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AssuredElectrical
AssuredElectrical, Master Electrician
Category: Electrical
Satisfied Customers: 4241
Experience:  Contractor-42+ Years in the ElectricalTrade
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what size of electrical wire do I need for an 800 amp single

Resolved Question:

what size of electrical wire do I need for an 800 amp single phase underground service that will be 350 feet from the transformer.
Submitted: 5 years ago.
Category: Electrical
Expert:  AssuredElectrical replied 5 years ago.

AssuredElectrical :

Hi, Welcome to Just Answer. My name is XXXXX XXXXX would be glad to assist.

AssuredElectrical :

800 amp , single phase, 350 feet. Will this be in conduits or buried directly?

Customer:

I'm not sure which route I want to go so am interested in an answer for both options

AssuredElectrical :

You have several options. There will be parallel runs.

AssuredElectrical :

Aluminum?

Customer:

yes

Customer:

im not sure what you mean by parallel runs

AssuredElectrical :

3 sets 400 mcm in conduit is an option 270 amp per set

AssuredElectrical :

What transformer is this? Power company?

Customer:

we live in rural district and is a setting for grain facility/general farm operation

AssuredElectrical :

You cannot get 800 amps from just 3 cables. Takes multiple sets of 3.

AssuredElectrical :

So, multiple conduits

AssuredElectrical :

I assume you have already verified with the power company that they can accommodate you?

Customer:

so i need 3 runs of conduit with 400 mcm triplex in each one? yes the power company has been notified and says that they have more than enough to accommodate us.

AssuredElectrical :

Tri-plex? Conduit would be single cables. THWN or the like. Triplex would be the underground cable in earth.

AssuredElectrical :

Insulation of the cable is very critical.

AssuredElectrical :

Do you know exactly what it is you have in mind? Manufacturer?

Customer:

What size triplex would i need then if i did want to direct bury it.

Customer:

what do you mean by manufacturer.

AssuredElectrical :

It is all about the insulation class of the manufactured cable

AssuredElectrical :

Here is an example:

AssuredElectrical :

  • Type RHH/RHW-2 rating to UL 44

  • Type USE-2 per UL 44

AssuredElectrical :

With this cable, it would be 3 -350 mcm runs.

Customer:

we are considering URD triplex

AssuredElectrical :

Like here?

AssuredElectrical :

That is the same 3 runs- 350 mcm

Customer:

Yes that is the wire we are considering. so can't i just run 400 mcm triplex and run that through pvc conduit and bury it

AssuredElectrical :

I am trying to understand, the cable is made for direct bury. You want to conduit it too?

Customer:

yes. just for the ease of handling/running it through conduit. and thats what we've always done. is the loss of voltage less if run in conduit or has no effect

AssuredElectrical :

Cables are large, voltage drop is not your issue.

AssuredElectrical :

The key is whether you have to de-rate the cable in conduit.

Customer:

so if i would run 400 mcm triplex in conduit and bury it, this would handle 800 amps single phase 350 feet away? is that correct? and if so what would be the approximate diameter of one of the strands of triplex?

AssuredElectrical :

1 run of 400 mcm triplex will not carry the 800 amps

AssuredElectrical :

I am finding the information, be just a moment. Thanks

AssuredElectrical :

Do you understand on the 400 mcm?

Customer:

3 sets of triplex direct bury or in conduit (whatever I decide) would be sufficient. correct? as far as the 400 mcm I guess i really don't quite understand that -- is that wire size?

AssuredElectrical :

yes, it is wire size

AssuredElectrical :

diameter of the cables

AssuredElectrical :

3 sets will carry the 800 amp

AssuredElectrical :

I am trying just to verify putting underground cable in a conduit. Not common.

AssuredElectrical :

Diameter of 350 in that URD is 1.736" each cable

AssuredElectrical :

When you are going to purchase the cable, the company selling it should know on the conduit question.

Customer:

thanks for answering my questions and your patience

AssuredElectrical :

Your welcome. Been a pleasure. If your are satisfied with my answers , please do
click the Accept for my time. You can come back to this page anytime.

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