul (May 7, 2011)

Or got fired.


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