Underground Cable Ampacity

[jeff43222]

I'm in the middle of a job involving installing a new 200A underground service to a single-family dwelling. I've gotten the new meter socket and panelboard in, and the city inspector has signed off on my work, so the PoCo is in the middle of running the new cables underground.

I just stopped by the house and looked things over, and I found the PoCo's cables in place but not yet connected/energized. The phase conductors were marked "MT 1/0 AWG AL XLP/HDXLP". The grounded conductor was the same, but 2 AWG. Since those cables aren't listed in NEC Table 310.16 (or anywhere else I could find), I assume they fall under NESC or something like that, seeing as how they are the PoCo's cables.

Can someone on the utility side enlighten me as to what these conductors have for an ampacity? I'm curious if my installing 200A service was a waste if the PoCo's cables aren't capable of that ampacity.

 

[electricman2]

Re: Underground Cable Ampacity

Seldom will the service drop the POCO installs equal the ampacity of the service. They have a formula for demand that allows much smaller conductors. I installed a 150A service for a museum at a local cemetery. POCO connects to my 1/0 copper riser with No. 4 AL. :roll:

 

[peter d]

Re: Underground Cable Ampacity

This is not even a remote concern for us electrcians. In this case, I think the poco's are much more rational than the NEC. The load the we determine by the NEC calculation is way above the actual load, and will never come close to the maxing out the services that we install.

Can anyone say that their home will actually come close to drawing 200 amps? Not very likely. Much more unlikely is a home drawing 400 amps. I can see a large AC load in a large home in a warm climate, but in that case I'm sure the poco would compensate.

In my area, it is not uncommon for a 400 amp residential service to be supplied with 4/0 by the poco. If they install it, they are responsible for it. In reality, it will go a lifetime without trouble.

 

[bob]

Re: Underground Cable Ampacity

Can someone on the utility side enlighten me as to what these conductors have for an ampacity? I'm curious if my installing 200A service was a waste if the PoCo's cables aren't capable of that ampacity.

You did not say if the3 cable was in conduit but Okonite lists its 90C cable as:
1/0 underground 219 amps
1/0 in duct 159 amps
Either would carry your load with no problem.

 

[jeff43222]

Re: Underground Cable Ampacity

There were three separate cables, and I didn't see any evidence of the PoCo laying any conduit. They had already trenched and filled it in. What I found was a coil of conductors sticking out of the ground near the meter socket, and one coming up out of the ground at the pole. It looked to me like it was direct-buried.

I realize that the homeowner is unlikely to use his full capacity, and if the PoCo's wires burn up because they can't handle the load, it's the PoCo's problem. I did follow proper procedures in terms of notifying them of the size of the service, getting it inspected, etc. I was just curious since I have never encountered that kind of wire before.