Wire AWG/Conduit Size

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LLigetfa

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I want to eventually run a circuit underground to my shop and wondering how many amps I can run in a particular conduit size. I have a 1" sweep that I planned to use to go through the concrete slab and a stick of conduit I'd like to bury so that I can finish up the landscape/grading around the shop now before digging the 50 foot trench over to the house. What wire AWG can I fit inside that 1" conduit?

In my main panel, I have an unused 40A breaker but I have a feeling it is too big and will need to downgrade to at least 30A. I an in Ontario Canada so it is the ESA ( esasafe.com ) code that I need to follow.
 

LLigetfa

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Keep in mind that the conduit/cable will be underground so has to suitable for wet location. I want 120/240V in the shop so I would need 3 conductors. Would I also need a protection ground bonded back to the main panel or a ground rod at the shop?

If I decide to use direct burial metal clad Teck, rather than THWN in conduit for the 50 foot run, can I pull it through the 1" PVC stub at the slab and if so is it subject to fill rate and what AWG am I limited to?
 

wwhitney

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Here's some answers based on the US's National Electrical Code. You will have to check your Canadian Electrical Code to see if there are any differences.

You must have an EGC in your feeder to the shop; any connection through the earth only does not provide a sufficiently low impedance fault path to trip breakers at 120/240V. The NEC would also require a grounding electrode system at the outbuilding supplied, which is connected only to the EGC; there would be no neutral-ground bond on at the outbuilding, just the single such bond at the electrical service.

If you are using a short length of PVC conduit as a sleeve for a cable wiring method, with the cable entering one open end and exiting another, then the only limit is what you can make fit inside. Depending on the length, you could try using a cable diameter up to 75% of the inner diameter of the conduit. Which is 1.03" for Schedule 40 and 0.94" for Schedule 80.

For THWN-2 conductors, the cross-sectional areas of insulated conductors in mm^2 are #10 = 13.61 ; #8 = 23.61 ; #6 = 32.71 ; #4 = 53.16. For conduit with 3 or more wires, the allowable fill is 40%. That works out to an allowable fill in 1" Schedule 80 PVC of 178 mm^2; and in 1" Schedule 40 PVC of 214 mm^2. So even in Schedule 80 PVC, you could fit (2) #4 copper for the ungrounded conductors; a #6 grounded conductor (neutral); and a #8 EGC. With 75C rated terminals that would suffice for an 85A feeder, which may be protected with a 90A breaker (or, oddly, a 100A breaker if on a 100A residential service), so long as the maximum unbalanced 120V load is 65A or less. E.g. if the total load is 65A or less, or if you have say 20A of 240V 2-wire loads.

Aluminum conductors are more cost effective, and filling the conduit less will make the pull easier. Maximum 360 degrees of conduit bends between pull points.

Cheers, Wayne
 

LLigetfa

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#6 Teck90 (Teck 90) appears to have about a 0.90 OD. So I think that would be OK for shoving thru a long radius 1 inch schedule 80 PVC bend, but I would think that would be tight for a long run thru conduit.
I have a 10 foot length of 1" PVC and a long sweep on hand that I plan to stub up through the slab and out away from the building for now so that I can complete grading around the building. I will later decide to either continue the conduit run the 50 feet over to the house with THWN or direct bury Teck cable and fish it through the stub. I just don't want it to limit my options.

Last Winter I ran a 12 AWG extension cord on the ground under the snow and worried that rodents might chew through it. I hope to find the time to make a permanent proper feeder to the shop before the ground freezes. I have another outbuilding 150 feet in the opposite direction that I would like to run permanent power to as well. I've been trying to find an electrical contractor to do both but so far have not been able to get anyone to respond to my enquiries so it looks like I will have to DIY.
 

LLigetfa

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So even in Schedule 80 PVC, you could fit (2) #4 copper for the ungrounded conductors; a #6 grounded conductor (neutral); and a #8 EGC. With 75C rated terminals that would suffice for an 85A feeder, which may be protected with a 90A breaker
Thanks for that. So I now know that 1" conduit is plenty large enough.

If I were to use the existing 40A breaker, what would be the minimum AWG for the various conductors? Using the above max AWG that can fit in the 1" conduit is overkill and overly expensive for my small shop.
 

wwhitney

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If I were to use the existing 40A breaker, what would be the minimum AWG for the various conductors?
In copper, #10 EGC, #8 ungrounded, and #10 grounded (neutral) if the calculated unbalanced load is 30A or less. Or #8 grounded if you want to the freedom to supply over 30A of 120V loads on one ungrounded leg.

In aluminum, #8 for everything, if you confirm that the terminations are 75C rated. With 60C terminations, you'd either need to confirm the load calculation comes out to 35A or less, or use #6 aluminum for the ungrounded and possibly grounded.

Those are the NEC answers, I would expect the CEC to be the same.

Cheers, Wayne
 
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