Subpanel

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  #1  
Old 10-19-06, 07:21 PM
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Subpanel

I am installing a subpanel in an 230 sq ft addition, a run of 30' from the main. My plan for subpanel wiring is for a 120V 9A swamp cooler (summer only) 12/2 w/ground on a 20A-1P circuit; lights/recepticles 12/2 w/ground on a 20A-1P circuit; and 2, 1500W, 240V baseboard heaters on a 20A-2P circuit. The grounds and neutral are isolated.

My question is this: my main has a 240V 30A-2P 10/3 w/ground electric dryer circuit that I don't use. The plug is located on an outside wall that would be easy to tap into and continue the 10/3 via pvc conduit to the addition via a crawl space.

OK as is?

Thanks, Monk

***********See update below*************
 

Last edited by HarleyMonk; 10-23-06 at 10:43 AM.
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  #2  
Old 10-22-06, 06:27 PM
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No. Abandon the dryer circuit if you want, and use the breaker, but do not re-use the wire. Run new wire for your sub panel.

However, better yet would be to run a proper circuit to the subpanel. I would go at least 60 amps. You do want to allow for expansion. A 30 amp circuit leave no room for expansion.
 
  #3  
Old 10-22-06, 06:52 PM
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Your new panel will be rated at 7200VA.

690W - NEC mandated 3W/sqft power budget (lights & recepts)
and
1500W - Base heater 1
1500W - Base heater 2
or
1080VA - Swamp Cooler

Total is WELL within that 30A circuit It's a 230 sqft addition, so future growth is unlikely, and could always be taken back to the main panel for really the same effort it would take to do it now- No point in tearing up your house now for something you might never need! I see no problems with your plan. Just make sure to remove the dryer outlet and just use it as a splice box. Wouldn't hurt to oversize the PVC a size, too, just in case.
 
  #4  
Old 10-22-06, 08:54 PM
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Can you say more about the existing 10/3 cable? Is there writing on it that identifies the exact type of cable?

Can you also say how much trouble it would be to run new cable? Is it impossible, or merely difficult?

Finally, can you tell us in what year the house was built?
 
  #5  
Old 10-23-06, 07:08 AM
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I would agree with RAC on this, run a new line to the addition but increase it's size to allow for a 60A circuit. This will allow for a little expansion provided your existing panel can handle the additional amperage.

We will assume it can.....since not other info was posted regarding your existing service size and load factors.

Thinking you WONT expand it.....are some FAMOUS last words....point is if you have to install a SUB anyway....make sure it is not already maxed out before you even install it....bad planning if that is the case in my opinion..you never know WHAT you may add to that side of the addition and it only costs a little more for the wire.....
 
  #6  
Old 10-23-06, 10:42 AM
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Subpanel

Hey guys, thanks for your input and please forgive this retired old man for omitting a couple of essential details.

The addition is 8 feet x 30 feet and serves as a passive solar solarium/mini greenhouse. The long wall contains 27 feet of glass, each side wall 6 feet. As such, I have no plans (or wife) that would necessitate changes or expansions.

The 120V/9A (20A-1P) swamp cooler would only be used in the summer to cool the room. Fixed lights consist of a single 150W capacity ceiling light. There are 3 receptacles on the 30 foot wall 7 feet apart, one receptacle in the middle of the 8-foot walls. The inner wall (what was the front wall of the house) is cut in half by a doorway and there is a receptacle on each side of the door - all on a 20A-1P circuit.

There are 2, 6-foot, 240V, 1500W (20A-2P) electric baseboard heaters on the outer wall under the windows.

All the addition wiring is "12AWG/2 NM-B with ground 600V" Romex-type.

The run from the subpanel to the main service panel is exactly 35 feet via my preferred method (#3 below).

The existing dryer wiring is "Type NM-B, 10AWG/3 with ground, Cirtex Plastic, 600V, Cerro A (UL)." It is a heavy black shielded cable to a 30A-2P circuit.

The house is a 1987 double wide with no attic or ceiling space.

I have three options for running the line.
1. Up through the wall through the roof, then, via metal conduit, up the roof, across a gable, down the roof, through the roof to the subpanel. This gives me a run of 55 feet and the need to carefully maintain the seal around the conduits through the roof.
2. Down the wall then through the floor to a crawl space and then to the addition via schedule 80 PVC, up through the floor to the subpanel. The problem here is that the undercarriage is covered with 19" fiberglass, in 10 x 16-foot bats. The bats are held in place by a series of steel strapping bands. To run the wire I would have to cut through the bands and partially drop the bat to access the wire. I would not want to simply drill down through the floor and bats because I do not know the locations of existing plumbing and electrical runs. An alternative would be to cut out a plug from the bat, run my line, and then replug and seal the bat.
3. Tie into the existing 30A circuit through the outer wall (which is actually protected by an attached shed), drop down two feet through the uninsulated shed floor into the crawl space and continue the 10/3 NM-B line to the subpanel via schedule 80 PVC, and then up through the addition floor to the subpanel. This is my preferred method if feasible: itís the easiest and quickest for me, and requires less (cost) cable.

Your comments and suggestions are most appreciated. Thanks again.

Monk
 
  #7  
Old 10-23-06, 02:09 PM
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Originally Posted by ElectricalMan
I would agree with RAC on this, run a new line to the addition but increase it's size to allow for a 60A circuit. This will allow for a little expansion provided your existing panel can handle the additional amperage.
The way I see it, he's running conduit to the subpanel from abandoned dryer box. So, it would be easy to upgrade those conductors later without having to do any demo in the addition.

If he upgrades now, he'd have to tear apart his existing walls/crawlspace to pull in new cable he might never need.

If he doesn't... worst case is he'd have to tear apart his existing walls/crawlspace to pull in the new cable.

If it was a trivial difference in labor and just the difference in material, that would be one thing, but I see no reason to go to the extra effort it would take to run a 60A panel vice the 30A his load requires.
 
  #8  
Old 10-23-06, 02:49 PM
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> The existing dryer wiring is "Type NM-B, 10AWG/3 with
> ground, Cirtex Plastic, 600V, Cerro A (UL)." It is a heavy
> black shielded cable to a 30A-2P circuit.

It is legal to extend this circuit to your addition if you remove the dryer receptacle. You can use this cable to feed the dryer or the addition, but not both. If you're okay with losing the dryer hookup, then go ahead and extend this circuit to feed the addition subpanel.

As some posters have suggested, it may be a good idea to leave the dryer as is and run a bigger feeder to the addition, but you are not required to.
 
  #9  
Old 10-23-06, 10:26 PM
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Well, I think you've gotten both recommendations and requirements. Both are good. The decision is up to you. Whatever you do, do a quality job.
 
  #10  
Old 10-24-06, 03:27 PM
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Subpanel

All of you please accept my heartfelt thanks for guiding me in this process.

At 64, I have an absolutely reliable notion that I will have no need (nor want) to expand the addition. Living in SE New Mexico affords me an abundance of year-round sunshine and 10-25% humidity such that I simply have no use for a dryer. On SSI, I obviously have to watch my pennies so my goal is to accomplish what I need or desire as frugally as possible. Ultimately, my choices tend to follow my ability to do the work myself, guided by professionals, like all of you, (1) because I have the time and, (2) because I often cannot afford to do otherwise.

Since none of you have aired safety or code objections - which is a comfort to me - I will abandon the dryer line, remove the existing 240 recepticle and continue the 10/3 to the addition through PVC via the crawl space.

Once again, thanks for your guidance and selfless service.

Monk
 
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