SER feeder to 125A subpanel inside 2x6 wall, Conduit? Bend R?

[bugman-74]

Hey fellas - I have a question regarding feeder cables for a sub-panel. 3 paragraphs below is the background, and then my main questions are at the bottom:

Even with tandems and quads I’m running out of space in my main shop panel, so I’m planning to put in a 125A sub-panel inside the building located nearby the main. The 400A main on the shop is surface mounted to the exterior of the building (standard practice for stucco buildings here in AZ).

I would power the subpanel from a 125A breaker in the main panel, and locate the new sub-panel inside the shop, about 1-2 stud bays over from where the wires of the main panel pass through the wall from the exterior. It will be flush mounted between studs. Both the 125A breaker and subpanel are rated for AL conductors.

The feeders will run from the 125A breaker inside the exterior 400A panel down to a knockout at the bottom rear side of the 400A panel (below the bus bars), through the wall into a stud bay and over 1-2 stud bays and up into the 125A sub-panel. Note that the stud bays will be insulated. I realize the bend radius of the feeders is probably going to be my biggest challenge. I’m estimating the total run to be under 8 feet.

Questions:

• Is SER most appropriate for this application, or is there a better alternative that may have a tighter bend radius and easier to work with? (I was planning on Aluminum 2/0 4-wire SER)
• Does SER require conduit in this situation?
• Given that 2/0 SER is about 1-1/8” OD, what is the best way to attach it along studs/blocking?

I would still be interested in protecting the feeders inside the wall, but seems like rigid conduit would be a nightmare for something like this. The last thing I want to do is run a nail/screw into these feeders.

 

[theoldwizard1]

Conduit and individual copper conductors.

 

[Terry D]

You could use a 1/0 SER cable. It is rated for 120 amps, but since they do not make a 120 amp breaker, you are allowed to size up to the next available size. As far as protection, If you drill and strap it to the center of the 2x6, you should have no problem. Add horizontal blocking in the stud cavity to strap it to. Since it is only 8 ft, EMT would be a good option if you are concerned about protection. If you went EMT, then just use single XHHW aluminum conductors. You would need 1 1/2" conduit.

Other options would be to go with just 100 amp. That would be #1 SER cable or single conductors in 1 1/4" conduit

Is it possible to come out of the inside panel.

Maybe a few pictures might help to see the best way to do it.

 

[bugman-74]

Thanks for the responses. I like the thought of XHHW inside EMT, but not quite sure how best to route it - I suppose it would generally be a "J" shape coming into the wall space near where you see all the romex, and then over and up into the subpanel.

Attached a few photos for clarity.

• First pic is the Eaton 400A main panel on the exterior wall of the shop (breakers have mostly been reconfigured since this pic was taken, so don't mind the details). The 200A and 4/0 shown feeds the load center on my house which is detached from the shop.
• Second pic is the interior side of the same wall. It is currently open, but will be insulated and drywalled. Red square is approximately where I was thinking about putting the subpanel.
• Third and Fourth pic are stock photos of a Square D 125A 24 space that I was considering. It can be rotated "upside down" so that the feeders enter from the bottom.

 

[Norcal]

Why mix the panel brands? While I despise the Eaton BR "Zinsco II" panels, mixing in a SQ D panel makes it a hodge podge, and the breakers are not classified to used between them, they might fit but not kosher to use them.


BTW, there is no "upside down" or "right side up" with modern loadcenters, they are either top, or bottom, feed.

 

[Terry D]

I thought there was a panel inside that you might be able to come out of. Using SER cable may be your best choice for this. If you went with the 1/0 or #1 ( if you decided 100 amp) Bending the cable would not be a issue. You could still pipe it, but there would be a LB inside of that wall that you would have to put a access panel inside to be able to get to it. There is no way to come out of the back with a 90 and keep it in the wall. The only other option would be to pipe out of the 400 amp panel and have the conduit outside and LB into the back of the sub panel. All the conduit would be outside. BTW, you should have really put a chase ****** where all those Nm-b cables are coming out of the back of the outside panel. I agree with Norcal keep panels all the same brand. Eaton Br and Square D Homeline are not interchangeable.

 

[bugman-74]

Hey guys, thanks for the feedback, some answers:

Why mix the panel brands?

I attempted to keep everything Square D... But according to my POCO the only 400A meter panel that they would approve is the Eaton. Long story short I have the Eaton on the shop and a 200A SQ D load center on the house. Either way I go on this new sub-panel I will have some mis-match. I personally prefer Square D, so figured that's what I would go with for the new sub-panel. I would only ever share breakers between the load center on the house and this new subpanel (they would use the same breakers), so the Eaton will just be the odd one out. I keep lots of spares for both brands - it only hurts my wallet.

there is no "upside down" or "right side up"

I may have described this wrong. I read somewhere that this model # (HOM2448L125PQGC) accommodates "Overhead/​underground feed simply by rotating the device before installing." Also this link

BTW, you should have really put a chase ****** where all those Nm-b cables are coming out of the back of the outside panel.

