Conductors from Existing House Panel to Detached Shop

[Weirth It]

Hello and thank you in advance for any technical guidance provided, especially on the electrical side of this project (I am strictly a mechanical mind).

Kitsap County has issued my building permit and we will be breaking ground on a 40' x 40' shop today. This will include a trench from the existing garage to the shop for the electric feed. I am looking for guidance on what conductors I should run from the existing panel (photo attached) to the sub-panel, what size breaker should be used, and if the conductors should be ran in conduit. I am looking at the Eaton Type CH 125-Amp 24-Spaces 48-Circuit Main Lug Plug-On Neutral Load Center for the sub-panel.

The distance between the two panels is approximately 40'. Not exactly sure what loads will be on the panel and I don't want to be short on the supply. I am hoping to have dust collection, table saw, small lathe, Bridgeport style knee mill, air compressor, small mig welder and maybe some other cool toys.

I imagine I have forgot to supply some critical piece of information so let me know.

Brian

 

[Terry D]

Since it is a detached garage, you will need a disconnect out there. The easiest thing to do is to get a main breaker panel instead of the main lug one you listed. If you need 125 amps out there, then get a 200 amp main breaker for the sub and feed it with a 125 amp breaker from the house. The 200 amp main in the sub will just serve as a disconnect.

If you only need 100 amps, then get a 100 amp main breaker for the sub and feed it with a 100 amp from the house. I would use XHHW aluminum conductors in PVC conduit. No need to worry about voltage drop with that short of distance.

I would use 1 1/2 conduit for either way

100 amp would be (3) #1 XHHW and (1) #6 XHHW for the Equipment ground

125 amp would be (3) 1/0 XHHW and (1) #4 for the equipment ground.

Note - some places might let you install #2 for 100 amp, ask the inspector

 

[wyliesdiesels]

is this a one man shop? if so, 90a will suit you fine

go with #2 AL MHF in 2" pvc conduit...

dont forget to isolate the neutral in the subpanel and add 2 ground rods

 

[Skiff Builder]

is this a one man shop? if so, 90a will suit you fine

go with #2 AL MHF in 2" pvc conduit...

dont forget to isolate the neutral in the subpanel and add 2 ground rods

I did the same system as above for my 100' or so shop run. The Mobile Home Feeder was priced right and easy to pull. My inspector had never seen it used in town...
he yelled at me for the two gr rods- said not needed as I had them back at the main house panel.........

My one man shop has not needed more than 60A yet, even with a 7.5K elec heater.

 

[pattenp]

Since it is a detached garage, you will need a disconnect out there. The easiest thing to do is to get a main breaker panel instead of the main lug one you listed. If you need 125 amps out there, then get a 200 amp main breaker for the sub and feed it with a 125 amp breaker from the house. The 200 amp main in the sub will just serve as a disconnect.

If you only need 100 amps, then get a 100 amp main breaker for the sub and feed it with a 100 amp from the house. I would use XHHW aluminum conductors in PVC conduit. No need to worry about voltage drop with that short of distance.

I would use 1 1/2 conduit for either way

125 (100A) amp would be (3) #1 XHHW and (1) #6 XHHW for the Equipment ground

100 (125A) amp would be (3) 1/0 XHHW and (1) #4 for the equipment ground.

Note - some places might let you install #2 for 100 amp, ask the inspector

Your 100A and 125A are backwards.

 

[Terry D]

Your 100A and 125A are backwards.

Oops, i do have them reversed. Thanks. I will change that

Sent from my SM-G960U using The Garage Journal mobile app

 

[Weirth It]

Your 100A and 125A are backwards.

Nice proofing. Thank you!

 

[Weirth It]

is this a one man shop? if so, 90a will suit you fine

go with #2 AL MHF in 2" pvc conduit...

dont forget to isolate the neutral in the subpanel and add 2 ground rods

This is a one-man shop. Does this look like the correct material? I will run the MHF cable in 2" PVC electrical conduit.

https://www.platt.com/platt-electri...On-2-Pole/Eaton/CH2100/product.aspx?zpid=9990

https://www.platt.com/platt-electri...r/Eaton/CHP22B100X2/product.aspx?zpid=1200056

https://www.wireandcableyourway.com/2-2-2-4-aluminum-mobile-home-feeder-cable

Thanks for the feedback,
Brian

 

[Terry D]

This is a one-man shop. Does this look like the correct material? I will run the MHF cable in 2" PVC electrical conduit.

https://www.platt.com/platt-electri...On-2-Pole/Eaton/CH2100/product.aspx?zpid=9990

https://www.platt.com/platt-electri...r/Eaton/CHP22B100X2/product.aspx?zpid=1200056

https://www.wireandcableyourway.com/2-2-2-4-aluminum-mobile-home-feeder-cable

Thanks for the feedback,
Brian

Depending on what your area requires, you might only be able to use a 90 amp breaker with that wire. We are allowed here to use #2 for 100 amp whether the building is detached or attached for residential. Commercial is different.

