Yet another subpanel thread :)

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  #1  
Old 02-10-05, 06:32 AM
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Yet another subpanel thread :)

I will be installing a Siemens 125A 12 space/24 circuit mainlug subpanel. I plan to feed it with either a 100A or a 125A breaker from my main, which is a 200A Murray outdoor panel that is mounted to a 2x4 exterior wall covered with brick (ie, wall is ~8" thick total).

This subpanel will feed (all to be built/remodeled later): Utility room with electric dryer, up to four circuits in the kitchen when I remodel it, master bedroom, master bath. I will probably also feed a subpanel in a detached garage with this subpanel (it'll be much easier to run from here rather than from the main). While the 125A breaker may be overkill, I may be able to acquire a new one for about what a 100A costs at HD, so the only extra expense is the wire/conduit price. I plan on being in this house for a LONG time, so I want to give myself room to grow.


Anyway, my questions:

I plan to run conduit from the main through my crawl space. I have access to the back of the panel from inside the exterior wall it is mounted on. I will go from the back of the main into the wall with a 90, and down 3 feet to an LB in the crawl space. From the LB ~60feet straight run to a 90, putting me in the wall the subpanel will be mounted in. Finally a few feet up into the bottom of the subpanel. I'm thinking 1 1/4" to 2" PVC, depending on what size wire I have to use. What size would be recommended?

If I feed it with a 125A breaker, can I use #2 copper THHN for my hot leads? If so, does the neutral also need to be #2? What size THHN for the ground? If #2 copper is inadequate, what size would you recommend?

If I feed it with a 100A breaker, what size copper THHN would be recommended?

Finally, any huge, glaring problems with my plan?
 
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  #2  
Old 02-10-05, 07:25 AM
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Are you adding the range/oven to the new subpanel? What's the total sq ft of the proposed remodel?
 
  #3  
Old 02-10-05, 08:09 AM
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Originally Posted by thinman
Are you adding the range/oven to the new subpanel? What's the total sq ft of the proposed remodel?

Good thought...I hadn't thought about the range. I prefer to feed it from the main. The range is currently fed by a three wire circuit from the main, so I will at least have to run a new line to it when the kitchen remodel happens. See any problem with me running a few feet of 6-3wg from the panel into a junction box in the crawl space while I have the wall open? I'd leave it disconnected from the panel, of course. Then, when the kitchen remodel happens, I can complete the run by going from the junction box to the range and then connect it to whatever size breaker the new range requires.


House is currently ~1200ft living space, plus a 2 car garage and a ~300sq ft sunroom. The remodel will close in the garage, bringing the total to roughly 1700 sq ft (house is ~24x70 with the sunroom sticking off the back side). The sunroom may also eventually be converted to living space, 2000sq ft is the max. All remodeling will be under the current roof line...


The main reason for a subpanel is the difficulty in accessing the main panel since it is mounted to the outside of a brick wall. To make matters worse, it is on the back corner of my house...even if I get into the wall and can get wires up into the attic, I have about a foot between the ceiling and the roof at the corner (4/12 pitch). 16" centers on the roof trusses too. Getting into the crawl space is relatively easy, especially since the bottom of the panel box is 24" from the interior floor (floor is a foot or two above grade). I cut a "access panel" into the current master bedroom wall (with my wifes approval and while she watched ), making it easy to get into the back if the panel box (the bottom 6" anyway). The top of my access panel is 28" from the floor, and goes to the floor. Our new 30" tall mattress hides it. Once all the wiring is done, and perhaps a spare conduit or two is stubbed into the crawl space (in case anything else needs ran to the main) I will want to get rid of the access panel (there will be no junction boxes or LBs there, so there should be no more need for it).
 
  #4  
Old 02-10-05, 08:31 AM
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OK...Update...I'll be going with the 125AMP breaker to feed this. Just one it on Ebay (new) for $22 shipped.

So...Wire size to feed subpanel from main with 125A breaker, ~65ft through conduit: Will #2 copper suffice for hots? What size for neutral (I assume #2) and ground (#4 or even #6???)?
 
  #5  
Old 02-10-05, 09:10 AM
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Hots: 2-#2 AWG copper. Grounded (Neutral)-#4 AWG copper. 1-#6 AWG copper equipment grounding conductor.
 
  #6  
Old 02-11-05, 02:24 PM
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Thanks thinman,

One last question...

Conduit size...Do you see any problem with using 1 1/4 (ID) SCD 40 PVC?
 
  #7  
Old 02-11-05, 02:56 PM
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My personal opinion...

Since your conduit route will take you through 2 90's and an lb in a crawl space if you oversize your conduit you'll be glad you did. I'd also make sure to put some lube in it and as far as fastening it to the floor joists or whatever...I'd err on the overkill side...
 