I didnt catch that... I'll ding my electrical sub on that one (at least they used a bushing)

 

[bugman-74]

Using SER cable may be your best choice for this.

After taking a good long look at it again, I agree. I do have some leftover diamondplate sheet and hazard tape I could attach on top of these bays to help prevent myself from going crazy with nails/screws down the road

 

[bugman-74]

Couple last follow up questions:

• 
  Could I partially sleeve the SER in EMT to provide "some" degree of protection in the wall (would this plus the addition of future insulation in the wall derate the SER?).

• 
  Would this new sub-panel require a main breaker disconnect (QOM1), or does the 125A breaker in the main panel that feeds it count? (can I have one anyway?)

 

[pattenp]

2017 NEC removed the derating of SER when ran within insulation. The subpanel if located in same building as the main panel is not required to have a main breaker.

 

[TRWham]

2017 NEC removed the derating of SER when ran within insulation. The subpanel if located in same building as the main panel is not required to have a main breaker.

Doesn’t need one regardless as long as it meets 6 throw limit.

 

[pattenp]

Doesn’t need one regardless as long as it meets 6 throw limit.

Are you quoting me as if I don't know that? The 6 throw limit isn't relevant since the OP's subpanel is adjacent to the main panel.

 

[TRWham]

Are you quoting me as if I don't know that? The 6 throw limit isn't relevant since the OP's subpanel is adjacent to the main panel.

I wasn't intending to insult anyone, but I read your post as indicating the only reason no main is needed is that it is in the same building. The reason no main is needed here is because there is a disconnect in the feeder to the panel AND it's in the same building. There are other options, and even cases where a main or 6 or fewer throws would still be required in the same building (a panel fed under the tap rules, for example).

 

[Terry D]

Besides the 200 amp breaker feeding your house coming out of your 400 amp panel, are all those other circuits feeding loads in the garage. Now you are adding a 2-pole for your sub. You have way more than six throws. I have a question for the rest of the electricians here, would that main 400 amp breaker suffice as a disconnect for that building since it also kills the house. Would this also possibly be a violation having multiple feeds to a building

As for the SER being in insulation, I didn't catch this before. Arizona is not a state wide NEC adoption state. You will have to check with your municipality to see what code cycle you are in. If you are in the 2017 or newer, you are fine. Anything prior to the 2017 and you are limited to a 60 degree rating for that cable.

So 1/0 would be limited to 100 amps. 2/0 is rated for 115 amps, but I believe you can go up to the next size breaker of 125 amp since 115 amp is not a standard size breaker. Someone correct me if I'm wrong. Same for #1 SER, rated for 85 amps, but can go up to a 90 amp breaker. If you are in the 2017 or newer code you only have to derate SER or SEU cables in insulation # 10 and smaller.

If you deicide to use conduit with individual conductors, none of this would apply, and you can use the 75 degree rating of the conductors

 

[pattenp]

There are not multiple feeds to the shop. The main panel is located on the shop. The circuits from the main into the shop are not feeders and all those circuits are disconnected by the main disconnect so there is only one throw to kill all the circuits within the shop plus it kills the house. I don't like it to service the shop that the house is killed also. But I maybe missing something looking at the picture.

 

[Terry D]

There are not multiple feeds to the shop. The main panel is located on the shop. The circuits from the main into the shop are not feeders and all those circuits are disconnected by the main disconnect so there is only one throw to kill all the circuits within the shop plus it kills the house. I don't like it to service the shop that the house is killed also. But I maybe missing something looking at the picture.

Yeah i thought so, but had to ask. I probably would have done that sevice a little different. Would have took 200 amps in the shop to a main breaker panel and disconnect on outside of shop feeding the house

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[bugman-74]

Great info - thanks

Is it allowable to partially sleeve SER in EMT inside the cavity for a little protection?

Arizona is not a state wide NEC adoption state

At my location we are on 2017 NEC

I don't like it to service the shop that the house is killed also. But I maybe missing something looking at the picture.

That is correct - the main disco inside the 400A panel kills the house and shop. (this is occasionally an annoyance when I'm working on the shop electrical).

 

[Terry D]

Great info - thanks

Is it allowable to partially sleeve SER in EMT inside the cavity for a little protection?


At my location we are on 2017 NEC


That is correct - the main disco inside the 400A panel kills the house and shop. (this is occasionally an annoyance when I'm working on the shop electrical).

You can sleeve the SER in EMT

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