Powering a detached garage

Question Icon
Posted by: from Hagersville
9/27/2016 at 2:32:35 PM

Is this a sound plan to submit to ESA for permit?

Just built a garage and closest point to house is 30'. Main service panel at house to garage sub panel will be about 60'. The sub panel is rated for 100 amp and 8 circuits House only six years old. Would like to add 40 amp single pole feeder breaker to main and then NMWU 8/2 cable across basement to properly buried conduit and up to garage sub panel. Wire that feed in and then have two 15 amp single pole circuits for lights and receptacles in garage with no more than 8 devices in each circuit.

Is the 8/2 fine to use for basic 15 amp circuits?

Is there any issue with load balance when you connect 8/2 to one side of main breaker?

Will the grounding for the main suffice or do i need to add a ground pole at garage sub panel?

If no grounding at garage then is the removal f brass screw on grounding bar in sub a must?

Any other things to note?


User Icon
Date/Time9/27/2016 at 5:30:57 PM

Overall your plan sounds good however I definitely recommend you run 8/3 NMWU with a 2 pole 40A breaker to bring 240V into your garage. The extra cost is negligible and is better for resale.

Remember your trench needs to be 18" deep measured to the top of your PVC conduit.

The ground wire in your NMWU cable is sufficient for grounding, connected at your house panel no ground plate or ground rod is required at the garage. Make sure you remove the brass screw from the neutral bar in your garage panel as you do not want to bond the neutral to ground at your garage panel- the neutral is already bonded to ground at your house panel.

Don't be afraid to talk to your electrical inspector, they are looking out for your safety and are very helpful.

All the best.


User Icon
Robert from ElecTriLight Ltd. in Oakville
Date/Time9/27/2016 at 5:36:10 PM

Do not use 8/2 cable. use 8/3 or 10/3 and split it out properly. 8/2 is harder to come by and may actually cost the same as it is not a common type. It doesn't make sense to run a single phase, anyone can simply add a jumper to feed the second side of the panel but if you imagine the 40 amp load the neutral needs to carry, can cause havoc on your panel in the house on one bus bar. you must use the ground within the cable and ensure the neutral is not bonded to the case of the sub panel either. Get an ESA permit for the trench and the wiring too.

User Icon
Date/Time9/27/2016 at 10:53:48 PM

I agree with the 8/3 vs the 8/2.

Just as a comment, NMWU is not suitable / permitted for use in conduit - Reference Table 19 CEC.

What my recommendation would be is to either create a "chase" for the wire to be put in or complete a transition from one wire type to another (NMD90 to junction box to THWN to junction box to NMD90 (or NMWU if required) to panel).


John Kuehnl-Cadwell

Master Electrician

Datawise Solutions Inc

User Icon
Jerry in Hagersville
Date/Time9/28/2016 at 8:27:30 AM

Want to thank John, Robert and Kevin. I will be changing my plan to 8/3 cable obviously, I had some access to 8?2 but I hear the experts. I also hear some other points in these replies so thanks guys, appreciate your help.


User Icon
Luciano from Cana Systems Limited in Burnaby
Date/Time9/28/2016 at 9:03:07 AM


My recommendation would be to install a 3c- #8 Teck-cable protected by a 2-pole 40 amp Breaker at your house panel, inure that you have room in your existing panel to except a two pole breaker. The 100 amp panel on the new garage side would be a 120/240v sub Panel. The ground wire in the sub-feed should suffice depending where you are located.The worst scenario is to install a 10' ground rod and connect a piece of number 8 to the sub-Panel. But in most place you should be fine with just the ground from your sub-feed.

I hope I have help you in your inquiry.ed

User Icon
Date/Time9/28/2016 at 7:14:45 PM

Luciano has a good point regarding the #8/3 Cond Teck; like the NMWU it can be buried directly and does not require the mechanical protection that NMWU is required to have both in the ground and at the 1.5m level. Having said that, I am a fan of future-proofing. If you put conduit in the ground, put a spare or two in there while you are at it. Remember however, like NMWU, Teck90 cable is not suitable to be run in conduit. Putting either cable in the a chase I think is a good idea; if there ever is a problem all you have to do is yank it out and put new in without digging up your yard again.


John Kuehnl-Cadwell

Master Electrician

Datawise Solutions Inc

Search the TrustedPros directory and discover the best contractors in your area.

Find your home service pro
Great renovations start with a great contractor.

Since 2004, TrustedPros has been helping homeowners find the right contractor for their home improvements and repairs.

Post Your Project

Within hours you'll be comparing offers from top-rated professionals. It's free to post and you're under no obligation to hire.

Trustedpros Inc. does not warrant the accuracy, completeness, safety, legality or usefulness of any Content, or Whether Content is Current and up-to-date, and TrustedPros Inc. Shall have no liability whatsoever with respect to your use or reliance upon any content or for content being removed or otherwise ceasing to be available. Please refer to the terms and conditions of use of this websites for more details.

Get quotes from top-rated contractors