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Date: 20 Oct 2006 23:27:20
From: Chris Friesen
Subject: garage/shop wiring question
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I'm purchasing a house with an attached garage, and will be adding a
subpanel for use as a shop. The garage is already insulated and
drywalled, so I'll be running conduit (most likely EMT).
The most-filled run will have three 20A 120V circuits for outlets wired
with #12, and 2 30A circuits for 240V wired with #10. (One 240V for the
dust collector, and one for everything else.)
I'm currently planning to run a single #10 ground wire (bare or green)
to ground everything on this run. I think this meets code, but I'd like
confirmation. (I'm in Canada so it's CEC rather than NEC, but I wanted
to get a general idea if I'm in the ballpark.)
Assuming the above is okay, I'll have 11 wires in that conduit. Given
that I'm allowed 11 #10 wires in a 3/4" conduit, does that sound like a
reasonable conduit fill? Max spacing between conduit openings will be
about 10 ft.
Since this is a one-man shop I'll only ever be using two tools at once,
maybe three if someone is helping. I'm working on the assumption that
my load diversity is enough that I can use the 70% ampacity derate for
10 conductors in a conduit. Is this reasonable, or do I have to go down
to the 50% derate? Should I go with two 1/2" conduits instead of a
single 3/4"?
Finally, what's the best way to pull this given that the various wires
are going to different places, and one of the 240V circuits is going
right to the end? Do I pull one section at a time with all the wires
for that section?
Thanks,
Chris
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Date: 21 Oct 2006 05:39:28
From: Lew Hodgett
Subject: Re: garage/shop wiring question
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Chris Friesen wrote:
>
> I'm purchasing a house with an attached garage, and will be adding a
> subpanel for use as a shop. The garage is already insulated and
> drywalled, so I'll be running conduit (most likely EMT).
>
> The most-filled run will have three 20A 120V circuits for outlets
wired
> with #12, and 2 30A circuits for 240V wired with #10. (One 240V
for the
> dust collector, and one for everything else.)
<snip >
No it won't.
Running multiple circuits in a common conduit requires some very
serious derating of the allowable current a conductor can handle.
As a result, one (1) circuit per conduit is the lowest cost way to do
the installation.
Don't feel alone, lots of folks see the table of max conductors per
conduit and think they can save some money, but alas, not so.
Lew
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Date: 21 Oct 2006 11:30:12
From: Chris Friesen
Subject: Re: garage/shop wiring question
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Lew Hodgett wrote:
> Chris Friesen wrote:
> > The most-filled run will have three 20A 120V circuits for outlets wired
> > with #12, and 2 30A circuits for 240V wired with #10. (One 240V for the
> > dust collector, and one for everything else.)
> Running multiple circuits in a common conduit requires some very serious
> derating of the allowable current a conductor can handle.
>
> As a result, one (1) circuit per conduit is the lowest cost way to do
> the installation.
Here's my reasoning.
Up to 6 conductors requires derating to 80%.
According to my simplified code book (I'm in Canada), 7-24 conductors
require derating to 70%.
I saw some more complicated stuff based on the NEC that gave a sliding
scale for the derating based on load diversity (ie how many circuits are
going to be used at the same time): if the load diversity is 50%, 7-24
conductors can also be used derated to 70%, but if the load is not
diverse then this requires derating to 50%.
Since I'm not likely to be using more than six of the 10 conductors at a
time, I should be okay even under the load diversity calculations.
Given that the derate can be done from the full ampacity of the
conductors, #12 T90 starts at 30A, and #10 T90 starts at 40A. Thus,
even derated to 70% I can still run #12 with a 20A breaker and #10 with
a 30A breaker.
Chris
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Date: 22 Oct 2006 02:40:48
From: Lew Hodgett
Subject: Re: garage/shop wiring question
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Chris Friesen wrote:
> Here's my reasoning.
<snip >
Sounds to me like you are trying to avoid running pipe since just
maybe your pipe bending skills are not quite as advanced as your wood
working skills.
NBD, bending pipe is an art form.
Use plastic conduit and the problem is solved; however, let's pursue
the idea of a bunch of circuits in a common pipe.
First things first, pipe is cheap, copper is not.
The economics of derating copper conductors will bite you in the
pocket book, big time.
Pulling several conductors will require a bucket of wire-eze and
probably a power take-up, not just a simple fish tape, to pull that
wad of wires thru a pipe.
Trust me, you don't want to go there.
If this is a typical 2-car attached garage, I question the need of
installing any conduit at all.
