Square D service switch trips on ground fault

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attomsriver

Member
Location
New Jersey
I have a 2,000 Amp 460 Volt 3 Phase,Square D disconnect switch
Twice it has tripped on a sensed ground fault of
128 Amps
AS a result of this
It was just serviced and calibrated
The tech produced a 128 Amp signal through the current transformer and it tripped at 128 Amps, on the money
He even changed the ground fault relay/ module
No breakers were ever tripped

my question is that we have six Air conditioning units
with the largest compressor at 460 Volt 3Phase, 7 H.P. ,connected to this switch
we megged 3 of the units so far
this includes the 5 H.P. blower motors and the compressors
So far nothing is out of the ordinary
1) Can a 7H.P. compressor cause a 128 Amp difference in phases to trip this ground fault device ?
2) Is it better to connect a ground fault tester to each component on the AC units?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
It is only better if you want to minimize nuisance trips and isolate a fault/failure to only one part of the system instead of bringing everything down. :)
128A is a lot of current in the EGC, even in the presence of surge loads. I would say not at all likely in the absence of an actual intermittent fault.
 

templdl

Senior Member
Location
Wisconsin
My guess it is a 3ph4w system. I may also assume that there are also 1ph L-N loads. It could be that the GF systern may not be sensing L-N loads and is responding to those as being a GF. This is only a guess as there has been nothing included with the OP regarding the type of GF system and howcit detects GFs.
If CTs are used double check to assure that they are configured correctly. I had one instance myself where a neutral CT was present but not wired correctly and every time a 277v parking lot lighting load was switched on it tripped the breaker on GF because it was responding to the neutral current as a GF.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
It would be helpful if the OP provided the 'as installed' trip set point for the device. Ideally the GF device would be coordinated with downstream devices, so that any fault is cleared closer to the fault.

I believe the minimum set point is about 200A.
The Square D service rep is not qualified to determine alternate settings for protective devices. they can 'install' settings provided by a qualified designer or from the customer.

Has anyone checked for L-G connections in the system.
 

attomsriver

Member
Location
New Jersey
the 128 Amps is the factory setting
WE are apprehensive to manually raise that setting

What does the engineer want the switch set for?
If there was an engineer or even some as built drawings
on this site ,that would be an easy answer

I wanted to eliminate the Six air conditioners first.
From your post ,I am getting an indication that
the AC units may not be enough to trip this ground fault?

In the electric closet,
There are ceiling hung step down transformers for 120 Volts
However,at this site the plug load is virtually zero
with the exception of some phone chargers

The telephone system is connected to this switch

the T-5 fluorescent bulbs are 277 Volts,also connected to this switch

Lastly there is 460 Volt passenger elevator also connected to this switch
I believe there is a rectifier it uses for DC Volts
 

zog

Senior Member
Location
Charlotte, NC
I have a 2,000 Amp 460 Volt 3 Phase,Square D disconnect switch

A "disconnect switch" dosent have an automatic trip capability, I'm guessing this is a bolted pressure switch but have the model # of the switch and the trip device info is your 1st step in getting any good advice here.

Twice it has tripped on a sensed ground fault of
128 Amps
AS a result of this
It was just serviced and calibrated
The tech produced a 128 Amp signal through the current transformer and it tripped at 128 Amps, on the money
He even changed the ground fault relay/ module
No breakers were ever tripped

my question is that we have six Air conditioning units
with the largest compressor at 460 Volt 3Phase, 7 H.P. ,connected to this switch
we megged 3 of the units so far
this includes the 5 H.P. blower motors and the compressors
So far nothing is out of the ordinary
1) Can a 7H.P. compressor cause a 128 Amp difference in phases to trip this ground fault device ?
2) Is it better to connect a ground fault tester to each component on the AC units?

You say "the" current transformer which leads me to believe you are referring to a neutral CT and you have a 4 wire system, providing details about the equipment again will help us help you.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Has anyone checked for L-G connections in the system.

This would be the 1st question I would ask.The have been quite a few times over the years that, as Mr. Dungar suggests, I have found problems identical to yours caused by improper termination of grounded/grounding conductors (wrong side of the CT).
 

templdl

Senior Member
Location
Wisconsin
A "disconnect switch" dosent have an automatic trip capability, I'm guessing this is a bolted pressure switch but have the model # of the switch and the trip device info is your 1st step in getting any good advice here.



