British Columbia - Buried Cable Questions

[DIMSWITCH]

I live in BC and am trying to run an electrical feed from the new, main (200A) panel in my house to another new panel (120A) in an outbuilding and I have a few questions. I have looked in the electrical code book but I can't seem to find a definitive answer. I have also had a broad spectrum of advice from friends, family and even strangers! As I once again dive into the electrical code books, I thought one of the resident guru's here might have some experience with this...

I don't intend to use the full 120A in the outbuilding, as once completed it will really only have the basic amenities for a renter; electric hot water tank, stove, fridge, microwave, switches, outlets, lighting, fans, baseboard heating, etc (no washer.dryer or dishwasher) and so shouldn't need the 120A.

There seems to be some disagreement in what I need to run from one panel to another. The 200Amp panel in my house is going to feed the panel in the outbuilding. I have dug a trench about 27' feet long between the two buildings in which I plan to lay the wire.

Can I run one length of cable from my main panel to a junction box just inside my garage and then run another length from the junction box, down through the trench and into the outbuilding? I was planning on using oversized PVC conduit to run the cable in the trench as I think it is safer for future digging in the yard.

I need three conductor wire, but what gauge of cable should I use? For different voltage/amperage draw I need larger gauge wire, and with the panel to panel length being about 75' total, I'm curious if voltage drop might be an issue-thus forcing me to upsize again.

Any advice as I once again crack open the electrical code books would be awesome!

Thanks.

[suemarkp]

I don't know the specifics to Canadian code, but some things are universal...

In the NEC, there is a minimum size of feeder or service for a dwelling. If you're making an "apartment", then you have a dwelling. In the US, the main disconnect for a dwelling must be 100A or larger.

Is your 125A feeder enough? I'm suspecting it isn't oversized based on the electric heat, cooking, and water heating. In fact, I think 100A would be the smallest size to consider. So your first step is to do a load calculation based on someone's rules (NEC, CEC) to get a ballpark size.

You should be able to install a junction or pull box in any accessible location. It would be better to use this as a pull box instead of a splice, as splices are better avoided in these larger wire sizes. But you can splice if you need to or are changing wire sizes. Also learn how you size junction boxes for large wire. In the NEC, it is based on conduit size, so oversizing the conduit can lead to a huge box (distance to opposite wall of a box is 6 to 8 times the conduit trade size, so you could need a 16" box if using 2" conduit).

Also look to see if you need 3 wires or 4. The NEC changed all feeders to 4 wires in the 2008 code cycle. Perhaps 3 is still OK in Canada. For a run of only 75', voltage drop should not be an issue at all. I think you'll be needing wires in the neighborhood of #2 to 1/0 copper or 1/0 aluminum. I would use 1.5" conduit for this run, 2" maximum. One thing to watch though is how you get these large wires out of your 200A main panel. Can you get a 125A breaker for that panel if you need it (I'm sure you can get a 100A)? Do you have the bending space for large wires? Will you have to use a subfeed lug instead? If so, will there be issues of having an overfused subfeed tap run inside your main house?

[Bruce88]

First, you need # 2 Copper conductors. But the questions you must ask are;
1 is the 200 amp panel loaded to its max?
2 what is the demand load of the out building?

If you are doing this job under a home owner permit, you will be required to do a load calculation. The area of the apartment and if it uses electric heat, range, hot water tank all contribute to the demand load. The size of the subservice will be what this calculation determines. A small out building will easily get by on 60 to 100 amps.

Why the juction box? Use teck for your underground run. Do not run it in conduit, there is no need for this and it is not allowed.
I would recomend you read P.S.Knight red book, code simplified, 21 edition. This will answer all your questions. Home Depot sells them. It is around 13 dollars.

[JCK]

Originally Posted by Bruce88

Use teck for your underground run. Do not run it in conduit, there is no need for this and it is not allowed.

Bruce,

Dimswitch did say that he was using PVC conduit, which is certainly more work than using TECK, but well worth the extra protection in my opinion.

Did you think he was referring to Rigid conduit or EMT, or am I missing something?

Best regards...

Jarett

[Bruce88]

When using cable of any kind, refer to table 19 and see if it can be used for the application you intend. PVC is a lot of work. With teck its just dig a trench and 6" of sand above and below and your finished. You can not run teck inside PVC conduit. Why would you. Teck is suitable for wet locations and direct earth burial. Mechanical protection is required by code if under driveways or lanes. That being said, if you want to run your 3conductor #2 copper teck in a 3" PVC conduit, and the enterance and exit to the trench are rigid PVC, ($$$$$$) it MAY pass. Odds are also that it may not pass, and you do it all over again.