URD cable for underground feeder to home?

Status
Not open for further replies.
C

copper123

Senior Member
I got a call from a friend that lives in another state and is putting in a manufactured home. His electrician installed a 2" Schedule 80 PVC conduit from the a pole mounted combination meter/panel to a stub directly under the house. After the house arrives, they are going to connect the stub coming out of the panel to the buried conduit. He asked me what size wire he needed to pull in. I told him to call the inspector and see what the local jurisdiction required. Also, I asked him to ask the inpsector if he could use table 310.15b6. He called back and said the inpector told him to use a direct burial URD cable. Two 4/0's and one 1/0 and a #4. I have never heard of URD. Its not in the code, so i searched it on the net. I found a little bit about it, and am thinking that the inspector wants him to use a direct burial, Aluminum, multi-conductor USE cable. (I am sure its Alum since its 4/0 and only about 20 feet from the house.) So question number one. Anybody else use URD? Next question, upon trying to do a conduit fill calc I ran into another snag. 2" Sch 80 PVC has a IN.squared fill number at 40% of 1.150. The problem I am having is I can't find a USE insulated conductor anywhere in Table 5. Its a little odd because it has its own article, 338. Also its listed in table 310.13. What do i use to do a calc. Does RHW apply? Also, it would appear that at any type of insulation, these conductors wouldn't fit into a 2" schedule 80 PVC conduit. I think that he might have to go with XHHW and copper to make it all fit. It's conduit the entire way, so it should be fine.
Thanks for any input.
 
Re: URD cable for underground feeder to home?

All we use is URD cable. It is normally XHHW but is has no type letters since we don't purchase listed material. URD stands for underground residential distribution and we also apply the term to the secondary cable. You will need to purchase listed cable, USE is the closest you will get to URD cable. You are not permitted to go inside the unit with USE unless it has a dual rating like USE/XHHW. :D
 
Re: URD cable for underground feeder to home?

In table 310.13 you will find the insulation thickness specifications for USE cable. URD is just a type of USE cable that has 3 or 4 conductors twisted together.

You will have a very hard time getting this into 2 inch schedule 80 conduit. See chapter 9 Fine Print Note #2 concerning jamming criteria. #6 and larger USE alledgedly has the same insulation thickness as THW. A larger conduit will always lead to an easier wire pull and in some cases it actually PAYS to use a larger conduit expecially if I cannot hook up a winch or a forklift truck.

The most practical thing in your application would be to use THWN-2 wire which is waterproof but not as waterproof as XHHW. Using the larger of table 310.15(B)(6) and table B.310.7 you will need 2/0 copper for the hot leads, #1 copper for the neutral, and #6 copper for the equipment ground. If you decide to use 3/0 copper so that it runs cooler, you will need to increase the EGC to #4 copper. See 250.122(A) and 250.122(B).
 
Re: URD cable for underground feeder to home?

I find the jargon we use interesting. For example, to us THHN means copper wire with insulation rated THHN, THWN, MTW, and THWN-2 (All THHN I have ever seen is quadruple rated). In my area, if you want copper, you say "THHN" and if you want aluminum, You say "URD" Which is three USE cables wrapped together, two full size and a two size reduced neutral. Its the same thing with SE cable, You dont have to go to the supply house and say give me aluminum SEU, even though you can get copper SEU. Copper123, what do you call and use for aluminum conductors in you area?
 
Re: URD cable for underground feeder to home?

Copper123, what do you call and use for aluminum conductors in you area?

I have been doing electrical work since 93 and have never used alum as a feeder or a service lateral. :eek: We are in a colder climate, and due to the expanding and contracting of the material, all the guys that are in the know say its not practicle and even a little dangerous? Maybe its a wife's tale, but that is what I have heard. And I have seen a bit of wire. For anything underground, direct burrial, its always USE individual conductors, Copper. If its pulled in conduit and outside its always XHHW. We also use XHHW outside for all branch ckts. #12 and up. It wont crack in the cold. If you even try to pull a outside outlet out of a weatherproof enclosure at -30F wired with THHN, the thermoplastic can almost just explode off the copper.

[ April 16, 2005, 02:00 PM: Message edited by: copper123 ]
 
Re: URD cable for underground feeder to home?

Mc5w, Hey, i didnt believe you until I did the calc. You are dead on.
"If you decide to use 3/0 copper so that it runs cooler, you will need to increase the EGC to #4 copper. See 250.122(A) and 250.122(B)."

My calc comes out to
33080.9 circ mills. Table 8, got to be a #4
thanks
 
Re: URD cable for underground feeder to home?

We are in a colder climate, and due to the expanding and contracting of the material, all the guys that are in the know say its not practical and even a little dangerous?
Click to expand...
I think there a song that goes, ". . . and it don't snow in Indianapolis in the wintertime." Maybe I have it wrong . . . HMMM. :D
 
Status
Not open for further replies.
Top