Sub-panel for detach garage

[GWerks]

Looking to wire up power from 200amp main panel 175’ away that is from connection points. The garage goals… a small office which will need 20amp for a mini split, 4 post 30amp 110v lift for storage. (2)15 amp for led lights and outlets. 20 amp for TV/ coffee, 20 amp for mini fridge. I wont be adding anything else in addition as this will be max. Will run 2” schedule 40.
I have existing 500’ roll of 3awg THHN. Also new GE 125 amp sub-panel available. Located in central TX for reference…

1. What size breaker would be recommended for main panel to feed the subpanel?

2. What size ground from main panel to the subpanel (175’)

3. Will i also need a ground rod with solid #6 copper at the detached garage?

4. How deep do i need to set the schedule 40 in the ground?

Appreciate any advice needed!!!
Thank you

 

[mm08822]

1. 100a, I assumed you have Cu
2. You need a neutral #4 Cu and a grd @ #6 Cu
3. 2 Rods
24" min

Edit: fixed neutral size.

 

[GWerks]

1. 100a, I assumed you have Cu
2. You need a neutral #1 Cu and a grd @ #6 Cu
3. 2 Rods
24" min

Yes Cu roll of southwire 3 awg THHN. Can i run 3-3-3-6?

 

[BreeStephany]

Is your mini-split 120V or 240V and is your lift's pump motor and controls capable of being wired for 240V? You have a lot of 120V loads which puts more load on the neutral, so I would suggest wiring as many of the larger loads (larger motor loads, heating/cooling loads, etc.) for 240V if they are capable of being wired as such.

I know 12ga (20A) circuits are more expensive than 14ga (15A) circuits, but I would suggest that all of your receptacle circuits be 20A circuits within the garage area itself. Also being a location where you may use power tools, I would also suggest keeping your lighting circuit separate from your receptacle circuits primarily for safety purposes so you don't loose lighting if you happen to trip a receptacle circuit while a tool is in use.

Per NEC 310.16, #3 under the 75deg column is rated at 100A, so #3 will work for your purposes and you can use a 100A breaker at your main 200A panel to feed the subpanel at the detached garage / separate structure.

You will need to run a #6 THHN ground through the conduit for a ground, place a ground rod 24" from the structure and then place an additional ground rod 6' from that ground rod. You can use #6 solid bare copper for the grounding electrode conductor at the subpanel.

The neutral will need to be isolated from the ground at the subpanel, as the ground and neutral shall only be bonded at the first point of disconnect from the utility company and at no point beyond that point.

Also remember that all 120V non-dedicated equipment circuits within the garage shall be GFCI protected. You can accomplish this either by placing a GFCI receptacle at the at the first receptacle from the breaker and wiring all receptacles past the GFCI receptacle to the load side of the GFCI or through the use of a GFCI breaker at the subpanel.

Just my two cents.

 

[Norcal]

Is your mini-split 120V or 240V and is your lift's pump motor and controls capable of being wired for 240V? You have a lot of 120V loads which puts more load on the neutral, so I would suggest wiring as many of the larger loads (larger motor loads, heating/cooling loads, etc.) for 240V if they are capable of being wired as such.

I know 12ga (20A) circuits are more expensive than 14ga (15A) circuits, but I would suggest that all of your receptacle circuits be 20A circuits within the garage area itself. Also being a location where you may use power tools, I would also suggest keeping your lighting circuit separate from your receptacle circuits primarily for safety purposes so you don't loose lighting if you happen to trip a receptacle circuit while a tool is in use.

Per NEC 310.16, #3 under the 75deg column is rated at 100A, so #3 will work for your purposes and you can use a 100A breaker at your main 200A panel to feed the subpanel at the detached garage / separate structure.

You will need to run a #6 THHN ground through the conduit for a ground, place a ground rod 24" from the structure and then place an additional ground rod 6' from that ground rod. You can use #6 solid bare copper for the grounding electrode conductor at the subpanel.

The neutral will need to be isolated from the ground at the subpanel, as the ground and neutral shall only be bonded at the first point of disconnect from the utility company and at no point beyond that point.

Also remember that all 120V non-dedicated equipment circuits within the garage shall be GFCI protected. You can accomplish this either by placing a GFCI receptacle at the at the first receptacle from the breaker and wiring all receptacles past the GFCI receptacle to the load side of the GFCI or through the use of a GFCI breaker at the subpanel.

Just my two cents.

There is no exception for dedicated equipment from GFCI requirements.

 

[GWerks]

Is your mini-split 120V or 240V and is your lift's pump motor and controls capable of being wired for 240V? You have a lot of 120V loads which puts more load on the neutral, so I would suggest wiring as many of the larger loads (larger motor loads, heating/cooling loads, etc.) for 240V if they are capable of being wired as such.

