Detached garage MWBC or Sub panel

[ehbaseball025]

Hello,

Im estimating a project and the customer has had some high estimates (3,700$) and makes me think that the other contractors are bidding to install a 60 Amp sub panel vs MWBC (10/3) from the main panel inside the house to the detached garage.

Details

-50 ft from panel to transition to under ground PVC then 30ft of PVC to detached garage
-Only needs to power garage door opener, 4 interior receptacles, 1 exterior receptacles, 2 exterior lights and 2 interior lights

I think according to 225.39 all I need is to run a MWBC 2- 30 amp circuits 10/3 Romex spliced on to #10 underground conductors then to a 30 amp double pole switch inside the detached garage as the disconnecting means and have everyone in the garage GFCI protected to satisfy the code. Please help advise. I am a new E1 contractor mainly experienced in industrial enviroments.

 

[augie47]

For the most part the items you list would not be permitted on a 30amp circuit.
Back to the Code book....................

 

[ehbaseball025]

For the most part the items you list would not be permitted on a 30amp circuit.
Back to the Code book....................

2- 30 amp circuits 10/3

 

[winnie]

10/3 can carry 30A, but you've listed a bunch of items that don't belong on 30A circuits.

If you run 10/3 at 30A, then you need to install a subpanel and ground rods.....

-Jon

 

[ehbaseball025]

10/3 can carry 30A, but you've listed a bunch of items that don't belong on 30A circuits.

If you run 10/3 at 30A, then you need to install a subpanel and ground rods.....

-Jon

Receptacles on its own #10 wire 30 amp breaker and then the garage door opener and LED lights on the other #10 30 amp breaker. Would I need a 10/2/2 wire with separate neutrals

 

[don_resqcapt19]

Receptacles on its own #10 wire 30 amp breaker and then the garage door opener and LED lights on the other #10 30 amp breaker. Would I need a 10/2/2 wire with separate neutrals

You would have to use 30 amp receptacles on that 30 amp circuit, and 15 and 20 amp plugs do not mate with 30 amp receptacles. See Table 210.21(B)(2).

 

[ehbaseball025]

You would have to use 30 amp receptacles on that 30 amp circuit, and 15 and 20 amp plugs do not mate with 30 amp receptacles. See Table 210.21(B)(2).

So because article 225.9(B) says that a MWBC CAN be used with a minimum rating of 30 amps I can't run a 30 amp circuit because Table 210.21(B(2) doesn't permit a #10wire / 30 amp overload protection be connected to 15/20 amp receptacles for the garage door opener and general purpose plugs?

 

[augie47]

225.39(B) actually addresses the rating of the disconnect and not the branch circuit. You need to go back to 225.30 and 225.33 and install a 20 amp MWBC with disconnect switches to handle your loads.

 

[Little Bill]

So because article 225.9(B) says that a MWBC CAN be used with a minimum rating of 30 amps I can't run a 30 amp circuit because Table 210.21(B(2) doesn't permit a #10wire / 30 amp overload protection be connected to 15/20 amp receptacles for the garage door opener and general purpose plugs?

You can run a 20A MWBC and use #12. You can't use 15A or 20A receptacles on a 30A circuit.

 

[ehbaseball025]

225.39(B) actually addresses the rating of the disconnect and not the branch circuit. You need to go back to 225.30 and 225.33 and install a 20 amp MWBC with disconnect switches to handle your loads.

So, just to be clear,
-12/3 to a 2 pole 20 amp breaker at main panel
-20 amp double pole switch as disconnecting means in detached garage
- 1 20 amp circuit for lights and garage door opener ( 20 amp rated gfci for garage door opener)
- 1 20 amp circuit for receptacles

 

[augie47]

 

[AC\DC]

3700 is cheap. Don’t do it for less than thst

 

[tthh]

Subpanel is a better idea.

 

[readydave8]

So, just to be clear,
-12/3 to a 2 pole 20 amp breaker at main panel
-20 amp double pole switch as disconnecting means in detached garage
- 1 20 amp circuit for lights and garage door opener ( 20 amp rated gfci for garage door opener)
- 1 20 amp circuit for receptacles

you can still run 10 if desired for voltage drop but use 20 amp breaker