Ground current check
- Thread starter karl riley
- Start date
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brian john
Senior Member
- Location
- Leesburg, VA
Re: Ground current check
Bennie;
In the case of the 4000 amp bus duct we found did not own a large flexible CT. Since that investigation we have purchased several 48” flexible CT’s. We were alerted to the problem when the main kept tripping on GFP the GFP relay was set at 250 amps. We measured current on the neutral disconnect link in excess of 200 amps. We assumed this to be the cause of the GFP tripping. While awaiting a power outage we installed a line disturbance analyzer with long term trending capabilities to capture ground current and loss of power (switch tripping).
With the grounded sup panels, this was a new building and once again the main switch was tripping due to GFP operation. We found the problem very easily. (Grounded panels are number two on our list when checking a facility for net current problems, with generators being item one.) Once again we measured ground current on the neutral ground disconnect link at the main service.
We have done numerous net current investigations and have measured current on steel structural members, conduits, water pipes ECT. Depending where the accidental/intentional short to ground of the grounded/neutral conductor is influences where the current will be located. Multiple downstream grounds just complicate the matter.
Some of the problems we have found when doing Net current investigations.
Generator with the neutral grounded at the generator, and an ATS that does not switch the neutral.
UPS systems that are 3 phase 4 wire in 3 phase 4 wire out (neutral is solid for bypass) with neutral grounded.
Neutral grounded at a panel or FSS downstream from the main service.
Branch circuits from two separate SDS tied together.
Branch circuits from separate panels sharing a neutral.
GEC used as a neutral.
Neutral used as a GEC (grounded on one end).
Neutral grounded at the XO of a XMFR and in the panel.
Ground conductors tied to neutral termination block in distribution equipment.
Neutral conductors tied to ground termination block in distribution equipment.
The afore mentioned bus duct problem.
2-inch screws cutting insulation on neutral in an outlet box.
Quick wire outlets with the screws not screwed in completely, and the neutral screws shorting out to the box.
Nicked, cut shorted neural conductors (almost all were branch circuits neutral)
VAV boxes with resistance heat, one end of the elements broke off and shorted to ground, the heaters continued to work. (We have seen this several times).
Bennie;
In the case of the 4000 amp bus duct we found did not own a large flexible CT. Since that investigation we have purchased several 48” flexible CT’s. We were alerted to the problem when the main kept tripping on GFP the GFP relay was set at 250 amps. We measured current on the neutral disconnect link in excess of 200 amps. We assumed this to be the cause of the GFP tripping. While awaiting a power outage we installed a line disturbance analyzer with long term trending capabilities to capture ground current and loss of power (switch tripping).
With the grounded sup panels, this was a new building and once again the main switch was tripping due to GFP operation. We found the problem very easily. (Grounded panels are number two on our list when checking a facility for net current problems, with generators being item one.) Once again we measured ground current on the neutral ground disconnect link at the main service.
We have done numerous net current investigations and have measured current on steel structural members, conduits, water pipes ECT. Depending where the accidental/intentional short to ground of the grounded/neutral conductor is influences where the current will be located. Multiple downstream grounds just complicate the matter.
Some of the problems we have found when doing Net current investigations.
Generator with the neutral grounded at the generator, and an ATS that does not switch the neutral.
UPS systems that are 3 phase 4 wire in 3 phase 4 wire out (neutral is solid for bypass) with neutral grounded.
Neutral grounded at a panel or FSS downstream from the main service.
Branch circuits from two separate SDS tied together.
Branch circuits from separate panels sharing a neutral.
GEC used as a neutral.
Neutral used as a GEC (grounded on one end).
Neutral grounded at the XO of a XMFR and in the panel.
Ground conductors tied to neutral termination block in distribution equipment.
Neutral conductors tied to ground termination block in distribution equipment.
The afore mentioned bus duct problem.
2-inch screws cutting insulation on neutral in an outlet box.
Quick wire outlets with the screws not screwed in completely, and the neutral screws shorting out to the box.
Nicked, cut shorted neural conductors (almost all were branch circuits neutral)
VAV boxes with resistance heat, one end of the elements broke off and shorted to ground, the heaters continued to work. (We have seen this several times).
karl riley
Senior Member
Re: Ground current check
Brian, it's a boost to see that someone else knows these N/G connection sources. That's a great list. I was saying "yes, yes". I spend so much time trying to tell other electricians about these errors, just to bring it to their awareness.
I would only add - two neutrals from different branch circuits connected together (you mentioned from different panels, which I have seen also). Also, neutrals mixed up in a junction box, with the wrong neutrals connected with the wrong hots.
Here's a variety of the nail scenario: the electrician was called in to deal with a short. A sheetrock nail had shorted the hot to the GEC. His solution: Don't bother to dig into the ceiling, just switch terminations in the panel and use the grounded conductor as the hot, and the hot as the grounded conductor. This left the (now) black grounded conductor still shorted to the GEC, resulting in net current fields. You can't fool a gaussmeter.
And Bennie, I know this would not result in a magnetic field unless the GEC was also interconnected with other metallic paths: it was.
Brian, about your flex CTs. I was also frustrated once because I could not get the 3' flex around a bus duct. (Though by taking a few gaussmeter measurements I could estimate the net current). I had two flexes, so I experimented when I got back to my lab, and found that you can connect two in series and that works.
