Need help with Subpanel for attic renovation

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  #1  
Old 12-27-12, 12:15 PM
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Need help with Subpanel for attic renovation

Hello, I was hoping to get some advice from the experts in this forum. I am doing an attic renovation in my home and need to install a subpanel. To give you background as efficiently as possible:

1. I have a permit
2. The space is a walk up attic with plenty of possible locations for a code compliant panel.
3. Need to provide power for: air handler (gas - just igniter?), full bath, bedroom, main room to be used as an office, wetbar with small refrigerator and maybe a microwave and coffee maker.
4. Probably several flat screen TV's
5. 2 or 3 ceiling fans (1 in bedroom, 2 in main room).
6. I already have one 20A and one 15A spare circuit run to the attic from the main breaker panel but I think it better to have a subpanel for the space as I may renovate the other half of the attic one day.
7. I have two 200A service panels in the first floor garage and each has plenty of space for a 2pole breaker. These panels are SquareD and use the Homeline breakers.
8. Attic is essentially the third floor.
9. There is no pre-installed conduit to make the feeder run easy.

So, my questions are:

1. What size panel to install? I think 60A is plenty big but it is difficult to find them.
2. Is it compliant to use a 100 or 125A panel while only using a 60A 2-pole breaker in the main panel to supply it? Is it wise?
3. There doesn't appear to be any easy way to run the feeder to the attic. Any tips on doing this?
4. What size feeder wire should I use? Should they be individual conductors or the bundled wire?
5. What type of wire?
6. It should be be 2 hots, neutral, and a ground. Correct?
7. If I decide to go through the walls, does NEC code specify how it needs to be run? Through conduit? Secured by staples?

Thank you for your help!
 
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  #2  
Old 12-27-12, 01:10 PM
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1. What size panel to install? I think 60A is plenty big but it is difficult to find them.
2. Is it compliant to use a 100 or 125A panel while only using a 60A 2-pole breaker in the main panel to supply it? Is it wise?
You can install any size panel you desire. Since it is in the same building as the service (main) panel you would use a MLO (Main Lug Only) panel rather than a panel with a main circuit breaker. Feeding a larger panel with a smaller feeder circuit is done every day of the week. You must use the proper wire sizes and circuit breakers to protect the feeder wires.

3. There doesn't appear to be any easy way to run the feeder to the attic. Any tips on doing this?
There is ALWAYS a way. It might not be easy. Since no one on the Internet can see your house or the construction it is doubtful anyone can answer this question. Sometimes you can use a plumbing chase or sometimes alongside the chimney works. Other times you will need to run conduit on the outside of the house.

4. What size feeder wire should I use? Should they be individual conductors or the bundled wire?
5. What type of wire?
For a 60 ampere feeder you would use #6 copper conductors. If you run conduit then individual wires and without conduit you would use a cable. If the conduit has any outside exposure you need to use type THWN insulation on the individual wires but if the entire conduit run is inside then THHN insulation is sufficient. Truth is, most individual conductors are dual rated THHN/THWN so probably not a problem. There are a few different types of cables so I will let others comment on that method.

6. It should be be 2 hots, neutral, and a ground. Correct?
7. If I decide to go through the walls, does NEC code specify how it needs to be run? Through conduit? Secured by staples?
Individual conductors MUST be run in conduit. Cable generally does not require conduit as long as it is protected from damage. Conduit needs to be fastened in place with straps and screws. Cable can sometimes be fastened with staples but in the size required straps and screws is more common.

I strongly suggest that you purchase the book Wiring Simplified and read it cover to cover. This book is available from Internet bookstores and usually at the big box mega-mart homecenter where it is more likely to be found in he electrical aisle than the books and magazines section. Wiring Simplified is written for the lay person but has more information than a dozen of the regular "How-To-Do-It books that are commonly found in the books and magazines section. The cost is less than $10.
 
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Old 12-27-12, 01:23 PM
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1. What size panel to install? I think 60A is plenty big but it is difficult to find them.
2. Is it compliant to use a 100 or 125A panel while only using a 60A 2-pole breaker in the main panel to supply it? Is it wise?
Actually that is the way it is normally done. A 100 or 125 amp panel is used to provide enough breaker spaces and is fed bu a 60 amp two pole breaker.

Easiest is to run conduit on the outside of the house. In that case you would use four #6 individual THWN conductors in at least 3/4 inch conduit. (1" would make an easier pull.) Or you can use 6-3 NM-b fished through the wall. There is no need to fasten it in the wall if you fish it in a finished wall but it needs to be secured at the breaker box and subpanel.

At the subpanel you need to add a ground bar and isolate the neutral bar. Because it is all in the same building you can use a main lug panel but if you find a cheaper buy on a service panel kit that includes main breaker and BCBs you can go that way.
 
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Old 12-27-12, 03:37 PM
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To both of you, thank you! I picked up the "Wiring simplified" book at Home Depot a little while ago. Looks like $6 well spent. I'm guessing that, if I go with cable, I need to get 4 gauge? That is some big ass cable so I will try to stay with the 6ga THNN and stay indoors.
 
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Old 12-27-12, 03:57 PM
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No. #6 NM-b should be okay.
 
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Old 12-27-12, 04:23 PM
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Thanks for the tip on wiring simplified book. Most places sell them online for around $10 plus shipping. I can't find a digital book anywhere.
 
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Old 12-27-12, 04:35 PM
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ray2047, I keep reading that #6 NM-b is only rated to 55 Amps. Will this be ok with the 60 Amp service I'm taking to the subpanel? Is the individual conductor method the better way to go if it is possible to get conduit through the walls/floors? Thanks!
 
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Old 12-27-12, 05:20 PM
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Getting conduit through finished Sheetrock is going to be a lot more trouble then cable. You can use a 50 amp breaker if you want.
 
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Old 12-27-12, 06:23 PM
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Ok... I think I can get the conduit through the walls so I will go with the THHN individual conductors. I'll be buying it by the foot for $0.61/ft (I think a good deal). This brings up an important question. What colors do I need? I assume that the NEC code calls for specific colors for the hots, neutral, and ground. I'm pretty sure ground would be green. Then I'd guess that neutral would be white and the hots can be black or red. I, however, look to your expertise to know for sure before I buy it though. Thank you again!
 
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Old 12-27-12, 07:00 PM
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I keep reading that #6 NM-b is only rated to 55 Amps.
Per code, since there is no 55 amp breaker avaliable, you are allowed to go to the next sized breaker up which is 60 amps.
 
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Old 12-27-12, 08:10 PM
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What colors do I need?
You are correct about the green and white, the "hot" leads can be any color except white, grey or green and do not need to be two different colors. Black and red are traditional but not required by the NEC.
 
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Old 12-27-12, 09:49 PM
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I'd guess that neutral would be white and the hots can be black or red.
I would buy white, green, and twice as much black as needed. I would cut the black in half and mark each end of one of the pieces with a bit of red on each end.

When making up the connections, I'd use the tagged wire to connect to the B leg and the plain black wire to connect to the A leg. After cutting and stripping the tagged wire, I'd wrap it, overlapping, with red tape, for the first 6" back from the end of the insulation.



Does any of this matter in a single-phase 240V residential system? Nope, not at all. Would I do it? Yep. Why? It will strike the inspector as a professionally done job. Seriously. That's the only reason.
 
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