[Erico]

I have a Hom6-12L100 load center I intend on using for a sub panel in my detached garage.

It’s rated for 100 amps but I need to go with lower amperage due to the size of wire I will need to fish through existing 3/4 inch metallic conduit (under concrete).

I’m probably only going to be able to fit #8 wire in the existing metallic conduit. Red,black,white.

Is it kosher to use #8 wire in those load center lugs as long as I use a 40 amp breaker in the house main load center?

Can I get away with 50 amps on number 8 copper wire (not NM cable) in metallic conduit? It’s about a 25 foot run.

 

[surferdude2]

You can get 3 #6 thhn/thwn and a #10 ground in that 3/4" conduit. Breaker it a 70 amps.

But to answer your original... yes, you can breaker the #8's at 50 amps.

 

[Erico]

You can get 3 #6 thhn/thwn and a #10 ground in that 3/4" conduit. Breaker it a 70 amps.

But to answer your original... yes, you can breaker the #8's at 50 amps.

Can I skip the ground since I’m using metallic conduit? Typically we don’t see ground wires here since everything is in metallic conduit. None of the branches in the house or in the garage have ground wires.

I’m worried about being able to pull larger wire. There is one turn under the concrete

 

[surferdude2]

Yes, you can leave the ground wire out but be sure to use a bond bushing & conductor if landing where concentric ko's remain.

Use wire lube for the pull (if going with #6, not needed for #8) to make it go easy. "Yellow77 or equal"

 

[Erico]

Yes, you can leave the ground wire out but be sure to use a bond bushing & conductor if landing where concentric ko's remain.

Use wire lube for the pull (if going with #6, not needed for #8) to make it go easy. "Yellow77 or equal"

I don’t install the provided green screw in the neutral bar. Correct?

And thanks for your help. I appreciate it.

 

[seharper]

You need a different panel. The 6-space won't work.

first, go big. Go really big on panels. Service panels are the worst possible place to scrimp! Nothing is more frustrating than running out of spaces. Especially when you run out of spaces a lot sooner than you expected (which you're about to). Extra spaces cost very little when you are buying the panel, and that is the time to buy it right.

For $30 more you can get a much larger panel. Like this here HOM2040M100PCVP. Okay, that one's $48 more but you get $20 worth of breakers I gather you will use. And it has the main breaker you do need for a disconnect switch. And you won't ever have to worry about space. Which means when a project comes up "need a space for that" you can just do it, instead of having to hack something. Tell me that is not worth $30. Seriously, this panel is NOT overkill.

The problem is that "20 space / 40 circuit" is a lie. That relies on double-stuff breakers, and you haven't been able to use those for much of anything since NEC 2014. Every breaker needs AFCI, GFCI, or some other nonsense. NEC 2020 seals the deal; everything will need full-width.

Disconnect switch. Because your panel is in an outbuilding, it requires a local main disconnect switch. A separate knife switch is about $80, so people normally just choose a service panel with a main breaker. We don't give a hoot about the breaker ampacity (as long as it's enough) - it'll only be used for a disconnect switch. That would've bit you with that 6-space panel, gobbling up 2 of the 6 spaces since a back-fed breaker used as a disconnect can't be double-stuffed. See what I mean? Spaces go so fast!

By the way, there's no way to make the local breaker "trip first". It just doesn't work. Not likely to be an issue at 70A.

It’s rated for 100 amps but I need to go with lower amperage due to the size of wire I will need to fish through existing 3/4 inch metallic conduit (under concrete).

That's fine. You wouldn't want to run the panel at redline anyway. If you lived in Wyoming and drove 85 mph all the time, you wouldn't want 85mph-rated tires on your car.

I concur with Surferdude that you can run #6 Cu and breaker it for 70A ("officially" 65A, but you get to round up.)

 

[surferdude2]

I don’t install the provided green screw in the neutral bar. Correct?

And thanks for your help. I appreciate it.

That's correct, do not use the neutral to ground bond screw. (only for main service panels... not sub-panels.)

 

[Erico]

You need a different panel. The 6-space won't work.

first, go big. Go really big on panels. Service panels are the worst possible place to scrimp! Nothing is more frustrating than running out of spaces. Especially when you run out of spaces a lot sooner than you expected (which you're about to). Extra spaces cost very little when you are buying the panel, and that is the time to buy it right.

For $30 more you can get a much larger panel. Like this here HOM2040M100PCVP. Okay, that one's $48 more but you get $20 worth of breakers I gather you will use. And it has the main breaker you do need for a disconnect switch. And you won't ever have to worry about space. Which means when a project comes up "need a space for that" you can just do it, instead of having to hack something. Tell me that is not worth $30. Seriously, this panel is NOT overkill.

The problem is that "20 space / 40 circuit" is a lie. That relies on double-stuff breakers, and you haven't been able to use those for much of anything since NEC 2014. Every breaker needs AFCI, GFCI, or some other nonsense. NEC 2020 seals the deal; everything will need full-width.

