Sub-pane in attached garage

[mrramsey]

Ok so I have a question I can't find an answer to. I am converting my garage into a workshop. I would like to add a sub panel for a few branch circuits for outlets and a gas heater. There is already an existing circuit for general lighting and the overhead door.

I have a 220v 30A circuit already in the garage that my compressor is plugged into. I plan to sell that compressor as it is waaaay overkill for what I do.

My thought is to re purpose the 10/3 30A run of wire and feed the sub-panel. My question is will I need to run a dedicated ground from the main panel to the sub panel? the main panels neutral lugs are bonded and all of the wires on those lugs are mixed (i.e neutrals and grounds).

 

[mrramsey]

Haha, well I answered my own question. I went back and looked at the cable. I already have 10/3 w/Ground. For some reason I was thinking I only ran a 10/3 cable.

 

[pattenp]

You may know but it bears repeating, the neutrals are isolated from the grounds in the subpanel.

 

[mrramsey]

You may know but it bears repeating, the neutrals are isolated from the grounds in the subpanel.

Yeah that's what prompted my question initially until I realized that I had a ground there already. Whats the difference anyway? (not that I won't adhere to the code) just wanting to understand the why. If they are bonded in the main panel why the difference in the sub panel.

 

[tyme2par4]

If your ground and neutral are bonded prior to the main panel, it provides 2 separate paths for the fault current. This could lead to the circuit breaker not functioning as intended.

 

[wyliesdiesels]

The other issue is u could have neutral return current flowing on grounded metalic pathways which needless to say is not good.