Wiring sub panel...shared common and ground.

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  #1  
Old 11-12-13, 11:09 AM
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Wiring sub panel...shared common and ground.

Previous owner installed a sub panel directly next to the main for 2 220v electric baseboards in an addition. A 4 conductor cable was run from the main via a dedicated 40amp double breaker. Hot wires to each side of sub panel, common to bus bar and ground to sub panel case. Sub panel is attached to main via metal conduit. So far all looks good, however I'm looking to run another circuit out to my shop...just 3 outlets...can I share common and ground in the sub panel? Or should I attach a new buss bar for grounds where the 4 conductor ground is coming in? And if I do that, what do I need to do with the existing common buss bar? I'd imagine I have to isolate it from the box somehow. Thanks for all the help.
 
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Old 11-12-13, 11:49 AM
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Welcome to the forums!

Previous owner installed a sub panel directly next to the main for 2 220v electric baseboards in an addition.
Those heaters are on 240V power. Your service is a 120/240V single-phase service. It doesn't supply 220V.

A 4 conductor cable was run from the main via a dedicated 40amp double breaker. Hot wires to each side of sub panel, common to bus bar and ground to sub panel case. Sub panel is attached to main via metal conduit.
Since there is no common conductor in an AC electrical system, I'll assume you meant "neutral."

I'm looking to run another circuit out to my shop...just 3 outlets...can I share [neutral] and ground in the sub panel? Or should I attach a new buss bar for grounds where the 4 conductor ground is coming in?
As you suspected, you should add a small buss bar, bonded to the enclosure, for all of the grounding conductors.

And if I do that, what do I need to do with the existing [neutral] buss bar? I'd imagine I have to isolate it from the box somehow.
Yes, if it isn't now. Have you tested for continuity between that bar and the enclosure? Everything else you described about the subpanel sounds well done.

That said, though, isolating the neutrals is one thing that is often overlooked.
 
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Old 11-12-13, 11:58 AM
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Yes, currently the bar is attached to enclosure. What can I use to physically isolate it from the box? Plastic washers? Thanks again
 
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Old 11-12-13, 12:09 PM
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currently the bar is attached to enclosure.
Yes, but is it electrically bonded to the enclosure? Is there a large green machine screw in it that's threaded into the enclosure?
Originally Posted by Nashkat1
Have you tested for continuity between that bar and the enclosure?
Between the neutral and the ground?

What can I use to physically isolate it from the box? Plastic washers?
If it's bonded to the enclosure you'll have to either buy and install a pair of isolation mounts or a new neutral bar with isolation mounts. What is the make and model of your subpanel?
 
  #5  
Old 11-12-13, 01:21 PM
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Yes there is large green screw in the enclosure. This is where the ground from main panel terminates. I get continuity between bar and ground and bar and enclosure. Looks like best bet is to use this as ground bar and install new isolated bar for commons. Don't have the make and model on hand. Thanks again.
 
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Old 11-12-13, 01:29 PM
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Looks like best bet is to use this as ground bar and install new isolated bar for [neutrals].
That's one solution..............................
 
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Old 11-12-13, 03:05 PM
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:NO NO NO:
Looks like best bet is to use this as ground bar and install new isolated bar for commons.
You don't have any commons, remember?
 
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Old 11-12-13, 03:08 PM
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ground to sub panel case.
A ground bar should have been installed when the subpanel was installed. Where are the grounds for the baseboard heater circuits terminated?
 
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Old 11-12-13, 03:59 PM
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The normal process is to use the built in neutral bar without the bond screw or strap for the neutrals. The grounds get added to a separately added grounding bar screwed to the enclosure.
 
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Old 11-12-13, 05:25 PM
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A ground bar should have been installed when the subpanel was installed. Where are the grounds for the baseboard heater circuits terminated?
Grounds for baseboard heaters terminate in a separate junction box above sub panel where heaters connect to a 2 circuit relay controlled by a traditional 24v thermostat. This box is connected to sub panel via metal conduit.
 
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Old 11-12-13, 05:59 PM
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Grounds for baseboard heaters terminate in a separate junction box above sub panel where heaters connect to a 2 circuit relay controlled by a traditional 24v thermostat. This box is connected to sub panel via metal conduit.
They don't need to be terminated there. The need to be fed into the subpanel and terminated in it, so they're in the enclosure that houses the overcurrent protection for the circuits.
 
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