Hi all:
After a full day with a trencher, I’ve nearly finished my 200 odd feet of trenching between house and shop. This place was built over a swamp about 30 years ago, and I think the original builder found a cheap source of highway fill to bring the land up (I trenched up dozens of bowling ball sized chunks of asphalt…) about 2 feet. Ah, for the good old days… Nothing like filling in a wetland with highway tailings… Fortunately, my trench is now half full of water, so I can justify taking a day off before my back turns into a pumpkin.
When I talked this over with my electrician buddy, we figured that the 100A subpanel (I’m powering a full woodshop with a ton of lights, electric heat for the first year, and eventually a greenhouse, so yes, I do need 100A service!) would require 2/0 Aluminum URD to carry the load. We were looking at ~200′ at that time, now it’s looking more like 240 feet. According to online calculators (240 feet, 240V, 100A, 2/0 Aluminum) I’m still below 3% voltage drop, so I think I’m still okay here, right?
Anyways, I’m about to buy my line, and I was hoping to get some insight before I call on prices. 2/0 URD seems to come as 2/0, 2/0, #1. My question is this: what size for the ground? Does it need to be direct burial #1 (same as the neutral), or can I go smaller yet? My copy of code check doesn’t really spell this out very well. I’ll be doing the final install with the licensed electrician, but he’s out until next week and I’d like to get the wire purchased and ready to go beforehand.
I’m out in WA state (King County), so general NEC guidelines seem to be acceptable.
Thanks for any advice that can be offered.
-t
Replies
For 100 amp circuits the EGC needs to be #6 AL and #1 for the phase coductors
But if the phase conductors are upsized then the EGC needs to be upsized proportionally. so for 2/0 phase conductor that works to #4 EGC.
The NEC does not show any reference to URD. USE would not be the appropriate cable.
URD is used for distribution, from the transformer to the meter, and the NEC does not cover anything before the meter.
But I believe that I have heard of people using it.
I would want some verification from the local inpsector before ordering it.
But you don't want to run a separate EGC.
Use 4 wire cable and URD does come in quadplex.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Hi Bill:Thanks - I didn't realize URD was available as quadruplex cable. It looks like most of the suppliers make this as 2/0, 2/0, #1, #1 (aluminum) so that takes care of the ground.I can't see what the problem would be bonding service panels using the same grade line as used for underground distribution? Any thoughts on the resistance drop over that run?thanks,-t
You could probably get by with 1/0. but if you have any 5 hp motors then stick with the 2/0
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Ughh. This thing is getting harder, not easier...So the local supply house claims they can't get quadruplex URD. I can get 1/0 (1.76/ft) or 2/0 (2.36/ft) as triplex, but that puts me in the same boat I was in before - what size/type ground line? It sounds like I go with a single conductor UD #4?I can see the appeal of having it all in one cable (until I start wrestling it out of the back of my truck...), but is there any reason other than expense why I wouldn't run the ground as a separate cable?Given the prices I'm getting locally, I'm starting to think I'd be better off trying to mail-order it. 260' is enough of a roll to make the savings start to compete with the shipping weight... -t
Well looking it up, the code does individual wires in a common trench."(B) Conductors of the Same Circuit All conductors of the same circuit and, where used,
the grounded conductor and all equipment grounding conductors and bonding conductors
shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus
assembly, trench, cable, or cord, unless otherwise permitted in accordance with
300.3(B)(1) through (B)(4).".
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Okay, that's good to hear, you've restored my faith in the electrician that recommended it!I was worried that I was misinterpreting 340.10 - which said "single conductors in trench must be grouped"
But I was right. YOU CAN'T USE URD.But theere is URD and then there is URD.I found this on Mike Holt's."
Quote:
Originally Posted by peter d
One poco in my area uses a utility version of the "mobile home cable" for all they UG laterals (triplex or quadplex 4/0 AL cable with yellow striped neutral.) I would assume that many other poco's do as well.That's just straight "URD". The stuff the PoCo uses doesn't really have any NEC conductor type markings on it, so you can't really use it for an NEC install. I have bought URD at my supply houses that is marked with NEC conductor types, normally XHHW. The PoCo stuff is just normally marked XLPE, if it is marked at all, which doesn't really square with the NEC."And I don't know why you can't get quadplex.Google found a couple.http://www.prioritywire.com/utility.htmlhttp://tinyurl.com/2w3t4lBut you might be asking for the wrong thing.Ask for mobile home feeder cable. That will all be 4 wire.http://tinyurl.com/2mwhd5http://tinyurl.com/2x83b3But these are URD, they are USE-2 or RHH or RHW..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Not sure what happened - I typed a response last night but it disappeared? I'll try again.You've gotten to the nut of my problem. I also saw the same Mike Holt post, and I take it to mean I just have to make sure the wire I get is marked up to NEC standards.It seems like a fair number of folks wire this way, although it might be more of a regional thing (we've been burying a lot of lines out here after the last two PNW storm seasons...). I know some people dislike direct burial lines on general principle.I can find quad cable on the internet without problem, it's obviously the tool of choice for mobile home feeders - I still can't figure out why the local supply house can't get it. The supply house guy basically said, I can get 2-2-4, which is a quad cable (#2, #2, #4, #4), but anything larger and it's triplex. I asked a bunch of different ways, but I didn't think to ask for mobile home or trailer feeder... I think I'll try a different branch of the supply house and see what they say.The dilemnia is: I can get wire off the internet at a good price, although I'll have to make sure it's USE labelled, and I'll have to pay for shipping. I can buy triplex plus a single conductor from the local supply house - it's more expensive, but I avoid shipping costs.It's too bad my trenching path is so screwy - conduit is starting to sound like less of a headache all the time...
Ted, greetings from Friday Harbor. The usual around here for that application would be called "2-2-4". It is AL, and there are 4 individually jacketed conductors. Bury them 2' or greater. Under the building or less than 2' deep they are in 2" PVC conduit. I assume L&I does your inspections, but I could be wrong, maybe the county does it there.
Hi David:Hello back from the other sunny side of the sound... at least for today!When I talked to the supply house, they said 2-2-4 is two #2 conductors and two #4 conductors, which just isn't big enough for the length run I've got going. I'm looking to size 100amp service about 240' away.