Electrical question...need expert advice

[Jason Morgan]

I am hooking up a dedicated 220V circuit ffor the dust collector and want to know if I can use #10/2 with ground for the circuit. If so, does the "ground" wire connect to the neutral bar or the ground bar in the sub panel? (Ground bar and neutral bar and DISCONNECTED in the sub panel of course)

Thanks,

[glenn bradley]

I'm no expert but have just gone through the learning experience. The ground and nuetral are seperate at the sub panel and are then joined back at your main panel. The important thing seems to be keeping them seperate until they physically meet at the main.

[Rick Christopherson]

First the easy part. Yes, you need to keep the ground and neutral separate at the subpanel, so your ground wire connects to the separate ground bus.

Why are you running #10 wire? If you do have a specific reason for doing this, then that is fine. However, for some reason, many people mistakenly believe that they need #10 wire for all of their 240 volt circuits. The frequency of people advising others to oversize their circuits doesn't help dispel this myth any.

#10 wire is needed for a 30-amp circuit, which translates into a 5 hp motor. If you truly have a 5 hp dust collector, then you need this. However, most dust collectors are less than 3 hp, with a greater percentage just 1-1/2 or 2 hp. If you have a 3 hp collector, then you need a 20 amp circuit with #12 wire. If it is 2 hp or less, you can use 15 amp and #14 wire. By default, I would install a 20 amp circuit.

[Jason Morgan]

Thanks guys. I am installing #10 wire in anticipation of future use. I dont NEED it now, but might in the future. Anyway. When running the 10/2 does the ground go to ground or to neutral in the sub panel? I looked at another site and it said to go to neutral with the ground in the sub

Thanks

[Tommy Curtiss]

in a sub panel, the ground and neutral bar should be separated ( the ground bar is screwed to the can and has a separate conductor going to it , and the neutral bar is insulated or should I say isolated from the can ) so,,ground the ground to the ground bar,( say that 3 times fast )

[Brandon Shew]

Sorry to hijack the thread here, but I'm looking for some education. Why do the neutral and grounds need to be separate in the sub panel? Does this apply if the sub panel is grounded back to the main panel or only if the sub panel is grounded independently of the main panel (or both)?

[Jim O'Dell]

From personal experience, do as Tommy, and the others, state. Ground to ground bar, neutral bar isolated from the ground bar in a sub panel.
Tommy was kind enough to come over and check my work when I wired my shop. I have a main panel for my shop with it's own service feed. I had failed to bond the neutral bar to the box, and he caught that very quickly. And so far, no smoke, no tripped breakers. You did say that would be a good sign, didn't you Tommy??
Good luck with the install, Jason. Let us know when you've got the power on! Jim.

Side bar. Good to see you posting Tommy. Hope you've gotten settled in the new house and have the shop together where you want it!

[Tommy Curtiss]

Now I can't quote the code, but it says that after the first means of disconnection,(main panel)then after that the ground bar and neutral SHALL be seperated,,they want all neutral difference to go back to the main breaker as fast as it can,,so during a large short or surge the main will trip and kill both panels,,the ground in a sub panel should trip the breaker in the sub panel,,but I am sure you will get a more detailed answer in a minute,,I'm no eng,,just a master

And yes Jim,,if you don't have to let that factory installed smoke out,,,that is a good sign!!!

[Jim Becker]

The ground conductor from your 240v machine goes to the ground bus in the sub panel. It's a ground, not a neutral.

[Suanne Lippman]

Thanks guys. I am installing #10 wire in anticipation of future use. I dont NEED it now, but might in the future. Anyway. When running the 10/2 does the ground go to ground or to neutral in the sub panel? I looked at another site and it said to go to neutral with the ground in the sub

Thanks

Thinking ahead, good move.
I wired a subpanel with 6/3 eventhough I was only planing on using 30A. Same work and not much more material; way better than finding out I needed more in 5 years.

Like others have said, ground to ground.

You need separate grounds and neutrals to subpanels because the alternatives aren't good. If you had two wires, connected in at both the panel and sub, you would have two paths which isn't safe. If you had one wire then you would lose both the neutral and ground if the single wire came lose, which isn't safe either. Two separate wires is the solution.

