Grouping of disconnects for feeders to separate buildings

[LarryFine]

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?

 

[Dennis Alwon]

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.

 

[electrofelon]

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.

Thats what I would do. 230.40 exception #3. Luv it....

 

[LarryFine]

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?

 

[augie47]

0 disconnects
3 wire

not much different from your feeding UG straight from the pole except the meter is in the line

 

[GerryB]

0 disconnects
3 wire

not much different from your feeding UG straight from the pole except the meter is in the line

So to finish this job what does the grounding look like at the outbuilding? Two rods, water if available, ground and neutral bonded?

 

[electrofelon]

So to finish this job what does the grounding look like at the outbuilding? Two rods, water if available, ground and neutral bonded?

YES

 

[LarryFine]

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?

 

[augie47]

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?

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.

 

[LarryFine]

If you come straight from the meter (no disconnect),,250.32 does not apply as you are installing new service conductors, not feeders.

Oh, that makes sense.

It is not a dwelling unit so #3 Cu or #1 AL if you are terminating in a 100a panel.

So does that. Thanx!

 

[LarryFine]

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?

 

[LarryFine]

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.

 

[electrofelon]

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.

 

[ActionDave]

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.

 

[Dennis Alwon]

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.

 

[ActionDave]

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.

You can run USE in pipe. It pulls easier than individual conductors.

 

[Cow]

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.

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.

 

[ActionDave]

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.

Jinx

 

[Cow]

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 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...

 

[LarryFine]

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?

I'm curious why you're concerned about a $20 difference

Because I multiplied the per-stick price by 120 instead of 12. :dunce: