Just built a WW shop about 50' (cable length) from my service panel.
What gauge wire should I be using? 4-4-4-6? If so, should I pull
them all individually? Or buy the premade 4-4-4-6? What size
Shop is 16X20, may consider a/c eventually too. Aside from that, I
have all the other goodies, Table Saw, dust collector, Compressors,
I'll need a ton of lighting, etc...
Would I ever really exceed 70 amps? Could I maybe get away with
That's why I asked for people's EXPERIENCE....
No offense, but I am not spending a grand for some yahoo to do the
same job I can do for $200.
I am VERY familiar with running electricity and how to accomplish the
job. I was looking for wire size recommendations.
My shop is located in the garage, less than 50' from the main panel.
I installed a 6 slot sub-panel in the garage and used 4-4-4-6 copper.
I run 60 amp breakers in the main panel. The sub-panel feeds a 120v
15A lighting circuit, a 120v GFCI protected 20A run (with motor delay
breaker), and a 20A 240 run. I could have used larger mains, but
don't need the capacity. If I add a welder in the future, it is
possible to easily upgrade. The 120v line uses 10G wire to reduce
voltage drop that is problematic with 120v equipment. There is an
existing lighting circuit in case the main trips (although unlikely).
Wiring in the garage is surface mounted and contained in conduit.
I used large 10G THWN wire for the 120v lines.
I used 12G THWN for the 240 lines.
I used 14g for the 15A fluorescent lighting lines.
I wouldn't use aluminum wiring - voltage drop and connection issues.
The slight cost involved in over-engineering your electricals will be
paid for in future flexibility.
You *must* perform an electrical consumption worksheet to discover how
much extra capacity is available from your existing main service. The
inspector will do this - and you will not pass if you stuff an 80 amp
sub-panel feed in a 3BR house with a 100AMP main panel.
You *must* perform a conductor quantity, electrical box and conduit
volume calculation to adhere to code. NEC 2002 - 314.16
Here is a link to a great electrical forum, run by an Electrical
Inspector in Indiana:
Almost any place you buy the cable at can tell you whats recommended. I
will say though that the bigger the conduit the better. Cable doesn't
go around corners for diddley squat so get something with plenty of room
Funny that. There's a plumbing/electrical supply place across the street
where my nice wooded vacant lot used to be, and they have a pallet of 5"
conduit sitting out there. That would be big enough for one wire,
Michael McIntyre ---- Silvan < email@example.com>
Linux fanatic, and certified Geek; registered Linux user #243621
First thing you should do is figure out your maximum current draw. Figure
out what you have now and what you are likely to have down the road. Then
pick an appropriate size load center and run the feeder to it.
is this an attached workshop or detached? if detached you will probably be
required to install an additional ground rod.
If detached its probably best to run underground feeder cable. if attached
you can probably use NM cable (Romex) if this is allowed for your
application, but you can't run Romex in conduit or outside at all.
I would not reduce the size of your neutral or ground wire, even if it is
allowed if running single wires. if you run a cable you have to take what
they give you.
The 50' distance probably will not result in all that much of a voltage drop
however you may want to upsize your wires just to reduce any voltage drop
when things are switched on. if you do this make sure you upsize your
ground wire size as well.
Wire and conduit are the things where labor exceeds the cost of the materials.
That said, I would think #4 in 1 1/4" pipe should be enough for a one man shop
and A/C. The extra size pipe just makes pulling a bit easier and could be used
for a bigger size if you guessed wrong.
Pull individual wires!!!!! I did #6 with 60 amp service. Its more than
adequate for my one man shop. I figure my maximum simultaneous draw (220v)
will never exceed 30 amps. (3hp table saw, 2hp dust collector, lights, small
shop heater). That would leave room for an air conditioner, if I ever do
On 21 Oct 2004 11:33:53 -0700, firstname.lastname@example.org (Elmar) wrote:
My shop is about the same size, etc. I have a 60 amp drop and about 150' of
cable run. The wires are individual #6 AL.
Lighting is 6 4' fluorescent fixtures w/4 40w bulbs in each. There is a small
window unit air conditioner on 120v. Most of the stationary tools are wired for
240. Heat is LP gas.
Maximum simultaneous load is lights plus A/C (on opposite phases) plus 3hp
cabinet saw. No dust collector, yet. The lights do react to saw startup, but
that is the only negative I've noticed. No breaker trips, so far.
However, if I had it to do over, I'd go with a larger gauge (and use CU feeders
instead of AL) for a couple of reasons. One, easier to increase capacity down
the road, and, second, reduced line losses today. I'm pushing the limits with
the existing installation.
Wichita, KS USA
Good afternoon Elmar,
According to my "Pocket Ref" (ISBN 1-885071-00-0), the following applies for
240 VAC feeds for a 2% drop using COPPER:
60 Amps @ 240 VAC (14,400 V-A), #4 is good for 150'.
50 Amps @ 240 VAC (12,000 V-A), #6 is good for 110'.
on the next page (122) they show that a 1-1/4" conduit is suitable for 5
each #4 wires or 6 each #6 when using type TW. The book recommends checking
the NEC (National Electric Code) when using wire types other than TW.
