Question . . .

[Bain]

I was cleaning my gutters earlier and saw this. Apparently a tree limb fell on the SE cables and cracked the ceramic bushing.

The utility company is going to repair the anchor, but while I THINK I understand all the ramifications, I'm curious about what the gurus have to say.

As an oh-by-the-way, I realize the masthead is too close to the shingles, but the installation was inspected and approved before I bought the house, and I haven't wanted to spend the dough to make corrections. Yet.

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[Jerry Simon]

I was cleaning my gutters earlier and saw this. Apparently a tree limb fell on the SE cables and cracked the ceramic bushing.

The utility company is going to repair the anchor, but while I THINK I understand all the ramifications, I'm curious about what the gurus have to say.

As an oh-by-the-way, I realize the masthead is too close to the shingles, but the installation was inspected and approved before I bought the house, and I haven't wanted to spend the dough to make corrections. Yet.

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I ain't got no answer, but on a related note, anyone else make a big deal about SEC's being within 12" of the roof? I used to flag it all the time, but quit doing so unless they're way too close (under 2" or abouts).

[Jim Katen]

I don't recall seeing connectors like that in my area. What does the piece of ceramic do? It doesn't look like it insulates the neutral from the mast.

[charlieb]

Odd, with the variety of screw ups I see here I don't recall seeing a short mast. I have found a couple of gas meters on top of the service equipment in the last month.

[Bain]

I don't recall seeing connectors like that in my area. What does the piece of ceramic do? It doesn't look like it insulates the neutral from the mast.

It was circular, and it WAS intended to insulate the neutral from the mast. The half circle that broke off is on the roof. That's what I was curious about. Now that the neutral's in contact with the mast, what are the possible consequences?

[Jim Katen]

A certain proportion of the imbalanced neutral current from your 120-volt circuits will be flowing over the mast.

[Bain]

The utility guy came and went. He said some power companies never insulate the neutral from the mast, but mine does.

The only danger with my kind of insulator, he said, is some companies use inexpensive anchors in which the pins aren't flared well, and the pins fail when they take a hit.

I didn't think it was a big deal when I saw it, but I didn't know if there was a possible problem I wasn't aware of.

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[Jim Katen]

The utility guy came and went. He said some power companies never insulate the neutral from the mast, but mine does.

The only danger with my kind of insulator, he said, is some companies use inexpensive anchors in which the pins aren't flared well, and the pins fail when they take a hit.

I didn't think it was a big deal when I saw it, but I didn't know if there was a possible problem I wasn't aware of.

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They don't use those things around here, but the little loop of wire that holds the neutral in place is dipped in plastic by way of insulation. I can't imagine that it's very effective.

[John Kogel]

We use insulators like that or similar on all service drops around here. Even the ones that screw into the fascia board are ceramic, for some obscure reason.

They are known as "emily knobs", but no one knows what ever happened to Emily?

I had a linesman tell me that he liked a weak connection at the insulator, because it was the easiest component to replace. There's one that uses a big cotter pin to hold the insulator, which just pops free when a branch hits the line.

In Canada, we are not allowed to run the service over the roof the way you'all do. Only at the eaves or the gables. They will install a bridle between the poles if they have to, to get the angle of approach away from the roof. Maybe we spend more time on our roofs, shoveling snow? Not me.

So yes, if I see a service drop crossing a roof with less than 8' of clearance it gets called out. It's an expensive repair.

[Jim Port]

The neutral should have been bonded to the mast already.

[Bain]

The neutral should have been bonded to the mast already.

Can you tell us why? It's never done that way in my area.

[Tom Raymond]

It could have been worse John. The utility ran this overhead more than 200' through three trees. The homeowner is going to have to eat the cost of the fix and the tree trimming.

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[Jim Port]

The neutral should have been bonded to the mast already.

Can you tell us why? It's never done that way in my area.

If the mast were not bonded to the neutral and it became energized it would not have tripped the breaker. It would also become a shock hazard were someone to complete the circuit.

[gpdewitt]

All the masts I've seen in my area, L A County, CA, have an insulator. Exceptions are where masts are too short for one, under 12" or so, and the neutral is tied to the roof near the masts, also with a ceramic insulator. These are houses built in the 50's. Some of these even have 3 insulators attached to the roof, one for each cable, but not usually still in use.

[Douglas Hansen]

Originally posted by Jim Port

The neutral should have been bonded to the mast already.

Can you tell us why? It's never done that way in my area.

The neutral must always be bonded to that mast. The place where you typically see that bonding connection is in the service equipment, and any additional bonding at the point of attachment should only be adding to what was already present. Using an insulator at the mast may provide a more reliable or durable connection from a mechanical standpoint, but not electrically.

