Installing new 320 Amp Service

[jsmithWired]

Hello, this is my first post, so good to meet you all.

I am an electrical contractor and will be doing a new install of a 320/400 Amp service. I have never done a 320 service before, only standard 200 and 100, etc. This is for a friend of mine, so it's basically a side job. Below is what I figured for the job and wanted to run it by some of you with experience with this type of setup. The install will be in rural Minnesota.

Underground service feed from the pad transformer to a 320/400 amp meter using 600MCM USE-2 aluminum. The run is about 350 feet, but I may have the Poco install the transformer closer to the property to shorten this up as much as possible.

The meter will be on a detached shop. From the meter, I will feed a 200 AMP MB within the shop and then run back underground to a 200 AMP MB in the house. The meter has dual lugs so I can easily run the smaller cable to each MB from there.

We want the full 200 AMP rating at both MB, in order to handle the load at each structure. Would 600 MCM aluminum handle this. The NEC reads only 385 amps for this cable but the meter is labeled at only handling up to 600 MCM on the line side. Would I need to change over to copper in order to get the full amps needed?

Also, does anyone have a good supplier for this type of cable? I usually just use Menards, HD, etc to purchase cable since I have never gone beyond 4/0. I cannot seem to find much 600 (or 650) MCM aluminum online. Everything else, just not much for 600.

Does anyone see any issues with this setup or having any suggestions? Like I said, I am unfamiliar with this type of setup and would greatly appreciate any feedback.

Thanks guys.

 

[Dennis Alwon]

As long as the calculated load is not more than 386 amps then 600kcm is fine.

Another option is to set the meter at the transformer and run two runs from there- one to each building. Of course you would have to run 4 conductors instead of 3 because you need an equipment grounding conductor with the meter remote.

 

[jumper]

You can only use the 90C column ampacity for USE-2 for derating and correction factors.

 

[augie47]

As long as the calculated load is not more than 386 amps then 600kcm is fine.

Another option is to set the meter at the transformer and run two runs from there- one to each building. Of course you would have to run 4 conductors instead of 3 because you need an equipment grounding conductor with the meter remote.

If have have only the meter would there be a need for an EGC in the runs to the building service panels ?

 

[kwired]

Getting the POCO to put transformer closer is a good idea, lessens the need to have to look as hard at voltage drop.

I suggest you look into cost difference between your 600 kcmil conductor and paralleling say a couple 4/0 or even 250 kcmil conductors.

cost per foot usually seems to take dramatic increases for over 2 inch raceway and for over about a 250 kcmil conductor.

600 aluminum is only good for 340 amps, you must use 75C ampacity for the terminals, 385 is 90C conductor and you can only use this value for ampacity adjustments since you are not going to find a termination that is rated for 90C.

But parallel aluminum 250's would be good for 410 amps, and likely cost less then single 600 and corresponding raceway.

If you wanted a single aluminum conductor that will carry 400 amps you need 900 kcmil.

 

[Little Bill]

As long as the calculated load is not more than 386 amps then 600kcm is fine.

Another option is to set the meter at the transformer and run two runs from there- one to each building. Of course you would have to run 4 conductors instead of 3 because you need an equipment grounding conductor with the meter remote.

If have have only the meter would there be a need for an EGC in the runs to the building service panels ?

That's what I was thinking. As long as it's all outdoors you just run to each panel/disconnect. If you're going straight into a panel (no runs inside before the panel) a disconnect is not necessary. Each set of conductors are SE conductors and not feeders. Here the POCO would size/run the conductors from the transformer to the meter. We use parallel 3/0 Cu. to the panels.

 

[Dennis Alwon]

If have have only the meter would there be a need for an EGC in the runs to the building service panels ?

Well not if there is no disconnect at the meter. I guess it would be cheaper to not have discos by the meter