Sub panel neutral bonding screw and grounding


Old 03-21-06, 12:16 PM
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Question Sub panel neutral bonding screw and grounding

I am adding a new sub panel ( I think this is the standard opening line) of sub panel questions.
I have a few questions about the sub panel neutral bonding screw if that is what it is called and the ground wiring, however before I ask the questions I will give a run down of what my plan is. I plan on installing a 100 amp sub panel next to my 200 amp main panel (less than 1 foot away). I am going to feed the sub panel from a 100 amp double pole breaker through one inch conduit with four runs of #4 wire, 2 hot wires, 1 neutral and 1 ground wire. Breaker to breaker wire length will be no more than 6 feet depending on how I run the conduit. The sub panel is a Siemens panel that can be used as either a main panel or a sub panel I believe and already has a 100 main breaker in it. It also has both a ground bar and neutral bar which are currently tied together with a jumper bar. In my research it is my understanding that the neutral and ground cannot be tied together at the sub panel, only at main panel which they are. So I will remove the neutral to ground jumper bar on the sub panel and run one #4 wire to the ground bar and one #4 to the neutral bar and 2 hot wires to the 100 amp main breaker. I plan on marking the ground wire with green electrical tape and the neutral with white tape and the 2 hot wires one with blue and one with red electrical tape. I have three questions unless someone sees something wrong with my plan if so feel free to comment.

Question 1: Could the ground wire be bare instead of insulated and could it be smaller than the neutral and hot wires? If so what size?

Question 2: On the Siemens sub panel neutral bar is a tab that has a green screw (Neutral Bonding Screw?) This screw is the same color as the screws used on other devices as a ground terminal. I believe this screw is used for bonding the neutral bar to the sub panel case if I am correct should I remove this screw?

Question 3: Should I then ground the case to the ground bar? It may be already but I have not checked the continuity yet to see. Or is the reason for the neutral bonding screw because the ground bar and the neutral bar are isolated from the case? So if this panel was used as a main panel you would leave the jumper between the neutral and ground bars and run the bonding screw into the case and this would then tie the case to ground.

I hope I haven’t confused anyone or given to much unnecessary information.

Thanks for any help
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Old 03-21-06, 12:27 PM
Join Date: Sep 2000
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1. The ground wire not only could be bare or green, it must be. And marking it with green tape is not good enough. And yes, it can be smaller. #8 is enough.

2. Yes, that is correct.

3. The grounding bar should already be bonded to the case. Double-check with an ohmmeter. And yes, if this was a main panel, you would do things differently.

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