Ground fault main tripping

Status
Not open for further replies.

USA

Member
Location
United States
We have an old Challenger 1200 amp frame ground fault breaker that has tripped multiple times. The breaker has a 1000 amp rating plug installed. We are unable to find any documentation on this breaker to be able to properly set it. We think the pickup frame rating should be set at 960 not 120. Any comments or information on this breaker or the settings would be much appreciated.
 

Attachments

  • CHALLENGER.jpg
    CHALLENGER.jpg
    66.9 KB · Views: 2

big john

Senior Member
Location
Portland, ME
What are you using to determine that 960 amps should be your trip setting?

What have you used to troubleshoot this so far?

Lots of buildings run with ground-fault pickup minimized and never trip, so if you're getting repeated trips, this may be less of a breaker problem and more of an issue with faults in your downstream system.
 

USA

Member
Location
United States
Ground fault main tripping

What are you using to determine that 960 amps should be your trip setting?

What have you used to troubleshoot this so far?

Lots of buildings run with ground-fault pickup minimized and never trip, so if you're getting repeated trips, this may be less of a breaker problem and more of an issue with faults in your downstream system.

The only thing has been to put a logger on the system to try and catch any events that may be contributing to the problem which we did not find anything abnormal. We are at a disadvantage that we can't shut down the system because of the site requiring power 24/7. To give you a little background on the system that we have been given from maintenance staff on site is that the breaker has been in service for over twenty years and has tripped once about ten years ago and recently has started to trip on Tuesday mornings every two weeks and three times day before yesterday and twice yesterday but not today so far. We will have to schedule an outage to do any further testing that is why we wanted to know what the settings should be and thought that the pickup frame rating should be set to what the rating plug is without going over.
 

big john

Senior Member
Location
Portland, ME
The only thing has been to put a logger on the system to try and catch any events that may be contributing to the problem which we did not find anything abnormal....
Does this mean you didn't trip while the recorder was in place? What was the sample rate on the logger? Was there a current sensor placed on the system bonding jumper? If you had an actual ground-fault, I would really think this would demonstrate it. Understand that regardless of what's going on, this isn't an issue of an improper setting. You either have a failing load causing a real ground fault, or a failing trip unit causing nuisance trips. Either way this is a hardware problem that won't be corrected by adjusting trip unit settings. The only reason that improper adjustments would come into play is if you knew for a fact you had a fault that downstream OCP was supposed to clear before it tripped your main and took of your entire facility. I am not a design engineer, so I can't tell you where that should be set, the closest I can get you is to say that you should look at the trip-curves for the feeders immediately downstream of this main. See what your ground-fault settings are on those breakers and coordinate your main so that it does not overlap that downstream curve. Be aware that depending on how this system was designed, that also may not be possible.
 
Last edited:

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Does this mean you didn't trip while the recorder was in place? What was the sample rate on the logger? Was there a current sensor placed on the system bonding jumper? If you had an actual ground-fault, I would really think this would demonstrate it. Understand that regardless of what's going on, this isn't an issue of an improper setting. You either have a failing load causing a real ground fault, or a failing trip unit causing nuisance trips. Either way this is a hardware problem that won't be corrected by adjusting trip unit settings. The only reason that improper adjustments would come into play is if you knew for a fact you had a fault that downstream OCP was supposed to clear before it tripped your main and took of your entire facility. I am not a design engineer, so I can't tell you where that should be set, the closest I can get you is to say that you should look at the trip-curves for the feeders immediately downstream of this main. See what your ground-fault settings are on those breakers and coordinate your main so that it does not overlap that downstream curve. Be aware that depending on how this system was designed, that also may not be possible.

Excellent points all around. It's far more likely that the breaker is doing EXACTLY what it is supposed to do. But beyond that, I agree it is then likely to be a hardware failure, not a settings issue.

In addition, asking an anonymous group what your settings SHOULD be is an exercise in futility, none of us can see what your system is or how it is coordinated (if at all). For all we know you have a resistance grounded system and in fact your 120A setting is too high already!

Lastly, "Turn it Up" is usually the first stage of what ends up being a much much bigger catastrophe...
 

USA

Member
Location
United States
Ground fault main tripping

Does this mean you didn't trip while the recorder was in place? What was the sample rate on the logger? Was there a current sensor placed on the system bonding jumper? If you had an actual ground-fault, I would really think this would demonstrate it. Understand that regardless of what's going on, this isn't an issue of an improper setting. You either have a failing load causing a real ground fault, or a failing trip unit causing nuisance trips. Either way this is a hardware problem that won't be corrected by adjusting trip unit settings. The only reason that improper adjustments would come into play is if you knew for a fact you had a fault that downstream OCP was supposed to clear before it tripped your main and took of your entire facility. I am not a design engineer, so I can't tell you where that should be set, the closest I can get you is to say that you should look at the trip-curves for the feeders immediately downstream of this main. See what your ground-fault settings are on those breakers and coordinate your main so that it does not overlap that downstream curve. Be aware that depending on how this system was designed, that also may not be possible.