There are other ways that are not only simple, but low cost and legal.
Lew
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Date: 21 Oct 2006 23:24:04
From: Chris Friesen
Subject: Re: garage/shop wiring question
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Lew Hodgett wrote:
> Sounds to me like you are trying to avoid running pipe since just maybe
> your pipe bending skills are not quite as advanced as your wood working
> skills.
>
> NBD, bending pipe is an art form.
Heh...my pipe bending skills are nonexistant. Guess I'll need some
extra for practice.
> First things first, pipe is cheap, copper is not.
>
> The economics of derating copper conductors will bite you in the pocket
> book, big time.
That's just it...from the numbers I saw, and based on the CEC, I can run
up to 24 conductors (of #12 and #10) with no real derating at all since
for those sizes THHN wire is basically already derated to 70% by the
breaker limitations.
> Pulling several conductors will require a bucket of wire-eze and
> probably a power take-up, not just a simple fish tape, to pull that wad
> of wires thru a pipe.
>
> Trust me, you don't want to go there.
Okay, fair enough. I don't have any experience pulling power cables,
just some mic cables for a sound system.
> If this is a typical 2-car attached garage, I question the need of
> installing any conduit at all.
>
> There are other ways that are not only simple, but low cost and legal.
Yes, basic two car attached. Already insulated, with vapour barrier and
drywall.
I'd love to hear your suggestions.
Chris
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Date: 22 Oct 2006 05:40:27
From: Lew Hodgett
Subject: Re: garage/shop wiring question
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Chris Friesen wrote:
> Yes, basic two car attached. Already insulated, with vapour
barrier and
> drywall.
>
> I'd love to hear your suggestions.
Had a similar situation in a house I once owned.
Consider mounting a surface mount load center sub panel in the garage
on a wall where it will be easy to run the 2P-60A feeder from the main
panel.
Below this new sub panel, mount a 4x4 piece of wireway gutter that is
connected to the sub panel by chase nipples, lock nuts and thread
protectors.
Mix and match as required receptacles that get mounted in the gutter.
Since all the connecting wires between receptacles and branch c'krs
are short and in a large cross section, the normal conduit fill,
conductor derating rules do not apply.
Connect extension cords as req'd for the various loads.
Know anybody who is an electrician?
If what I have just given you is confusing, they may be able to
explain it.
Lew
Lew
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Date: 22 Oct 2006 21:01:46
From: Chris Friesen
Subject: Re: garage/shop wiring question
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Lew Hodgett wrote:
> Consider mounting a surface mount load center sub panel in the garage on
> a wall where it will be easy to run the 2P-60A feeder from the main panel.
So far so good.
> Below this new sub panel, mount a 4x4 piece of wireway gutter that is
> connected to the sub panel by chase nipples, lock nuts and thread
> protectors.
>
> Mix and match as required receptacles that get mounted in the gutter.
I had considered something like this but had dismissed it as more
expensive...looks to be about $6 a foot for the gutter online.
Chris
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Date: 23 Oct 2006 03:39:56
From: Lew Hodgett
Subject: Re: garage/shop wiring question
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Chris Friesen wrote:
> I had considered something like this but had dismissed it as more
> expensive...looks to be about $6 a foot for the gutter online.
I haven't priced sheet metal for a while, but you only need 3-4 ft.
Less than $25 doesn't seem to be to bad.
Find a Hoffman distributor and get a price on Lay In, Type 1, Wireway.
Don't know where you are in Canada, but Hoffman has sales offices all
across Canada.
One of them can direct you to a distributor.
Lew
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Date: 22 Oct 2006 23:21:15
From: Chris Friesen
Subject: Re: garage/shop wiring question
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Lew Hodgett wrote:
> Chris Friesen wrote:
>
> > I had considered something like this but had dismissed it as more
> > expensive...looks to be about $6 a foot for the gutter online.
>
> I haven't priced sheet metal for a while, but you only need 3-4 ft.
>
> Less than $25 doesn't seem to be to bad.
Guess I misunderstood. I thought you meant running the gutter all the
way around the three walls of the garage--which is more like 70 feet.
Did you mean put all the receptacles right below the panel and have
extension cords running across the shop? What about lighting circuits?
> Find a Hoffman distributor and get a price on Lay In, Type 1, Wireway.
Good to know the technical term for the stuff, anyway.
