100A Subpanel - Questions

[kailor]

In my shop:

A Square D 125A QOC24UF subpanel-1 will feed a new Square D 100A QO612L100SCP subpanel-2.
In the new subpanel, I'd like 4 circuits, 3-20A circuits and 1-30A circuit.

1. What size breaker in subpanel-1?
2. What size feeder wire to subpanel-2?

Thanks in advance

 

[PCustoms]

You need to answer one question, then the other will follow.

I'd probably run the sub 2 at 50 or 60 Amps. Assuming al inside the same building and that walls are open #6 SER could work.

 

[mm08822]

First thing needed is the load calcs for both subs. Obviously sub2 is part of sub1's load calc input.

Ask yourself what loads will run simultaneously in each panel & also the worst-case max load.

Distance also plays a role in the answer, moreso for cost of cabling than rather voltage drop concerns. Install labor won't change that much.

 

[kailor]

I'm out of neutral lugs on the neutral bar. How can I add more?

 

[exranger06]

QOC24UF appears to be the part number for a replacement cover for the panel, not the model number of the panel itself.
I've never heard of anyone not having enough neutral lugs. There generally are always enough neutral lugs for the number of circuits. For example, a panel that can have up to 24 circuits/breakers will have at least 24 neutral lugs. Are the ground wires also attached to the neutral bar?

 

[75gmck25]

I haven't checked prices lately, but I used 2-2-2-4 AL MHF to feed my sub panel because it was relatively cheap. In most cases it is dual rated so it can be used indoors if run in conduit, and also run underground to reach another building.
I only used a 60 amp breaker because it was the largest available at the big box store, but you can use up to a 90 amp breaker with that size of SER. In your case I think #6 SER would be large enough.
I believe the main breaker in the 2nd panel doesn't really matter much (you can use the one it comes with), since it now serves only as a cutoff for the panel.

 

[PCustoms]

I haven't checked prices lately, but I used 2-2-2-4 AL SER to feed my sub panel because it was relatively cheap. In most cases it is dual rated so it can be used indoors if run in conduit, and also run underground to reach another building.

No. Your post is incorrect.

SER cannot be run underground.

It can be run indoors, and doesn't require conduit if not subject to damage.

 

[mm08822]

I haven't checked prices lately, but I used 2-2-2-4 AL SER to feed my sub panel because it was relatively cheap. In most cases it is dual rated so it can be used indoors if run in conduit, and also run underground to reach another building.
I only used a 60 amp breaker because it was the largest available at the big box store, but you can use up to a 90 amp breaker with that size of SER. In your case I think #6 SER would be large enough.
I believe the main breaker in the 2nd panel doesn't really matter much (you can use the one it comes with), since it now serves only as a cutoff for the panel.

SER is not permitted underground - conduit or not. It is permitted inside and outside.

Maybe you are thinking of MHF?

 

[Norcal]

I haven't checked prices lately, but I used 2-2-2-4 AL SER to feed my sub panel because it was relatively cheap. In most cases it is dual rated so it can be used indoors if run in conduit, and also run underground to reach another building.
I only used a 60 amp breaker because it was the largest available at the big box store, but you can use up to a 90 amp breaker with that size of SER. In your case I think #6 SER would be large enough.
I believe the main breaker in the 2nd panel doesn't really matter much (you can use the one it comes with), since it now serves only as a cutoff for the panel.

A bare aluminum conductor like the grounding conductor in SER will turn to a toothpaste like substance when wet, if it is not already your underground SER will be a unsafe installation.

 

[75gmck25]

I corrected my initial message - I used 2-2-2-4 AL MHF (not SER).

 

[PCustoms]

I corrected my initial message - I used 2-2-2-4 AL MHF (not SER).

Try again, missed a few spots

 

[BreeStephany]

I'm out of neutral lugs on the neutral bar. How can I add more?

Out of neutral lugs at subpanel-1 or out of neutral lugs at the panel feeding subpanel 1? Assuming you need a lug for the neutral on the feeder to subpanel-2? Most Square D, Eaton & Leviton panel lines have neutral lug kits for adding a larger lug onto your existing neutral bus that you can use for landing the feeder neutral.

On some panels, mostly commercial / industrial, you can use an appropriately sized chair lug, as they have 1/4" bolts or squares for carriage bolts in the neutral bus by the main neutral bar that can be used to add additional chair lugs. It is important to remember that anywhere past your first means of disconnect, the neutral and ground MUST be isolated / separated from one another so that your only bonding point between neutral and ground are at the first point of disconnect / meter.

Just my two cents.

 

[justler]

Do yourself a favor and price cable here before home depot or the supply house:

2-2-2 Aluminum SER Cable w/ 4AWG Ground

2-2-2 Aluminum SER Cable w/ 4AWG Ground

www.wireandcableyourway.com

2 AWG XHHW-2 Aluminum Building Wire

600 V Aluminum Alloy Conductor, UL recognized cross-linked Polyethylene Insulated Wire

www.wireandcableyourway.com

SER can be used inside without conduit typically. When you need to transition through the wall and to underground conduit (wet rated), splice the SER to XHHW in an above ground junction box with Polaris taps (mark black cables with colored electrical tape to differentiate them on both sides):

https://www.amazon.com/dp/B0BQX3HB42/?tag=atomicindus08-20

SER is not wet rated and underground conduit is considered wet, which is the reason for switching to XHHW or THWN in the junction box. Don't order SER and remove the jacket, the cables may not be labeled with ratings. Size everything off 75C as that's what your breakers are likely rated for.

Ground and neutral are not bonded in sub-2. If your garage is detached you should put in ground rods at the detached garage.