I want a very simple line to a shed, about 150 feet away. I assume that I
want about a 20 amp circuit, max. I want it for power drills, a grinder,
etc. Maybe even a 100 watt light, but not much more.
Am I correct in believing that I can use 12/2 UF wire for this purpose ?
Is there a need to go to 10/2 for this length of wire ?
Thanks for any helpful comments !!
Adding into the form a 10 amp load, I come up with 5.9 volt drop or 4.9%
As long as you never go over 10 amps your good to go.
Personally I would go for the number 10, just incase you decide to expand
Not really a *need*, but it would be a very good idea, in case you ever
want to get a table saw or air compressor. Even with high copper
prices, the wire is a lot cheaper than the trench to bury it.
Maybe, maybe not.
What is in store for the future? Telephone? Cable TV? Just bite the bullet and
install a duct bak consisting of 6- 4" PVC coated galvanized pipes encased in
a 2' x 3' concrete (dyed red) form.
3 conduits are future spares, and in the remaining 3 install in each a set of 4
x 500KcMil rubber insulated. Rack these feeders and arc-proof tape them where
exposed in manholes or handholes.
Use current-limiting crabs and hydraulic compression connections only, spliced
within 3M waterproof splice kits.
At least, that's how they feed a shed for garden tools in Central park, New
Crabs are sort of like, fuses a utility uses on underground feeders. Parallel
feeders serving multiple loads are connected through a "crab" which has very
little in the way of overload protection, but will blow for a short circuit.
Check this site for the size wire needed:
According to this calculator you need #8 wire for 15A and number #10
wire would provide only 9A for a 3 percent volatage drop. You need #6
wire to get 20A with a 3 percent voltage drop.
Don't know what your local code says, but if you are going to run
motors you need to consider the voltage drop. So, using a 20A circuit
breaker, if allowed, is a gross misrepresentation, since you would
never get satisfactory service with a 20A draw with #10 wire.
James Nipper wrote:
#10 wire and a 15A draw would give a 3.7% drop. Not many tools draw
over about 10 amps. At 20A, the voltage drop is 5%, which is still
acceptable (barely). For what the original poster described, #10 should
What are you using that shows the percent voltage drop? book, online,
etc.? I would not have expected only a 3.7% drop with 15A, given the
calculator result for 3 percent drop on #10 wire (9A draw). You are
right for what the op wants to use. But a 15A breaker would be more
reasonable for that length and size wire.
I was calculating them by hand at first, then I found this web
calculator that actually shows you what it's calculating:
It's not as simple to use as that one on elec-toolbox.com, but it has
the resistances for different gauge wires, and it calculates all of them
and lets you decide what to use.
If you can swing the cost, I'd go with 10-3. This will allow two separate
circuits, and any load on one circuit will reduce the voltage drop on the
other. Consider lights and any fixed loads on one circuit, the receptacle
for tools on the the other. Protect this with a double pole 15A or 20A
12 gauge wire is sufficient for the load(s) that you describe. The NEC
(recommended) total volt drop for feeders and branch circuits together is
5%. Since you aren't using a feeder, the total volt drop for the branch
circuit can be 5%. Drawing 10 amps on a #12 wire 150' yields a 5.9 volt
drop with 114.1 volts at the load (4.9%).
If you anticipate more load than what you described, a #10 wire would be
preferred. You may want to consider renting a direct burial cable machine.
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