New shunt-trip breaker failed - should I pay for the replacement?

[Mr. Serious]

For the past year or more, we've been wiring a convenience store under new ownership and being completely gutted and remodeled. They're just about to open, but we had a bit of a misunderstanding with fire suppression system controls wiring (the prints showed both fans supplied from the shunt-trip panel, which was incorrect), leading the system to be tested some number of times over the past few days. The system activates a 100A 3-phase shunt trip breaker, and after probably about 4 system tests, the breaker is now failing to turn back on and restore power to the items under the hood. Can this failure mode (breaker won't turn on) be caused by mis-application of shunt trip voltage?

The service is 600A 3-phase, 208Y120 volt. The shunt-trip breaker is the main breaker of a panel on the other side of the wall from the MDP. The MDP and panels right near it are 22 kA fully rated, so the shunt trip breaker is a GE THHQB32100ST1. We took delivery of this equipment in July 2023, so I am thinking this should still be covered under warranty from the supplier, but before I even ask, I want to make sure the failure is not because something was wired wrong. I find the breaker listed for $750 from one online supplier. I have not asked for quotes or approached anyone about purchasing it.

I didn't even think about this until after the failure, but it is my understanding that shunt-trip breakers are normally rated for only momentary application of voltage to the shunt coil. I am not sure if that is the way this system works. Another company built a control unit (brand: Amerex) and then I wired it up, using the diagrams they provided, which provide terminals to connect the shunt-trip coil, and state that the main control power supplying the controls themselves needs to NOT be interrupted. I have not tested so I don't know for sure, but the control unit may apply a continuous voltage to the shunt trip coil when the fire suppression system is activated. This may be relevant: I was told by someone who worked for the company that made the control unit that normally they had been using a single circuit board inside it, but because of the supply chain failures after 2020, they built this one out of discrete modules instead.

This is my first commercial job of this size and the only time I have wired a vent hood control unit. I don't know for sure who should be responsible for replacement of this bad breaker. I'm not on good terms with the supplier, but I believe they would still stand behind it if it truly was just a bad breaker, and not resulting from incorrect wiring. Assuming it's normal for a supplier to stand behind such things after this amount of time. The panels package was ordered in June of 2022, 75% of it was delivered to the supplier's warehouse in November of 2022, the other 25% of it in Feburary of 2023. I paid for it when it was delivered to them but they stored it and I took delivery of most of it (including the one with the bad breaker) at the job site on 3/31/23.

If my best option is to pay for the replacement myself, I'm wondering if a smaller amp rating and/or kAIC rating would be cheaper. There was only 11 kVA of load on the shunt-trip panel, and that's before moving the exhaust fan breaker to a different panel.

 

[LarryFine]

Years ago, I had to replace a shunt-trip breaker because the coil had burned out. It was such a waste, because the breaker had contacts to interrupt the coil power, but the installer didn't wire them in.

However, the breaker itself could still be set.

 

[Mr. Serious]

smaller amp rating and/or kAIC rating ...

Regarding the kAIC rating, I never had a study done, but had used the calculator available on Schneider's web site and plugged in sort of worst-case values. Although it's a 600A service, I believe the power company only used (3) pole-mounted 50 kVA transformers, so I used 150 kVA in the calc. The wire sizes are what we actually have installed. Two parallel 3/0 copper for about 110 feet to the MDP and then #3 copper for about 5 feet to the subpanel. Not included in the calculation is that there's also a 600A fused disconnect after the first 15 feet or so of wire. I don't know if that changes things.


How can available fault current be higher at the subpanel than at the MDP? Is that a bug or problem with the calculator?

 

[ramsy]

after probably about 4 system tests, the breaker is now failing to turn back on

Exercise doesn't cause failure, unless improper voltage is applied to controls.

I'm not on good terms with the supplier

If thats from too many returns, you may have trouble doing it again.

 

[ramsy]

How can available fault current be higher at the subpanel than at the MDP?

Cable 2 is figured from xfmr, not MDP.

You must manually do Point-to-Point, by starting new calc with 17084 MDP as xfmr.

 

[farmantenna]

according to Schneider Electric instructions the breaker has coil clearing contacts that open when the voltage is applied so maintained or momentary voltage can be used

 

[Mr. Serious]

according to Schneider Electric instructions the breaker has coil clearing contacts that open when the voltage is applied so maintained or momentary voltage can be used

Breaker is GE (ABB), not Schneider.

 

[Mr. Serious]

Cable 2 is figured from xfmr, not MDP.

You must manually do Point-to-Point, by starting new calc with 17084 MDP as xfmr.

Oh. I would consider that a bug then. I don't think that's how it was originally intended to operate, because the picture appears to show cables in series, one panel after another. It gives the correct result of cables in series if you do a single-phase calculation instead of 3-phase.

Fault Current Calculator

Let me know if you know of a better fault current calculator.

