UF Cable question

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  #1  
Old 04-23-13, 01:05 AM
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UF Cable question

Hi. I would like to run 8 branch circuits from my subpanel to my remodeled kitchen using 12/2 UF cable. 20 amp breakers. Two questions:

1. I would like to bury it at 12 inches. That is permissible if it is GFCI-protected before entering the ground. But as it's coming directly off the subpanel, could I not waive that requirement? If not, how would I GFCI ground it?

2. As there are eight circuits, I am concerned about conduit fill from the risers where it enters and leaves the ground. I was thinking of using 1.25" PVC Schedule 40, with runs of less than 24 inches, and direct burial between them. In that case, how many UF cables could I put into a conduit before derating?

Thanks a lot!!!
 
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  #2  
Old 04-23-13, 03:09 AM
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Just a curious question. Why must you go underground to install this wiring? A little more background will certainly help. GFCI protection isn't required for the underground runs, but will be required on the two small appliance circuits on the countertop once you get there with the cables. You say you are coming from a subpanel. Is it grounded and are the grounding wire and neutral wire busses separated in the box?
 
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Old 04-23-13, 06:00 AM
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1) You can either install a GFCI device (flat face or receptacle) in a box at the subpanel. Or install a GFCI breaker.

2) You are required to start derating when you have 3 or more current carrying conductors grouped together. So that would mean if you have 4 -12/2 cables in the same conduit, you would have 8 current carrying conductors. However, the derating adjustment factors do not start to make a significant effect to the current carrying capacity of the wires until you get to more than 9 wires. That is because you start derating at the 90 degree column for UF-b wires as they are THHN/THWN wires inside the cable. So bottom line is, to keep it to less than 9 wires ( 4 - 2 wire cables, or 3 - 3 wire cables) in the conduit and you will be OK.
 
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Old 04-23-13, 06:42 AM
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Thanks, Chandler. The reason is that the inspector in this town says that exterior EMT is illegal. Even though there's lots of it on my house. I had two runs of THHN installed perfectly, and he made me tear it all down. There is no crawlspace and I have a cement foundation all along the home run. Going inside the house is not possible due to wacky layout. So digging was the only choice. Through a French drain no less! So I have already dug 12". Cannot get an 18" trencher back there, sothe next 6" would have to be by hand. I do believe, as per the next thread, that GFI is indeed required when the trench is 12" deep, but not required @ 18". Massive :>(
 

Last edited by debeze; 04-23-13 at 07:51 AM.
  #5  
Old 04-23-13, 06:51 AM
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Odd they don't except EMT outside. Perhaps it is a salt thing if your close to the ocean.

What about using PVC conduit attached to the outside?
 
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Old 04-23-13, 06:56 AM
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UF Cable question

Thanks Tolyn. Extremely helpful. Upon a close reading of 310.15 (B)(2)(a) Exception 3, I have to in order to get the 24" exemption from derating, I have a nipple between two enclosures. But I won't have an enclosure in the ground, so that's gone.

So my my options are:
A. Invest a fortune in eight GFI breakers.

B. Run conduit from the subpanel inside to a bank of GFI flatface receptacles... like thsLeviton X7590-W. I didn't know they existed!

I assume that being done, I don't need more GFI in the kitchen for my two required circuits, as there is a straight run from this box to the kitchen. that is what a logical inspector would presume, right?

Also, just to confirm, in 12/2 UF with ground, the ground wire does not count as a current carrying connector, right? I need eight circuits to the kitchen. Thus, in this case I would be using 4 2-wire cables in each conduit @ 20 amps= 2 conduits. Grounds don't count?

Thanks so much. I don't want to dig another 6" or I will put myself in the damn trench.
 
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Old 04-23-13, 07:21 AM
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Not sure if you saw my suggestion of using PVC conduit attached to the wall, rather then putting them into the ground. Inspector shouldn't complain about that. You then would not need GFCI protection at the panel, and you could use THHN/THWN wire, which would be much cheaper than 8 runs of UF.

If you GFCI protect the circuits at the panel, either by devices or breakers, you would not need additional GFCI's down stream. I would suggest coming out of the panel into 2 - four gang steel boxes, connecting the circuits to the GFCI's. Then continue the circuits to the pipe in the ground.

