Service Wire Size, Gen Info Plz


Old 11-17-04, 04:07 PM
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Thumbs up Service Wire Size, Gen Info Plz

As previously posted, I am upgrading my 100 amp panel to a 200 amp service.

My local code says that only certified electricans are allowed to upgrade service panels and connect/disconnect power from the meter. And I'm A'Ok with that.

So I called an electrican and asked them to come out and check my incoming line (underground) to the house for proper wire size for the 200 amp service. The electrical contracting company (very reputable in this area) said that I would be ok with 1/0 aluminum wire because I have never tripped the main breaker. My service panel is full (20 circuits in the 100 amp) and I need a little breathing room in it to add a few extra circuits. I will be adding 5 15Amp Circuits (for basement, nothing on it will demand much), a 60 amp circuit (for a 54Amp hottub), and a 50-70 amp circuit (for a welder/tablesaw/big tools, etc...) in addition to my exsisting setup.

I checked the 2002 NEC, and the best I can find for the 1/0 aluminum burried cable is still under 200 amps. Now I understand what the company is telling me but, in your opinions is this going to be ok? What are the problems that could arise if 199 amps are drawn?

The incoming service cable's ratings are: Cablec MT 1/0 XLP 600V UL listed.

Thanks in advance! I truly appreciate your input.
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Old 11-17-04, 04:52 PM
Join Date: Sep 2000
Location: United States
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Your power company doesn't follow the NEC, and it should be your power company who makes the determination.

However, deciding that the wire is okay for your future needs because you've never tripped the main breaker with your current usage is not a valid algorithm.
Old 11-17-04, 05:56 PM
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Join Date: Dec 2001
Location: New York
Posts: 1,365
The power company may very well determine that the existing cable on their side of the meter is acceptable, but that is for them to tell you. They generally size their conductors based on expected load/demand, not service size.
Old 11-17-04, 06:13 PM
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Actually, the power company told me to have an electrican look at the service line and tell me wether or not it needs to be replaced. So based on their assesment, the power company either replaces it or doesn't.

Mainly, what problems can arise to my structure if the size is in fact too small?

I mean if the wire melts together underground, the transformer will just blow?? I don't want any damage to the house. I couldn't give a poop less about the power companies stuff.

Old 11-17-04, 07:52 PM
Join Date: Aug 2004
Location: Bella Vista, AR
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The wire coming from the power cable has nothing to do with you or your electrician. However, the wiring coming from your weather head to your meter base needs to be the correct size. Whats the worst that could happen? Well, if you have more current on the wires than they can handle, they will most likely overheat, melt off the insulation and either cause a phase to phase short or a phase to ground short. Since these wires are connected between your meterbase and the power company wiring, it isn't protected with a breaker and could very easily cause some major trouble. The transformer could blow, your house could burn down, someone could get electrocuted, etc. Also, if you blew the transformer, the problem would probably come back to you or the electrical contractor because you didn't have the correct guage wiring for the size service. You or the electrician could be held liable for paying for a replacement. Anyways, it could take a few years for something catastrophic to happen or it may never happen, depending on how much of a load you have on the panel at one time. Play it safe, follow the NEC recommendations. What may save you money now may screw you in the long run. You may want to consider replacing the aluminum cable anyways, as you can have the same load with a smaller copper cable and copper is safer than aluminum in most cases. However aluminum is very safe and reliable if installed properly, it is better to go with copper.
Old 11-17-04, 10:24 PM
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I appreciate the advice morph but you're preaching to the choir. I'm not talking about the cable from the meter to the service panel (which will be upgraded to 4/0 Aluminum wiring and installed by the proffesional electrican as required by local authorities).

I understand 90% of the interworkings of a home electrical system. (10% is the details which is really 90% of the applicable information aka practical: like conduit size and service loads and the 18 million other things that will take time to memorize).

What i'm talking about is the service feed from the transformer box to the meter. It is the 1/0 cable. And the question I'm posing, is if that cable is too small what are the inherent risks?

Now, I've said this a few times. I CALLED the power company on 3 occasions. I asked them if they would check the service feed to the house in case I needed to replace them. Every single time their response was "Call an electrican, and if it needs to be upgraded we will come out and do it. If the electrician does not think it needs to be upgraded you are ready to go."

So, basically the electrican says "It's good enough for your load". And I'm wondering, if that company makes a mistake, what is possible that could happen (within the boundaries of sense and reason).

This isn't about pinching pennies. I love doing carpentry, plumbing, electrical, and anything associated with construction of new and pre-exsisting homes. I'm always looking to learn new things and I have a high aptitude.

Smart people learn from their mistakes. Wise people learn from the mistakes of others. That's what DIYing is all about. And the reason why I read/post here. John is a very knowlegeable man as well as some of the other moderators on this site.

Thanks for the info! Sorry for the text size
Old 11-18-04, 06:47 AM
Join Date: Sep 2000
Location: United States
Posts: 18,497
I think the only risk to you is that you may get some dimming lights if the service cable becomes overloaded. You may also get some reduced voltage under heavy load, which could shorten the life of any motor-driven appliances.

If your power company will upgrade the cable if your electrician recommends it, then ask your electrician if this is at all marginal. If so, encourage him to recommend the upgrade to the power company.

If you don't get the upgrade now, and you have problems later, you can probably talk the power company into upgrading later.
Old 11-18-04, 08:25 AM
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Excellent. Thank you very much John!

Have a good day.

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