 

[hillbilly1]

according to Schneider Electric instructions the breaker has coil clearing contacts that open when the voltage is applied so maintained or momentary voltage can be used

OP’s is a GE, but still should have clearing contacts built in. Probably wrong coil voltage. I had the office send one that was a 200 amp 24 volt coil. They tried to run it of a doorbell transformer. When I got on site, and found out what they had done, the manufacturer literature called for a power source capable of 20 amps, 24 volts, I believe, had to redesign everything the engineer called for because they ordered the wrong voltage, and the trip contacts were only good for 5 amps.

 

[Mr. Serious]

Coil voltage is 120. Should take about 4 amps, then? Equivalent to your 20A at 24 volts. I have #14 wire running from the control panel about 50 feet back to the shunt trip breaker. That should be capable of supplying several amps with very little voltage drop.

 

[ramsy]

Let me know if you know of a better fault current calculator.

I only do service of existing equipment & always load test for SCC, before replacements.

Desk jockeys like the Busman calculator

Eaton's Bussmann Series - Available Fault Current Calculator

 

[Mr. Serious]

Regarding the supplier issues - I said I'm not on good terms with them, but really it's just one man there, a "Contractor Outside Account Manager" who gave us special treatment for a while, but then he suddenly got mad and wouldn't talk to us anymore. I think he got annoyed because:

1. a couple of times I cancelled a panel off a package deal and only bought the rest of the stuff (in my defense, I didn't know they were supposed to be package deals; also on one of them, they were trying to supply a panel with 200A main breaker but only 125A bus rating).
2. I kept comparing them with another supplier.
3. My estimator kept asking questions without understanding what he was really asking for.
4. We got a few bids without following up and buying the stuff.

So, not really from too many returns.

 

[hillbilly1]

Coil voltage is 120. Should take about 4 amps, then? Equivalent to your 20A at 24 volts. I have #14 wire running from the control panel about 50 feet back to the shunt trip breaker. That should be capable of supplying several amps with very little voltage drop.

Should be good, knowing GE, they probably didn’t have clearing contacts. Can’t remember installing a GE shunt trip breaker of that size. I think the bigger breakers you had an option that you installed it yourself. I know I’ve done a few, but can’t remember the manufacturer.

 

[Mr. Serious]

I'll see if I can find some manufacturer documentation on whether it has clearing contacts built in. And also test to see if the control system perhaps already applies only a momentary pulse. I really don't know for sure.

Regarding reply #11, test for short circuit current capability? I haven't heard of doing that. What do you do, rig up a big switch to close onto a dead short at the exact moment of the zero crossing of the voltage waveform, put in series with a 100 amp fuse, and monitor the result using a 100000:1 current transformer?

 

[ramsy]

What do you do, rig up a big switch to close onto a dead short at the exact moment of the zero crossing of the voltage waveform, put in series with a 100 amp fuse, and monitor the result using a 100000:1 current transformer?

Ideal makes a SureTest model with built-in ASCC function, to check L-N, 1 leg at a time. I agree with the assumption that L-N faults should be worst case scenario, and therefore L-L checks are redundant.

Other voltage drop meters checking rN+rL under a calibrated load require the ASCC formula :

ASCC = E/Z
Z = VD/I
VD = Volts Dropped
I = calibrated resistive load, such as 100W light bulb.

 

[Mr. Serious]

Thanks, I figured it was different from what I said. I was trying to make someone snort their coffee reading my obviously stressful method.

 

[texie]

After reading this thread I'm confused for sure. The OP says the breaker will not reset after multiple test, not that it will not shunt trip. Even if the shunt coil was bad the breaker should be able to reset. Maybe the shunt works fine but it still has voltage supplying it so the breaker will not reset. Did the OP check that there is no voltage to the shunt coil?
And the discussion about fault current what does this have to do with the price of rice? Unless the breaker was closed into direct short repeadedly this has no relevance on why the breaker won't manually reset.
There must be more to this story.

 

[ptonsparky]

After reading this thread I'm confused for sure. The OP says the breaker will not reset after multiple test, not that it will not shunt trip. Even if the shunt coil was bad the breaker should be able to reset. Maybe the shunt works fine but it still has voltage supplying it so the breaker will not reset. Did the OP check that there is no voltage to the shunt coil?
And the discussion about fault current what does this have to do with the price of rice? Unless the breaker was closed into direct short repeadedly this has no relevance on why the breaker won't manually reset.
There must be more to this story.

FWIW, I agree.

Pesky details.

The use of a couple meters would answer most.

 

[hillbilly1]

What happens sometimes, is the goo melted out of the coil will gum up the actuator, causing it to keep the trip mechanism from returning. Depends on how the manufacturer designed the components.

 

[qcroanoke]

After reading this thread I'm confused for sure. The OP says the breaker will not reset after multiple test, not that it will not shunt trip. Even if the shunt coil was bad the breaker should be able to reset. Maybe the shunt works fine but it still has voltage supplying it so the breaker will not reset. Did the OP check that there is no voltage to the shunt coil?
And the discussion about fault current what does this have to do with the price of rice? Unless the breaker was closed into direct short repeadedly this has no relevance on why the breaker won't manually reset.
There must be more to this story.

My thought too.
Did you reset the fire panel before attempting to reset shunt trip?