Todays' Service Call (Solve this service call)

Status
Not open for further replies.
480sparky said:
OK, here's the AC / lighting issue: The owner had it all screwed up in his head.

He noticed the furnace was blowing air, but not cold air. So he checked the breaker. It was tripped. He reset it, and it tripped the breaker feeding the subpanel that had the AC breaker in it. This killed the entire subpanel which had that side of the building's lights in it. We tried resetting it, but it tripped immediately. I crawled up on the roof and took the cover off the compressor. There was a boost capacitor added. So my guess is it was toast and that's what is causing the breaker to trip.... too much current trying to start the compressor.

So we had the owner contact his HVAC guy. But we still have the glow-in-the-dark wiring to deal with.

The POCO arrives and finds the noodle splice at both the weatherhead and at the transformers out on the pole were not correct. It appeared they weren't crimped far enough and we could see burn marks on them. So those were replaced by the POCO.

But we still had arcing after that.
Click to expand...
You still looking for a problem or are you waiting to see if we figure out what you did find for a problem?
 
Why is the conduit the best path to ground? You mentioned four wires in the conduit from meter base. Where are the ground rods and ground wire?

An open neutral on the service side let’s you see ground problems that usually go unnoticed.

Oops, missed that the arcing is still happening. I’d be going over all neutral connections with a fine toothed comb.
 
480sparky said:
It goes outside to the meter socket.
Click to expand...
So there is parallel neutral current on it if neutral is bonded at meter socket as well as the panel. How much neutral current is there and is the neutral connections at each end in good condition? If not in good condition then that conduit may be carrying a majority of neutral current, but no matter what is carrying some current as long as it isn't completely "open".

To be code compliant should have a bonding bushing or other means besides a standard locknut to assure bonding of the service raceway, but will still carry parallel neutral current.
 
A green screw for the MBJ is kinda weak of course, but at 200A main I would think you shouldn't have that much current flowing on metal on the supply side of it, if the problem is merely a ground-fault on the load side.

Where is the GEC connection? And did the POCO also check the neighbors neutral connections? (The neighbors on the same tranny, that is. Hmmm, high-leg delta: maybe there aren't any such neighbors though.)

480sparky said:
OK, here's the AC / lighting issue: The owner had it all screwed up in his head.

....
Click to expand...

If this is supposed to be puzzle-solving for fun, it makes it a bit less fun if the initial information is misleading. :huh:
 
This is just a guess but I am betting the arcing occurs even if the main breaker is turned off. If it does, it is an issue with a neutral at a service that is immediately adjacent to this service. I'm guessing that the conditions must be adequate for current to actually flow from this location to the adjacent service through the soil.
 
rlundsrud said:
This is just a guess but I am betting the arcing occurs even if the main breaker is turned off. If it does, it is an issue with a neutral at a service that is immediately adjacent to this service.
Click to expand...

Yeah, that's where I'm going for now. Could explain why the customer's neutral connections were burned, if it was carrying current for two services.

I'm guessing that the conditions must be adequate for current to actually flow from this location to the adjacent service through the soil.
Click to expand...

More likely an area with older continuous metal water mains to which both GECs are connected.
 
jaggedben said:
.........Where is the GEC connection? ......
Click to expand...

There was none.

jaggedben said:
.........And did the POCO also check the neighbors neutral connections? (The neighbors on the same tranny, that is. Hmmm, high-leg delta: maybe there aren't any such neighbors though.)......
Click to expand...

This was the only service on those transformers.


jaggedben said:
.........If this is supposed to be puzzle-solving for fun, it makes it a bit less fun if the initial information is misleading. :huh:
Click to expand...

Welcome to real life troubleshooting.
 
well, at least I am learning more by watching this thread... so it looks like a neighbor also may have problems as well? Or is it due to improper grounds as well..kinda watching to learn more.
 
There still could have been a GEC, just not intended or compliant.

I saw one, residential customer lost a neutral. Triplex passed through the tree branches where rubbing caused the fault in midair. I was surprised looking up the neutral was burned open with a pretty big gap in the middle of the run. Found it right away.

