100A Subpanel Wire Size?

[CoogarXR]

I googled it and I searched it here, but I am seeing so much conflicting info... I have a small main panel in the kitchen of the new house I bought. I have the kitchen gutted. I don't want to have to open the walls every time I need to add a circuit, so I am going to add a subpanel in the basement, almost directly below the main in the kitchen. I have a ton of wiring to do after the kitchen needs to be finished, plus I don't think there is room for all the breakers I need, so a subpanel in the basement will give me room to grow, plus easy access.

Anyway-

So my question would be- What size wire would I need to run for a 100A subpanel that is probably 20-25ft from the main? It is an indoor run, just down the inside of a soon-to-be finished wall, down into an unfinished basement, and maybe 10ft across the joists. Conduit would kind of be a pain in the *** (200-year-old log home with non-traditional framing), so I am thinking mobile home feeder cable? If so, what gauge? Aluminum or Copper? Help me out sparkies, lol.

 

[dcg9381]

There are various "calculators" out there that can get you to the correct wire size for wire type. Someone will come along to remind us that not all of these calculators agree, but they get you close.

MHF is often the "go to" for sub-panels on GJ because it's the "bang for the buck" solution, but it won't support a full 100A. It will (off the top of my head) support 90A. I believe, indoors, it MUST be in conduit.

If I "had" to get 100A to the sub panel, I'd look at:

• 2AWG copper wire
• 1AWG Aluminum or CopperClad Aluminum

Someone will give you more specific advice if you want to run this wire w/o conduit.

 

[sparky 1971]

Mobile home cable woild have to be in conduit and the sizes don't work out well for a 100 amp sub, what I'veseen are #2, 1/0, and 4/0. For a true 100 amp sub you will need #3 copper or #1 aluminum. A much more economical approach that would work fantastic in this situationis #2 aluminum SER cable which is really nothing more than big romex and a 90 amp breaker at the main panel. I went the #2 route when I put a new service in but it was during Covid and couldn't get a 90 amp breaker so I used a 100, showed the inspector the paperwork showing I had two 90's on backorder and he was good with it. The 90's came in, but I wound up using them on other jobs so the 100's are still in use four years later. Maybe someday I will lose some sleep over it but I don't see it happening in the near future.

 

[luvtheheat]

Some years back I had a sub-panel added to my house for AC compressor/future shop. Max load 100 amps. Main panel on north side of house; sub-panel on south side outdoors. It was a +- 70' run thru attic. Electrician ran 1-0 aluminum with bare 2ga ground, covered with sheathing. No conduit except out the wall on southside. See pic.

It was permitted/passed against 2010 electric codes.

 

[mike93lx]

Barring some wild kitchen setup, 90a will be plenty. #2 SER and a 90a breaker to feed it.

The subpanel can be any size you want. 100, 125,150, 200. Doesn't matter. Just go with something that has enough spaces to comfortably cover current and future needs.

 

[75gmck25]

2-2-2-4 AL SER is easy to find and usually reasonably priced. It maxes at 90 amps, so just use a 90 amp breaker for the main panel connection. This is fine to use with a 100 amp sub-panel, since the breaker in the sub-panel is now just shutoff.

 

[sparky 1971]

This is fine to use with a 100 amp sub-panel, since the breaker in the sub-panel is now just shutoff.

Or, since both panels are in the same structure, use a main lug panel for the sub.

 

[theoldwizard1]

Or, since both panels are in the same structure, use a main lug panel for the sub.

Not a code expert, but I though if the second panel was NOT mounted "close" to the first panel, a "disconnect" (shutoff, main breaker) was required.

 

[sparky 1971]

If it's in a separate structure (building) a disconnect is required. If in the same structure a main lug is fine. The "close" you're probably thinking of is the grouping of disconnects for the six throw rule.

Not a code expert, but I though if the second panel was NOT mounted "close" to the first panel, a "disconnect" (shutoff, main breaker) was required.

 

[CoogarXR]

I will probably just buy one of those 100A Square D kits with the main breaker and an assortment of branch breakers. Hopefully that's not a violation. 90A upstairs on the feeder breaker should be fine. There won't be much current pulled through this panel anyway, I just need the space and accessibility.

Like I may have said, it's a weird house. It's an 1830s log cabin with a basement, and a 1940s addition on the back with no basement. The 1940s part is almost a whole house to itself. The previous owners didn't do much with the cabin part; they just lived in the addition. The log cabin has 5 rooms with almost no existing electric. I think there are 2 receptacles downstairs, none upstairs, and 4 lights (2 are pull-chain). So rather than fight with fishing a million branch circuits through a damn-near two-foot-thick log wall with stud walls on both sides of it, I'd just drop a sub panel in the basement of the cabin, and I'd have nice unobstructed (and shorter/cheaper) runs.

Thanks for entertaining my brainstorming as usual. I'll have to call the electric supply and order some 2-2-2-4 AL SER.

I have the plumbing 95% done in this house, and it's almost time to move on to electrical.

 

[Norcal]

Not a code expert, but I though if the second panel was NOT mounted "close" to the first panel, a "disconnect" (shutoff, main breaker) was required.

If in the same structure, a main will not be required.

