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Joined: Mar 2004
Posts: 16
J
JG Offline OP
Member
I recently saw a job with 4/0 al sevice single phase entrance conductors feed a 320 amp service, two 200 amp panels, a load calc of 228 amps. The engineer gave me a cut sheet listing the 4/0 at 315 amps, buried @90 deg C. Does this override 310.15 if 90 deg terminals are used?

2017 / 2014 NEC & Related Books and Study Guides
Joined: Feb 2002
Posts: 182
B
Bob Offline
Member
You are required to use table 310.16 for NEC installations unless you want to invoke
310.60D Engineering Supervision. I am not sure what you are considering terminations but if it the compression connectors that not
correct. The terminals are for the meter socket and any other connectors involved. Ratings per 316.16 for 4/0 AL is 180 amps.

Joined: Jan 2004
Posts: 1,507
G
Member
I have no idea how he came up with 315a. If I understand the question, you are talking about a Service lateral sized at 4/0. This is figured differently than an electrician would size Service Entrance conductors. The Utility company have a different rating system based on established demands.


George Little
Joined: Mar 2004
Posts: 16
J
JG Offline OP
Member
You are correct GL, it is a lateral, only customer owned. I was under the impression 310.15 must be adhered to, when not installed by the utility. Please correct if misguided.
Thanks

Joined: Jan 2003
Posts: 4,391
I
Moderator
JG are you asking about Table 310.15?

You may use that table in some applications you never have to use that table.

If this service lateral is customer owned and covered by the NEC the choices are Table 310.16 which would allow 180 amps per 4/0 AL or as option you could use Table 310.15 which would allow the 4/0 AL to run a 200 amp service.

Any chance you have two sets of 4/0 AL?

Any chance the 4/0 was copper not aluminum?

It is worth noting that the service conductors feeding two or more disconnects do not have to be rated as high as the total overcurrent protection.

Service conductors feeding two or more disconnects only have to be rated to handle the load.

With a load calc of 228 amps 4/0 AL is out of the question.

4/0 copper would do it with a rating 230 with a calculated load of 228. [Linked Image]

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Dec 2000
Posts: 4,287
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We have a couple of local utilities that have us supply and install the service lateral conductors. The are sized and specd by the PoCo's engineering.

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Posts: 182
B
Bob Offline
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"We have a couple of local utilities that have us supply and install the service lateral conductors. The are sized and specd by the PoCo's engineering."
electure
When you do this does it become the property of the utiltiy?

Joined: Dec 2000
Posts: 4,287
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Yes, it does. Is it different elsewhere?

Joined: Feb 2002
Posts: 182
B
Bob Offline
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electure
You are acting as a contractor for the utility. Since the NEC does not cover installations that are part of the distribution, they do not follow the same rules that the NEC applies to other installations. They caculate the load differently than required by section 220.
They estimate the load that will occur any give n moment and size the conductor to match this estimated load. That is why they can use 4/0 AL. In this case the conductor belongs to the home owner and it should be installed according the the NEC. In my opinion 4/0 is not large enough for this load.


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