I thought that was the only damage and was almost done when I noticed a 14-2 or so Romex leaving the panel had melting damage. I followed it back and it fed the well pump. So the well pump EGC must have been carrying neutral current and bonded to the well casing.

Looked like it had been that way for a long time. Place was running with the typical bright dim lights but running. I have no idea how. With no neutral, you have a voltage divider through the loads on opposite phases. But then the EGC to the well casing is carrying the imbalance caused by the voltage raise. But where does it go to. It's enough current to heat the wire and melt it out of the RX jacket. Well was out to the back so the return path had to be through the Earth to the neighbor's well or the ground rod at the pole.

****

Arcing at the locknut is a good one. Heat or arcing is caused by the localized high resistance, which is extremely rare with RGS and steel locknuts. As noted earlier, the locknuts must be loose. They should carry a lot more current with no complaint or heating.

To find a bad neutral I will usually load one leg heavy with the Fluke on it to see if the voltage bumps a little. Usually have the homeowner engage the washer on spin cycle while I watch the Fluke 87. If the neutral is solid, no voltage wag on a single phase bump load, the conduit is carrying fault current. Flipping breakers is next.

Homeowners bill is going to drop $100 month when you fix it.
 
__dan said:
...

Looked like it had been that way for a long time. Place was running with the typical bright dim lights but running. I have no idea how. With no neutral, you have a voltage divider through the loads on opposite phases. But then the EGC to the well casing is carrying the imbalance caused by the voltage raise. But where does it go to. It's enough current to heat the wire and melt it out of the RX jacket. Well was out to the back so the return path had to be through the Earth to the neighbor's well or the ground rod at the pole.

...
Click to expand...

Strictly speaking it is the impedance of the service neutral - and any alternative paths found back to the utility transformer - that primarily determines the voltage imbalance (not the other way around). Well casings have a lot of metal contact with the earth (many many times that of a ground rod, for example), so it's not thoroughly surprising that such a path would have a low enough impedance to keep the voltages within a somewhat functional range. The amount of current that can flow is a good reason for treating the well casing as an grounding electrode and bonding it to the rest of the system per 250.50, and not just with a #14 EGC as you describe. Certainly your anecdote is lucky and unusual, but in theory it's perfectly explainable. A lot more easily explainable than what's going on with the main thread here.
 
__dan said:
.............
To find a bad neutral I will usually load one leg heavy with the Fluke on it to see if the voltage bumps a little. Usually have the homeowner engage the washer on spin cycle while I watch the Fluke 87. If the neutral is solid, no voltage wag on a single phase bump load, the conduit is carrying fault current. Flipping breakers is next...........
Click to expand...

Voltages never fluctuated much, regardless of which phase I shut down.


jaggedben said:
Interesting. How about the neutral connections on the customer's side of meter?
Click to expand...

Unfortunately, we never got into the meter socket. The line crew had bigger fish to fry so after the bucket work they beat feet.
 
EMT to a die cast set screw connector, coupling, then a die cast offset nip. Coupling doesn't look right, looks too big (thick) for steel threaded. Looks like it could be a PVC coupling.

THW conductors with the fiber bushing is old school, like 1960's or before. Die cast fittings are, I am guessing, from a later era. So the panel was taken apart and moved a little then put back reusing old parts (?).

Is the coupling PVC slipped over the EMT set screw connector, so they could neatly join to the die cast offset nip (?). I don't see the fourth THW, the neutral, but assuming it is there and bonded to the can. So they damaged the THW when they took it apart and put it back together and it is faulting to the offset nip, and since the coupling is (maybe) PVC there's no useful N to G bond at the meter socket and it has to flow through the loose locknut to the panel bonding screw (???).
 
rlundsrud said:
You never said if the arcing continued if the main breaker was shut down. This is probably the most important step in resolving where this issue lies.
Click to expand...

So, again just trying to learn, if the arcing continues with the breaker shut off that means that the problem is in the neighborhood or coming from the service, not in the house, right?
 
This is a 200a 3-ph service to a small restaurant.

Arcing stopped when main is shut off.

There are no other services on the transformers.
 
Status
Not open for further replies.
Top