 

[inphx]

And coincidentally these guys at Nassau National Cable have URD on sale with code URDSEP7 for 7% off . https://nassaunationalcable.com/search?q=2-2-2-4*+AL*+SER&type=product

 

[mike93lx]

And coincidentally these guys at Nassau National Cable have URD on sale with code URDSEP7 for 7% off . https://nassaunationalcable.com/search?q=2-2-2-4*+AL*+SER&type=product

Urd is the most incorrect wire for this.
Its outdoor only and requires conduit when above grade, outdoors

The ser they have listed is the right answer

 

[wyliesdiesels]

And coincidentally these guys at Nassau National Cable have URD on sale with code URDSEP7 for 7% off . https://nassaunationalcable.com/search?q=2-2-2-4*+AL*+SER&type=product

completely wrong wire

 

[inphx]

Thanks.. can you make it a 'teaching moment'... it not simply having it in a conduit for code compliance ? or is it materially different wire?

 

[mike93lx]

Thanks.. can you make it a 'teaching moment'... it not simply having it in a conduit for code compliance ? or is it materially different wire?

The issue is the wire insulation. Due to how it burns, it isn't allowed indoors. A very similar wire, mobile home feeder, has a different rating and is allowable indoors, but since neither have an outer jacket, conduit is required above grade.

The required rating is RHH/RHW-2. MHF will have that, but URD may only be USE-2 rated and wire with just that rating is not allowed in structures at all. If you can find "dual rated" URD, that would be ok indoors

Conduit doesn't change indoor vs outdoor allowance.

 

[u2slow]

Log homes are usually miserable to hide/fish wire through so that it is all concealed.

Up here we can get NM aluminum cable up to #2. Maybe you can fashion some 'log like' trim/chase to conceal it. Armoured w/PVC coating is just a bit more $ and then there's no issue with it being exposed (except for unsightliness).

 

[sparky 1971]

The issue is the wire insulation. Due to how it burns, it isn't allowed indoors. A very similar wire, mobile home feeder, has a different rating and is allowable indoors, but since neither have an outer jacket, conduit is required above grade.

The required rating is RHH/RHW-2. MHF will have that, but URD may only be USE-2 rated and wire with just that rating is not allowed in structures at all. If you can find "dual rated" URD, that would be ok indoors

Conduit doesn't change indoor vs outdoor allowance.

And even if it was dual rated URD it would be a miserable SOB to install in conduit, it's bad enough sliding it up a riser and through an LB. It would take a different breed of hard working sumbitch that I wouldn't mess with to want to do it.

 

[mike93lx]

And even if it was dual rated URD it would be a miserable SOB to install in conduit, it's bad enough sliding it up a riser and through an LB. It would take a different breed of hard working sumbitch that I wouldn't mess with to want to do it.

Found the guy that doesn't use 4" sewer pipe for conduit

 

[PCustoms]

Found the guy that doesn't use 4" sewer pipe for conduit

Begs the question, is there a MAX conduit size?

Like if I run 3 strands of #14 in a 6" PVC conduit, have I violated anything other then common sense?

 

[Norcal]

Begs the question, is there a MAX conduit size?

Like if I run 3 strands of #14 in a 6" PVC conduit, have I violated anything other then common sense?

How will you terminate a 6" pipe in a modern loadcenter?

 

[sparky 1971]

Begs the question, is there a MAX conduit size?

I could be wrong, but I believe the largest EMT is 4", rigid is 6", and I think PVC can be 8" but have never seen it and don't want to. Ever. The largest I have ever used is 3" EMT and that's enough for me.

Like if I run 3 strands of #14 in a 6" PVC conduit, have I violated anything other then common sense?

That wouldn't be any kind of violation, but if you want to add a few more 14's, don't forget to de-rate.

 

[PCustoms]

How will you terminate a 6" pipe in a modern loadcenter?

Reducer bushings?

And I never said anything about where the conduit was connected. But I can tell that this basic question as a thought experiment isn't going anywhere

 

[sparky 1971]

How will you terminate a 6" pipe in a modern loadcenter?

I've got a couple of 30X30X12 junction boxes in my shop. It could go into one of those and use a 1/2" ****** from the box to the panel.

 

[mike93lx]

Begs the question, is there a MAX conduit size?

Like if I run 3 strands of #14 in a 6" PVC conduit, have I violated anything other then common sense?

Culvert.

Send it

At what point is it no longer conduit and just a room?

 

[PCustoms]

Culvert.

Send it

At what point is it no longer conduit and just a room?

Kind of where I was going...does it just become a chase or tray?

 

[KenC]

I haven't encountered this is a few years, but about 15 years ago the local AHJ (small city in OK), not allow aluminum inside a building. I had used 4/0 from the weatherhead to the panel on a remodel. Made me take it out and replace with copper. Knee-jerk reaction to the aluminum wiring fiasco in the 70s.

Anyone else encountered a ban on indoor aluminum?

 

[mike93lx]

I haven't encountered this is a few years, but about 15 years ago the local AHJ (small city in OK), not allow aluminum inside a building. I had used 4/0 from the weatherhead to the panel on a remodel. Made me take it out and replace with copper. Knee-jerk reaction to the aluminum wiring fiasco in the 70s.

Anyone else encountered a ban on indoor aluminum?

Written ammendment?

Never heard of those shenanigans

 

[mike93lx]

Kind of where I was going...does it just become a chase or tray?

I bet if it is not an accepted trade size and a standard material, the inspector would tell you to pound sand