Adding a subpanel to my garage extension

[Moto-Dude]

I've built out my attached garage an additional 14'. I am adding a 100a subpanel, running 1/0 AL lines from the main to the subpanel.

I have a 220v circuit for a 18,000 btu mini split. According to the manufacturer, it draws about 6.82 Amps. I am planning to run a 30a breaker and 8ga 3 wire (2 hots and a ground). The wire is overkill but I may add a welder later, so this would handle that. My question: the mini-split should not cause any problems, it doesn't draw that much, right? But I've seen comments that say if the minisplit develops a problem and shorts out, the 30a breaker won't trip and protect the mini-split wiring...? It was suggested that a fusible link be added to the line where the minisplit joins the disconnect.

I thought that if a device shorts out, it will draw a ton of amps and that would trigger the 30a breaker...

I've also been told the breaker is there to protect the circuit wiring, not the device.

Definitely open to suggestions, thanks!

 

[wyliesdiesels]

I've built out my attached garage an additional 14'. I am adding a 100a subpanel, running 1/0 AL lines from the main to the subpanel.

I have a 220v circuit for a 18,000 btu mini split. According to the manufacturer, it draws about 6.82 Amps. I am planning to run a 30a breaker and 8ga 3 wire (2 hots and a ground). The wire is overkill but I may add a welder later, so this would handle that.

Wire for AC circuits is sized based on the MCA- minimum circuit ampacity. the breaker is sized based on the MOCP. both figures are found on the nameplate of the unit. I wouldnt run oversized wire. youre just wasting money.

so post a pic of the nameplate or make and model so we can look at the manual

also this circuit should be dedicated. i wouldnt run a welder on this circuit.

My question: the mini-split should not cause any problems, it doesn't draw that much, right? But I've seen comments that say if the minisplit develops a problem and shorts out, the 30a breaker won't trip and protect the mini-split wiring...? It was suggested that a fusible link be added to the line where the minisplit joins the disconnect.

I thought that if a device shorts out, it will draw a ton of amps and that would trigger the 30a breaker...

I've also been told the breaker is there to protect the circuit wiring, not the device.

Definitely open to suggestions, thanks!

this is just a ton of speculation when you havent given us any info on the unit

some AC units do indeed require fuses to protect the unit because the breaker wont respond fast enough.

if the nameplate says max fuse then you need to use a fused disconnect

 

[u2slow]

Leave the mini-split on its own (small) circuit. It's circuit breaker requirement is to protect the equipment.

Wire a separate welding circuit based on the welder's needs, after you get it. If you have to rough something in, install a conduit; or, if you surface mount the panel you can easily pipe out of it later.

 

[Moto-Dude]

Ok, very good, thanks! I had not thought of it needing to be a dedicated circuit only for the AC.

The wire: I already have the 8ga wire left over from a previous project, somehow I am losing sleep over not using it

I haven't bought the mini-split yet, I am leaning towards this: DuctlessAire-21-SEER-18-000-BTU
It seems to be a decent unit, although the installation pdf is super-generic

I don't have access to the nameplate, so suppose I need to buy the unit and then I can determine what wire and breaker to use for this circuit?


There are 750 Q&A for this unit but they vary wildly!

 

[mike93lx]

Any 18k mini that isn't a flaming POS will work fine #14 (assuming 240v). I'd likely run 12 in case it's ever swapped for a larger unit when it fails.

My 30k central air units are on #12 with 25a breakers and they are far from the most efficient

 

[mm08822]

And most likely your dedicated welder recept could be wired with 12-2nmb.

Since you would have a mini split, I doubt you would ever be plugging a heater into the welder recept.

 

[Moto-Dude]

You guys rock, thanks for steering me away from my janky idea. I ordered this Senville Aura unit,

I will use 12-2 wire and a 20A DP breaker.

 

[mike93lx]

Looks good.

What is the #8 wire that you have on hand? 8/2 NM-B?

 

[Moto-Dude]

This is it. It has 3 insulated wires.

 

[mike93lx]

You steal that from a manufacturing plant?

If the individual conductors are labeled thhn/then (I know they are same spec, but don't know about labeling) you could strip the outer cover and run in conduit. I doubt it would be code to run it in walls as-is though

What colors are they?

 

[Moto-Dude]

No, lol, I bought it from an electric supply place in Freeport, TX about 6 years ago. I had a camper and a 70' run and my friends scolded me because I was using 12-3 wire for 50A service.

All three conductors are black.

 

[mike93lx]

No, lol, I bought it from an electric supply place in Freeport, TX about 6 years ago. I had a camper and a 70' run and my friends scolded me because I was using 12-3 wire for 50A service.

All three conductors are black.

Interesting they sold you that.... Not a cable that would be used for that application.

You can't use a black conductor for ground, so you'd have to buy a new one for at least that.

 

[wyliesdiesels]

cant use black for the neutral either.

that looks like tray cable. not something id use in wall for residential

 

[mike93lx]

cant use black for the neutral either.

that looks like tray cable. not something id use in wall for residential

I was thinking it would only be used for 240v, so I didn't call it out, but worth mentioning for sure.

 

[u2slow]

You can't use a black conductor for ground, so you'd have to buy a new one for at least that.

I dont know about NEC... but, stripping one conductor of the cable completely bare at both ends may be acceptable.

 

[alfredeneuman]

I dont know about NEC... but, stripping one conductor of the cable completely bare at both ends may be acceptable.

