Service Neutral Shorted to Mast

[pdickerson]

If the service neutral is bonded to ground at the service panel, does a short to ground at the electrical mast result in any safety issue? What would have to go wrong for this manifest in an injury?

I found this at today's inspection and informed the cient and home owner, who was present. The owner called the utility, who arrived an hour later. The utility employee imformed the owner that it was not a problem and did not need to be fixed, though he did fix it after the owner asked him to.

Comments please.

[Robert Meier]

Since the mast is bonded to the service neutral in the meter enclosure, electrically I don't really see a problem. But since the fix was simple one it doesn't hurt to keep it isolated.

[pdickerson]

I am not sure I see a problem either, but I suspect there probably is one even if I don't understand it. The code would not require the service neutral to be isolated from the service mast without a good reason. anyone know the reason?

I suppose if the service neutral is grounded at the main panel and also shorted to the mast, then a significant amount of current will pass from the neutral bus bar in the main panel, into the panel enclosure, up the service mast conduit, and then back into the service neutral conductor through the short at the insulator on the mast. The conduit should not carry current. Also, a poor connection at the short circuit could result in arcing. Did I just answer by own question?

[Robert Meier]

I've given this some more thought. Since the neutral is now connected to the mast it will allow the conduit to carry some of the neutral current since the conduit is a parallel path with the neutral. This should be avoided if possible. Metallic service raceways will always have this problem. For example a metal nipple between the meter enclosure and the service panel will always carry some of the neutral current since the meter enclosure and the panel have the neutral bonded directly to each metal enclosure.

In the photo since the neutral will have a much lower impedance than the rusted connection of the service drop it's likely that the conduit will carry very little current. It still should be avoided and Paul was correct to point out that it needed to be corrected.

[Frank P. Newman]

If it was OK for the neutral conductor to be in contact with the mast, then why would they use an insulator in the first place. Every system shouls have only one grounding connection.

[Robert Meier]

Originally Posted by fnewman

If it was OK for the neutral conductor to be in contact with the mast, then why would they use an insulator in the first place. Every system shouls have only one grounding connection.

It's funny we all agree that this should have been fixed but the NEC doesn't really seem to care about it. In fact in the NEC the grounded service entrance conductor is permitted to be bare when within the service raceway.

230.41 Insulation of Service-Entrance Conductors.
Service-entrance conductors entering or on the exterior of buildings or other structures shall be insulated.
Exception: A grounded conductor shall be permitted to be uninsulated as follows:
(1) Bare copper used in a raceway or part of a service cable assembly.

[Frank P. Newman]

Just goes to show the power of the utility industry lobby ! They don't have to abide by the NEC anyway.

[pdickerson]

Robert,

Thank you for the code section post. That is news to me. I don't believe I have every seen a bare service neutral wire, and I am surprised the code allows this given the obviouse parallel path of neutral current through the service mast. Can one of our resident experts confirm that we are applying the code section correctly here?