Dumbfounded

[CDS]

I am dumbfounded with an issue. The following are the specs.
New Eaton Panel with 3P 200a MCB 277/480
Breakers are mostly a mix of 3 poles for 480v AHU Equipment.
The 1-3/20 breaker feeds a humidifier is giving me trouble.
When breaker was initially turned on we read 480 across phases and 277 to ground. All is good.
When the Mechanical contractor turned on the disconnect at humidifier the problems started.
Phases A&B where good however C phase dropped to 57 volts. Between A&B still read 480 but AC & BC were way out of whack. I don't remember exact voltage reading but something like 240 AC and 140 BC.
I assumed it may have been a bad breaker. Luckily we had a spare 3p/20 so we replaced.
Well I took readings again once we re-energized panel at the 3/20 breaker and everything was normal when no load was present. Again they closed the disconnect at humidifier and powered the unit up. Again the same exact issue. We "exercised" the replacement breaker and even intentionally tripped it to see if "something internal" would reset. When turning back on (without any load and disconnect open) we still only got 57 volts on C phase which again tells me this breaker is now bad too.
Obviously these breakers are not cheap and we cant just try another breaker.
Has anyone else had this problem and if so what was your solution? I personally think something in the humidifier is doing this to the breakers. They are not tripping and the 3 pole breaker opposite side is all good with 277/480 readings so I know its not the buss. All other breakers in panel above and below are working normal.
All suggestions welcome.

 

[romex jockey]

bum noodle.......~RJ~

 

[gadfly56]

bum noodle.......~RJ~

For a 3 phase load??

 

[LarryFine]

Welcome to the forum. In no particular order:

I recommend using a solenoid or other low-impedance tester; Hi-Z voltmeters are misleading.

I would test from another hot line terminal to each line of the feeder, looking for a ground fault.

Then the same thing at the disconnect terminals with it open, from a line to each load terminals.

Temporarily install both bad breakers, using appropriate poles of each to mimic one good one.

 

[LarryFine]

For a 3 phase load??

He was describing dinner.

 

[CDS]

Welcome to the forum. In no particular order:

I recommend using a solenoid or other low-impedance tester; Hi-Z voltmeters are misleading.

I would test from another hot line terminal to each line of the feeder, looking for a ground fault.

Then the same thing at the disconnect terminals with it open, from a line to each load terminals.

Temporarily install both bad breakers, using appropriate poles of each to mimic one good one.

Benn a while since posting a couple years back and had to come on as a newby. Lost my credentials like losing my mind over this issue. Anyway appreciate the input. Sometimes I overthink the issue instead of doing the obvious and easy.
I like the idea of using both breakers and mimic the phases that work.
The Mech Contractor switched the probes in his equipment and isolated the current sensor. We will try this along with your suggestion. But I still think the Condair Humidifier is acting up and hurting our breakers somehow. I found out the other exact Condair humidifier that was turned on only a year and a half ago is out of service too. Will keep this up to date on the final verdict. I have the Eaton rep stopping out on Monday to review issue as he too is stumped.

 

[don_resqcapt19]

Does that panel have bus fingers that connect the breaker to the main bus? If so, I would take a look at the connection between the finger and the main bus.

 

[ptonsparky]

I’m curious what the current draw is.

 

[infinity]

Does that panel have bus fingers that connect the breaker to the main bus? If so, I would take a look at the connection between the finger and the main bus.

Bingo, this has happened to me on more than one occasion. The bolt connecting the stab to the bus was missing or loose. In one case the bus stabs to a disconnect switch (bucket) were completely missing.

 

[CDS]

Does that panel have bus fingers that connect the breaker to the main bus? If so, I would take a look at the connection between the finger and the main bus.

I did not physically try to tighten the fingers to the main bus. Only looked and made sure the new breaker was tight but will check it out at bus connection. Hopefully its that simple of a fix. Otherwise I am back to being perplexed.

 

[CDS]

I’m curious what the current draw is.

13.5 amp per equipment nameplate.

 

[ptonsparky]

13.5 amp per equipment nameplate.

Actual draw. It would have shown the bad connection. That and a FOP from C at main lugs to C of breaker load lug.

 

[CDS]

Actual draw. It would have shown the bad connection. That and a FOP from C at main lugs to C of breaker load lug.

Gotcha. I will do this when I use the 2 "bad breakers" A&B phases and mimic one of those on breaker #2 for a C phase and read amps. One would think it would trip the breaker if its way too high to begin with though. But who knows?

 

[LarryFine]

One would think it would trip the breaker if its way too high to begin with though. But who knows?

Could be a bad connection somewhere, possibly in the EGC, that is limiting current.

 

[ptonsparky]

I’m thinking the humidifiers of any size Ive seen were heating elements in water. Current would have been low on C.

 

[grich]

Our 480V humidifier at work has been rewired three times in the 7 years it's been in service...burned connections at contactors and fuse blocks. Had our share of shorted heating elements. This is the first winter we haven't had a major failure...probably because our building maintenance guy has figured out a good schedule to descale the thing. May want to give your unit a good once-over.

Could be a bad connection somewhere, possibly in the EGC, that is limiting current.

Perhaps the phase is being pulled to ground through a failed heating element.

 

[CDS]

Our 480V humidifier at work has been rewired three times in the 7 years it's been in service...burned connections at contactors and fuse blocks. Had our share of shorted heating elements. This is the first winter we haven't had a major failure...probably because our building maintenance guy has figured out a good schedule to descale the thing. May want to give your unit a good once-over.

Perhaps the phase is being pulled to ground through a failed heating element.

This is the first thing we thought of. However why would that lead to 2 breakers going bad instead of tripping the breaker itself or tripping the internal fuses in the unit? It’s just odd how both brand new breakers read 480 across phases and 277 to ground until unit was turned on. Now both breakers read only 57 volts on C phase even when there is no load. Like I stated the 3 pole breaker parallel to this one works as it should operating a CU. The bus has fingers so all phases are the same parallel of each other.

 

[kwired]

Measure FOP across the input and output of breaker, while under load. Measure FOP across any joint in the bus or even bus to breaker connnections - again while under load. Any higher potential reading is showing you a series resistance exists somewhere between meter leads, but you must have current before there will be voltage drop. If there is bad enough connection even a low impedance meter might add enough load to expose the problem.

 

[ptonsparky]

Measure FOP across the input and output of breaker, while under load. Measure FOP across any joint in the bus or even bus to breaker connnections - again while under load. Any higher potential reading is showing you a series resistance exists somewhere between meter leads, but you must have current before there will be voltage drop. If there is bad enough connection even a low impedance meter might add enough load to expose the problem.

Yes, I almost always forget to include "while under load". Not thinking it would be done any other way.

 

[LarryFine]

Measure FOP across the input and output of breaker, while under load. Measure FOP across any joint in the bus or even bus to breaker connnections - again while under load.

This. There should be no voltage between the bad phase's bus and the wire attached to that pole on the breaker.

Voltage is being lost, or dropped, across some point where it shouldn't be. You need to find that place in the circuit.