I'd take the time and discuss this with your electrical inspector before
pulling the wire. My preference is to use the #4 to minimize the voltage
drop ... but I'm not buying the wire! If you want, there's a whole page
(page 120) dedicated to calculating the voltage drop for a given distance
and cable size ... armed with this information, you may well be able to
convince the electrical inspector you do know what you're doing. You could
also ask several electricians for a quote on the job, requiring a detailed
BOM as part of the quote. You can also ask for the rate where you supply the
labor, they provide the materials and do the final hookups.
I haven't bothered with aluminum wire, though the calculations page does
include the conversion factor required. I don't like aluminum wire; the
cold-flow, corrosion and resultant I2R losses make it no fun. Yes, I know
NoAlox, proper CU/AL fittings and PROPER torque on the fittings prevents
most of the problems, but I just don't like the additional I2R losses as
The Pocket Ref by Thomas J. Glover, 2nd Edition, 28th Printing - January
2001 (C) 1989-2000 by Thomas J. Glover ISBN 1-885071-00-0
P.S. You'll find that over the years the REC has remained pretty much the
same ... lots of people with highly valued opinions (well, THEY value them),
some snide remarks, and a few people willing and able to point facts your
way. Take it all with a grain of salt, and verify everything, and you'll be
fine. Funny though, I haven't checked the REC for about a year, and nothing
has changed except some of the familiar names are gone. Back to the woodwork
(literally AND figuratively).
I am not surprised at all that you are having problems. #6al is only good for
50a at it's 75c rating. The base 60c rating is 40a. Add the 150' length and you
can expect the line sag.
At 60a you will be dropping 14.5 volts
On 22 Oct 2004 19:05:30 GMT, email@example.com (Greg) wrote:
Yeah, the #6AL was what the builder installed when my house was built. I asked
him to run the wire for a 60 amp drop because I knew that I would eventually
build a separate outbuilding for a workshop.
I am now in the process of adding a 32x48 extension to the original 16x24
outbuilding to serve as an equipment shed for tractors and implements as well as
an increase in shop space. Foundation is poured. Will backfill this weekend and
do the concrete flatwork next week.
As a part of the project, I'm going to bump the electrical service up to 100
amps. Needless to say, the existing 6 ga AL wire won't hack it. I'm thinking 2
ga CU is what I'm going to want. But, I'm going to pick up a copy of Glover's
Pocket Ref and run some calculations before committing to anything.
Wichita, KS USA
2 ga. copper is the -smallest- you should consider using.
I tend to go on the basis of "figure out what the requirements are, and go
one size larger", so I'd likely run #1 in that situation. <grin>
As you know, materials cost for a project like this is trivial, relative to
the labor effort involved -- some 'over engineering' is 'cheap insurance' for
handling expanded future needs.
On Mon, 25 Oct 2004 00:48:44 +0000, firstname.lastname@example.org (Robert Bonomi)
Thanks for the comments. I've still got a lot of "figure out what the
requirements are" calculating to do before I commit. My 100amp figure is
straight off the wall and may wind up either being serious overkill or woefully
inadequate. All I really know is that the current service won't do.
Wichita, KS USA
Comment: cost of materials is relatively insignificant, compared to the
labor investment. 'over-engineering' is a cheap investment in future
Now, start budgeting the top-end (less may be sufficient, but consider 'worst
case' situations) energy needs:
lighting 5-8A @240
A/C 20-30A @240
Compressor 15-40A @240
Dust Collector 15-20A @240
Cabinet Saw 15-20A @240
Drill Press 5-10A @240
Jointer 10-15A @240
Planer 15-30A @240
Next, what all might be running at one time, _worst_case_.
obviously the lights, plus the air conditioning. The compressor
can be 'trusted' to kick in at 'the worst possible time'.
Add in the dust collector, and the the biggest hog power tool.
Wups! what if there are _two_ people in the shop. might have
two tools running. That puts the theoretical total draw into
the 100A range. which looks like 3 ga wire.
Obviously, one can 'get by' with less -- maybe the tools you have are
lower power; maybe you don't need to plan for two tools running; maybe
the compressor is run only when you actually need to use it -- you're
not keeping a pressure reserve on hand; etc., etc., ad nauseum.
Going 'oversize' on conduit is *not* a 'bad thing', either. makes pulling
the wires easier. And gives additional flexibility down the road. There
is something to be said for having the lighting on a _completely_ different
run from the main panel -- hit (or overload) the main breaker in the
sub-panel, and all the 'sharp stuff' powers down, *but* you can still see.
Also provides a simple way to 'lock out' the tools, without clobbering the
Robert, I think your technical description is accurate. However, there is
one very important key point to remember. The current ratings you use are
full load amps. A table saw cutting 3/4" redwood doesn't draw anywhere near
the current when cutting 2" hard maple. A 2hp and 5 hp motor will draw
approximately the same current when subjected to the same loads. An air
compressor does not draw full load when it first kicks in (excluding initial
startup inrush). The current climbs as the pressure in the tank approaches
maximum. A drill press is rarely used anywhere near full load, unless
swinging a large forstner in hard wood.
The rather dim scenario you painted is highly unlikely to occur, in my
opinion. But it does point out the need to consider useage patterns and
simultaneous loads. Actually this works in favor of most users. Otherwise,
they would be tripping circuit breakers constantly.
I put a Fluke clamp on to my compressor and the reality is it pulls the most
from about a fourth to half way through bringing up the tank pressure. This has
to do with the bite of air it gets to compress, When it is close to the max it
is throttled and doesn't take in much air. That is similar to a vacuum cleaner
with a plugged hose. It actually runs faster at lower current because there is
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