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Service Drop Size


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Then I guess it would be worth mentioning it is a 7 unit apt. bldg.

I would report on the service size in the building but I rarely mention the service drop unless there is a visible problem with the installation. Does the building have a common laundry room and gas heat? Then maybe 200 amps is adequate. And if it wasn't the breaker would be tripping, but that's never been a good excuse.

It is common here for the service cable to appear to be undersized, but it is in free air and not limited by the sizing requiremnets for residential wiring, or so Ive read.

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I seriously doubt that any utility would ever knowingly install #3 service drop conductors on a 7 unit all-electric apartment building.

If there's no AC's and all major appliances are gas then maybe, but just maybe.

Marc

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Very old building. All gas appliances. 200 amp main fuse serving 8 subpanels. 2 outlet receptacles per room.

I am just guessing on the service drop size from a distance. Looked #3-ish.

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With no 240 volt breakers, I believe I'd not make a ruckus over it...unless...I see portable microwaves, window units, portable electric heaters or hot plates in the apartments, then I'd write up the electrical installation as needing a fresh load calculation by an electrician and suggest the utility be updated on the results of that new calculation as well as following any upgrade recommendations the electrician makes.

Could turn out to be a big finding.

Marc

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Here is an ampacity chart for future reference.

Download Attachment: icon_adobe.gif ampacity2010.pdf

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Thanks. But I don't think this chart applies to open air conductors such as a service drop.

It might be my computer but I could not view that PDF.

Here's the link:

http://cerrowire.com/files/file/ampacity2010.pdf

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With no 240 volt breakers, I believe I'd not make a ruckus over it...unless...I see portable microwaves, window units, portable electric heaters or hot plates in the apartments, then I'd write up the electrical installation as needing a fresh load calculation by an electrician and suggest the utility be updated on the results of that new calculation as well as following any upgrade recommendations the electrician makes.

Could turn out to be a big finding.

Marc

Marc, what bad thing do you see happening from the service drop being smaller than the SEC needs to be?

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I've made no connection to the SECs. Someone else on this thread may have. SEC's and utility drops answer to different standards, different authorities. The utility drops are basically out of my scope during an inspection but that won't stop me from speaking up if I see something that can affect the property in a significant way.

It has to do with the heat developed in air suspended conductors and what the limits are. Too much heat and they could fail, denying the customer service until repair crews can arrive, perhaps even damaging customer property.

Marc

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It has to do with the heat developed in air suspended conductors and what the limits are. Too much heat and they could fail, denying the customer service until repair crews can arrive, perhaps even damaging customer property.

Marc

OK, that's a bad thing. Now I'm curious: has anyone ever heard of a service drop failing because it overheated? How much heat would it take for it to fail?

Personally, I can't believe that in a million years that would happen for 90 feet of #3 Cu to a 200 amp service.

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It has to do with the heat developed in air suspended conductors and what the limits are. Too much heat and they could fail, denying the customer service until repair crews can arrive, perhaps even damaging customer property.

Marc

OK, that's a bad thing. Now I'm curious: has anyone ever heard of a service drop failing because it overheated? How much heat would it take for it to fail?

Personally, I can't believe that in a million years that would happen for 90 feet of #3 Cu to a 200 amp service.

I took a look at an EE pocket book I have. The resistance of #3 copper wire is 0.1970 ohms/1000 feet. A 90' foot long service translates into 180' of wire. The power developed in that wire at 200 amps is 1,420 watts, a little higher than common 120 Volt portable heaters. So it's not as bad as I thought, but all that's needed is for the insulation to burn or melt then a short does the rest. The voltage loss would be just under 8 volts out of 240, about 3% voltage drop.

Aluminum wire would generate more heat than that.

Decide for yourself if you're going to write it up.

Marc

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