We did have a trip while the recorder was on the system at a 15 second sample rate which found no voltage or amperage abnormality's. That is what pointed us to a ground fault situation. I wasn't aware we could place the current sensor on the bonding jumper to detect the fault. I am trying to think how we will narrow down the cause of the ground fault given the amount of the equipment that is connected to this service. The down stream breakers have no ground fault protection. It is basically a needle in a haystack and that is why I thought if the pickup frame rate was set higher that it might eliminate the smaller loads so we can track it down.
 

big john

Senior Member
Location
Portland, ME
Not sure why the forum deleted my paragraph spacing. Sorry if that was hard to read.
We did have a trip while the recorder was on the system at a 15 second sample rate which found no voltage or amperage abnormality's....
While I agree it's better than nothing, based on your time-delay your best-case scenario for capturing that fault would've been a 1 chance in 30, and could've been even worse based on the fault magnitude. You would need something capable of recording any transient event that lasts any more than a couple of cycles. I can point you to the folks we sometimes rent from if you're interested.
...I wasn't aware we could place the current sensor on the bonding jumper to detect the fault. I am trying to think how we will narrow down the cause of the ground fault given the amount of the equipment that is connected to this service....
Intermittents can be very difficult to find even with the luxury of shutting stuff down, if you don't have that luxury then a really good recorder is basically your only option.
...That is why I thought if the pickup frame rate was set higher that it might eliminate the smaller loads so we can track it down.
I see where you're going: You're just hoping it would start taking out branch protection, instead.

That's risky enough that I would not do it without exhausting all other options. Neither choice is ideal, but I would not want to willingly increase the fault stress a system is experiencing.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Turning the setting to a higher value may help in your troubleshooting, if you have an actual ground fault you might simply need to follow the smoke.:)

What has changed in the way the building operates?

Ground fault tripping may be due to improperly connected equipment that is now being used.
I remember an insurance building, where the main GF started tripping one winter. After asking what changed, it turned out that they had added electric duct heaters several years before. The heaters each had an improper connection to ground instead of neutral, so after enough units were turned on the cumulative ground current caused a GF trip.

Of course the involved parties wanted my permission to turn the GF pickup higher.
 

templdl

Senior Member
Location
Wisconsin
We have an old Challenger 1200 amp frame ground fault breaker that has tripped multiple times. The breaker has a 1000 amp rating plug installed. We are unable to find any documentation on this breaker to be able to properly set it. We think the pickup frame rating should be set at 960 not 120. Any comments or information on this breaker or the settings would be much appreciated.
This is actually A Westinghouse seltronic NCG31200 breaker with 1000a rating plug.
If you can get a hold of a seltronic test kit, it will test the breaker for you. The serltronic breaker is s "peak sensing" besker, that is it us sensitive to voltage spikes such as those that may be the result of PFCC switching which in turn creates a current spike that results in nuisance tripping.The electronics for this breaker was designed prior to the availability of RMS sensing. As such look for voltage spikes.
Another place to double check is that the external neutral current sensor is present and connected correctly. The information as provided is incomplete in that the system voltage was not specified. I may "assume" that it is most likely a 480y/277 which has a neutral. As such it most likely has L-N loads. Should the neutral current sensor be omitted or connected incorrectly any L-N current would be interpreted as a GF which will result in a trip. There should also notice (4) terminals on the left side of the breaker which may not be visible unless you remove the dead front cover. The terminals are marked 1, 2,N, and G. Make sure that the neutral current sensor is connected to the N and G. The 1and 2 are reserved for a remote trip indicator.
Also, unless you are have done a coordinating and have reason for your settings turn then all the easy up. I went on a service call to trouble shoot a breaker where the OEM had miswired the neutral sensor connected it to 1 and 2 which keep shutting down a fairly large warehouse grocery store that they were just commissioning shutting down the whole store.
Back to the seltronic test kit, you will note that there are 4 small plugs to the right by the rating plug, that is where you would connect the test kit.
I hope this helps you out.
 

USA

Member
Location
United States
Ground fault main tripping

We did a little more investigation today and found that there is only one 480/277 volt load in this panel. All the other branches are 480 volt only. With that being said there is only one wire attached to the Neutral current sensor. Is this the only way that this breaker detects a ground fault?
 

Attachments

  • neutral.jpg
    neutral.jpg
    70.2 KB · Views: 0

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
Turning the setting to a higher value may help in your troubleshooting, if you have an actual ground fault you might simply need to follow the smoke.:)

What has changed in the way the building operates?

Ground fault tripping may be due to improperly connected equipment that is now being used.
I remember an insurance building, where the main GF started tripping one winter. After asking what changed, it turned out that they had added electric duct heaters several years before. The heaters each had an improper connection to ground instead of neutral, so after enough units were turned on the cumulative ground current caused a GF trip.

