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Unsure about main disconnect size


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A house I was in today had a 200 amp breaker for the main disconnect, and 3/0 service entrance conductors out to the drip loop (good for 200 amps, I believe). The conductors of the service drop from the splices out to the street were 2 gauge (good for 125 amps).

I want to write this up as being unsafe (better to be on the safe side?), but I've heard that wires for service drops can be smaller because they're in free air, and won't overheat. This small house doesn't have electric heat, and a simple load calculation would not come anywhere near 125 amps.

Can someone with much more experience help me out?

Thanks

Woody Mayne

Mayne Home Inspections Ltd.

Ontario, Canada

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The size of the service drop conductors is not a problem.

Here in the U.S., the utility is exempt from the NEC (per NEC 90.2C) and they are free to size their conductors based on anticipated load, not the rating of connected equipment. I don't know if it is the same up there. John will chime in with that answer.

Conductors in free air also are allowed much higher ampacity than those in a raceway. Aluminum 2 AWG conductors are given an ampacity of 135 amps in table 310.17, though I think a case could be made for going straight to the 90 degree ampacity of 150 amps. My only Canadian Electrical Code is very old, yet seems to have similar numbers (only 140 amps though for 90 degree insulation).

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That 2 gauge wouldn't be mentioned in my report.

I always describe the condition of the service drop. It's either new, newer, or damaged. I don't care what size it is.

We have two big utilities and several small municipal coops here and all will replace damaged/deteriorated service drops at no charge to the customer. I have even seen the coops fix stuff that was run through trees at no cost, the big guys could care less.

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You would have to call Ontario Hydro for the final answer, but what has been said above about sizing holds true for BC Hydro. We don't concern ourselves with that end unless the insulator or connection to the mast needs repair.

We do need to keep our eyes open these days, because much of this work is now contracted out and those guys will sometimes goof up. For example, after a new pole installation, the service conductors were stretched so tight, they were lifting the gutter.

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FYI to clarify. As a former Lineman, I can assure you "we" do follow the NEC (NFPA 70) when it applies. While I can't speak for the entire U.S., most POCOs follow the rules, which most come from the NESC (National Electrical Safety Code) along with other standard operating procedures and guidelines. I think is inaccurate to inform that the power companies are exempt and the like; gives one the illusion "we" just make up our own rules that are unsafe. (Perhaps some do -- I don't know how every POCO performs) Just saying. :-)

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FYI to clarify. As a former Lineman, I can assure you "we" do follow the NEC (NFPA 70) when it applies. While I can't speak for the entire U.S., most POCOs follow the rules, which most come from the NESC (National Electrical Safety Code) along with other standard operating procedures and guidelines. I think is inaccurate to inform that the power companies are exempt and the like; gives one the illusion "we" just make up our own rules that are unsafe. (Perhaps some do -- I don't know how every POCO performs) Just saying. :-)

Section 90.2(B)&© of the NEC does indeed mean that electric utilities are exempt from the NEC. I'm sorry if you assume the implication of that statement is that they make up their own unsafe rules. It would be great if every utility behaved like yours or the ones described in Tom Raymond's post, but they don't.

Here in California, our utilities are "regulated" by PUC orders 95 and 128, each hundreds of pages long, and each modeled on the NESC. They are widely ignored. Our local utility (sponsor of the San Bruno gas explosion) will not respond to a call for much less than their equipment being on fire. I have been through too many just plain ridiculous situations with them, including refusing to respond to broken service drop conductors. For a simple service update, they require a $2,000 deposit for "engineering services" which are nonexistent, and the process to recover the deposit (or what they are willing to part with) takes months.

As far as the utility sizing conductors based on their anticipation of the customer's load, rather than the rating of the service equipment or disconnects, the worst I saw was an 800-amp 3-phase switchboard fed by 250kcmil aluminum. Equipment all through the facility was failing due to the voltage drop caused by the utility's undersized conductors. That was an example of them just making something up, and the customer taking it on the chin.

Last year I inspected one where tens of thousands of dollars worth of equipment had been destroyed by water vapor because the utility forgot to seal their underground conduits. The facility was about 5 feet above the high tide line. The utility refuses to allow the contractor to seal them, insisting that only their own folks get to do that work. They take no responsibility when they subsequently forget to do it.

I could go on but I think you get the idea. I know there are many utilities that do care about getting it right. I wish ours was one of them.

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