  #8  
Old 02-11-05, 03:22 PM
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I agree with going overkill to some degree. However, I only have to turn one 90 on each side of the LB, so I don't think the pull will be that difficult. I would prefer to determine the minimum conduit size for 2 #2's, 1 #4, and 1 #6, then go up one size. I'll probably fasten to every other floor joist (16" centers)...am I correct that every 4' is all that is required?

I may be able to pull the wire through the 50' straight shot to the LB, then up into the wall 3' and into a 90 that goes into the main...all before connecting the other 90 and the 3'-4' piece that goes up to the subpanel (I'll be putting this into a wall as I build the wall, so its flexible how its done). I'll just keep ~8 feet of wire loose, then feed it through the 90 and other piece as I connect them.


The chief limiting factor that prevents me from just going ahead and running 2" PVC is the fact that the 90 that connects into the back of the main has to fit into a wall that is 2x4 covered with brick...I only have ~8" to work with...I think I'm going to have a problem even getting a 1 1/4" 90 in that area. I don't want to put an LB there since I want to eliminate the access panel I cut out of the wall when I'm done. Any thoughts as to how to deal with that problem?
 
  #9  
Old 02-12-05, 05:42 AM
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Just my opinion

Given the fact that posts on these public forums come from all walks of life, experience levels, and backgrounds, I offer just that--my opinion/experience.

Your thhn copper wire size (#2 feeders, reduced neutral, #6 ground) sounds fine-unless you are buying a spool, then I'd use all #2. Your pull plan with 1 1/4" pvc is good based on making the pull and then piecing the pipe together at the sub panel end etc. No way will you pull from one panel to the other through one 90, through an lb, and through another 90. I'd still take the time to put a shot of wire lube in here and there. I believe every 4' fasteners is right, where in doubt do more-you are the one to gain. Running across joists I'd use conduit straps/screws, with joists I'd use minnies or even (plumbers tape) metal strapping/screws. I'd also think about how you pipe in that lb (per how the cover plate faces), sounds like you will be up against the foundation wall, know what I mean...?

Let's talk about the 200 amp main. Sounds like it is surface mounted outside. If there is no way you can drop out the bottom or side with your conduit run and go through the foundation, AND the back of the box is the only option, AND you are not going to use a sized entrance cable as a feeder of any variety, these are my thoughts....

I agree, you are going to be hard put to squeeze a 90 sweep from the back of the box down to the crawl space and stay inside the wall space. It's not unheard of to snip a bit of the sweep off, thereby shortening it for some help. May be a better plan to keep that access into the back of the panel and use an lb. You could put some molding around it and a door on it and use it as a place to hide all your money....Your creativity is limited only by your imagination.... At least that way you could pipe that lb in line first and save some frustration and head scratching.

A final thought. Sounds like when you go through the back of the 200 amp main box you will also have to go through wood siding etc. I'd measure twice, drill a pilot hole through the box and in toward the house, then come from the other way with a hole saw so you can oversize around the knockout-or if you are drilling your own knockout for your 1 1/4" hole for your term adapter, hole saw just the wood-and then drill out your smaller hole for the term adapter. If you do end up using the sweep, this will give you a little more gain...

And shut off the main before drilling that panel. Run an extension cord to a neighbor, use a generator, use a cordless...whatever. But please stay safe.

Hope any ideas here helps...
 
  #10  
Old 02-15-05, 06:51 AM
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TRS4594: Thanks for all your comments...I'll answer a few of them.

Originally Posted by trs4594
Your thhn copper wire size (#2 feeders, reduced neutral, #6 ground) sounds fine-unless you are buying a spool, then I'd use all #2.
I'll just need ~65' total run length, so I planned to buy by the foot. All #2's would only be ~260'. You may have a good point though. A 500' spool of #2 may very well be about the same price as [email protected]#2 + [email protected]#4 + [email protected]#6. I'll compare prices. At the very least, I may go ahead and use #2 for the neutral.

Originally Posted by trs4594
Your pull plan with 1 1/4" pvc is good based on making the pull and then piecing the pipe together at the sub panel end etc. No way will you pull from one panel to the other through one 90, through an lb, and through another 90.
I'd like to think I could do the pull with it 100% assembled, even though I'll potentially cheat as I previously mentioned by assembling it after pulling. I wonder if LB's can be bought with 1 1/4 on one end and 1 1/2 on the other. If I had 1 1/2 on the long run, I should be able to pull that with no problem. Then I could push the 5' into the panel box after the LB through 1 1/4 (keeping the smaller size there due to the restraint on turning room for a 90).


Originally Posted by trs4594
I'd also think about how you pipe in that lb (per how the cover plate faces), sounds like you will be up against the foundation wall, know what I mean...?