[Rick Christopherson]

Sorry to hijack the thread here, but I'm looking for some education. Why do the neutral and grounds need to be separate in the sub panel? Does this apply if the sub panel is grounded back to the main panel or only if the sub panel is grounded independently of the main panel (or both)?

First, and you didn't specifically ask this, the neutral is tied to ground as a reference point. If we did not ground the neutral, then it will literally "float" to whatever voltage it felt like (more or less).

As for a subpanel, if you connected the ground and neutral there as well as back at the main load center, then you would have a parallel path for normal current to flow. Current through the neutral wire is normal, and required for a circuit to operate. Current through the ground wire is not desired or normal (there will always be a little bit though, but that's because the ground wire is doing its job). So if you had two parallel paths for current to flow, then 1/2 of the current between the sub and main load centers would flow through the neutral, and the other half would flow through the ground. The key point here is that you cannot have normal current flowing through the ground wire.

For this reason, there can be only one connection between neutral and ground, otherwise you will have a ground loop. Also, because there is only one connection, then there cannot be a completed circuit path for current to flow. It is just a sharing of the same voltage, but not a complete circuit.

[Tom Veatch]

...For this reason, there can be only one connection between neutral and ground, otherwise you will have a ground loop...

Thanks, Rick. I've run across the term "ground loop" before, but never understood what it meant. Now, maybe I do.

[David G Baker]

I am having a 200 amp service added to my home. There will be a 200amp box outside with a 200amp main breaker and 2 100 amp breakers feeding two 100amp boxes in my basement. One of the boxes already exists and a new one will be added. All of the neutral and ground wires will have to be separated in the existing box because it now becomes a sub panel. It looks like a new ground bar is going to have to be added to accommodate the separation of neutral and ground wires.
Thanks Rick, I knew there was a reason for the neutral and ground separation in a sub panel but I have never had an explanation that I could visualize.

[Brandon Shew]

First, and you didn't specifically ask this, the neutral is tied to ground as a reference point. If we did not ground the neutral, then it will literally "float" to whatever voltage it felt like (more or less).

I'm clear on that point - basic completed circuit wiring.

As for a subpanel, if you connected the ground and neutral there as well as back at the main load center, then you would have a parallel path for normal current to flow. Current through the neutral wire is normal, and required for a circuit to operate. Current through the ground wire is not desired or normal (there will always be a little bit though, but that's because the ground wire is doing its job). So if you had two parallel paths for current to flow, then 1/2 of the current between the sub and main load centers would flow through the neutral, and the other half would flow through the ground. The key point here is that you cannot have normal current flowing through the ground wire.

For this reason, there can be only one connection between neutral and ground, otherwise you will have a ground loop. Also, because there is only one connection, then there cannot be a completed circuit path for current to flow. It is just a sharing of the same voltage, but not a complete circuit.

I think that I understand this as well, but my situation is slightly different from what you are describing so I want to make sure that this still applies. We bought our house last year and I inherited a small shed behind that I am converting to a workshop. I have a subpanel in the shed that is fed by three 6 gauge wires (2 hot, 1 neutral). There is a 60 Amp breaker on both ends. The subpanel is grounded independently from the main panel via 8' ground rod, and I do not have a ground path back to the main panel. For this reason, I am thinking that there is no possibility of a ground loop as you describe it above, but I am wondering what the pros/cons to this arrangement are and whether or not the neutrals and grounds still need to be separated here as well. The wiring was done by the previous owner and currently they are not separated, but I could easily fix that. I want to make sure that I am am not risking frying any tools or myself.

[David G Baker]

Brandon,
A building that is separated and isolated from the house ground system and only has three legs, 1 neutral and two hots you bond the neutral and ground to the box along with adding ground rods. The problem with this is you should not have any other connection to the house grounding system, telephone lines, water lines, gas lines, etc, or you could still get the ground loop.
The panel in the shed no longer qualifies as a sub panel.
If you had 4 legs running to the building, 1 neutral, one ground (that goes back to the main panel) and two hot legs, it would be wired as a sub panel with the neutral and the ground separated at the shed panel and the neutral "not" bonded to the panel.
This topic has been hotly debated on several forums that I belong to and varies from community to community depending on local code enforcers.