Electrical sub panel

canuck · #1 03-26-2017, 10:15 AM

Yes, I know I should just hire an electrician but I'm cheap and poor

I want to put a sub panel in a detached garage, 100' away from the main panel
I will have a couple lighting circuits (15 amp) and 3-4 20 amp receptacles on two separate breakers.
I happen to have plenty of #10 3 conductor teck 90 cable on hand, as well as an unused 40 double pole breaker in my main panel.
Question is, can I get away using this breaker for my minimal load or should I buy a dbl 30 (which I believe is code?)

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RancheroMan · #2 03-26-2017, 10:39 AM

*Not an Electrician*

Breakers are there to protect wire, not equipment. A 40amp breaker will allow to much current for #10 wire and could possibly cause excessive heating of the service wires (would you ever be in a situation where you are drawing all 40 amp, tough to say). I think a double pole breaker is around 20-30 bucks depending on your panel. Pretty cheap insurance.

Dick284 · #3 03-26-2017, 10:43 AM

Hire an electrician, as there is far more to this than first appears.

Not to mention the permitting requirements, which can effect resale and insurance.

wellpastcold · #4 03-26-2017, 11:01 AM

As Dick suggested just hire an electrician. There are plenty around who would work with you. Dig your own trench. Drill the holes in the studs and do any of the other "grunt" work you can handle. Let them know you have the tech cable. Let a pro pull the permit and do the tie ins and wiring. You will be happy you did when you go to sell or if you ever had any kind of issues with your garage involving insurance.

dodgeboy1979 · #5 03-26-2017, 11:44 AM

you can always pull the permit yourself, however you will be required to have it inspected. That's what i did for my garage. With a #10 wire you should be good for up to 30 amps.

Alephnaught · #6 03-26-2017, 12:03 PM

Totally DIY-able. From your post, you've got a fair bit of thinking & learning to do on this, but it's completely achievable. Pick up a copy of the CEC and a couple of DIY electrical manuals & do some reading. Then, draw up a plan for what you're gonna do & go in and grab a permit. Have the work inspected & off you go. These skills are totally learnble.

Mountain Guy · #7 03-26-2017, 12:05 PM

You don't need an electrician to do that simple job....pull your own permit and just do it right.
Don't have my calculator handy but I'm thinking #10 might be a little undersized to go that distance @ 40A.

roger · #8 03-26-2017, 12:08 PM

im not an electrician either and ive never played one on tv, with crime being what it is of late it wont be easier than being one wire or two.

i would suggest that run a length underground cat5 and/or a empty pvc conduit for security cam wiring, intercom, thermal controls and such.
also run NMWU 12/2 for the exterior lites so that when you turn on the house lites it turns on th eexterior lites on the garage as well.
if you plan on heating it one day you can run underground plastic gasline and steel gas risers too in the same trench.

you mentioned that your cheap but doing things twice isnt.

whiteout · #9 03-26-2017, 02:05 PM

I did this exact thing this past summer, just with heavier gauge wire and bigger breakers.

You can easily do all the required work by yourself, from pulling the permit to doing the final terminations. The municipality will provide you with all the code information you need as well.

Where are you located?

CBHurricane · #10 03-26-2017, 05:37 PM

Pick up the CEC, #10 is only good for 30A. This calculation changes due to distance though as well, with codes being changed due to % loss limits.

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trophybook · #11 03-26-2017, 07:22 PM

Go with#6 ALU and a 40 amp sub panel

nick0danger · #12 03-26-2017, 07:34 PM

I'll check the IEC when I get home but I'm pretty sure the smallest wire to feed a panel is #8awg

SteveY66 · #13 03-26-2017, 07:41 PM

I'm a master electrician and you will need a new 2P 30 amp breaker as 40A is too large for that wire. Depending on how big your garage is and what equipment is present 30A is plenty.

However keep in mind most stand up compressors are 20A. I have a 32'x30' triple garage and I have a 60 amp sub panel installed.

Do it right pull a permit and have inspected

Grizzly Adams · #14 03-26-2017, 08:39 PM

Quote:

Originally Posted by SteveY66

I'm a master electrician and you will need a new 2P 30 amp breaker as 40A is too large for that wire. Depending on how big your garage is and what equipment is present 30A is plenty.

However keep in mind most stand up compressors are 20A. I have a 32'x30' triple garage and I have a 60 amp sub panel installed.

Do it right pull a permit and have inspected

No. 10 wire for a hundred foot run ?

Grizz

Mountain Guy · #15 03-26-2017, 09:05 PM

Quote:

Originally Posted by Grizzly Adams

No. 10 wire for a hundred foot run ?

Grizz

Sure why not..... light bulbs aren't as bright that way.
#2 AL minimum I'd say.

canuck · #16 03-26-2017, 10:19 PM

Thanks everyone for your info and even your opinions

As I thought, a 30 amp breaker is required for the #10 wire
Just to clarify, this is a simple vehicle storage structure and nothing more - it will have 6 lights and 2 (split) receptacles to plug block heaters into (likely no more than one at a time)
The power is being fed from my main shop where I do have the large demand (air compressor,welders,etc)

SteveY66 · #17 03-26-2017, 11:19 PM

Quote:

Originally Posted by Grizzly Adams

No. 10 wire for a hundred foot run ?

Grizz

Yes don't be tricked. Breakers are set to trip at 80% of their rating for this case and residential. He is actually bringing 240 volt to the garage not 120 volt, hence why the 2 Pole breaker. See voltage drop values below.

canuck · #18 03-27-2017, 05:52 AM

Quote:

Originally Posted by SteveY66

Yes don't be tricked. Breakers are set to trip at 80% of their rating for this case and residential. He is actually bringing 240 volt to the garage not 120 volt, hence why the 2 Pole breaker. See voltage drop values below.

Is that a phone app Steve?
Pretty cool, we use something similar to figure our min/max allowable pressures on a pressure factored (NG) meter set.
Thanks for your help.

Mountain Guy · #19 03-27-2017, 06:23 PM

Quote:

Originally Posted by SteveY66

Yes don't be tricked. Breakers are set to trip at 80% of their rating for this case and residential. He is actually bringing 240 volt to the garage not 120 volt, hence why the 2 Pole breaker. See voltage drop values below.

I'm not an electrician but I think Breakers are set to trip at rated amperage
Most breakers I've seen don't trip till 20% overloaded.
Are you referring to not being allowed to exceed 80% of the service size when calculating total load?.

LSLAKER · #20 03-29-2017, 05:12 PM

Quote:

Originally Posted by SteveY66

Yes don't be tricked. Breakers are set to trip at 80% of their rating for this case and residential. He is actually bringing 240 volt to the garage not 120 volt, hence why the 2 Pole breaker. See voltage drop values below.

He's not just bring 240 volts to the garage. He stated that he needs 120 volts for lighting and for the 120 volts receptacles. He will be installing a sub panel in the garage that will have both 240 volts and 120 volts. The 2 pole breaker will feed L1 and L2 to the sub panel.
L1 to L2 is 240 volts and either L1 or L2 to neutral (identified grounded conductor) is 120 volts.

If he stays within the loads that he has stated that he intends to place onto the sub panel he will be fine with #10 AWG conductors. Having split receptacles will share the 120 volt loads between L1 and L2 conductors.

Breakers are set to trip at their rating. If one knows the calculated load of the circuit then the load can not exceed 80%.