ECN Forum Forums Code Related Discussion NEC & other Code issues volt drop

I'm confusedtoo.

Someone clue me in on 'URD' please. Not a term I know.

URD = Underground Residential Distribution.
It started out as a twisted set of individual MV conductors, but is now gaining populatity for LV as well.
It's generally not allowed inside a structure, so you should check with the AHJ to see if you can run it all the way or if you have to splice to something else before entry.

Typically the URD terminates at the meter and they go with a more smoke proof conductor for the service entry into the building. I assume the NEC calls it USE but twisted up in a triplex or quadplex.

URD started life as a Poco oriented product -- to run at medium voltages.

The scheme morphed over the years... becoming quite economic for low voltage feeders, too.

(In the Poco world, low voltage means 600VAC or less.)

So what had been strictly a Primary Loop conductor came to be accepted by the Pocos for Secondary Service Taps.

If buried directly in the soil, URD carries ampacities of over 200 in 1/0. The industry makes this with or without a reduced size neutral. For our OP, I would recommend staying with a full sized neutral as he does not have any meaningful 240VAC loads. He has to anticipate that the neutral for this installation will see wildly unbalanced return currents.

[The only time that you can safely get away with a reduced neutral is if you have significant line-to-line loads that won't load the neutral -- ever.]

IIRC, the OP claimed that this feeder would be limited to 100A across 240VAC. So the fact that he's feeding a 200A sub-panel is not a deal killer.

I can't say as I'd recommend it: 125A and 100A single phase panels are common as dust and much more appropriate.

With such intermittent loads, the actual panel size is not indicative of the load to be imposed. Watch out for build out at the new location. I'd certainly leave behind documentation as to the limits of the feeder, etc.

I'd also recommend using only high quality splice techniques in the outdoors for aluminum URD connections.

I tend to favor epoxy encapsulation -- or its equivalent with Polaris and its rivals. That's no junction where you'd want to take a risk.

Be sure to lay down caution tape and a backfill with sand around the URD. Sand is dirt cheap, and easy to compact. It won't bite you. It's astonishing what shifting cables and stones can do to the dialectric.

Thanks for the info gentlemen.

Not a common thing around here. Our POCOs do UG distribution (BUD) up to the line side of the meter pans.

When a HO or builder wants 'underground' for a new SFD in an overhead zone, it is the customers responsibility to supply & install conduit & conductors from a designated pole to the meter pan. The POCO has requirements for the conduit larger than the NEC requirements.

Reduced neutrals on the service side are not allowed by the POCO, for customer installed services.

FPL will do the lateral for a price and most builders I know go that way. The price is certainly competitive and it is one less thing they have to worry about

PSE&G installs BUD systems within the sub-divisions that have sprung up at a cost to the builder. My Twp has limited 'open space' for any more new sub-divisions. Most that have been built are <10 SFDs.

New SFDs are 'tear downs', and the few remaining empty lots.

A side note to the BUD areas are the people calling wondering how a 'downed power line' is affecting them!!

FPL even says in the web site that underground SFD laterals are mostly aesthetic. The MV distribution out on the hard road will be overhead.
They are very aggressive with their tree trimming (to the dismay of a lot of home owners) and we don't see the tree damage you see in other areas.

Here in northern NJ, we have JCP&L and they are a little lax on the tree trimming. That is one of the major reasons for power outages here. Either a squirrel jumps on the HV wire and blows a fuse, or a tree branch will touch it. The primary wire around here is a bare #6 cu wire running along the top wire from pole to pole. If they kept that wire covered and ran a messenger wire along with it, I bet it would cut out a lot of blown fuse call outs.

Greg:
Since hurricane(s) Irene and Sandy, our POCOs have widely publicized tree work to reduce 'future' outages.

I have the same POCO at my home that Harold has in his area, and yes, they have distribution (MV) that leaves a lot to be desired. Comments from the out of state crews that were here after Sandy were not very good.

They did tree work in my neighborhood; notices in all mailboxes, blah, blah.

One tree at my front yard was 'trimmed' complete on the street side. The end result was I had a tree guy come and take it down, before it got blown into my neighbors house.

Great tree trim job by the utility contractor. No recourse to get reimbursed to have the tree removed.

rant over