Chris
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Date: 21 Oct 2006 13:17:20
From: Doug Miller
Subject: Re: garage/shop wiring question
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In article <koi_g.12483$Y24.11603@newsread4.news.pas.earthlink.net >, Lew Hodgett <lewhodgett@earthlink.net> wrote:
>Chris Friesen wrote:
> >
> > I'm purchasing a house with an attached garage, and will be adding a
> > subpanel for use as a shop. The garage is already insulated and
> > drywalled, so I'll be running conduit (most likely EMT).
> >
> > The most-filled run will have three 20A 120V circuits for outlets
>wired
> > with #12, and 2 30A circuits for 240V wired with #10. (One 240V
>for the
> > dust collector, and one for everything else.)
><snip>
>
>No it won't.
>
>Running multiple circuits in a common conduit requires some very
>serious derating of the allowable current a conductor can handle.
Excuse me???
Please cite the section of the Code you're basing this on.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.
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Date: 21 Oct 2006 09:55:59
From: John Sellers
Subject: Re: garage/shop wiring question
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"Doug Miller" <spambait@milmac.com > wrote in message
news:A5p_g.16172$vJ2.8407@newssvr12.news.prodigy.com...
> >
> >Running multiple circuits in a common conduit requires some very
> >serious derating of the allowable current a conductor can handle.
>
> Excuse me???
>
> Please cite the section of the Code you're basing this on.
>
Notes for Table 310-16.
More than three current-carrying conductors in a raceway requires
derating of ampacity.
This has been part of the NEC for a long time.
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Date: 21 Oct 2006 11:01:31
From: cdc
Subject: Re: garage/shop wiring question
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The Canadian code (BC) requires derating whenever there are cables in
contact with each other for distances exceeding 24". The specific derating
requirements are:
1 - 3 conductors 100% load
4 - 6 conductors 80% load
7 - 24 conductors 70% load
25 -42 conductors 60% load
43 or more 50% load
Cables supplying general lighting or standard plug outlets are derated to
80% under another rule so you can run 2 3-wire or 3 2-wire cables together
when running lighting or standard plug outlet circuits.
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Date: 21 Oct 2006 13:13:32
From: Mike Marlow
Subject: Re: garage/shop wiring question
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"John Sellers" <sell1892@bellsouthNOSPAM.net > wrote in message
news:uCp_g.17387$Zn1.2477@bignews2.bellsouth.net...
>
> "Doug Miller" <spambait@milmac.com> wrote in message
> news:A5p_g.16172$vJ2.8407@newssvr12.news.prodigy.com...
> > >
> > >Running multiple circuits in a common conduit requires some very
> > >serious derating of the allowable current a conductor can handle.
> >
> > Excuse me???
> >
> > Please cite the section of the Code you're basing this on.
> >
>
>
> Notes for Table 310-16.
> More than three current-carrying conductors in a raceway requires
> derating of ampacity.
>
> This has been part of the NEC for a long time.
>
>
I'll expose myself a bit here - a conduit is not a raceway is it? I always
thought that section of the code referred to running the likes of romex
through a hole in a floor joist, not to wire in a conduit.
--
-Mike-
mmarlowREMOVE@alltel.net
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Date: 21 Oct 2006 18:00:21
From: Nova
Subject: Re: garage/shop wiring question
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Mike Marlow wrote:
>
> I'll expose myself a bit here - a conduit is not a raceway is it? I always
> thought that section of the code referred to running the likes of romex
> through a hole in a floor joist, not to wire in a conduit.
>
Conduit: Round cross section electrical raceway of metal or plastic.
Electrical Raceway: Conduit that houses electrical cables giving them
support.
--
Jack Novak
Buffalo, NY - USA
novasys@verizon.net
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Date: 21 Oct 2006 03:57:18
From: Dick Keats
Subject: Re: garage/shop wiring question
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Can you explain your response further?
Thanks,
Dick
"Lew Hodgett" <lewhodgett@earthlink.net > wrote in message
news:koi_g.12483$Y24.11603@newsread4.news.pas.earthlink.net...
> Chris Friesen wrote:
> >
> > I'm purchasing a house with an attached garage, and will be adding a
> > subpanel for use as a shop. The garage is already insulated and
> > drywalled, so I'll be running conduit (most likely EMT).
> >
> > The most-filled run will have three 20A 120V circuits for outlets
> wired
> > with #12, and 2 30A circuits for 240V wired with #10. (One 240V
> for the
> > dust collector, and one for everything else.)
> <snip>
>
> No it won't.
>
> Running multiple circuits in a common conduit requires some very serious
> derating of the allowable current a conductor can handle.
>
> As a result, one (1) circuit per conduit is the lowest cost way to do the
> installation.