You are correct on your options. You could also use standard GFCI receptacles on the circuits that do not prohibit it, such as the small appliance circuits. They may only serve the counter top of the kitchen.

You are also correct, grounds do not count for derating.
 
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Old 04-23-13, 07:39 AM
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UF Cable question

Hi, Tolyn. You are so helpful. I appreciate it. I did indeed see your suggestion. And this is exactly what I installed. However, the inspector came and dinged it, and told me that this town does not permit external conduit. So I had to tear it all off the house. I cannot run it in the house due to lack of access: cement foundation, no crawlspace, etc. So losing the external conduit kicked over the ****bucket. I managed to dig 12" into French drain alongside the house. #$%^789 You have given me a great way out. I am trying to keep the trench at 12 inches, and not have to go to 18 as I cannot get that big a machine back there, and digging through stones is horrendous experience.

I am allowed to have two risers of conduit to do underground at entrance and access to the trench by our building inspector. That's it. Given the local code limitations, would your suggestion be allowable?

Want 500 feet of slightly used THHN?
 
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Old 04-23-13, 07:42 AM
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I had a run of PVC and a run of EMT and they made me take both down. We are not near the ocean. It's "aesthetics." Meanwhile, this side of the house came with four kinds of siding on that side: shiplap, shake shingle, batten, and shingle, and he wants to talk to me about "aesthetics." My advice: find another town.
 
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Old 04-23-13, 07:56 AM
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Sounds more like a homeowners association rule then electrical.
 
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Old 04-23-13, 12:46 PM
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UF Cable question

Very astute, Ray. Sad, but true. All the tradespeople, etc., hate working here.
 
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Old 04-23-13, 01:35 PM
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Also, just to confirm, in 12/2 UF with ground, the ground wire does not count as a current carrying connector, right? I need eight circuits to the kitchen. Thus, in this case I would be using 4 2-wire cables in each conduit @ 20 amps= 2 conduits. Grounds don't count?
That's correct. When determining whether the conductors need to be derated due to the number of current-carrying conductors in one raceway (conduit, in this case), the grounding conductors (the "grounds") are not considered because they will only carry current in the event of a fault.

In addition, a grounded conductor, a.k.a. a "neutral," is only considered if it is paired with only one ungrounded conductor (only one "hot" wire) to supply a single hot-to-neutral circuit. To say that another way, if a neutral is serving more than one hot wire in a multiwire branch circuit, it isn't considered as a current-carrying conductor for this purpose.

What that means in your case is that you could pull 13 individual conductors in one conduit without derating: 8 hots, 4 neutrals and 1 ground, because only the hot wires count. You wouldn't be allowed to run 4 lengths of 12-3/G Type UF at 12" direct burial, though, because you wouldn't be able to provide GFCI protection from the panel.

If I were doing this, I would run 1" rigid conduit in the 12" deep trench, pull the "slightly used" THHN/THWN into it, bond the ground wire on each end, call the inspector for trench closing final, and start making up the loads. But that's me.

I'm curious about one thing, though. You say you're having to run the new wiring outside the house because of the lack of access through the house. So how is the existing wiring run? Not through the attic?
 
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Old 04-23-13, 05:49 PM
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I ran across this item that might be helpful.

315.15(B)(2)(a) exception 3

3) No derating is required for conduit not longer than 24"
 
  #14  
Old 04-23-13, 09:57 PM
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TI, I'm wondering if you meant 310.15(B)(3)Adjustment Factors, Informational Note No. 2, (2) Adjustment factors shall not apply to conductors in raceways having a length not exceeding 600 mm (24 in.).

Sebeze, there's also this: 310.15(B)(3)Adjustment Factors, Informational Note No. 2, (3) Adjustment factors shall not apply to underground conductors entering or leaving an outdoor trench if those
conductors have physical protection in the form of rigid metal conduit, intermediate metal conduit, rigid polyvinyl chloride conduit (PVC), or reinforced thermosetting resin conduit (RTRC) having a length not exceeding 3.05 m (10 ft), and if the number of conductors does not exceed four.

Just for fun.
 
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