Slightly OT: Power distribution issues.

We have some issues with our main 1200A service that feeds part of our plant. It has ground fault interrupter relay which tripped four times since yesterday. That 1200A service feeds a lot of items including offices, plant lighting, and two stamping presses.
According to the manufacturer of the switch ground fault interrupter relay will trip when it senses more than 30mA for preset delay (ours is set at 0.5sec).
Twice when this happened we were starting parts washer (that is fused for 200A), when washer was started it took about 5 seconds and the main service was tripped. The other two times it happened when the washer was running for quite a while.

I just wanted to bounce this off of all the forum users and see if anyone had similar experiences and what was the cause/cure.
Is there a chance for the ground fault interrupter to go bad?

Thanks for your input.
Tom

Yes, they do go bad,

BUT

most likely it is tripping for a reason. You really need to identify that reason first. There's something going on with the parts washer!!

Ah yes ground problems. Remember em well from submarine service where all distribution was ungrounded. Navy was real picky about grounds so we had to fix em quick.

TomekPLC said:

That 1200A service feeds a lot of items including offices, plant lighting, and two stamping presses.
According to the manufacturer of the switch ground fault interrupter relay will trip when it senses more than 30mA for preset delay (ours is set at 0.5sec).
Twice when this happened we were starting parts washer (that is fused for 200A), when washer was started it took about 5 seconds and the main service was tripped. The other two times it happened when the washer was running for quite a while.

Is there a chance for the ground fault interrupter to go bad

Click to expand...

Let us do the simple one first YES the ground detector can go bad.
BUT
what if it is correct?

Seems to me
1. Parts washer in this era of no solvents means soap and water. That means a good conductor to ground.
2. If your ground detector trips when the parts washer is running then maybe that is teh place to start looking.

Buy a megger then check ground resistance on load side of disconnect to washer - make SURE you have all solid stage compenents isolated - megger will blow em.

Send round trip plane ticket. Will bring megger.

Dan Bentler

Thanks for the replays.

Dan, I will place a request for a round trip ticket for you and your megger
Oh, wait we do have one (that is hardly ever used).
Thanks for the tip!
Tom

TomekPLC said:

Thanks for the replays.

Dan, I will place a request for a round trip ticket for you and your megger
Oh, wait we do have one (that is hardly ever used).
Thanks for the tip! Tom

Click to expand...

You bet.

30 mA on a 1200 amp distribution system with all these various load seems to me to be awful low.

ASSUME you have 10 GFIs each with a leakage of 3 mA each. In theory then you would total 30 mA and dump your main breaker.
YET 3 mA on a GFI is not a trip point for that individual GFI.

THis is a poor example since GFI as I am using term is a 120 VAC device and your droppping transformer would isolate the grounding. IF they were 480 VAC GFI then example would be relevant.

I think it may be a good idea to see if 30 mA is a realistic value or if you are creating a nightmare by setting your setpoint to low.

As rough comparison the Navy setpoint was one megohm to ground on all 450 VAC distribution and 50 K ohm on 250 VDC.

Dan Bentler

One thing I did not mention.
Part of the plant we have issues with was commissioned about 8 years ago, and we never had those issues.
Washer is there for about 3 years. For the last few months we keep going through heating elements on it. But we never tripped ground fault relay before.
Thanks,
Tom

TomekPLC said:

One thing I did not mention.
Part of the plant we have issues with was commissioned about 8 years ago, and we never had those issues.
Washer is there for about 3 years. For the last few months we keep going through heating elements on it. But we never tripped ground fault relay before. Thanks, Tom

Click to expand...

Hmm blowing out heaters eh??

Hmm if those are immersion types then there is one source of grounding. Also from experience immersion heaters even without blowing them are a good way to keep electricians busy fighting ground problems.

Dan Bentler

Dan,
Thanks again!

Megging is a great way to check equipment but with a parts washer you do add a wrinkle. If the solution is causing the ground fault you may not see it with the Megameter because the washer is not running. If as you siad you have been replacing heater alot lately I would check and make sure they are installed correctly. A conductor laying in the right spot can cause all kinds of headaches.

TomekPLC said:

According to the manufacturer of the switch ground fault interrupter relay will trip when it senses more than 30mA for preset delay (ours is set at 0.5sec).

Click to expand...

Extremely unlikely. I have never seen a main service GFI with a setting lower than 200A. Yes, they make devices in the 30mA range, but theses should never be installed on the main device.

Is there a chance for the ground fault interrupter to go bad?

Click to expand...

Yes, it is possible.

But it is more probable that the parts washer has gone bad instead, and that the GFI is doing its job correctly.

I agree with Jim Dungar

I was going to write almost exactly what he wrote but not using American systems here I have waited till some one else in the US also mirrored my view.

To go further,
Could it be that the relay is set to .30 amps, of the 5 amp current transformer, this would give on a 1200 to 5 CT a setting of 72 Amps and as ground fault on mains breakers often use a 1 Amp tapping that 72 amps X 5 = 360 amps.

This is in the region of my expectations on a mains breaker.