hot legs 4/0, neutral leg 2/0 at main

[Kenton H. Shepard, CMI]

The enclosure and diconnect were both rated at 200 amps. The hot conductors were 4/0 aluminum (200 amps) , the neutral conductor was 2/0 aluminum (150 amps). I know the rating of the disconnect shouldn't exceed the rating of the service entrance conductors, and this rule does include the neutral conductor too, right?

Also, this was a pretty clean-looking Square D box, but with no schematic showing where the bonding screw for the neutral bus bars should be. There is a grounding conductor bonding the neutral and grounding bus bars, is this how it's typically done? I expected to see a scew that would bond the box.

[Michael Larson]

Kenton,

The reason the grounded entrance conductor can be smaller is because on 220 V circuits like a water heater or AC or Electric range the current does not flow back through the neutral as it is flowing from one hot leg to the other. It requires a bit of calculation but it is permited.

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Size the Neutral Conductor: 220.22

310-15(B)(6) states that the neutral service and/or feeder conductor can be smaller than the ungrounded (hot) conductors, provided the requirements of 215.2, 220.22 and 230.42 are met. 250.24(B)(1) states that the neutral cannot be smaller than the required grounding electrode conductor specified in Table 250.66

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SERVICE-ENTRANCE CONDUCTORS shall be copper or aluminum. Aluminum is not recommended. The minimum size "hot" conductors shall be # 6 except when the service is for any dwelling the minimum size shall be # 4. The consumer shall be responsible for determining whether larger conductors are required based upon load requirements. The NEUTRAL conductor shall be the same size as the "hot" conductors or a maximum of two standard size smaller. No conductor shall be smaller than # 6. The ampacity of all conductors shall be per the National Electrical Code. See the Conductor Chart for minimum size "hot" conductors. Each conductor shall extend a minimum of 36" out from the weatherhead.

[Speedy Petey]

4/0, 4/0, 2/0 AL, or 2/0, 2/0, 1/0 CU, is absolutely typical service entrance cable.


No, there is no bond screw in that panel. The hole is empty. They compensated for this by using a #4cu from the neutral bar to the added ground bar. This is perfectly fine.
Actually it is a bit of wasted work. There was no reason for the added bars and no reason to separate the grounds and neutrals.
They probably did it for more space on the bars. Looking at it if they did not add a bar the factory neutral bars would have been full.

[Paul W. Abernathy]

Originally Posted by Speedy Petey

4/0, 4/0, 2/0 AL, or 2/0, 2/0, 1/0 CU, is absolutely typical service entrance cable.

Yep...those are the sizes I use...

[Marc D. Shunk]

That yellow stripe tells me that this is utility grade URD, which is not permitted inside the home. URD is not an NEC approved conductor. Some URD is dual rated as XHHW. XHHW is an NEC approved conductor type. The URD with the yellow strips is 99% of the time regular old underground URD, and is a violation as pictured.

[Speedy Petey]

Honestly Marc, I never knew that. That is all I can get around here and it is what everyone uses.

[Bob Elliott]

Marc do you know why it is not allowed as far as what sort of problem that neutral might cause.

[Marc D. Shunk]

Originally Posted by relliott

Marc do you know why it is not allowed as far as what sort of problem that neutral might cause.

The aluminium conductor is fine. The insulation is the problem. URD does not have an NEC compliant insulation type. URD will freely burn, for instance.

[Bob Elliott]

I knew there had to be a reason, but was actualy thinking under ground would be tougher without considering that aspect,cool,thank you.