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# New Main Panel

#1
11-04-06, 07:46 AM
Member
Join Date: Dec 2001
Location: Volusia County, Florida (Central)
Posts: 249
New Main Panel

Hello,

We are adding a sizable addition. We will be changing meter box to 400amp and adding a 400amp panel of which we will feed the old 200amp panel.

We will also be adding 1ea 60amp, 1ea 100amp and 1ea 200amp panel from the new 400amp.

We just had our power changed from overhead to pad mount transformer (buried) and saw they connected the old pole wires to the new pad mount. There were 4/0 + 4/0 + #2 for a total of three wires to the old meter (asked the sizes) but had to run off and couldn't ask the questions that occurred to me later.

Know the two big wires are 120vac. What is the smaller wire?
Neutral or ground? Guessed it was neutral and thought the ground is provided at the home. If that is true, how does one provide the ground for the main panel?

Had an electrician due the loads from the addition plans to get the permits (submitted and pending) and he told me we would be running 4 wires (4/0 4/0 4/0 #2) to each of the new panels.

The new 200amp panel will be a little over 150' from the 400amp panel. Found it odd we would be using the same grounds for all panels although the electrician is reputed to be very competent and we assume he's right. Forgot to ask and wondering; Can make another ground at each new panel connection and run 3 wires rather than the two?

Will greatly appreciate some insights.

Thanks,

hopro

#2
11-04-06, 09:27 AM
Member
Join Date: Apr 2006
Location: USA
Posts: 133
"There were 4/0 + 4/0 + #2 for a total of three wires to the old meter (asked the sizes) but had to run off and couldn't ask the questions that occurred to me later."

The 4/0 are the power legs and the #2 is the neutral.

"Guessed it was neutral and thought the ground is provided at the home. If that is true, how does one provide the ground for the main panel?"

The main panel ground is connected to ALL of the grounding
electrodes that are present and listed in 250.50(A)1 thru 6.

"Had an electrician due the loads from the addition plans to get the permits (submitted and pending) and he told me we would be running 4 wires (4/0 4/0 4/0 #2) to each of the new panels."

2 - 4/0 are hot legs 1 4/0 neutral and #2 equipment grounding conductor.

"The new 200amp panel will be a little over 150' from the 400amp panel. Found it odd we would be using the same grounds for all panels although the electrician is reputed to be very competent and we assume he's right. "

He's right
All grounds must be bonded together. Suggest you read 250.53

"Forgot to ask and wondering; Can make another ground at each new panel connection and run 3 wires rather than the two?"

All grounds must be bonded together. You may install a ground wire to one of the listed electrodes but it then must be bonded back to the main grounding electrode.
If you have separate grounds at each panel you have a voltage difference at each panel and subject to someone being shocked
or killed. You seem to be limited on the NEC requirements in this area. Suggest you read all of section 250 and get up to date.

#3
11-04-06, 12:10 PM
Member
Join Date: Apr 2004
Posts: 1,767
If they are in the same building, the ground for all the subpanels must originate from the main panel, which is the one that connects to the grounding electrode system, not each panel. If one/some are in separate structures, they can have only their own GES if there are no other metallic paths between it and any other building, otherwise they need a ground wire as well, although need a GES as well.

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