Karl
Brian, it's a boost to see that someone else knows these N/G connection sources. That's a great list. I was saying "yes, yes". I spend so much time trying to tell other electricians about these errors, just to bring it to their awareness.
I would only add - two neutrals from different branch circuits connected together (you mentioned from different panels, which I have seen also). Also, neutrals mixed up in a junction box, with the wrong neutrals connected with the wrong hots.
Here's a variety of the nail scenario: the electrician was called in to deal with a short. A sheetrock nail had shorted the hot to the GEC. His solution: Don't bother to dig into the ceiling, just switch terminations in the panel and use the grounded conductor as the hot, and the hot as the grounded conductor. This left the (now) black grounded conductor still shorted to the GEC, resulting in net current fields. You can't fool a gaussmeter.
And Bennie, I know this would not result in a magnetic field unless the GEC was also interconnected with other metallic paths: it was.
Brian, about your flex CTs. I was also frustrated once because I could not get the 3' flex around a bus duct. (Though by taking a few gaussmeter measurements I could estimate the net current). I had two flexes, so I experimented when I got back to my lab, and found that you can connect two in series and that works.
Karl
brian john
Senior Member
- Location
- Leesburg, VA
Re: Ground current check
Karl: When You series (?) two flex CT's do you use two multimeters and add the result?
Karl: When You series (?) two flex CT's do you use two multimeters and add the result?
G
Guest
Guest
Re: Ground current check
I can vouch for hearing stories from old electricians suggesting switching the black and white conductors if the black gets shorted out.
I have also heard stories in older concrete buildings where an outlet lost its neutral so they chip into the concrete and tie onto the rebar to make a new "neutral". These buildings are really old and had no grounding system-- just a 2-wire system. I guess you'd call that a Ufer neutral!
The EMF chatter didn't seem to increase until the early 90's-- and then it seemed to die down a lot.
I can vouch for hearing stories from old electricians suggesting switching the black and white conductors if the black gets shorted out.
I have also heard stories in older concrete buildings where an outlet lost its neutral so they chip into the concrete and tie onto the rebar to make a new "neutral". These buildings are really old and had no grounding system-- just a 2-wire system. I guess you'd call that a Ufer neutral!
The EMF chatter didn't seem to increase until the early 90's-- and then it seemed to die down a lot.
brian john
Senior Member
- Location
- Leesburg, VA
Re: Ground current check
My concern around EMF has never been the health issue. Though I did build an EMF friendly (?) Maybe safe is the better word house. I have thought that since I have been in and out of high voltage, medium voltage and just plain old low voltage high current environment for 33 plus years, what to heck...........
My concern has been from the PC PQ side, screen shake, the concern for proper operation of GFP protected services and the possibility of current flow on a NO 12AWG conductor should a service neutral or sub-panel neutral open.
My concern around EMF has never been the health issue. Though I did build an EMF friendly (?) Maybe safe is the better word house. I have thought that since I have been in and out of high voltage, medium voltage and just plain old low voltage high current environment for 33 plus years, what to heck...........
My concern has been from the PC PQ side, screen shake, the concern for proper operation of GFP protected services and the possibility of current flow on a NO 12AWG conductor should a service neutral or sub-panel neutral open.
karl riley
Senior Member
Re: Ground current check
Brian, you just use one multimeter and let the other connector just dangle. Try it and see if it doesn't give ytou the same reading as a single. It did for me.
About the health aspect of EMFs: most of my calls are due to computer monitor jitter or other electronic EMI. So I don't have to get inv olved with the health issue.
I get occasional calls from individuals who have read enough to be concerned and call me in to check out their house. Some have gaussmeters and know there is something unusual going on. I have dealt with several who have become chemo/electro sensitive, and are physically suffering. But I have never tried to convince anyone there is a health risk. At best I name some books to read, or periodicals that keep up with the research.I may mention a recent study which hasn't been covered by the media.
One child (1 1/2 yrs, I think) had developed leukemia. His crib was over the only net current source in the house, the feed to the panel, due to neutral shunted to the water pipe. 12 mG at his crib. He did not survive chemo.
As for myself, I am old enough that I don't worry about what I am going to die of. One thing is certain, we all die.
So on that note I am announcing that I am going to take a break from this forum for awhile. I need to concentrate on my book revision, and let my blood pressure come back down to normal.
Karl
Brian, you just use one multimeter and let the other connector just dangle. Try it and see if it doesn't give ytou the same reading as a single. It did for me.
About the health aspect of EMFs: most of my calls are due to computer monitor jitter or other electronic EMI. So I don't have to get inv olved with the health issue.
I get occasional calls from individuals who have read enough to be concerned and call me in to check out their house. Some have gaussmeters and know there is something unusual going on. I have dealt with several who have become chemo/electro sensitive, and are physically suffering. But I have never tried to convince anyone there is a health risk. At best I name some books to read, or periodicals that keep up with the research.I may mention a recent study which hasn't been covered by the media.
One child (1 1/2 yrs, I think) had developed leukemia. His crib was over the only net current source in the house, the feed to the panel, due to neutral shunted to the water pipe. 12 mG at his crib. He did not survive chemo.
As for myself, I am old enough that I don't worry about what I am going to die of. One thing is certain, we all die.
So on that note I am announcing that I am going to take a break from this forum for awhile. I need to concentrate on my book revision, and let my blood pressure come back down to normal.
Karl
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