Suppose that inside the mast the insulation on a hot conductor is damaged and that it energizes the conduit. The path for current is from the conduit to the enclosure of the service equipment, across the main bonding jumper, and over to the incoming service neutral. There is no breaker in that circuit - it is on the "line" side of the service equipment. A fault as described here is going to cause something pretty bad - it could possibly cause a fire or blow up the utility transformer. If you were lucky it would trip the overcurrent protection on the primary of the transformer and just knock out power to all the customers served by it.

Suppose we have the exact same thing, only this time there is no main bonding jumper in the service panel. Now nothing blows up. Instead, something much worse happens. The conduit sits there with 120-volts potential, waiting for you to touch it while also contacting a grounded surface. You become a human bonding jumper.

If the service mast had been anchored with metal to metal contact instead of that insulator, we are back to plan "A" (a noticeable fire or explosion instead of a potential electrocution).

The reason we require bonding jumpers around concentric knockouts on the line side of the service is to assure that we are using plan "A" rather than the human bonding jumper.

[Erby]

Human Bonding Jumper. What a way to go!

[Bain]

Originally posted by Jim Port

The neutral should have been bonded to the mast already.

Can you tell us why? It's never done that way in my area.

The neutral must always be bonded to that mast. The place where you typically see that bonding connection is in the service equipment, and any additional bonding at the point of attachment should only be adding to what was already present. Using an insulator at the mast may provide a more reliable or durable connection from a mechanical standpoint, but not electrically.

Suppose that inside the mast the insulation on a hot conductor is damaged and that it energizes the conduit. The path for current is from the conduit to the enclosure of the service equipment, across the main bonding jumper, and over to the incoming service neutral. There is no breaker in that circuit - it is on the "line" side of the service equipment. A fault as described here is going to cause something pretty bad - it could possibly cause a fire or blow up the utility transformer. If you were lucky it would trip the overcurrent protection on the primary of the transformer and just knock out power to all the customers served by it.

Suppose we have the exact same thing, only this time there is no main bonding jumper in the service panel. Now nothing blows up. Instead, something much worse happens. The conduit sits there with 120-volts potential, waiting for you to touch it while also contacting a grounded surface. You become a human bonding jumper.

If the service mast had been anchored with metal to metal contact instead of that insulator, we are back to plan "A" (a noticeable fire or explosion instead of a potential electrocution).

The reason we require bonding jumpers around concentric knockouts on the line side of the service is to assure that we are using plan "A" rather than the human bonding jumper.

Thank you.

[Garet]

If the service mast had been anchored with metal to metal contact instead of that insulator, we are back to plan "A" (a noticeable fire or explosion instead of a potential electrocution).

Wouldn't that cause the service mast to act as a parallel conductor to the neutral? That seems like a bad idea. No? If not, then why the insulator?

[Douglas Hansen]

If the service mast had been anchored with metal to metal contact instead of that insulator, we are back to plan "A" (a noticeable fire or explosion instead of a potential electrocution).

Wouldn't that cause the service mast to act as a parallel conductor to the neutral? That seems like a bad idea. No? If not, then why the insulator?

It would cause the service mast to act in parallel with the neutral. I don't see that as a bad idea. It would have current on it. It would have only barely measurable voltage.

The NEC allows the neutral to be a bare (copper) conductor inside that service riser (230.41Exc.1). A bare neutral would also allow current on the service riser.

We've already seen what happens in a fault situation with the bonding jumper missing. So, let's look at what happens in a no-fault situation:

Suppose you have 2AWG aluminum service conductors and service drop conductors. To give us some measurable voltage on them, let's say the service drop is 100 feet back to the transformer, and that we have 10 feet of 2-inch steel conduit between the service equipment and the weatherhead. Next let's assume a really huge imbalanced load, like maybe 60 amps, which is more than you would ever see in real life. The voltage drop on the service conductors would be approximately 2 volts (60 amps times 0.0319 ohms). In the first 10 feet of that, the voltage drop would be 0.2 volts. That would be your maximum theoretical voltage potential between the service neutral and the mast at the top. In practice it would be much much less. There isn't a need to insulate it to try to maintain voltage potential between them. Again, I think the insulator is someone's idea of a mechanically more reliable connection.

In the same vein, the service enclosure also carries a small amount of current, yet if everything is connected right it is safe for you to touch it. It and the grounding electrode conductor are in parallel with the service neutral. Jerry Simon has taken many pictures of his ammeter clamped around the grounding electrode conductor and showing fairly high amperages. Those grounding electrode conductors can show that kind of current while still having barely measurable voltage. Same story here at the weatherhead.