Circuit Addition ?

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Ken9876

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I need to add a circuit at this home, went there tonight. Circuit is for a 50 amp heat pump heater for a pool. There is a 3/4" conduit running from a outdoor meter/main with a panel to a pool sub panel 20' away, digging would be a problem because of the fancy landscaping in place. The existing circuit is a 30 amp 240volt. 4 #10 in pipe(RNC) now I want to add 2 #6 Thwn to this conduit. By my calcs. #10 = .0211sqin., #6=.0507 sqin. so I would use the existing # 10 grounding conductor and add 2 # 6 thwn's giving a total sqin of .1858, 3/4" is good for .203 sqin. With derating the 10's would still be good for 32 amps and the 6 for 60 amps. Anyone see anyproblems with this?
 
Although your calculations work I have a questions? Is this sub panel in a separate building? If so you may want to check article 225.30
 
No its not in a seperate building, it is attached to the outside of a large shed. The pool panel only serves loads for the pool and does not serve the shed.
 
Ken9876 said:
So anyone else see any problems?
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It is an interesting question because you have 2 sets of feeders going to another building but you are not feeding that building with the feeders. I don't think article 225.30 can apply.

Something doesn't feel right about it but I can't code anything to it.
 
I think you have a branch ciruit and a feeder going to the shed.The heater is a branch, and the sub is a feeder.

225.30 Number of Supplies
Where more than one building or other structure is on the same property and under single management, each additional building or other structure that is served by a branch circuit or feeder on the load side of the service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (E).
Rick
 
I contacted the local inspector he was out today so I'll have to wait on his ruling. I'm not really sure about this one, trying to avoid ripping up his yard. I could figure out the load for the heat pump, pool pump and other associated loads and come up with one feeder that would fit in 3/4" PVC but I think I'm pressing my luck and I would have to change the pool sub panel as it's only rated at 60 amps max. The neutral would only have to be sized for the unbalanced loads, I'll have to try and work this out.
 
I'd agree with Rick, there is a feeder and a branch circuit going to the shed.

However, I'd say neither are serving the shed, so the shed's just a convenient post to hang a panel on. So, the structure referred to in 225.30 would not be the shed, it would be the (appliances of the) pool, wouldn't it?

Where are the pumps? All in one location (perhaps the shed?) or in different locations?

What are the existing loads/circuits on the pool panel as it stands? Why not just install a 100A panel and be done with it?
 
Yes, everything is in the same location, right now it's just the filter&pump and santizer unit, the heater will be added next to this equipment, all outside and next to the shed. The only problem with adding a 100 Amp panel is all his landscaping, trying to use the existing conduit 3/4" PVC feeding to a 30amp(60 amp rated) pool panel. The pump draws 4.6A at 240V, the pool light 120V maybe 2 amps, if that and the santizer unit maybe 5 Amps, going back to get exact ratings. The heater is 50amp with a min, circuit ampacity of 40, so the max load 125% of the heater =50 and the pump 4.6 with another 5 amps on each line would get me 60 amps, if I'm doing that right.
 
Ken9876 said:
3/4" is good for .203 sqin....
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It occured to me this morning - You're basing all your sizing on Schedule 40 RNC.

Around here, the area between roughly 18" below grade and roughly 8' above grade is generally considered "subject to physical damage" and we are required to use Schedule 80 in those locations due to this; 300.5(D)(4).

I'm just throwing that out there as a caution to be sure you don't have to install Sch 80, or that you don't have to reduce your overall conduit size available to .164 sq. in.

From your last post, I'd say (three #6 + gnd) or perhaps (two #4, derated neutral + gnd) would fit in the 3/4 even if it was Schedule 80. Even if you wind up upsizing the panel to a 125A, you can put it on a 70A feeder and squeak through on all counts if your exact loads call for it.

Bear in mind, I haven't whipped out a calculator yet, I've just been looking at the Cheat tables. :)
 
George-- I thought about refeeding the panel with #4's and 2 10's but I don't think they will fit in a 3/4 " conduit. At least not with my calc. .2612 sq. in. for the wire and the pipe is .2140 sq. in.

If it is only 20 feet you might consider 1 " galvanized so the damage is minimal. 6" deep and be done with it. I don't know if this is even possible with the landscaping. I still can't find anything in the code that would be a problem with your initial idea.
 
georgestolz said:
How'd you get that?
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My bad -- that's for LFNC-A > Doesn't matter cause 3/4" PVC Sched 40 is
.203 sq. inches. 3/4 rigid or Sched 80 will work but if you have to change pipes I'd go with 1"
 
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