grounding and bonding of subpanels.

[djwireman]

Hello, I've got a question with reguards to sub-panels on a 120/240v. Say I've got a feeder of 4/0 alum, 4 wire romex. And my question is, where can I find literture on or nec ref.,on connecting ground and neutrals in? I was told to remove the big ground screw from sub-panel to float the nutrals, but if it's connected together at the main panel.. What I'd like to know is any references on this subject availible? So I'll know for my own knowledge. Thanks. DJW.

 

[infinity]

Start with 250.24.

 

[electrofelon]

Hello, I've got a question with reguards to sub-panels on a 120/240v. Say I've got a feeder of 4/0 alum, 4 wire romex. And my question is, where can I find literture on or nec ref.,on connecting ground and neutrals in? I was told to remove the big ground screw from sub-panel to float the nutrals, but if it's connected together at the main panel.. What I'd like to know is any references on this subject availible? So I'll know for my own knowledge. Thanks. DJW.

What do you mean by 4/0 alum, 4 wire romex?

 

[kwired]

but if it's connected together at the main panel..

I assume you were asking a question with this particular text.

Think for a moment about what you have if you connect both ends together. Effectively you don't have separate neutral and equipment grounding conductors at the sub panel end you just have a parallel conductor from the main serving both purposes.

Why do we separate them? Because the grounded conductor (neutral) carries current during normal operation and the equipment grounding conductor only carries current during abnormal conditions. Tying them together results in voltage drop on the neutral being subjected to all metal components that are bonded to the equipment grounding system, as well as potentially having neutral current flowing on all sorts of unintended paths, increasing risk of electric shock and electrocution throughout the system from just touching anything directly or indirectly bonded to the grounded conductor.