The NEC prohibits stripping 1 conductor bare and using it for a ground unless it's #4 or larger

 

[Moto-Dude]

Ok, thanks, that makes sense. I ran the 12-2 wire to the rough in, now: the big question! I need 50' of cable to connect the main circuit panel to the subpanel. I am going with

1/0-1/0-1/0 Aluminum SER Cable w/ 2AWG Ground​

1/0-1/0-1/0-2 Aluminum SER Cable (By-the-foot)

1/0-1/0-1/0 Aluminum SER Cable w/ 2AWG Ground

www.wireandcableyourway.com

However... there is a 15' section that will be outside the garage and buried in sched 40 electrical PVC conduit.

Applications:
SER is type SE, Style R cable, used as an above ground service entrance cable, a panel feeder and in branch circuits. The cable is rated at 600 volts and 90°C for use in wet and dry locations. SER cables are LEAD FREE and RoHS compliant.

The NEC prohibits SER cable from being installed underground at all; not direct buried and not in buried conduit.

Any suggestions? I don't want to run conduit in the walls and attic. Just outside the garage and when underground.

 

[mike93lx]

You'll need to transition to another wire type, like xhhw, find another path, or just do conduit end to end.

Why are you running 1/0? Running #2 and a 90a breaker to feed it will be cheaper and easier to run. You can still use a 100a sub

 

[Moto-Dude]

You'll need to transition to another wire type, like xhhw, find another path, or just do conduit end to end.

Why are you running 1/0? Running #2 and a 90a breaker to feed it will be cheaper and easier to run. You can still use a 100a sub

2ga wire and a 90a breaker, yeah, that could work, I guess.
The conduit is a problem. The path the subpanel needs a sharp 90 to stay in the wall cavity.

 

[mike93lx]

2ga wire and a 90a breaker, yeah, that could work, I guess.
The conduit is a problem. The path the subpanel needs a sharp 90 to stay in the wall cavity.

Can you keep a junction box or an LB accessible to make that corner?

 

[Moto-Dude]

I guess I can slap a junction box at the bottom, seems like an awkward way to turn wire, though.

 

[mike93lx]

Could do a lb on the interior too.

Why are you going outside for an attached garage?

 

[Moto-Dude]

2" LB won't fit in the wall

Why are you going outside for an attached garage?

about 80' closer.

 

[mike93lx]

If you do #2, you can go smaller on the conduit

 

[mm08822]

What if you put the LB directly into the back of the panel and paint conduit to match siding?

You can also reduce to 1.5" with the #2's. (Even 1.25")

 

[sparky 1971]

You can't put an LB below the panel if you're going to cover the walls, burying it. You could come in the back of the panel with an LB outside or put a junction box below the panel to feed up, just make sure that the cover for the box winds up flush with the wall finish. If you've already drill the hole down low for the LB, the options just became limited. About the only other easy thing I can think of is an LB below the panel with an access panel over it.

 

[Norcal]

You can't put an LB below the panel if you're going to cover the walls, burying it. You could come in the back of the panel with an LB outside or put a junction box below the panel to feed up, just make sure that the cover for the box winds up flush with the wall finish. If you've already drill the hole down low for the LB, the options just became limited. About the only other easy thing I can think of is an LB below the panel with an access panel over it.

With a little bit of planning it would have been simple, just stub up a conduit in the stud bay prior to pouring concrete, all it would of taken, just a little bit of planning..........

 

[Moto-Dude]

Can you keep a junction box or an LB accessible to make that corner?

Could do a lb on the interior too.

Why are you going outside for an attached garage?

I think I can. I will plumb it in above the sill plate and the LB should just protrude from the drywall for the all-important "access".

What if you put the LB directly into the back of the panel and paint conduit to match siding?

You can also reduce to 1.5" with the #2's. (Even 1.25")

I thought about that, yeah, just really don't want that massive ugly LB at eye level

You can't put an LB below the panel if you're going to cover the walls, burying it. You could come in the back of the panel with an LB outside or put a junction box below the panel to feed up, just make sure that the cover for the box winds up flush with the wall finish. If you've already drill the hole down low for the LB, the options just became limited. About the only other easy thing I can think of is an LB below the panel with an access panel over it.

Yes, sounds good. I'm still a little miffed the options are so limited. I'll get over it.

With a little bit of planning it would have been simple, just stub up a conduit in the stud bay prior to pouring concrete, all it would of taken, just a little bit of planning..........

Where were you 14 months ago!? Yeah, the concrete guy even asked about it but I was so far from the electrical phase I said I wasn't sure what I needed and let it go at that. Man, I wish I had known. You have to remember, this is my first electrical project, I had a lot to learn.

Completed wiring in the sub-panel. Man, I can't believe electricians get paid to do this, it's a lot of fun!


Feel free to point out any issues or mistakes, I'm still learning.

 

[mike93lx]

Where were you 14 months ago!? Yeah, the concrete guy even asked about it but I was so far from the electrical phase I said I wasn't sure what I needed and let it go at that. Man, I wish I had known. You have to remember, this is my first electrical project, I had a lot to learn.

Next time, I'd just stub up a couple pieces of conduit in the most likely spots with a sweep 90 at the bottom. Worst case, you cut it flush if you don't need it.

But that doesn't help you now.

I would have flipped the panel over. No need to have the feeder wrap all the way through to the top

 

[dave*99]

I'd cut back all that jacket on the NM-B at the top of the panel shown in post #28.

Lots of folks use this labeling technique.

 

[Norcal]

I would have flipped the panel over. No need to have the feeder wrap all the way through to the top

That is a peeve of mine, with most panels it is easy to flip them for bottom feed.

 

[Moto-Dude]

Yeah, that kinda thing doesn't bother me. As long as it works!

 

[mike93lx]

Yeah, that kinda thing doesn't bother me. As long as it works!

Makes it harder to work on the panel and it wastes wire.

Also causes a high current feeder to run through an area that you are workinging whenever you are in the panel.

I'd flip it and get block offs for the knock outs you used