#4 AWG Feeders

[jeff48356]

Suppose I get a contract to wire a new 2-car detached garage. I would normally quote them on a 40A subfeed, underground with PVC, which includes a subpanel and 120V lighting/receptacles. Let's say they plan to use an electric car, and need a charger outlet. I would now have to upgrade to an 80A subfeed and panel. I would now need to use #4 copper conductors, rather than #8.

Can I use a 4-11/16" square box with #4 conductors for the junction where the romex would connect with the PVC in the basement, like I normally would with #8? Or does #4 require a larger box than that?

 

[augie47]

#4 and larger conductors have j boxes sized per 314.28 based on the raceway.. A 4-11/16 would be too small.

 

[infinity]

#4 and larger conductors have j boxes sized per 314.28 based on the raceway.. A 4-11/16 would be too small.

I agree. The minimum size raceway for 3-#4 conductors plus an EGC would be 1" so the minimum 6X distance of the box would be 6".

 

[Dennis Alwon]

This is a bit of track here but I am curious why 225.39(D) is always ignored. As I see it the feeder to the garage must be a minimum of 60 amps. I know everyone will say the disconnect only has to be 60 amps but how do you have a feeder disconnect of 60 amps without having 60 amp wiring.

(D) All Others. For all other installations, the feeder or
branch-circuit disconnecting means shall have a rating of not
less than 60 amperes.

 

[kwired]

This is a bit of track here but I am curious why 225.39(D) is always ignored. As I see it the feeder to the garage must be a minimum of 60 amps. I know everyone will say the disconnect only has to be 60 amps but how do you have a feeder disconnect of 60 amps without having 60 amp wiring.

I'm with you on this, and #4 aluminum might even be less cost than #8 copper or close enough to the same at least.

 

[jeff48356]

This is a bit of track here but I am curious why 225.39(D) is always ignored. As I see it the feeder to the garage must be a minimum of 60 amps. I know everyone will say the disconnect only has to be 60 amps but how do you have a feeder disconnect of 60 amps without having 60 amp wiring.

The inspectors here allow 40A feeders to detached residential garages. Perhaps Michigan waives 225.39(D) as applied to garages. After all, not too long ago, all that was required was one 20A branch circuit for everything. Now they require two, so it makes more sense to just run a 30A or 40A feeder and create the branch circuits within the garage from that subpanel.

Besides, how would having a 40A capacity versus a 60A pose any safety hazards, especially if no heavy loads are ever likely to be used?

 

[kwired]

The inspectors here allow 40A feeders to detached residential garages. Perhaps Michigan waives 225.39(D) as applied to garages. After all, not too long ago, all that was required was one 20A branch circuit for everything. Now they require two, so it makes more sense to just run a 30A or 40A feeder and create the branch circuits within the garage from that subpanel.

Besides, how would having a 40A capacity versus a 60A pose any safety hazards, especially if no heavy loads are ever likely to be used?

Two circuit installation this would be acceptable, you likely have 15 or 20 amps for your two circuits and 40 feeder is overkill anyway, but code says it must be at least 30 amp feeder.

If you are trying to do as cheap as possible instead of a 30 amp feeder and two circuits - just run a MWBC to supply the building.

 

[infinity]

Two circuit installation this would be acceptable, you likely have 15 or 20 amps for your two circuits and 40 feeder is overkill anyway, but code says it must be at least 30 amp feeder.

Just wondering why 30 amps?

 

[kwired]

Just wondering why 30 amps?

Can't answer that one.

Used to see a lot of old farm buildings with only 120 volt distribution to them -8-2 SE cable from an overhead line to a two pole 30 amp fused disconnect. Don't know if that was ever code compliant, but kind of wasn't in past 30 years for sure.