Disconnect switch. Because your panel is in an outbuilding, it requires a local main disconnect switch. A separate knife switch is about $80, so people normally just choose a service panel with a main breaker. We don't give a hoot about the breaker ampacity (as long as it's enough) - it'll only be used for a disconnect switch. That would've bit you with that 6-space panel, gobbling up 2 of the 6 spaces since a back-fed breaker used as a disconnect can't be double-stuffed. See what I mean? Spaces go so fast!

By the way, there's no way to make the local breaker "trip first". It just doesn't work. Not likely to be an issue at 70A.



That's fine. You wouldn't want to run the panel at redline anyway. If you lived in Wyoming and drove 85 mph all the time, you wouldn't want 85mph-rated tires on your car.

I concur with Surferdude that you can run #6 Cu and breaker it for 70A ("officially" 65A, but you get to round up.)

I’m not sure I’m going to get that #8 wire through that buried conduit. Let alone #6. It appears to have a sharp turn up under the concrete in to the sill plate in the garage.

If I use that larger box with a 100 amp main breaker, won’t that be too much for even the #6 wire? Or will having the smaller amp breaker inside cover me?

 

[seharper]

I’m not sure I’m going to get that #8 wire through that buried conduit. Let alone #6. It appears to have a sharp turn up under the concrete in to the sill plate in the garage.

If I use that larger box with a 100 amp main breaker, won’t that be too much for even the #6 wire? Or will having the smaller amp breaker inside cover me?

The smaller breaker on the supply side (e.g. 30, 50 or 70) will protect the wire and decide the limits of the circuit. The "main" breaker on the subpanel simply does not matter.

If you're shoving wires down there and hit a point that is freakishly hard, and that is some place an accessible access point (conduit body etc.) could exist, there's a fair chance there's an access point there. Use of access points is mandatory; you can't pull through one.

Other than that, pulls can be tough, that's why electricians have a truck full of pulling tools. Also if the metal conduit is outdoors it may have corrosion damage; borescopes are getting pretty cheap and it might be worth a look.

 

[surferdude2]

Pulling wire on that short run won't be a problem unless the conduit is damaged. You'll need either a fish tape or use a pull line blown in with compressed air.

There are some cheap 50' fish tapes for under $10 that will be OK for infrequent use but if you have an air compressor you can blow a pull line in instead. I have blown a mason line in and used it to pull a 1/4 poly or whatever for harder pulls. Just tie a tuft of plastic shopping bag on the line and it'll blow right through... even a shop vac output hose can work. We used the full shopping bag on 4" conduit and a leaf blower. lol McGyver it if/when you must.

FYI, code allows a maximum of 4 90° bends on a conduit run. Yours likely has only 2 and will sail right on in easily.

edit: add link.... 50' fish tape

 

[Erico]

The smaller breaker on the supply side (e.g. 30, 50 or 70) will protect the wire and decide the limits of the circuit. The "main" breaker on the subpanel simply does not matter.

If you're shoving wires down there and hit a point that is freakishly hard, and that is some place an accessible access point (conduit body etc.) could exist, there's a fair chance there's an access point there. Use of access points is mandatory; you can't pull through one.

Other than that, pulls can be tough, that's why electricians have a truck full of pulling tools. Also if the metal conduit is outdoors it may have corrosion damage; borescopes are getting pretty cheap and it might be worth a look.

Plan B might be running conduit along the fence. The entire yard is concrete that I may tear out in a few years (just bought this place). Plan B means I can do what I want with wire size. That has its own challenges and questions so it doesn’t look like a hack job.

Yeah, I was wondering about the local disconnect. If I stick to plan A, I have to take up two spaces with a 50 amp breaker and feed the hots through the breaker and label it main and add an additional fastener? Like pictured below? I guess that’s why there is a “main” sticker in the kit.

 

[seharper]

Plan B might be running conduit along the fence. The entire yard is concrete that I may tear out in a few years (just bought this place). Plan B means I can do what I want with wire size. That has its own challenges and questions so it doesn’t look like a hack job.

In that case, well depends what size service you have, but "preparing for 100A" wouldn't be wrong. Throw three #1 Aluminum conductors and a #8 ground, and you're good for 100A in the sub.

And if you're going to do a class act like that, the cost of the subpanel becomes a footnote.

Yeah, I was wondering about the local disconnect. If I stick to plan A, I have to take up two spaces with a 50 amp breaker and feed the hots through the breaker and label it main and add an additional fastener? Like pictured below? I guess that’s why there is a “main” sticker in the kit.

Yes, exactly. And surely the threaded spot for the hold-down clamp. Of course that leaves you 4 spaces, which only allows 4 circuits, or absolute max 8 circuits if they are all 120V and you can use the EMT-to-AFCI-recep trick.