The cover plate of the LB will be parallel to the floor, facing the ground. The run from the breaker box will go through the 90, down ~three feet into the back of the LB. Then the long, straight run from the LB will go out the end of the LB.


Originally Posted by trs4594
Let's talk about the 200 amp main. Sounds like it is surface mounted outside. If there is no way you can drop out the bottom or side with your conduit run and go through the foundation, AND the back of the box is the only option,
Yep, surface mounted outside on a bricked 2x4 wall.

It is possible to go out the bottom and through the foundation, but I would have to go out, turn a 90 to the left, go 12' along the wall, THEN into an LB to enter the crawl space. That and it adds several feet to my run, and I've overshot where the conduit needs to be, so I'd have to be more creative once inside the crawl space. Plus, I'd prefer to keep it as hidden as possible, so I'd like to minimize any surface mounted conduit. Trying to go straight down and into the crawl space puts the LB below grade...not good.

Originally Posted by trs4594
AND you are not going to use a sized entrance cable as a feeder of any variety,
That is a direction I have considered. If I could find some *COPPER* SER, I would consider using it, eliminating conduit altogether. Aluminum SER is readily available, but I'd rather stay away from AL. I'm not sure I am too crazy about SER cable running through my crawl space though. I'd rather use conduit and THHN.


Originally Posted by trs4594
I agree, you are going to be hard put to squeeze a 90 sweep from the back of the box down to the crawl space and stay inside the wall space. It's not unheard of to snip a bit of the sweep off, thereby shortening it for some help. May be a better plan to keep that access into the back of the panel and use an lb. You could put some molding around it and a door on it and use it as a place to hide all your money....Your creativity is limited only by your imagination.... At least that way you could pipe that lb in line first and save some frustration and head scratching.
I can be pretty creative. I don't want to leave the panel as this is the master bedroom. Right now, a 30" tall mattress more or less hides the panel (which is 28" tall), but this room eventually may be rearranged leaving the panel visible. If I have to, I'll come up with something.

I may create my own tighter 90 with a little warm air. (Warm PVC is more flexible ) If I do that, I'll use 1 1/2" PVC to form it.

I am a little confused on the concept of hiding all my money...do you really think someone would take my jar of pennies? LOL


Originally Posted by trs4594
A final thought. Sounds like when you go through the back of the 200 amp main box you will also have to go through wood siding etc.

Well, the people that built the house made this easy. They cut out a HUGE opening in the sheathing (aka, hack job). Once I cut my access panel and removed the section of insulation, I was staring at the back of the panel box (and a pile of mouse poop, but that's another story...suffice it to say a little silicone will be sealing some holes). All I need to do is remove the knockout and have someone hold the threaded end while I go outside and tighten the nut. The power will definately be off while my hands are in the panel box...Standing outside on dirt makes for a easy path to ground...

Thanks again! Charles
 
  #11  
Old 02-15-05, 09:20 AM
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Originally Posted by chirkware
One last question.. Conduit size...Do you see any problem with using 1 1/4 (ID) SCD 40 PVC?
No problem using 1-1/4" Sch 40 PVC.

1-1/4" PVC has to be fastened every 5 feet or less.
 
  #12  
Old 02-16-05, 05:52 PM
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Originally Posted by trs4594
I agree, you are going to be hard put to squeeze a 90 sweep from the back of the box down to the crawl space and stay inside the wall space. It's not unheard of to snip a bit of the sweep off, thereby shortening it for some help.

I picked up a 1 1/4 90. It takes 10" to go the 90 degrees. However, its 3 1/2" before the radius begins. I can cut 2.5" off, and still have 1" straight pipe to glue the threaded end on to go into the panel. That puts me turning a 90 from the back of the panel in ~7 3/4". I'll have to measure the opening, but I believe it is about 8.5" from the back of the panel to the inside edge of the stud wall (4" thick brick, 1/2" gap, 1/2" sheathing, 3 1/2" stud). Looks like it will make it.

I know if I had romex 3/4" from the edge of the stud, I'd have to protect it. SCD 40 PVC shouldn't require any other protection though, should it?
 
  #13  
Old 02-16-05, 06:38 PM
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Glad you can get the 1 1/4" to work. As far as protecting the pipe, I'm assuming you are going down through the wall baseplate to the lb in the crawl space. My thoughts there are if the sweep coming out of the back of the panel puts you against the inside wall, that pipe is flexible enough so you should still be able to maneuver however you need to get your vertical drop where you want it.

If it is wobbly coming out of the back of the panel you might be able to build the stud out from one side of the panel with pieces of 2x for something to fasten the pipe against. Otherwise, I think you should be in good shape, sounds like limited stress on the pipe.

You have a good plan.
 
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