Electrical service from house to detached garage – can I do this?
I am planning to build a new 2 car detached garage with workshop space. I would like to have two single-phase 240V 20A circuits and a couple of 120V 15A and 20A cicuits in the garage. I think a 100A panel would be enough.
I have an external service panel (where electic meter is located) on the north side of my house. This panel has a 200A main breaker (with places for circuit breakers – which are not used) that feeds to a 200A sub-panel in my laundry room where the all hosue breakers are located.
I would like to use this exterior 200A panel to feed a new circuit to a sub-panel to be located in the new garage. I will also need to run the conduit/service from the house panel through the attic and then back out to the new garage on the south side of the house. (It’s a single story ranch). I can’t easily go underground to the new garage because I have pool to the west and septic system to the east.
So, is there any reason I can not use the existing exterior service panel to feed 100A to my new gagrage? If I can do this, do I just get one 240V 100A breaker (or largest size that will fit the panel) then feed the appropriate sized wires (sized for load and voltage drop) to the new garage sub-panel?
Thanks for your advice.
Replies
Thanks for the positive feedback. Now I have some confiendence that I can achive my objective.
I was looking at breakers and panels - and see that I can get a 240V 150A breaker for my current service panel (Seimens QP) and a new 150A subpanel for the garage. Do you know of a website or palce where I can go to figure out what size conductors I wil need?
I know I need a minimum conductor size of 1/0 (copper) for a 150A panel, but I don't know if I need to "upsize" due to the length (voltage drop). I don't have a total distance from panel to garage yet (I'm stil in the palnning phase) but its proably going to be around 250 feet .
Why would you need 150a in a homeowner workshop?
Also be sure you understand the implications of running overhead conductors over a pool?
i would recommend a licensed electrician. do you know how loaded your house panel is? what is your average load use in the house? you could an additional service ran to the house.
another concern I would have is running 250' overhead...
When you run power to a detached building you open a can of worms. And keep in mind that this work must be inspected.
...must be inspected....
only if you have nosey and unfriendly neighbors
None of the electic service is going to be overhead. The current service is underground up tp the meter and panel on north side of the house. I would then run the new service from that panel up the north exterior wall into the attic, accross the attic and down the south wall where it would go underground to the new garage subpanel. Teh new garage is going to be about 40 feet from house. I think going through the attic is the best choice since its the most direct route to the new garage and it's unfinished space. BTW the current electrical service runs accross the attic the houses' subpanel in the laundry room.
Regarding having a 150A service in the garage - well maybe that's over kill. Perhaps 100A is enougth.
Here's what I thinking I'll want.
240V 20A for my air-compressor (which can be shared with my table saw and other future 220V woodworking equipment).
240V 30A for mini split-AC unit (to cool 2nd story storage space) -- maybe I won't do this. Just thinking out loud.
240V 20A circuit for "car lift" (my dream tool)
120V 15A or 20A convienence outlets
120V 20A circuit for shop area
120V 15A lighting circuit (maybe two circuits)
Also this work would be done by an Electical contractor. I just want to think it through before I get to point of hiring anyone. I will most likely hire a GC to build the garage - leaving some finish work for myself.
I would not share the air compressor circuit at all with anything else. Lighting is pretty low energy nowadays, if you use 2 15 amp circuits, you wont pull 30 amps. I think 150 amps is overkill, but that beats being undersize. Compare the cost difference with 150a vs 100a and see if you can get by on 100a with a reasonable margin of capacity.
The issue will be the price of the wire and that will depend on the design power consumption. The code will determine the size to match the breaker but design load will determine what you use for voltage drop.
True, but that applies to any circuit.
This starts to be important when we are deciding between 1/0 and 2/0 with 250' or more of it when his actual load might be fine on #4 on a 60a breaker.
well glad your going to have an electrician wire this up.
your info was a little conflicting. specially if an electrician will wire your garage, you should just be able to tell him what you plan on using there and what your future plans are and he will do what he needs to do.
Whoa, Nelly!
When I was looking to buy my house, I looked at several that had power run to detached buidings: sheds, garages, apartments, workshops. EVERY such arrangement was done improperly.
Folks seem to fear inspections. Heck, YOU pay the inspectors' salary whether he works or not ... might as well draw upon his experience. Talk to him. Have him look. Listen to him.
Your first step is a PROPER load calculation. There are different things to consider for different equipment. For example ... did you know that a "2 horsepower" motor can require as much as six horses of power to get started? Details like that can affect your wire size.
OK, so you think you need a '100 amp' panel. Fine. Yet, your main panel - even if it's a 200-amp service- might be limited by the manufacturer to maximum 70-amp breakers. It doesn't matter that a larger breaker can 'fit' in the space.
The wires to the garage panel, BTW, are called 'feeders.' There are no 'service' wires after the meter.
You want to run the feeders through the attic, out the side, and then over the yard to the garage? Yes, that's allowed. Te usual pactice is to run such a feeder in pipe through the attic, ending in a 'can' on the outside of the house. There you will have a mast, with a guy wire to a similar mast on the garage. You want to run the wires HIGH, and the masts secure enough to survive an ice storm or a hurricaine. the garage, the wires will go to a disconnect switch mounted on the outside of the building.
While power company rules don't apply here, it's worth looking at their requirements for for a overhead servce. Found on their website, they usually have really nice art showing how it's done.
read #7
Overhead or Underground?
In my earlier post I detailed running power overhead. There was the assertion that nothing could be buried because of a pool and other obstructions.
Here are the preferred underground installation details:
Dig DEEP. By 'deep' I mean a ditch about 30" deep, so that the pipe will always be at least 24" below grade. I say this regardless of what will be over the run; you want the pipe deeper than a casual shovel point when someone repairs the lawn sprinklers, bangs in a tent peg, whatever.
You'll want to run at least three, maybe four, pipes. Electric, phone, water, gas. Even if you don't want to use them today, this will save your having to dig again some day.
Electrical conduit is cheap. Go BIG, the bigger the better. For this job, probably 2" for the electrical and 1" for the phone / data / alarm / cable TV / whatever.
Cover the bottom of the ditch with a layer of (preferably) decomposed granite or clean sand. The 'granite' looks like gray sand, and does not compress. Later, use more of the same to cover the pipes.
The pipe runs themselves should use PVC conduit. Where you begin to transition from the horizontal run to the vertical stub-ups, change to heavy (rigid) pipe. Wrap this pipe in PVC 'pipe wrap' tape. Where the steel pipe comes out of the ground, anchor it to the stem wall using a short piece of Unistrut; this will space the pipe about 1-1/2" off the wall, just right to enter your 'can" and clear any siding. We use the metal bends so that wires won't rub grooves in them as we pull them through the line.
Thanks everyone. Lots of good points.
Even though I'm going to hire a GC to do the work - I still want to understand the process and be able to discuss the project details with the GC. I have had too many jobs where I paid someone to do the work that turned out less than satisfactory (code compliant but IMO could have been done better or differently) becuase I didn't discuss or review the details with the tradesman. Now I prefer to go over the steps with the GC or whomever and understand what their doing. Also this helps me figure out roughly what to expect as far as costs (at least I can get a rough idea of material costs).
Regading the panel's "max size of a single breaker that is allowed" comment - this is very useful - now I will go out and research this to see if I can even get the power I need/want to garage. It would be a real bummer if I couldn't get at least 100A to new garage.
And I agree that 100A is enough for my needs (plus I priced the conductors for 100A versus 150A (1/0 or 2/0) and their is quite a difference.
Thanks again. Great forum!
A compromise on the feeder size would be to install oversized conduit, so that it can be enlarged later.