I'm running electric to a new shop building underground for about
185 feet. I'm considering using aluminum tri-plex #4 or #6 inside
1" PVC buried about 2 feet. I'll be running a 120V air compressor,
an arc welder, and a 120V window A/C but not all at the same time.
The reason I'm looking at the aluminum tri-plex is the cost which
is .70/.85 cents a foot in my area. Is this the best and least
expensive way to do this job ? I'm doing it myself so I'm not
worried about code but I will have sufficient breakers on both
ends. Any suggestions/ideas please ?
If I were you, I'd definetly go for the copper, as for amp draw, #6 awg
is usually good for
60 amps at 100 ft and #4 is 80 amps at 100 ft, BUT for aluminum #6 is
only good for
40 amps at 100 ft and #4 is 60 amps, so you see you loose 20 amps by
The air compressor and 120v window unit won't be a problem, but your
get pretty hot with the welder after running awhile, it happened to me
once, got real hot
real fast, even with a breaker.
I'm not sure if you want the best way to do the job or the cheapest.
From my own experiences repairing underground aluminum conductors, I would
never use it that way even in conduit. Copper is the way to go underground.
I suggest that you use a larger conduit such as 11/4" to make it easier to
pull. It might be cheaper to buy individual conductors instead of the
triplex. It is a long run so you should go with the larger size wire. For
a 220 volt service you will need 4 conductors. The grounding conductor can
be smaller based on the size of the other conductors.
Since you are doing it yourself it is all the more reason to pull a permit
and have the work inspected.
Check the price of #4 (or #3) aluminum UF cable; individual conductors
rather than triplex. I'd be tempted to direct-bury that with a bare #6
solid copper wire for the ground. I don't know if you can double-up the
neutral and ground wire that way or if you'd need 4 conductors. (For
overhead wiring you'd only need three, but underground is probably
If you use triplex or quadplex cable, make sure it is rated for
underground use and isn't just for overhead wiring.
BTW, overhead wiring is a PITA, so I don't recommend that method.
See if you can rewire the air compressor for 240V; some of them are
convertible. It will be a lot happier on 240V.
It's your house so do as you please but we would need to know what the
motor size is on your air compressor, the name plate current draw of
your arc welder, and the amperage draw of your window air conditioner in
order to answer your question.
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
I don't see a allot or Aluminum used any more, that says something . I,I'm
not an electrician but when I did my shop he said Copper. Also aluminum
corrodes, When I wired my new oven they used aluminum wire in the house I
had to use a special lube for the wire nuts. He also said panel box
connection have a tendency to get lose. Spend the extra Copper
I am an electrician (retired)
But most areas do not even allow aluminum to be used any more.
(too many corrosion problems when terminations/joints are not done properly)
Also aluminum wires have to be heavier than copper for the same load, so #6
aluminum can be #8 in copper, you may find the prices are about the same in
Copper wiring is still the best.
Gauge of wire you need depends on the loads you will be drawing, and also
local codes , but it's always a good idea to figure out what you need then
go up one size
(you may decide next year to buy a heavier welder)
The codes are there for a reason, follow them (or better them) even if you
decide to do it without an inspection/permit.
As with the other posts I agree that you can pull individual cables and save
a few bucks over the cost of triplex.
You can easily go up a size or two more than you need on the conduit to
make it easier to pull, and provide room for more wires later if you need
I too, have no way to tell from the info you provide, what size feeder you
need, but also agree that copper would be a better choice. Keep in mind the
conductor insulation must be approved for "wet" locations like THWN. Most
insulation has multiple ratings, however in larger sizes you can still find
straight THHN wire which is not rated for wet locations
When we wired our detached garage (100A, 120' worth of sub feed),
it would have cost about $700 in copper versus $300-ish in Al.
#3 Al triplex versus #4 Cu NMW (aka US UF).
In our area (Canadian codes), you can direct bury NMW (no conduit
or other protection) as long as it's >24" underground (goes to >30"
under driveways/roads). You can subtract 6" from the depth if you
put it in CSA-rated PVC tubing. (I don't think the NEC permits
PVC tubing of any kind, has to be real conduit).
We used a PVC sleeve under the driveway, but not under other parts
because the trench was 24" thruout.
Given the price difference, we went with the aluminum. Haven't
regretted it. But it does have to be carefully done exactly
to code (grease etc).
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
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