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2nd Floor Re-Wire Question

sands35

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St. Joseph, MI
I'm doing some long term planning for a re-wire project.

The house was build in '62 and has a mish-mash of wire projects in it.

The original wire has no grounds and is that nasty tar paper fabric stuff.

I know of a couple outlets and lights that have mixed hot/neutral wires and a couple other issues.

The bathrooms are grounded and has GFCIs. There is nothing that needs to be fixed right now. Eventually, I'll do the 1st floor as well.

The basic plan is to run a sub panel to a craft room on the 2nd floor, then wires up into the attic, then down into the rooms as appropriate. Most of the job is pretty basic, if a PITA. A couple outlets are on exterior wall that will be interesting. Once I get the sub panel in, I'd just go slow and do it room by room. (I need to get more insulation in the attic too, but want to do the electrical 1st).

4 bedrooms, 2 baths, 1 hall and one craft room and 5 closets with one light each.

Question:
What amp rating on the sub panel to service that?


My 1st look suggested 40 amp feeder would be OK. 8-3 NM or 6-3?

About 1200 sq ft on the 2nd floor. (basic load calcs based on sq ft is under 30 amps)

The basement is conditioned space - location of the main panel I'll pull from.

The run is about 75 feet. The math suggests a ~3% drop at 30 amp draw for #8.

The bathrooms will have their own 20 amp and I'll probably use 1 breaker for 2 bedroom's outlets and 1 breaker for 2 bedroom's lights.

I'll need to put in conduit to get to the 2nd floor (can go through a coat closet below on 1st floor). I'd rather avoid putting up conduit in in the unfinished basement if I can.

There is nothing special about the rooms. Ceiling fans, clock radios, a sewing machine, iron, etc. Standard normal house usage. About the heaviest use would be 2 blow-dryers going at once with lights and bath fans.
 
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theoldwizard1

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The house was build in '62 and has a mish-mash of wire projects in it.

The original wire has no grounds and is that nasty tar paper fabric stuff.

The bathrooms are grounded and has GFCIs. There is nothing that needs to be fixed right now.
Don't bet on the grounds being "good" !

When remodeling my daughter kitchen (house built in '48), we found the external "ground" wire for the kitchen and bath went to the cold water pipe that was cut off when copper was installed in the 80s !

GFCI is the answer in those cases.
 

theoldwizard1

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Question:
What amp rating on the sub panel to service that?


My 1st look suggested 40 amp feeder would be OK. 8-3 NM or 6-3?

Wrong question !

The real question is, based on the load what size breaker should be used to feed the panel and with what size wire ?

No "main" breaker is required in a sub-panel in the same building (although I think it is a good idea, even if the feed is through the "side").

8/3 is good for up to 60A at your distance based on the Southwire Voltage Drop Calculator. Shop for a 12 space panel. They typically will handle up to 60A and are not very expensive.
 
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sands35

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St. Joseph, MI
@wizard - with respect, I think you are thinking about my question backwards.

I'll put in whatever sized wire and breaker I need to feed the 2nd floor. My question isn't wire protection or breaker sizing.

I want to know, based on experience of others, how many or Watts do I need to avoid breaker tripping issues? I don't need 100 for the 2nd floor and I need more than 20.

If I start with the calculation used to size a main panel for a new house, based on square footage, I need 30 amps. I'll add on 10 more just 'cause. Given common household usage, is 40 amps adequate? Or do I need 50 or 60 to avoid tripping breakers with common usage?

The cost difference between 6-3 and 8-3 isn't that much, so I may just use 6-3 on a 60 amp breaker.

The basic household load calculations assume 3 va / ft^2. (that is, if I read the rules correctly). But I don't know how to figure the bathroom loads out. Should I think about those as "small appliance circuits"?

@1,200 sq ft that is 30 amps.

Using "residential load calculator" art 220.**

As for the grounds, some parts of the house have been re-done. As far as I can tell, have been done properly. They pass basic circuit tests. The boxes are tidy and the home runs are clear. It's the old stuff that I want to get rid of and where there are problems.
 
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TractorJeff

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This is not correct!
"10/3 will carry 240V @ 30A, but that is basically 15A per leg"
It should be 30 amps total in each leg, not 15 amps in each leg.
 
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theoldwizard1

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@wizard - with respect, I think you are thinking about my question backwards.

I'll put in whatever sized wire and breaker I need to feed the 2nd floor. My question isn't wire protection or breaker sizing.

I thought you already made that decision !

... My 1st look suggested 40 amp feeder would be OK.

40A @ 240V would be plenty.

The cost difference between 6-3 and 8-3 isn't that much, so I may just use 6-3 on a 60 amp breaker.

8/3 is more than adequate and you can still run a 60A breaker in the main panel.
 

volleyball

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I would go with 60a service. I bet you are only going to use half that at this point but the use of power tends to increase with time like our waistlines.
Want in floor heat in the bathroom? Maybe a space heater if someone is sick. Maybe you put an air handler in the attic.
Little more money, little more effort. Zero worries about outgrowing it soon.
 

zmaxmotorsports

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What size is the main service in the house?
I generally wouldn't run less than a 60a sub panel myself,Instead of using the lugs I would install a 60a 2p breaker and mechanically connect it to the panel as a main disconnect.
That would save you from having to run to the basement incase of an emergency.;)
 

wyliesdiesels

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Modesto, CA
Wrong question !

The real question is, based on the load what size breaker should be used to feed the panel and with what size wire ?

No "main" breaker is required in a sub-panel in the same building (although I think it is a good idea, even if the feed is through the "side").

8/3 is good for up to 60A at your distance based on the Southwire Voltage Drop Calculator. Shop for a 12 space panel. They typically will handle up to 60A and are not very expensive.


Wizard- u really need to get a copy of 310.15(b)(16) and study it....8/3 nm is limited to 40a...
 
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sands35

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St. Joseph, MI
What size is the main service in the house?
I generally wouldn't run less than a 60a sub panel myself,Instead of using the lugs I would install a 60a 2p breaker and mechanically connect it to the panel as a main disconnect.
That would save you from having to run to the basement incase of an emergency.;)
Uh, the house was build by the CEO of the company i work for. Extravagant in 1962, but modest by todays standards. Just a bit over 3,000 sq ft in total. It is fed by a 200amp meter to 3 Square D disconnects with three main panels. Lol. Stuff you normally only see in industrial buildings.

I was planning on a 2p feed breaker and a 100amp panel on the 2nd floor. The main panels are Square D QO, so i am going to use the same upstairs.

60 amps sounds good.
 
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