subpanel conduit size

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  #1  
Old 08-22-06, 02:23 PM
wgc
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subpanel conduit size

I'd like to ask a conduit fill question from the other direction ...

I have an existing subpanel fed from the main with 8/3 cable and I'm considering a future project to add EMT conduit for better protection of the cable and future expandability. What size conduit should I use?

- The distance is about 30'. If I add conduit panel to panel, I can't try to feed the NM cable through it, can I? If I can, how can I tell what size conduit would work?

- The expected goal would be to replace the feed with 6 AWG individual wires to upgrade the service to 60A. What size EMT will accommodate that and what size pull boxes?

- It's conceivable that someone would want to upgrade the service more, so I'd want to allow for that. What's the typical next step up, what size individual wires would that require. What size EMT will accommodate that and what size pull boxes?
 
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Old 08-22-06, 02:32 PM
wgc
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will standard radius bends work?

Oops, missed an important part of the question ...

Do I need to do something different with the bends to be able to feed the larger wires or will standard bends (hand held bender from a big box store) work? Looking at the likely routing, there would be 180 degrees of bends between boxes.
 
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Old 08-22-06, 03:05 PM
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1) Don't install the NM cable in conduit; it is not required and up until the 2005 edition of NEC, there was some speculation as to whether or not it was even allowed. Moreover, you will have a heck of a time trying to make the pull.

2) EMT 3/4" is the minimum size for (3) #6 + (1) #10 60A subpanel feeder; this conduit would work, but could be a little tough to pull through.

3) Given my choice, I would use 1" or 1-1/4" PVC conduit. Bump up to 1-1/4" schedule 80 PVC if you want substantial protection and the ability to upgrade to a 100A feeder in the future.

4) Use prefab bends for any conduit larger than 3/4" or for PVC conduit. Pull boxes are not required with 180 degrees of bends over 30 feet.
 
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Old 08-22-06, 07:16 PM
wgc
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EMT is a preference

So, it sounds like 1" EMT with pre-made bends will work for 60A/6awg service and up to 100A up if anyone ever chooses to do it, right?

Thanks for the commonsense advice about PVC, but I know EMT is beyond what is required and I guess it's a personal preference. My understanding is EMT will provide significantly better damage protection, is allowed, and has no downside other than time and labor. If I were paying someone, I'm sure I wouldn't want to pay for the extra labor. Since I'm not, it might be an interesting learning experience while making it that much harder for my kids to do something dangerous.

If I wasn't clear on the pull box description, the likely route would have four 90 degree bends but there are two convenient places to put boxes such that no segment has more than 2 90 degree bends. My initial plan was to do both: I know that's not required but they seem like they would make it much easier to run the conduit if I did.
 
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Old 08-23-06, 09:04 AM
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Originally Posted by wgc
So, it sounds like 1" EMT with pre-made bends will work for 60A/6awg service and up to 100A up if anyone ever chooses to do it, right?
Yes, 1" EMT will allow for a feeder of (3) #4 + (1) #8 copper conductors to a 100A subpanel.

My understanding is EMT will provide significantly better damage protection, is allowed, and has no downside other than time and labor.
EMT certainly offers more protection than schedule 40 PVC; schedule 80 on the other hand is really tough stuff. Code recognizes schedule 80 PVC as suitable for protection from damage. Based on cost, ease of installation, and corrosion resistance I would choose PVC; however if you prefer EMT there is no rule that would prohibit its use. One inch is very difficult if not impossible to bend by hand, so I highly recommend prefab fittings.

If I wasn't clear on the pull box description...I know that's not required but they seem like they would make it much easier to run the conduit if I did.
My preference is to use conduit bodies instead of actual boxes. The type "LB" is most common, but they come in many configurations.
 
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