You say "the" current transformer which leads me to believe you are referring to a neutral CT and you have a 4 wire system, providing details about the equipment again will help us help you.

A GF trip because of this would be in responded to single phase L-N loads, the neutral loads being interpreted as a ground fault.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
A GF trip because of this would be in responded to single phase L-N loads, the neutral loads being interpreted as a ground fault.

I had a situation that involved duct heaters which were wired L-G and not L-N. During typical weather only a few heaters were on at any one time, but not enough to exceed the GF trip point. During cold weather additional units came on line resulting in a GF trip. The contractor replaced the GF equipment and then the main switch, all 'under warranty', before confirming that L-G loads existed (basic meggering did not catch the problem, as all the heater contactors were open during testing).

Maybe 99% of the time 'properly commissioned' GF equipment tripping is caused by the wiring and the loads, so why do most people trouble shoot the 1% chance of it being equipment?
 

big john

Senior Member
Location
Portland, ME
We see a lot of these. Put an ammeter on your main bonding jumper. If you have dozens of amps of current flow you very likely have an improper neutral bond downstream.

Often the current exists all the time, it's only with sufficient 1 phase imbalance does it finally hit your GF pickup.
 

templdl

Senior Member
Location
Wisconsin
I had a situation that involved duct heaters which were wired L-G and not L-N. During typical weather only a few heaters were on at any one time, but not enough to exceed the GF trip point. During cold weather additional units came on line resulting in a GF trip. The contractor replaced the GF equipment and then the main switch, all 'under warranty', before confirming that L-G loads existed (basic meggering did not catch the problem, as all the heater contactors were open during testing).

Maybe 99% of the time 'properly commissioned' GF equipment tripping is caused by the wiring and the loads, so why do most people trouble shoot the 1% chance of it being equipment?
Because it is easy. My experience has been that all too often these in sales find it easier to blame the product as being the problem and replace it under warranty if within the warranty period or recommend a replacement. Then when the issue persists after replacement either the product is judged to be poor quality product or someone finally zeros in of what is causing the problem. Sometimes it is frustrating to deal with the sales people and distributors.
My example of GF tripping was due to the OEM not connecting the neutral current sensor to the correct terminals on the breaker which shut down an entire new warehouse pickandsave grocery store that was scheduled to open when the 277v parking lot lights were turned on.
The neat thing about these challenges is that it presents an excellent learning experience.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Because it is easy. My experience has been that all too often these in sales find it easier to blame the product as being the problem...
I have made a living from being there, when the troubleshooter has no idea what to do after the parts have been swapped.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Jim,

Q: How many (insert trade of your choice) does it take to change a flat tire?




A: Five.
Four to lift up the car and one to swap tires until he finds the one that is flat.
 

kwired

Electron manager
Location
NE Nebraska
Because it is easy. My experience has been that all too often these in sales find it easier to blame the product as being the problem and replace it under warranty if within the warranty period or recommend a replacement. Then when the issue persists after replacement either the product is judged to be poor quality product or someone finally zeros in of what is causing the problem. Sometimes it is frustrating to deal with the sales people and distributors.

Was working in a new fitness center recently, they got TV's in certain places there and one of them had poor picture quality right from the start.

I did not do any of the TV or sound, but suggested to the owner that maybe the cable was bad (was like a 50 foot HDMI cable to satellite receiver)

He ended up sending TV back and getting a replacement, I was working there the day he connected the replacement - still had picture quality issues:huh:

I finally convinced him to try it at a different location (on a different cable) - and it worked fine.
 

templdl

Senior Member
Location
Wisconsin
I have made a living from being there, when the troubleshooter has no idea what to do after the parts have been swapped.

When it was in my area that's what I did. But, trying to reason with those when supporting products across the country is challenging. My biggest challenge was an issue with GF at a gold mine in the frozen tundra of Russia. A picture that they Emailed me illustrated a 3p breaker with GF that they had suspended with twine in the panel because there was no room to mount it. Amaising. I wish I knew where I filed those pictures as that was over 15 years ago. They didn't have the correct panel and had to tell them what they needed to replace it.
 
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