That wire will go in 1 1/4 conduit. I would use that or 1 1/2 for that short distance. Unless you are switching over to a SER cable inside your house, that 2 inch would have to go all the way to your main panel. A liitle smaller pipe might be easier to work with.

 

[75gmck25]

Also check to see that the 2-2-2-4 AL MHF you use is dual rated. I believe it will be marked as USE-2 RHH RHW. This allows you to run it as direct bury or in conduit in the ground, and also run it in conduit inside the building and up to the panel.

I used 2" conduit for about a 50 foot run. The conduit is definitely large enough for an easy pull, but keep track of which way the joints run in the conduit. MHF is multiple wires that are periodically taped together, and its way easier to pull when you aren't catching that tape on the joints in the conduit.

Bruce

 

[13mo]

Depending on what your area requires, you might only be able to use a 90 amp breaker with that wire. We are allowed here to use #2 for 100 amp whether the building is detached or attached for residential. Commercial is different.

According to the NEC, 2 AWG XHHW aluminum (which is what the 2/2/2/4 mobile home feeder wire is) to a non-dwelling structure landing on a typical 75 C rated breaker is good only for 90 amps. They allow over-rating dwelling service entrance breaker sizes where the amperage capacity of the wire only needs to be 83.3% of the circuit breaker size. This is why 2/2/2/4 aluminum mobile home feeder wire can be used at 100 amps for a mobile home but only 90 amps for an outbuilding. The NEC also requires a disconnect at or near the meter, so all panels have to be fed by a four-wire service.

Some localities like mine do not have electrical permitting or inspection, so the only "rules" are what the utility requires for wire leaving their equipment (meter base, disconnect, etc.) I have two utilities' lines on my property. The one I get service from will let residential and agricultural customers use the same wiring rating for an outbuilding as for a house, they do not require an exterior disconnect, and they will let you run three-wire (line/line/neutral) between the meter or disconnect and the panel in your house or building. They do not inspect anything on the customer side of their meter or disconnect unless there is an issue. The other utility mandates everything the NEC does and adds some mandates of their own, such as mandating that all customer service entrance wire be only full-rated copper (e.g. 3/0 copper for a 200 amp house service.)

Personally, I would recommend following the NEC guidelines using non-overrated four-wire aluminum and a disconnect, which in your case 2/2/2/4 mobile home feeder with a 90 amp breaker in the house and a 100+ amp main breaker panel in the outbuilding (its rating does not matter, as it is only a disconnect.) 90 amps should be plenty, I had that in a previous detached woodshop and I never had any issues, even with a 5 kW electric heater.

 

[Terry D]

According to the NEC, 2 AWG XHHW aluminum (which is what the 2/2/2/4 mobile home feeder wire is) to a non-dwelling structure landing on a typical 75 C rated breaker is good only for 90 amps. They allow over-rating dwelling service entrance breaker sizes where the amperage capacity of the wire only needs to be 83.3% of the circuit breaker size. This is why 2/2/2/4 aluminum mobile home feeder wire can be used at 100 amps for a mobile home but only 90 amps for an outbuilding. The NEC also requires a disconnect at or near the meter, so all panels have to be fed by a four-wire service.

Some localities like mine do not have electrical permitting or inspection, so the only "rules" are what the utility requires for wire leaving their equipment (meter base, disconnect, etc.) I have two utilities' lines on my property. The one I get service from will let residential and agricultural customers use the same wiring rating for an outbuilding as for a house, they do not require an exterior disconnect, and they will let you run three-wire (line/line/neutral) between the meter or disconnect and the panel in your house or building. They do not inspect anything on the customer side of their meter or disconnect unless there is an issue. The other utility mandates everything the NEC does and adds some mandates of their own, such as mandating that all customer service entrance wire be only full-rated copper (e.g. 3/0 copper for a 200 amp house service.)

Personally, I would recommend following the NEC guidelines using non-overrated four-wire aluminum and a disconnect, which in your case 2/2/2/4 mobile home feeder with a 90 amp breaker in the house and a 100+ amp main breaker panel in the outbuilding (its rating does not matter, as it is only a disconnect.) 90 amps should be plenty, I had that in a previous detached woodshop and I never had any issues, even with a 5 kW electric heater.

We have been through this discussion before. I live in a big city where electrical permits are required. We are allowed to use # 2 Alum for 100 amp residential services and sub panels in attached and detached garages. I fully understand it is not allowed everywhere. But it is allowed some places, that is why I told him to check first.

As far as an outside disconnect being required on services, that came out in the 2020 code. Until your state or local jurisdiction adopts it, it is not required by the NEC. And Missouri does have a state wide license now. But you still have to follow the rules of each jurisdiction as far as what code cycle they are in. Its not like a state licenses in other states. To my understanding no one here is in the 2020 code