Of course the involved parties wanted my permission to turn the GF pickup higher.
Good thought Jim. I was thinking along those same lines myself. Another thought. We were having kind of the same issue in a plant where I worked. We put on a meter and found that we were getting a spike at about 2:00 in the morning. Funny thing was the plant wasn't operational during those hours. Turns out that the utility was doing some sort of switch over at that time and for some reason it affected our equipment. I don't recall how we fixed the issue.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
We did a little more investigation today and found that there is only one 480/277 volt load in this panel. All the other branches are 480 volt only. With that being said there is only one wire attached to the Neutral current sensor. Is this the only way that this breaker detects a ground fault?
The breaker can sense each of the line currents passing through it. But to detect any residual current not flowing entirely in the combination of the line and the neutral wires it must also be able to sense and add vectorially the neutral current.
If the neutral current sensor (CT?) is not connected correctly the breaker will consider any unbalanced current on the neutral to be ground fault current instead.
 

templdl

Senior Member
Location
Wisconsin
We did a little more investigation today and found that there is only one 480/277 volt load in this panel. All the other branches are 480 volt only. With that being said there is only one wire attached to the Neutral current sensor. Is this the only way that this breaker detects a ground fault?

If I understood you correctly you said " only one wire." The external neutral current sensor has (2) wires connected to terminals N and G.
The way the breaker detects a ground fault is knowing that the (3) line conductors and neutral currents balance out to basically zero or and allowable amount as determined by the setting on the breaker. Should the neutral sensor not be connected or defeated the breaker will only consider the current on the line conductors and conclude that any current flowing on the neutral is a ground fault as it would for current flowing back to the source via ground.
One word of caution though, if you only have one wire connected to the breaker you will have one hell of a voltage across that wire and the one that remains disconnected. Both wires must be terminated on N and G.
 

ATSman

ATSman
Location
San Francisco Bay Area
Occupation
Electrical Engineer/ Electrical Testing & Controls
We did a little more investigation today and found that there is only one 480/277 volt load in this panel. All the other branches are 480 volt only. With that being said there is only one wire attached to the Neutral current sensor. Is this the only way that this breaker detects a ground fault?

Please clarify. As I view the pic it looks like the CT is mounted upside down. If the white dot on the side is the primary polarity mark then it should be pointing toward the source (up) instead of down to the load as shown in pic.
If this is the case then this may be causing the nuisance tripping on normal neutral current.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Please clarify. As I view the pic it looks like the CT is mounted upside down. If the white dot on the side is the primary polarity mark then it should be pointing toward the source (up) instead of down to the load as shown in pic.
If this is the case then this may be causing the nuisance tripping on normal neutral current.

Many ground fault neutral sensors, for breakers, are supposed to be mounted 'backwards'. But, I agree proper installation needs to be confirmed.
 

cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
Please clarify. As I view the pic it looks like the CT is mounted upside down. If the white dot on the side is the primary polarity mark then it should be pointing toward the source (up) instead of down to the load as shown in pic.
If this is the case then this may be causing the nuisance tripping on normal neutral current.
Remember that he said that it's been in service for 20 years.
 

jeremysterling

Senior Member
Location
Austin, TX
Remember that he said that it's been in service for 20 years.

We had a customer (middle school) that started experiencing nuisance tripping of a GF breaker. Like the OP we discovered a neutral CT that was wrong for the breaker and not terminated. The school had been like that for years and in the space of a couple months began having frequent trips. We assisted the gear manufacturer in installing a new breaker and CT. No problems since.
 

ATSman

ATSman
Location
San Francisco Bay Area
Occupation
Electrical Engineer/ Electrical Testing & Controls
Remember that he said that it's been in service for 20 years.

Please do not let that fact lead you down the wrong path. Experience has shown that in many cases the conditions can change through the years with regard to building loads, causing nuisance tripping. It is very possible that the increase in neutral load currents through the years (additional loads added) can rise beyond the GF pickup current to trip the breaker.
 

ATSman

ATSman
Location
San Francisco Bay Area
Occupation
Electrical Engineer/ Electrical Testing & Controls
Please do not let that fact lead you down the wrong path. Experience has shown that in many cases the conditions can change through the years with regard to building loads, causing nuisance tripping. It is very possible that the increase in neutral load currents through the years (additional loads added) can rise beyond the GF pickup current to trip the breaker.

Pardon me but time ran out during my editing.
I meant to further say:
Please do not let that fact lead you down the wrong path. Experience has shown that in many cases the conditions can change through the years with regard to building loads, causing nuisance tripping. It is very possible that the increase in neutral load currents through the years (additional loads added) can rise beyond the GF pickup current to trip the breaker.
I would recommend the following:
1. Check the polarity of the neutral inline CT to verify that the neutral current cancels the breaker phase currents. If not then correct by
reversing the wires at the CT secondary terminals.
2. If the polarity is correct then buy a breaker trip unit and hire a testing co. to function test the GF system (current injection) to determine exactly what current the
GF feature is picking up at. If defective then replace trip unit and retest.
 
Status
Not open for further replies.
Top