Grouping of disconnects for feeders to separate buildings

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LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Me again. I have a customer who is adding a large out-building. He has a 200a service on the house, meter outside, main-breaker panel inside, which supplies two electric-heat HVAC systems, meaning there's little headroom, amperage-capacity speaking.

Instead of adding a 100-amp breaker to the already-full panel by using tandems, if we upgrade the service, and place a disconnect for the new underground feeder next to the meter, must we also add a disconnect for the existing panel for the purpose of grouping, or is labeling adequate?
 
IMO, you don't need a disconnect for the 100 amp panel. Use double lugs and feed the detached structured directly from the meter. Since it is outside and underground there is no issue with not having a disconnect.
 
So, you're saying that we wouldn't even need ONE disconnect at the meter, much less two, correct?

Plus, with no disconnect for the outbuilding, the feeder need be only three conductors, not four, right?
 
0 disconnects
3 wire

not much different from your feeding UG straight from the pole except the meter is in the line
 
Doesn't 250.32(B)(1) mean I must run a separate EGC?

Next question: What size must the feeder conductors be for a 100a panel in the new building? In other words, can #3-cu or #4-cu or #2-al be used, or do I need #2-cu or #1-al?
 
LarryFine said:
Doesn't 250.32(B)(1) mean I must run a separate EGC?

Next question: What size must the feeder conductors be for a 100a panel in the new building? In other words, can #3-cu or #4-cu or #2-al be used, or do I need #2-cu or #1-al?
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If you come straight from the meter (no disconnect),,250.32 does not apply as you are installing new service conductors, not feeders.
It is not a dwelling unit so #3 Cu or #1 AL if you are terminating in a 100a panel.
 
I think I know the answer, but for a 120' run, which would be more economical in PVC, #3-cu in 1", or #1-al in 1-1/4"?

And, should I keep the neutral full-sized, or bother trying to calculate likely neutral loading to reduce it slightly?
 
Actually, the answer isn't so obvious. The copper wire is obviously more expensive, but so is the larger PVC.

It seems to almost be a wash. The 1-1/4" cost difference over 1" eats up the savings of using aluminum.

And what about XHHW vs THWN? Opinions, please.
 
I would probably use #1 "urd" (triplexed use/rhh with 2 size reduced neutral) just because it's easy and what is stocked around here. If i were to pull individual conductors I would probably use xhhw AL, again that's what is stocked around here. For some jobs where I want to make it real nice and/or I want some thing that pulls real easy, I might order in thhn colors.
 
I agree with the felonious feline. #1 Al urd is easy to get, there's not a reason for a full size neutral, and there is no way I see the cost increase of 1 1/4" pvc being enough to offset the price of copper.

BTW, I know about the whole "URD is not in NEC" thing, it's really dual rated USE that the supply house sells, but everybody calls it URD.
 
I would never use direct burial cable. I have seen it get ding so many times and need to be dug up that, IMO I would just run pvc with thwn-2 or xhhw-2. Whichever is cheaper.
 
Dennis Alwon said:
I would never use direct burial cable. I have seen it get ding so many times and need to be dug up that, IMO I would just run pvc with thwn-2 or xhhw-2. Whichever is cheaper.
Click to expand...

We use the DB aluminum cable in conduit.

In my mind, if the insulation is tough enough to be direct buried, if it's installed in conduit it should last forever.
 
LarryFine said:
I think I know the answer, but for a 120' run, which would be more economical in PVC, #3-cu in 1", or #1-al in 1-1/4"?

And, should I keep the neutral full-sized, or bother trying to calculate likely neutral loading to reduce it slightly?
Click to expand...

LarryFine said:
Actually, the answer isn't so obvious. The copper wire is obviously more expensive, but so is the larger PVC.

It seems to almost be a wash. The 1-1/4" cost difference over 1" eats up the savings of using aluminum.

And what about XHHW vs THWN? Opinions, please.
Click to expand...

I priced 120' of 1" and 1.25" pvc. No elbows or fittings. It was $44 for 1" and $64 for 1.25" conduit.

I'm curious why you're concerned about a $20 difference? In our shop, that's not even worth talking about. It would clearly be made up with the cost savings from using aluminum and then some...
 
So, what's the best (cheapest) form of three conductors of aluminum to pull that will fit into 1.25 PVC?

Dual-rated URD? SEU cable? Individual lengths?

Cow said:
I'm curious why you're concerned about a $20 difference
Click to expand...
Because I multiplied the per-stick price by 120 instead of 12. :dunce:
 
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