Surface electric wiring, Metal or PVC?

[Yuri Sadykov]

Jerry,

that is good write up and useful illustrations, thanks.
I am leaning toward EMT conduits, now.

[Steve Meliza]

Before I poured the concrete floor in my shop, I installed ½" PVC conduit from the breaker panel load center to locations where I felt wiring would be needed. One ½" PVC conduit run is to my multiple table saw island. Packing all the #10 and #12 THHN wires in the ½" conduit was a chore and probably violates code.

Uhm, yah, if you are having trouble putting wires into any size conduit then you're probably violating code.

The first violation is probably cable fill, you can't just jam it packed full of wires. The second issue is that once you pass a certain threshold of current carrying conductors in a conduit you have to start de-rating the wires. If memory serves, over 7 current carrying wires means a #10 is no longer usable for a 30A circuit and #12 is also not usable for a 20A circuit and so forth. What you end up with is are two requirements that feed off each other till you find yourself running 3" conduit and #6 wires so you can feed 20 15A circuits in a single conduit. If the conduit is going to be installed in a wall, buried, or otherwise inaccessible then yes, up-size a bit so you don't have to dig it up for a minor change in wiring, but don't think a single 3/4" or 1" EMT is going to give you more capacity than a pair of 1/2" EMT.

The key point to remember here is that more conduits of a smaller size are better than a few larger conduits.

[Jerry Hillenburg]

Steve thanks for that information.

I checked the 1/2" conduit run to my table saw island and it has two #10 and four #12 with a #12 ground - seven wires total. The four #12 wires are for the two 220v under the counter 1/4" dado saws and the two #10 wires are for the 220v 10" Unisaw.

If I read an NEC copied conduit fill table correctly, nine #12 THHN wires or five #10 THHN wires are allowed in 1/2" EMT. http://www.elliottelectric.com/Stati...ill_Table.aspx

Another table copied from the NEC appears to say schedule 40 PVC conduit can be filled with eight #12 THHN wires or five #10 THHN wires. http://www.sfasoft.com/look/46/Max_conductors_in_rigid_PVC_conduit_S40

I am surprised for it appears my installation just barely passes code - but I can tell you those wires were difficult to get into that 1/2" conduit. If I ran that conduit again I certainly would use at least 3/4" PVC which could have 15 #12 wires or 9 #10 wires. A bigger conduit would make modifying my table saw island wiring possible.

[Steve Meliza]

Yah, that's 96% filled to the max allowed by code. Another factor in difficulty of pulling is length of pull and number of corners you're trying to pull around. Code requires a pull access every 360 degrees, but even that could be a bear with the conduit stuffed that full. You made a good point that the numbers were talking about are for EMT, plastic is permitted fewer wires.

Keep in that if you were to pull 9 #10 wires into a 3/4" EMT that you can't connect them all to 30A breakers if you have more than about 7 of them carrying current. Ground wires don't count as current carrying so you could do three #10 240V 30A circuits and a ground wire in 3/4" EMT.

[Richard Wagner]

I second the EMT. One thing I wish I'd done in my shop was put the outlets at 54 inches instead of 48 like I did. The higher outlets would let you lean plywood against the wall underneath the electrical runs.

Amen for higher off the floor.

[John Coloccia]

I ran PVC, the major advantage being that my entire electrical system is almost hermetically sealed. I have gasketed, outdoor lights too. You would be shocked if you saw how much dust accumulates in outlets over time. My building inspector specifically requested the PVC and "in-use" covers, switch covers, etc. I'm very happy I did, now, especially the lights. They've been in my shop for 5 years and the amount of dust in the lights is absolutely minimal.

[Michael W. Clark]

I ran PVC, the major advantage being that my entire electrical system is almost hermetically sealed. I have gasketed, outdoor lights too. You would be shocked if you saw how much dust accumulates in outlets over time. My building inspector specifically requested the PVC and "in-use" covers, switch covers, etc. I'm very happy I did, now, especially the lights. They've been in my shop for 5 years and the amount of dust in the lights is absolutely minimal.

Not to hijack, but can you provide a link to the light fixtures and outlets similar to what you have? I have an outdoor project coming up and would like to take a look at something like this. (Turning the underside of my deck into storage and want to put some lights under it. It will be dry, but exposed to outside conditions, no direct water)

[John Coloccia]

Not to hijack, but can you provide a link to the light fixtures and outlets similar to what you have? I have an outdoor project coming up and would like to take a look at something like this. (Turning the underside of my deck into storage and want to put some lights under it. It will be dry, but exposed to outside conditions, no direct water)

I used these lights:
http://www.homedepot.com/Lighting-Fa...1#.UFHid47Re_c

I generally used these outlet covers:
http://toolmonger.com/2010/02/26/get...in-use-covers/

On 4-gang outlets, I just used a regular cover, not an in use. I wasn't going for any awards. I was just trying to be reasonable about it.