Getting ready to add electric to my new garage. I will require mostly 120v
outlets with maybe one 240v for and air compressor. The distance from house
panel to garage panel is about 60 feet. House was built in `84 and at that
time contractor said 100a would be fine but insisted a 150a due to doing
some hobby welding at times, well water pump, central AC. The guys at HD
suggested 8/3 with ground. My question is what size circuit breaker should I
have at the house panel, and is 8/3 enough for the shop. My collection of
tools are all 120v, TS, Ridgid BS, Ridgid TP1300 are the big consumers but
will not be running more than one at a time. My Sears 4hp compressor is
advertised as 4hp, but like anything today I bet it's only 2hp since it
draws about 7amps at 240volts.
8ga Romex is good for 40a. THHN in conduit is good for 50a if you have 75
degree terminals in your sub-panel and breaker feeding it. (most do when you
get over 30a)
For a few more bucks you could go with 6 ga and have some extra capacity but I
doubt you need it unless you expect to have more than one person running tools
... or a heater.
If you are looking at electric heat, 80a may be more in line.
Your sub-panel will probably have 100a busses and the breakers are pretty much
the same price in these ranges so it is really just the price of the wire.
Look back a few weeks in these electric threads here and there will be more
than you want to know about 4 wire feeders and whether you need supplimental
grounding rods. Supplimental grounding and disconnect issues only come up if
this is a separate building.
Been there and done that. The 8/3 should be OK.I put a 100Amp box in
I have a 50 AMP breaker in my house. I designed the electrical
circuits in my shop as not to overload either leg of the circuit.
The 220V incoming is actually 2 independent 110V "legs" or a single
220V line. As long as you do not overload either leg the breaker will
not trip. I have 8 4ft fluroescent (sp?) fixtures - 4 on each circuit.
I have an air conditioner 110V on the leg with the scroll saw and
sander with 4 of the lights. The air compressor is on the other leg.
The TS and dust collector are wired to 220V so they are on both legs.
Sketch your shop and determine the demand for the 110V and the 220V.
Arrange the source of the 110V legs to balance the usage.
Balancing the loads allows me to operate up to 100 amps of current at
110V on the 50 Amp circuit.
I have the following.....
3hp TS @220 Actually Craftsman 1.5 hp
2hp DC @220
1 hp Drill Press
5 gallon Air Compressor
10,000BTU Air Conditioner
8 4' light fixtures
Delta air filtration unit
Without being under load I can run all the above tools in the shop.
without tripping the breaker.
I have a single man shop so the loading is not a problem.
A little planning and you can really squeeze a lot out of your wiring
without the overloads.
It is almost _never_ a bad idea to 'over-size' the wire. Especially on a
distribution run. The cost of materials is comparatively insignificant
to the labor of running it. Bigger guage wiring results in less voltage
drop in the wiring, regardless of load.
One of the "standard sizes" sub-panel is rated for 60A, 'generally adequate'
for a garage shop.
Postulating the use of that size/rating of sub-panel, I'd run 6 ga wire,
and use a 60A breaker in the main panel.
I just built a new shop next to my house and ran about 50 feet of cable to
the building. I installed a 100 amp breaker in the main box in the house and
ran 4 gauge lead in cable[3 separate wires ] to the shop where I installed a
100 amp box with 20 circuits. I ran the cable in plastic conduit all the
way to the shop. The lead in cable was not very expensive ,bought it at
Lowe's and the plastic conduit is inexpensive.
With this set up, can you run any 220 lines? I'm going from my main panel
in the basement (200 am service) into a sub-panel in the attached garage. I
looked at the 20 circuit box at Lowes - But, I'd like to have 3 plugs that
are 220 - jointer, table saw, and dust collection. Can I do it with a set
up similar to yours, using 4/3 lead in to the sub?
The electrician wants $500 to do the sub panel, and $1,500 to the rest of
the garage - seems high. I've added circuits to a main panel before - is
this very much harder?
Thanks for any suggestions -
So far, there are two questions in this thread about adding subpanels.
The phrasing of the questions leads me to make the following points:
1) At this point in time, you are in over your head. If you are
willing to invest the time to learn about home wiring, the NEC, local
codes, and whatnot, you can accomplish the task of adding a subpanel
safely. All it takes is some time spent reading and learning, and you
can save quite a bit of money. Most libraries have a copy of the NEC
(1999 or 2002) and it's actually easy to read and understand.
2) GET A PERMIT! If you perform any substantial electrical
modifications to your home, and said modifications cause a fire, your
insurance company will absolutely look into whether or not the
modifications were done with the blessings of the local building code
people. If not, you can bet your sweet bippy the insurance company
will NOT honor your claim. Most jurisdictions allow you to perform
your own work as long as it is 'up to code'. This they determine by
inspecting your work. In my county, an electrical permit costs less
than $40.00. Cheap insurance.
3) I'm currently in the closing phase of adding two subpanels to my
house - one in a newly built wall that separates my three-car garage
into a two-car garage and a workshop. That panel is protected by a
60A breaker in the main panel. It is fed by three 6ga wires (two hots
and a neutral) and one 10ga equipment ground. This panel contains two
220VAC circuits (table saw and dust collector), one 15A lighting
circuit, and one 20A outlet circuit. The second subpanel (located on
the outside back wall of the house) is protected by a 100A breaker in
the main panel; it's fed by three 2ga wires (two hots and a neutral)
and one 8ga equipment ground. This subpanel currently contains one
50A circuit for a spa.
4) If you want to learn how to do this stuff right, I'd suggest you
obtain a copy of the following:
a. Black & Decker's "The Complete Guide to Home Wiring" - ISBN
b. Practical Electrical Wiring, by Hartwell and Richter - ISBN
Lastly, seek out a retired electrician that you can hire to 'look over
your sholder'. I found a guy that charged me $25.00 per hour for his
advice. I only used three hours of his time, but it was invaluable in
answering questions that came up.
If you have any specific questions, feel free to ask away.
On Mon, 3 Nov 2003 18:38:13 -0500, "Woodchuck"
Rob Jones, Developer
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