Arcing GEC

[meternerd]

I had a weird one the other day. Still don't feel too good about the fix, but outside of our POCO jurisdiction.

I was called out by the service crew to help try and figure out why the bare wire from the ground rod was arcing to the pedestal (located in a mobile home park). Complaint was flickering lights. We pulled the cover off of the utility pull section and saw that the GEC went directly to the neutral bus, bypassing the cabinet bonding lug. There was no jumper in the breaker section from ground to neutral either. We no longer allow a bonding termination in our sealed section, but since this was a really old installation, I figured we'd let the electrician bond there. It happened just before quitting time, so I had to leave, but the service crew stayed until the electrician finished. With the main breaker off, he read no grounds on either phase and high resistance to the case. After bonding, the arcing stopped. But it seems to me there must be a downstream ground on the neutral for return current to be coming back through ground. Is it safe to leave it this way?

 

[ptonsparky]

Some current will flow thru the earth back to the xfmr if the neutral is connected to earth at more than one location, and I know you know that. It all depends on where the connection is made and I haven't figured out from you description of the problem if it is normal or not. An arc in a darkened enclosure can seem pretty large and not really be meaningful. An arc burning the paint is another situation.

No grounds found by the electrician doesn't mean much. Most of the electricians I know do not have access to a megger and the testers most use do not have the capabilities. Even the Fluke TPro.

The spark could also be coming from your primary neutral pole grounds. Hard to tell from here.

So, not enough information to form an opinion one way or another.

 

[meternerd]

Some current will flow thru the earth back to the xfmr if the neutral is connected to earth at more than one location, and I know you know that. It all depends on where the connection is made and I haven't figured out from you description of the problem if it is normal or not. An arc in a darkened enclosure can seem pretty large and not really be meaningful. An arc burning the paint is another situation.

No grounds found by the electrician doesn't mean much. Most of the electricians I know do not have access to a megger and the testers most use do not have the capabilities. Even the Fluke TPro.

The spark could also be coming from your primary neutral pole grounds. Hard to tell from here.

So, not enough information to form an opinion one way or another.

Thanks for responding. This was in broad daylight, and was enough to burn almost completely through the #6 GEC. Burned maybe 1/8 inch into the cabinet. We read 10 volts from neutral to the enclosure and 117 volts from each line to the case. Line to neutral was 124. But this was with a Fluke, so voltage readings probably didn't mean much. I didn't take a current reading since it was really not our jurisdiction, and an electrician was on the way. We lifted the leads from the transformer so the electrician could do testing. Probably fine, since the bond is likely to stay connected, because it's in the sealed utility section. Just a little paranoid, because we had a 6 year old girl killed last year when she got between a stove and a water faucet. Major bonding problems.

 

[cadpoint]

... With the main breaker off, he read no grounds on either phase and high resistance to the case. After bonding, the arcing stopped. But it seems to me there must be a downstream ground on the neutral for return current to be coming back through ground. Is it safe to leave it this way?

No

 

[ActionDave]

I had a weird one the other day. Still don't feel too good about the fix, but outside of our POCO jurisdiction.

I was called out by the service crew to help try and figure out why the bare wire from the ground rod was arcing to the pedestal (located in a mobile home park). Complaint was flickering lights. We pulled the cover off of the utility pull section and saw that the GEC went directly to the neutral bus, bypassing the cabinet bonding lug. There was no jumper in the breaker section from ground to neutral either. We no longer allow a bonding termination in our sealed section, but since this was a really old installation, I figured we'd let the electrician bond there. It happened just before quitting time, so I had to leave, but the service crew stayed until the electrician finished. With the main breaker off, he read no grounds on either phase and high resistance to the case. After bonding, the arcing stopped. But it seems to me there must be a downstream ground on the neutral for return current to be coming back through ground. Is it safe to leave it this way?

I'm confused a bit by your description but it sounds like a neutral problem upstream.

What do you mean by utility pull section? Where is the meter and the service disconnect- outside the mobile home or at a bank of meters that serve other mobile homes in the park?

 

[meternerd]

I'm confused a bit by your description but it sounds like a neutral problem upstream.

What do you mean by utility pull section? Where is the meter and the service disconnect- outside the mobile home or at a bank of meters that serve other mobile homes in the park?

This is a pedestal type 120/240 single phase service, with a bottom section (called a pull section) containing the three wires from us, the POCO. The meter and service disconnect panel is plugged into our section with three vertical stabs and sockets similar to a meter socket. In most MH parks, we have master meters and leave the individual metering to the park, but this is an OLD part of the park, so we supplied power all the way to the pedestal. The bonding lug screwed to the back wall of the lower cabinet (pull section) is behind the utility seals. No other bonding point exists. We are not code enforcers, and mobile home parks are exempt from inspection by the town building department. As I said above, there was no neutral problem from our splice box to the connections inside our section. We read 124V on both legs to neutral and to the GEC conductor. But...we read 10V to the enclosure before the electrician bonded the new GEC wire through the lug and then to the neutral bus. I left before the repairs were completed, but the electrician told the service crew there was no longer any voltage from neutral to the enclosure after they were bonded to the neutral. I can see where there could be "objectionable current" coming back on any ECG conductor if a downstream ground/neutral bond exists, but what upstream could cause this? And why would current return on the ground rod. I'm betting that there was no EGC wire going to the sub-panel in the trailer, but as I said, we didn't go that far and apparently neither did the electrician. We're pretty hesitant to dive into customer related problems unless we see an immediate safety concern. Liability thing, I guess.