>
>
> Don't feel alone, lots of folks see the table of max conductors per
> conduit and think they can save some money, but alas, not so.
>
> Lew
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Date: 21 Oct 2006 05:56:30
From: Swingman
Subject: Re: garage/shop wiring question
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"Dick Keats" wrote in message
> Can you explain your response further?
I believe what Lew is stating is that multiple conductors in the same
conduit reduce the allowable ampacity of the circuit to a point of
diminishing returns that is quickly reached. IIRC, this reduction in
ampacity is a heat related issue ... but it's been a while.
--
www.e-woodshop.net
Last update: 10/01/06
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Date: 21 Oct 2006 15:36:21
From: Stoutman
Subject: Re: garage/shop wiring question
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"Swingman" <kac@nospam.com > wrote in message
news:JqadnS-8V6lXYaTYnZ2dnUVZ_sWdnZ2d@giganews.com...
> "Dick Keats" wrote in message
>> Can you explain your response further?
>
> I believe what Lew is stating is that multiple conductors in the same
> conduit reduce the allowable ampacity of the circuit to a point of
> diminishing returns that is quickly reached. IIRC, this reduction in
> ampacity is a heat related issue ... but it's been a while.
I'm definitely not an electrician, but I remember something from college
about the "right hand rule" and magnetic fields. If two conductors are
laying next to each other there magnetic fields will appose each other.
Even thought we are talking about AC currents they will still be in the same
phase, meaning there magnetic fields will always be opposing each other. I
guess this will lead to a small amperage drop?
Not sure??
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Date: 21 Oct 2006 17:37:53
From: Edwin Pawlowski
Subject: Re: garage/shop wiring question
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"Chris Friesen" <cbf123@mail.usask.ca > wrote in message
>
> Assuming the above is okay, I'll have 11 wires in that conduit. Given
> that I'm allowed 11 #10 wires in a 3/4" conduit, does that sound like a
> reasonable conduit fill? Max spacing between conduit openings will be
> about 10 ft.
> Finally, what's the best way to pull this given that the various wires are
> going to different places, and one of the 240V circuits is going right to
> the end? Do I pull one section at a time with all the wires for that
> section?
I'm not so sure you have a good idea. Forget codes, allowed or not, is it
sensible to pull that many wires and have them stop at different branches?
You may avoid a lot of frustration and aggravation by running two or three
conduits for the system.
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Date: 21 Oct 2006 21:20:04
From: Mike M
Subject: Re: garage/shop wiring question
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I won't go into code at this point but as an installer I would stick
to no more than a boat in 1/2" and two boats in 3/4" pipe. A boat
being three hots and a nuetral for a three phase circuit. If you
have single phase and distances aren't too long and wire is thhn then
go up to 4 hots and two nuetrals but use some monkey cum to pull the
wires. Anything more go 3/4" pipe. If you have more than 180 degrees
in bends back off on the wire fill. Invariably some one will come
along and go can you get another circuit in that pipe.
Mike M
On Fri, 20 2006 23:27:20 -0600, Chris Friesen
<cbf123@mail.usask.ca > wrote:
>
>I'm purchasing a house with an attached garage, and will be adding a
>subpanel for use as a shop. The garage is already insulated and
>drywalled, so I'll be running conduit (most likely EMT).
>
>The most-filled run will have three 20A 120V circuits for outlets wired
>with #12, and 2 30A circuits for 240V wired with #10. (One 240V for the
>dust collector, and one for everything else.)
>
>I'm currently planning to run a single #10 ground wire (bare or green)
>to ground everything on this run. I think this meets code, but I'd like
>confirmation. (I'm in Canada so it's CEC rather than NEC, but I wanted
>to get a general idea if I'm in the ballpark.)
>
>Assuming the above is okay, I'll have 11 wires in that conduit. Given
>that I'm allowed 11 #10 wires in a 3/4" conduit, does that sound like a
>reasonable conduit fill? Max spacing between conduit openings will be
>about 10 ft.
>
>Since this is a one-man shop I'll only ever be using two tools at once,
>maybe three if someone is helping. I'm working on the assumption that
>my load diversity is enough that I can use the 70% ampacity derate for
>10 conductors in a conduit. Is this reasonable, or do I have to go down
>to the 50% derate? Should I go with two 1/2" conduits instead of a
>single 3/4"?
>
>Finally, what's the best way to pull this given that the various wires
>are going to different places, and one of the 240V circuits is going
>right to the end? Do I pull one section at a time with all the wires
>for that section?
>
>Thanks,
>
>Chris
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