I know 12ga (20A) circuits are more expensive than 14ga (15A) circuits, but I would suggest that all of your receptacle circuits be 20A circuits within the garage area itself. Also being a location where you may use power tools, I would also suggest keeping your lighting circuit separate from your receptacle circuits primarily for safety purposes so you don't loose lighting if you happen to trip a receptacle circuit while a tool is in use.

Per NEC 310.16, #3 under the 75deg column is rated at 100A, so #3 will work for your purposes and you can use a 100A breaker at your main 200A panel to feed the subpanel at the detached garage / separate structure.

You will need to run a #6 THHN ground through the conduit for a ground, place a ground rod 24" from the structure and then place an additional ground rod 6' from that ground rod. You can use #6 solid bare copper for the grounding electrode conductor at the subpanel.

The neutral will need to be isolated from the ground at the subpanel, as the ground and neutral shall only be bonded at the first point of disconnect from the utility company and at no point beyond that point.

Also remember that all 120V non-dedicated equipment circuits within the garage shall be GFCI protected. You can accomplish this either by placing a GFCI receptacle at the at the first receptacle from the breaker and wiring all receptacles past the GFCI receptacle to the load side of the GFCI or through the use of a GFCI breaker at the subpanel.

Just my two cents.

Thank you so much for the detailed info.
The mini split is 110v
I can run 12/2 and get all outlets onto 20amp breakers.
The lift pumps are also 110v and 30 amp and will only use them to store and wont be in use regularly.
I have battery operated tools For simple wheel changes but have a full workshop across from this garage. This will mainly be housing for some vehicles and battery charger when needed. And the office lounge to hang out occasionally.
For the ground rod..24” from the proximity of the sub-panel? Or within 24”? Can i run that on the side of the conduit where it feeds into the garage? 6” from the slab?
Didnt have any idea about the GFCI but i will add that in.
I wasnt sure on the ground as i was told by some 8 would work but did see 6 thhn in existing main panel so that ill make sure to run the same as well.
Also to confirm at the sub-panel do not bond the neutral and ground. Keep them isolated to separate bars??
Thank you again for the help!!!

 

[Poolshark314]

If your lift motor uses a standard 110v 15 amp plug, I would run 12/2 and get a high magnetic 20 amp breaker for that circuit. A lot of lift manufacturers recommend 30 amp breaker, but I don't like the idea of a 30 amp breaker on a 20 amp receptacle

 

[mm08822]

Yes Cu roll of southwire 3 awg THHN. Can i run 3-3-3-6?

I assumed you were at 175' as you stated. 500'/3 = 167'.
If I already owned the wire and hade enough for 3 legs, then I would made all the same size.

I wasnt sure on the ground as i was told by some 8 would work but did see 6 thhn in existing main panel so that ill make sure to run the same as well.
Also to confirm at the sub-panel do not bond the neutral and ground. Keep them isolated to separate bars??
Thank you again for the help!!!

#8 would normally be correct but the longer distance using upsized conductors requires the increase in size for the ground.

Correct, neutral bar remains isolated from the ground (don't use bonding screw). The ground wire should land on its own seperate block.

 

[mm08822]

Is your mini-split 120V or 240V and is your lift's pump motor and controls capable of being wired for 240V? You have a lot of 120V loads which puts more load on the neutral, so I would suggest wiring as many of the larger loads (larger motor loads, heating/cooling loads, etc.) for 240V if they are capable of being wired as such.

The feeder neutral will only carry the imbalance between the hot legs, so not really an issue. Since the panel buss bars alternate between phases, simply stacking the cb's next to each will provide a random loading of the phases and prevents every load being on the same phase.

 

[BreeStephany]

There is no exception for dedicated equipment from GFCI requirements.

I stand corrected and willfully admit that I need to study more.

Per NEC 2020, which most jurisdictions / AHJs are currently following:

210.8 Ground-Fault Circuit-Interrupter Protection for Personnel
A listed Class A GFCI shall provide protection in accordance with 210.8(A) through (F). The GFCI shall be installed in a readily accessible location.

• (B) Other Than Dwelling Units
  All 125-volt through 250-volt receptacles supplied by single-phase branch circuits rated 150 volts or less to ground, 50 amperes or less, and all receptacles supplied by three-phase branch circuits rated 150 volts or less to ground, 100 amperes or less, installed in the following locations shall be provided with GFCI protection:
  • (10) Garages, accessory buildings, service bays, and similar areas other than vehicle exhibition halls and showrooms.
    
