Sub panel bonding question

[hosspuller]

What do you do if the ground and neutral bars are joined in the panel? Just break a piece of the connecting bar out?

Look closely... there will be a portion of the neutral bar that is pre scored to remove or there is a piece that bonds the box to the neutral bar.

 

[aczlan]

Look closely... there will be a portion of the neutral bar that is pre scored to remove or there is a piece that bonds the box to the neutral bar.

Yep. Many panels will also have a bonding bolt that goes through the neutral bar and into the back of the panel to bond neutral and ground.

Aaron Z

 

[buickanddeere]

Yes,unbounded gnd. @ neut at sub panel is correct. Code says ground rod at sub panel if more than 1 breaker at panel, not required if only one. So what's the difference? Essentially the code says "eh, sometimes.", but they drew a line somewhere at 1 ckt.
Realistically, ground rods will help drain static charges and maybe disperse lightning better, but from a human safety perspective, your ground wire is what will carry ground fault current back to the transformer neutral in quantities big enough for the breaker to pop.

One receptacle means it's grouped in with extension cords.
A pair of ground rods at the remote panel improves the round plain. Good to see four wires ran to remote panel and the neutral/ground isolation.

 

[arlen4720]

Yes,unbounded gnd. @ neut at sub panel is correct. Code says ground rod at sub panel if more than 1 breaker at panel, not required if only one. So what's the difference? Essentially the code says "eh, sometimes.", but they drew a line somewhere at 1 ckt.
Realistically, ground rods will help drain static charges and maybe disperse lightning better, but from a human safety perspective, your ground wire is what will carry ground fault current back to the transformer neutral in quantities big enough for the breaker to pop.

If a building is SERVED by a single branch circuit, then a grounding electrode is not needed. BUT!!!, if a building is served by a feeder, then a grounding electrode is needed in the separate building. A building with a subpanel would automatically be considered being fed by a feeder because it has overcurrent protection on both ends.
If you read the code closely you will see that they are talking about a single branch circuit supplying an entire building, not a branch circuit being derived out of a panel in the building.
What the code is really trying to address is a small building where you may only need a light and a receptacle. In that case you wouldn't need to have a grounding electrode. It is a good thing, as it would be a real pain to bond it to the equipment ground.
As a rule, subpanels in remote buildings need 4 wires ran to them (if they are 120/240 panels), and need a grounding electrode system. The neutral is not bonded at the subpanel. Remember also that agricultural buildings need to have a covered COPPER equipment ground.

 

[MNBobcat]

If your neutral and ground are bonded at the sub-panel you will be sending power back to the main panel via the ground wire. That's bad. The neutral should complete the circuit.

So go to home depot or lowes and buy a neutral bar. Screw the neutral bar to the back of the sub-panel and off to one side. Make sure to scrape some paint off the panel where you are mounting the neutral bar. All your grounds would go to this bar. The neutrals would go to the original neutral bar that is part of the panel. Thus your neutrals and grounds are electrically separated. This is the proper way to wire a sub-panel.

I found a photo to illustrate (however the green screw on the crossover arm needs to be removed for a proper sub-panel implementation)

 

[Mac25]

If your neutral and ground are bonded at the sub-panel you will be sending power back to the main panel via the ground wire. That's bad. The neutral should complete the circuit. So go to home depot or lowes and buy a neutral bar. Screw the neutral bar to the back of the sub-panel and off to one side. Make sure to scrape some paint off the panel where you are mounting the neutral bar. All your grounds would go to this bar. The neutrals would go to the original neutral bar that is part of the panel. Thus your neutrals and grounds are electrically separated. This is the proper way to wire a sub-panel. I found a photo to illustrate (however the green screw on the crossover arm needs to be removed for a proper sub-panel implementation) <img src="http://www.tractorbynet.com/forums/files/projects/394873-sub-panel-bonding-question-ar123670746083421-jpg"/>

If the neutral bars are insulated from the metal panel via plastic like the picture, they would already be separated right? My question is.... If my main panel that I am receiving my feed to the sub panel is bonded, meaning neutral and ground have continuity, then the neutral and ground at the sub panel will have continuity as well so are they actually unbonded?

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[MNBobcat]

If the neutral bars are insulated from the metal panel via plastic like the picture, they would already be separated right? My question is.... If my main panel that I am receiving my feed to the sub panel is bonded, meaning neutral and ground have continuity, then the neutral and ground at the sub panel will have continuity as well so are they actually unbonded?

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In the photo, for the neutral bars to be insulated from the panel that green screw on the bonding strap needs to be removed. That photo was used to show a problem which was the person forgot to remove the screw. But yes...had the screw been properly removed you're correct in that the left/right neutral bars would be insulated from the metal panel itself.

In a sub-panel you don't want your neutral wires and ground wires to have continuity between each other. You need to isolate the grounds. Instead, install a neutral (terminal) bar for the ground wires and attach them as shown in the illustration.

You are correct that at the main panel the neutral and grounds have continuity because they share the same neutral bar connection.

Another way to think about it is if you were wiring an electrical receptacle. You don't hook the ground wire to the silver screw where you hook the neutral wire. The only place where the ground and neutral wires are bonded is at the main panel. Nowhere else, including a sub-panel, should they ever be joined.

The reason its wired that way is there is a small amount of current that flows back on the neutral wire. If you bond the neutral and grounds at the sub-panel, you'll have current flowing on your ground wires . Those ground wires go to things you might touch (stuff you plug into the outlets wired off your sub-panel) and that's a hazard.

 

[arlen4720]

I think what the OP is saying is that after it is all wired, he has continuity between the neutral and ground at the remote panel. This would be normal because they are bonded at the main panel.
For those who don't know, the whole purpose of not bonding at the subpanel is to avoid the neutral current parallel paths. If you bonded at both ends, you would have 3 paths...the neutral, the equipment ground, and the earth between the grounding electrodes. It IS a safety hazard, but not as big of a one as many people think.

 

[Mac25]

I think what the OP is saying is that after it is all wired, he has continuity between the neutral and ground at the remote panel. This would be normal because they are bonded at the main panel. For those who don't know, the whole purpose of not bonding at the subpanel is to avoid the neutral current parallel paths. If you bonded at both ends, you would have 3 paths...the neutral, the equipment ground, and the earth between the grounding electrodes. It IS a safety hazard, but not as big of a one as many people think.

YES!!! That is what I was trying to say, when I was done wiring, the neutral and ground at the sub panel have continuity. Is this normal with the bonding screw removed??

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[buickanddeere]

Yes there will have to be continuity between the neutral and the ground at the pony panel, they are bonded up at the utility service.
Most folk are still missing the point of keeping neutral current in the neutral and no neutral current in the ground path.