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Old 06-06-2013, 07:50 AM   #16
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My rewire journey


Thanks again - I posted my location info. A city of 26,000. I placed a call yesterday to a local electrictian suggested by my home inspector and hoping to hear back. I'm more than happy to compensate for the time and help.

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Old 06-06-2013, 08:37 AM   #17
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I talked to the inspector - he said one permit, with service done first and inspected (as TarHeel said) and then rest of house. So:

1. Pull permit
2. Power company disconnects
3. Run new service and panel
4. Inspection passess
5. Power company reconnects
6. Then on to the rest

Ok - back to my planning
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Old 06-06-2013, 09:02 AM   #18
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Originally Posted by dgfit View Post
I think I'm tracking with you but might need to provide a few more details:

1. The overhead drop comes to front SE corner of house with no obvious practical alternatives. The garage is about 30 ft NW diagonal from the house. so garage feed will have to cross basement and trenched to garage. Of all the items on my list the garage is my lowest priority (but still important). Does knowing the orientation change your recommendations? I kind of thought you might think the service drop was to the garage.

2. The old attic fuse box is only the attic. fwiw, the cable runs up the outside wall beside the incoming service drop that runs to the basement. The second floor is now on main panel. The new attic subpanel was meant to avoid voltage drop over 5% for both attic and second floor but maybe I shouldn't calc based on the full 80% allowed on each circuit cuz it is unlikely that would ever happen? Especially on lighting only circuits. I have also worried about derating due to bundling through the chute and the attic, while finished, is not cooled - but that was probably overthinking. I have 3 bedtooms and two baths with fans/lights/heaters. I have also not wanted to put overhead lights on same circuits as outlets. But we're you thinking to do the second floor first because I had it listed first? To be honest it was just that I thought it would let me clear out as much old wire as possible in the basement before tackling the more densely wired lower levels. But I am trusting your advice on avoiding the attic subpanel provided I am ok on voltage drop and derating.

3. The tool room subpanel really had more to do with my hvac ducts. I am going to need to do an asbestos abatement on the ducts due to tape, but feel the electrical is more pressing. Avoiding the ducts coupled with spaghetti gas and plumbing (yet another project) give me a single joist bay path from the main panel to half the first floor including kitchen and figured it easier to run the subpanel and wire from that. Again, do I worry about derating running so many runs through a single bay? Also, I know code let's me cross a single bay cold air return, but I really don't want to. But, then again, if I'm redoing the ducts later I can just redo the returns.

Thank you so much for this discussion - I have needed this.
On question #2-

NEC recommends 5% VD is for combined feeder and branch circuits- it's only 3% for branch circuits. Don't worry about it inside of a normal dwelling unit.

It's very typical to combine lighting and receptacles on circuits. The bathrooms need one 20A circuit, and if shared on more than one bath, is for receptacles only. The light/fan/heat light combo needs a dedicated circuit per unit.

Derating NM is necessary when more than two cables are run without spacing through the same penetration, which will be sealed with insulation, caulk, or sealing foam, or installed in contact with insulation. If you're running NM in a joist bay without insulation, don't worry about derating.
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Old 06-06-2013, 09:18 AM   #19
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Thanks - my voltage drop calculatiions have been based on total run from main with 6 AWG feeder from main to sub panel, and then for each branch from that on 12. Attempting to rewire with as few holes as possible means a fair amount of up and down which increases the length. But I have been calculating based on 80% amps.
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Old 06-06-2013, 11:02 AM   #20
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One suggestion... you had mentioned using all 12ga. I would rethink that and use 12ga where required and 14ga for general receptacles and lighting circuits. You will find it much easier to work with the 14ga in multigang boxes and 3-way/4-way situations.
Using 14ga is not just to save a few dollars.
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Old 06-06-2013, 04:19 PM   #21
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Yeah I have wired a few double gangs with 12 in the past but agree (at least for lighting) that 14 makes more sense due to ease of handling. But the root of my question in all of this is the voltage drop calcs. I have seen posts both ways saying do or don't worry about it, but when I run the calcs (verified with multiple online calculators) I have to be careful to not get up to 10% drops. It must be that I just shouldn't have to use the full 80% amps in the calcs for GP. Would love any advice on this.

Last edited by dgfit; 06-06-2013 at 04:25 PM.
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Old 06-06-2013, 04:29 PM   #22
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Quote:
Originally Posted by dgfit View Post
...but when I run the calcs
single pole breakers are cheap.
pull an additional circuit (et voila!) you have capacity again
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Old 06-06-2013, 04:35 PM   #23
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AFCI's are pricey (but worth it in my opinion), but I would go that route. 120 feet (up and down walls, etc. to avoid holes) on 14 from main panel is ok?
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Old 06-06-2013, 05:02 PM   #24
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120 feet (up and down walls, etc. to avoid holes) on 14 from main panel is ok?
For voltage drop? Not a problem up to about 300LF

Do you know how to find (and drill) cap and sill plates?
Focus on that approach.

Homerun to the first device on the circuit then loop to the next by going down (or up) along that wall to the next device.

This level of Q really needs an experienced eye on site.
Find that person.
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Old 06-06-2013, 05:10 PM   #25
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Ok. Thanks for the help.

Voltage drop on 14 at 300 feet with

5 amps is 7.58 volts (6.32%)
10 amps is 15.15 volts (12.63%)
12 amps is 18.18 volts (15.15%) (this is max per NEC code)
15 amps is 22.73 volts (18.94%) (after this the breaker should trip)

I trust and will act on someone's experience telling me 300 feet are ok, but would really like to know the practical number of amps to use for voltage drop calculations that makes 300 feet ok.


Last edited by dgfit; 06-06-2013 at 05:42 PM.
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