• (D) Specific Appliances
  GFCI protection shall be provided for the branch circuit or outlet supplying the following appliances rated 150 volts or less to ground and 60 amperes or less, single- or 3-phase:
  1. Automotive vacuum machines
  2. Drinking water coolers and bottle fill stations
  3. High-pressure spray washing machines
  4. Tire inflation machines
  5. Vending machines
  6. Sump pumps
  7. Dishwashers
  8. Electric ranges
  9. Wall-mounted ovens
  10. Counter-mounted cooking units
  11. Clothes dryers
  12. Microwave ovens
      
• (F) Outdoor Outlets
  For dwellings, all outdoor outlets, other than those covered in 210.8(A), Exception No. 1, including outlets installed in the following locations, and supplied by single-phase branch circuits rated 150 volts or less to ground, 50 amperes or less, shall be provided with GFCI protection:
  1. Garages that have floors located at or below grade level
  2. Accessory buildings
  3. Boathouses
  4. If equipment supplied by an outlet covered under the requirements of this section is replaced, the outlet shall be supplied with GFCI protection.
  Exception No. 1: GFCI protection shall not be required on lighting outlets other than those covered in 210.8(C).
  Exception No. 2: GFCI protection shall not be required for listed HVAC equipment. This exception shall expire September 1, 2026.

Other than listed HVAC equipment, all circuits supplying receptacles within the garage area and on the exterior of the outbuilding shall be GFCI protected by either a GFCI breaker or GFCI receptacle. For receptacle locations in non-readily accessible locations within the space, the receptacle shall be protected either by means of a GFCI receptacle at a readily accessible height, a dead-front GFCI at a readily accessible height or by means of GFCI breaker.

 

[exranger06]

#8 would normally be correct but the longer distance using upsized conductors requires the increase in size for the ground.

Who said anything about upsizing wire? #3 Cu has an ampacity of 100A, before applying any correction factors or upsizing for voltage drop. #8 is the standard size ground wire for 100A. He only needs a #8 ground, not #6.

 

[GWerks]

Who said anything about upsizing wire? #3 Cu has an ampacity of 100A, before applying any correction factors or upsizing for voltage drop. #8 is the standard size ground wire for 100A. He only needs a #8 ground, not #6.

Would it be safer to run a slightly smaller breaker for example a 80-90amp instead of 100amp? Run 3-3-3-8 all buried? For 80-90amps should be plenty for what im needing correct? The mini fridge would be the only thing that'll be pulling constant power.

 

[mm08822]

Would it be safer to run a slightly smaller breaker for example a 80-90amp instead of 100amp? Run 3-3-3-8 all buried? For 80-90amps should be plenty for what im needing correct? The mini fridge would be the only thing that'll be pulling constant power.

So when I factored in the the 175' distance, 85A was the limit for 3% voltage drop. If I told you to use a 80 or 90A cb, then technically the conductors would be upsized. Using a 100A cb is cheaper, more readily available on the shelf, but the VD is higher than 3%. Not really a concern as I doubt you will ever get close to 100A load.

If you can now get 3 lengths out of 500', then the distance has to be less than 167'. Running a larger ground wire won't hurt anything.....you are right on the fence for #8 or #6 IMO.

 

[GWerks]

So when I factored in the the 175' distance, 85A was the limit for 3% voltage drop. If I told you to use a 80 or 90A cb, then technically the conductors would be upsized. Using a 100A cb is cheaper, more readily available on the shelf, but the VD is higher than 3%. Not really a concern as I doubt you will ever get close to 100A load.

If you can now get 3 lengths out of 500', then the distance has to be less than 167'. Running a larger ground wire won't hurt anything.....you are right on the fence for #8 or #6 IMO.

Thanks. Sounds good. Ill keep the 100amp breaker as you mentioned they are readily available. I think i saw a 90 amp CB at the local lowes. 80 CB is nearly impossible to locate. So if the 90 is available ill grab that instead of the 100CBJust wanted to make sure that its safe for 3awg. Yes i figured I will have to get additional wiring as ill be short but have other work ahead that i can save it for off this roll.
6 it is for the ground as well to be on the safe side! Going to be trenching this weekend and hope to get all the parts needed together and in!!!
Thanks again for clarifying!!!

 

[wyliesdiesels]

I assumed you were at 175' as you stated. 500'/3 = 167'.
If I already owned the wire and hade enough for 3 legs, then I would made all the same size.

#8 would normally be correct but the longer distance using upsized conductors requires the increase in size for the ground.

Correct, neutral bar remains isolated from the ground (don't use bonding screw). The ground wire should land on its own seperate block.

how is #3 cu for a 100a feeder upsized? #8 should be fine here

EDIT: I see you already responded to that...