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Will my voltage drop? RayV 09-05-2006
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Posted by RayV on September 5, 2006, 3:25 pm
I am in the thinking it out stage of re-wiring my house. I know my
bank balance will drop with the current price of copper but will my
voltage? The house is two-story standard construction with an
unfinished basement and attic access, the breaker box is in the
basement. My goal is disturb as little drywall as possible. The
furthest run will be to an upstairs bedroom.

Rough calculations give me:
50' to the other side of house
30' to first outlet (up to attic and drop to outlet)
25' to next outlet (up to attic, over a few feet, and drop to next
outlet)
25' to next outlet (up to attic, over a few feet, and drop to next
outlet)
25' to next outlet (up to attic, over a few feet, and drop to next
outlet)
25' to next outlet (up to attic, over a few feet, and drop to next
outlet)
25' to next outlet (up to attic, over a few feet, and drop to next
outlet - 6 outlets in room)
205' total estimated feet of wire.

Will voltage drop be a problem using 14/2 wire on a bedroom circuit
205' feet from the panel?

A friend who will be helping me suggested I put a sub panel on the
second floor to cut back on the amount of wire run. While this may be
true I'm not that thrilled with this idea. Main reason being I assume
the inspector will want the sub panel in an accessable area (not a
closet) that will require a 'decorative' picture. Any thoughts on
this?


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Posted by on September 5, 2006, 3:35 pm
in a word, yes.
firstly, I assume you have 15amp circuits throught, which should only
run 30' on a #14wire to keep under a 2% drop. Even with 10 amp ciruits
you shouln't go over 45'

heck jumping to #12 wire won't do it at that distance either, I would
recomend following your friends advice.

Empress2454 #124457


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RayV wrote:
> I am in the thinking it out stage of re-wiring my house. I know my
> bank balance will drop with the current price of copper but will my
> voltage? The house is two-story standard construction with an
> unfinished basement and attic access, the breaker box is in the
> basement. My goal is disturb as little drywall as possible. The
> furthest run will be to an upstairs bedroom.
>
> Rough calculations give me:
> 50' to the other side of house
> 30' to first outlet (up to attic and drop to outlet)
> 25' to next outlet (up to attic, over a few feet, and drop to next
> outlet)
> 25' to next outlet (up to attic, over a few feet, and drop to next
> outlet)
> 25' to next outlet (up to attic, over a few feet, and drop to next
> outlet)
> 25' to next outlet (up to attic, over a few feet, and drop to next
> outlet)
> 25' to next outlet (up to attic, over a few feet, and drop to next
> outlet - 6 outlets in room)
> 205' total estimated feet of wire.
>
> Will voltage drop be a problem using 14/2 wire on a bedroom circuit
> 205' feet from the panel?
>
> A friend who will be helping me suggested I put a sub panel on the
> second floor to cut back on the amount of wire run. While this may be
> true I'm not that thrilled with this idea. Main reason being I assume
> the inspector will want the sub panel in an accessable area (not a
> closet) that will require a 'decorative' picture. Any thoughts on
> this?


Posted by RayV on September 5, 2006, 3:47 pm

empress2454@wowway.com wrote:

in a word, yes. firstly, I assume you have 15amp circuits throught,
which should only run 30' on a #14wire to keep under a 2% drop.

<snip>

Are you certain about the 30 feet? That wouldn't even get me to the
far side of the first floor for one outlet.


Posted by Chris Lewis on September 5, 2006, 4:01 pm
>
> empress2454@wowway.com wrote:
>
> in a word, yes. firstly, I assume you have 15amp circuits throught,
> which should only run 30' on a #14wire to keep under a 2% drop.
>
> <snip>
>
> Are you certain about the 30 feet? That wouldn't even get me to the
> far side of the first floor for one outlet.

Yes, 30 feet is more than a bit extreme.

30' of #14 (approx 1 ohm/1000') has a voltage drop of about .96V at 15A.
Which is 1%. At 2%, that's 60'.

Our codes consider a 3-4% drop permissible - I don't think the
NEC is any stricter. Which is over 100' at 15A.

But 200' is clearly too far.

I wouldn't think twice about using #14 (breakered at 15A) for a general
outlet circuit up to 120' or so, and branches to fixed lighting somewhat
longer. That said, if there's any fixed/heavy/motorized equipment on
it (including a garage door opener or A/C), I think somewhat differently.

You have a number of options to finesse this. Subpanels are nice, but
of course they have to be accessible. Using 12/3 to get two 15A
circuits (shared neutral) "most of the way" (you're talking 200+ feet)
and splitting at a box to 14ga is another.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Posted by on September 5, 2006, 4:49 pm
Folks:

My copy of the NEC doesn't actually restrict the voltage drop for
residential
wiring, but recommends a 3.6v drop in the branch circuit and a 5v drop
including
both branch and feeder together 'for reasonable efficiency'. Seems to
me a
circuit coming right from the panel could use the 5v value. These
are both
for 120v circuits, by the way. (3% and 5% are the values given, I
think. I don't
have the book on me right now)

Using the 3.6 v value, you can run this much 2-wire cable to your
furthest
receptacle outlet:

15A - 64 ft. of 12 AWG or 40 ft. of 14 AWG
20A - 48 ft. of 12 AWG

Unfortunately this adds up pretty quick.

Using the 5 v value:

15A - 89 ft. of 12 AWG or 55.5 ft. of 14 AWG
20A - 66.5 ft of 12 AWG

I said 'receptacle' because it's not likely that a light would draw the
full 15A, and
it's easier to predict what the current will be. I don't think too many
residential
fixtures draw 1800 W.

Cordially yours:
A.P.M.F.


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