Main Electrical Service Wiring

[ragswl4]

Anyone have a good site or information to determine the gauge of wire to use for the main electrical service into a home? We have a run of 100 ft from the power company service to the main panel and I need to know the gauge of wire needed for this. The run will be underground in schedule 40 conduit. The local Borgs say 3/0 will be sufficient but looking for a more informed opinion. Thanks.

[eezlock]

electrical service wiring

Look at the inside of the panel...it should tell what the panel is designed/rated for in amps...ex: 100 amps, 150 amps, 200 amps...etc. This is the info. needed to determine the proper wire (awg size) for that panel. Call any electrical contractor or power co. service dept. they can tell you what wire size you need to buy for the service entrance cable. eezlock

[Uncle Cracker]

Look at the inside of the panel...it should tell what the panel is designed/rated for in amps...ex: 100 amps, 150 amps, 200 amps...etc. This is the info. needed to determine the proper wire (awg size) for that panel. Call any electrical contractor or power co. service dept. they can tell you what wire size you need to buy for the service entrance cable. eezlock

Ditto this info. In addition, it's a good idea to get your power company's take on this regardless of whether you get info elsewhere, because it will keep them from giving you any flak if you have some problem with their service in the future. When my neighbor built his house, he used wire for his service feed that was approved by the city building dept., but not by the power company, and so they refused to connect to the service, and he had to rip it out. The service purveyor is apparently given the latitude to establish its own standards in excess of the codes (although not inferior to them).

[Tom Slick]

I know that around here PG&E dictates what gets put in. they "own" everything up to the meter.

[Pathpounder]

Yep, that's the way it is here too and I had to shell out extra for the string in the conduit for pulling the wire.

[crokett]

Do check with the power co. When my dad got electrical service run to the barn earlier this year Duke Power put in a pole to get power across the road. My dad was able to do the trenching and run a line to the barn himself, but he had to get it inspected AND have the power company sign off on it before they put the meter in.

[ragswl4]

I believe I may not have been clear on what I am doing. We have a somewhat unique configuration for our power. SoCal Edison will be running the service line from their power pole to the meter and main breaker which will be in the garage. From there I have to run power lines to the house where the main panel will be located. That will be a 200 amp service panel. Then back to the garage with a 60 amp subpanel line.

The power company tells me it is my decision on the gauge of wire to use from their meter/main breaker to the service panel in the house. (Garage is 50 ft from the house). It seemed odd to me that the power company wouldn't tell me what size wire to use but that's the case. Thanks for the inputs and ideas.

[Tom Slick]

Here is how to calculate it using the NEC formula for a branch circuit by calculating the circular mils area of the conductor, I don't know if it applies to a main circuit, but it seems like it should.

CMA=(K x I x L)/(VD)
CMA: circular mils area
K: material constant, for copper it is 12, this number comes from a chart.
I: is max amps, for you 200a
L: length of conductors for one phase, hot leg and neutral, 100' x 2 = 200
VD: voltage drop, it's two 120v circuits, max voltage drop is 3% x 120v, so 3.6v drop max

so;
12 x 200 x 200 = 480,000
then
480,000 / 3.6 = 133,333 = CMA

look up 133,333 on the chart and it says to use 3/0.
This CMA is just slightly over the spec for 2/0 so 3/0 gives you a safety margin

or you can go to this page
http://www.csgnetwork.com/wiresizecalc.html


disclaimer: I am not an electrician, or an EE. I just have practical knowledge, a little education, and work experience. you should consult a licensed electrician for doing any electrical work.

[reddog552]

conductor size

You will nead to use 2/0 copper or 3/0 alum. 3wire for the 200 amp panel & #4/3 for the 60 amp. Both can be ran in 3" scedule 40 grey PVC pipe. No grounding electrode is needed or wanted at the 200 amp or 60 amp panels. The electric company has no say in the wiring from the meter cabinetm & disconnect,that is where local code comes in.check with your local inspector on this,but to my knolege this is the correct sizing

[Tom Slick]

I missed the 50' part from your second post, I calc'd using the original 100' in your first post. As reddog says, 2/0 will be fine.

[ragswl4]

Thanks for all the input, I think I got it now. Don't worry I won't send a lawyer if the inspector says something different. I really appreciate your inputs.

[chopnhack]

No grn electrode?

I missed something, wasnt the main service the 200 amp box? If that is the first entry from the utility side, that unit def. has to be grounded as far as I remember. After that the grnd can be carried on a conductor to each sub panel. Please correct me if I am wrong.

[iceman61]

Better make sure the inspector will pass it with schedule 40 while you are at it. Around here underground has to be in schedule 80. It would be a ***** to have to pull that cable all over due to the wrong schedule PVC. Just make sure to run everything by the inspector before you start, that way you know that the only thing you get a failed inspection on would be your connections.

Word to the wise. During the inspection, don't talk much if you don't have to. My father, God bless him, is a retired electrician & wired our new shop. During the inspection the inspector didn't find anything wrong until my father said, "how did you like the way we did this & that, & why you haven't even looked at how we tackled going thru the wall & into the panel in such a tight space. "SHE" immediately went inside to find an LB we use in a tight space instead of a 90* (no room for the 90* actually) & said to replace or put in an access panel. My father is still griping about it. Every time he does I just tell him "I bet you think twice before you go bragging about something else." LOL

[ragswl4]

Better make sure the inspector will pass it with schedule 40 while you are at it. Around here underground has to be in schedule 80. It would be a ***** to have to pull that cable all over due to the wrong schedule PVC. Just make sure to run everything by the inspector before you start, that way you know that the only thing you get a failed inspection on would be your connections.

Word to the wise. During the inspection, don't talk much if you don't have to. My father, God bless him, is a retired electrician & wired our new shop. During the inspection the inspector didn't find anything wrong until my father said, "how did you like the way we did this & that, & why you haven't even looked at how we tackled going thru the wall & into the panel in such a tight space. "SHE" immediately went inside to find an LB we use in a tight space instead of a 90* (no room for the 90* actually) & said to replace or put in an access panel. My father is still griping about it. Every time he does I just tell him "I bet you think twice before you go bragging about something else." LOL

The county code here is Sched 80 above ground and 40 below. We are going with 80 just to be sure. Our inspector is pretty easy going (as long as things are done right) so we are insuring that everything we do is at code or better. Thanks for the advice about keeping a tight lip during inspections.