How to Ground a Residential Sub-Panel

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chiefkona1145

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I was recently cited by the AHJ for not having a grounded sub-panel on a 120/240 volt, 1 phase, 3 wire system that was installed in 1985. The panel has 2 hots and one neutral run from the main panel, there is no ground conductor, ground lug, or ground bus in the sub-panel. It is a Square D type QO load center. My question is, in the 1983 NEC, was this a requirement?

I would appreciate any responses. :)
 
Re: How to Ground a Residential Sub-Panel

I don't know about the code in 1983 I was only two years old, but I have to ask if you did any work inside of that panel. In some areas of PA if you touch something like that some feel that you must bring it up to code.
 
Re: How to Ground a Residential Sub-Panel

Is the subpanel in the same building? Is there a raceway, GRC, EMT, AC from the main to the sub panel in which the conductors are in? If there is metal piping there is your ground. If not it would be safe to say you need one. Be sure to land the EGC on an isolated grounding bar and to remove the paint on the can, (subpanel) before you fasten the bar to the can. You could possibly safe someone's life!
 
Re: How to Ground a Residential Sub-Panel

250-61(b)of the 1981 code prohibited the grounded conductor from being used for grounding on the load side of the service disconnect. 250-57(b) required an EGC to this sub-panel. It was not in compliance with the code when it was installed.
Don
 
Re: How to Ground a Residential Sub-Panel

Thank you for the information. The panel has a type NM feed to it of 6/2 with grd.. The 2 hots land on the main lugs and the grd. lands on the bottom mounted solid neutral bus. Yes, the sub panel is in the same part of the house as the main panel.

[ June 03, 2004, 06:56 AM: Message edited by: chiefkona1145 ]
 
Re: How to Ground a Residential Sub-Panel

Since the panel appearantly did not meet code when it was installed, I believe the AHJ could rightly require it to be brought up to code whether you touched it or not. That may not necessarily be your responsibility if it is outside the scope of your work on this project, but it would be the current owners responsibility to have it done.
 
Re: How to Ground a Residential Sub-Panel

Using this example, what hazard exists during normal or fault conditions?

There are no metallic paths between the two panelboards. The wiring method is non-metallic. Why can't the grounded conductor/neutral be used for the second panels return path for both conditions? :confused:
 
Re: How to Ground a Residential Sub-Panel

Assuming they bonded neutral to the panel enclosure, the loss of the neutral to this panel will make the panel enclosure instantly hot and any metal enclosures that are bonded to it will also be hot.

And IMO this is different from a 3 wire range / dryer feed.

In this case the loss of a neutral will cause all the grounded loads on the panel to have hot enclosures :eek: instead of just one appliance.

Bob

[ June 06, 2004, 10:50 AM: Message edited by: iwire ]
 
Re: How to Ground a Residential Sub-Panel

Did i read this right ? 6-2 w ground ? What did they use for neutral ? the bare ground.
Yes an open neutral could cause major problems in this case.
I too got grounded a lot for removing shorts :D
 
Re: How to Ground a Residential Sub-Panel

Isn't the grounding conductor in a 6/2 NM only a #10? :eek:
Is the neutral bar bonded to the panel? If it is this bond will have to be removed and a seperate bonded grounding bar installed. a 4 conductor (H#6,H#6,N#6,G#10) will have to be ran from the service panel to this sub panel and the neutrals have to be kept isolated from the can.

One other note watch out for three-wire dryer feed's from this panel as they will now have to be installed to the main panel or reinstalled as a 4-wire circuit.

[ June 06, 2004, 11:19 AM: Message edited by: hurk27 ]
 
Re: How to Ground a Residential Sub-Panel

The bare neutral is my major issue with this.Could he not feed that 3 wire dryer from a junction box coming out of that repaired panel.That way the neutral will not touch ground ?
 
Re: How to Ground a Residential Sub-Panel

Well, whats the difference if the grounded conductor is opened before the service and the main panel is also the loadcenter to all loads? All grounds and neutrals are bonded there.

The presence of a grounding electrode system does not reduce the potential of touch voltage nor will serve to open the OCD. :confused:
 
Re: How to Ground a Residential Sub-Panel

Originally posted by bphgravity:
Well, whats the difference if the grounded conductor is opened before the service and the main panel is also the loadcenter to all loads? All grounds and neutrals are bonded there.

The presence of a grounding electrode system does not reduce the potential of touch voltage nor will serve to open the OCD. :roll:

[ June 06, 2004, 11:55 AM: Message edited by: iwire ]
Click to expand...
 
Re: How to Ground a Residential Sub-Panel

However if you loose the service neutral you will be fine in the house as all the metal piping will be at the same potential as the equipment enclosures due to the bonding of the piping to the service enclosure.
Click to expand...
But Bob the concrete floor in the basement or in a house on a slab will not be.

Home owner reaches to turn off the water while takeing a shower. :eek: :eek:
 
Re: How to Ground a Residential Sub-Panel

Wayne I am by no means saying that the loss of any neutral is a good thing.

It is just my opinion that the loss of a neutral for a subpanel that uses the neutral as the EGC is a worse situation.

Under the current NEC rules we can and are required to avoid this at a subpanel, at the service we can not avoid this.

[ June 06, 2004, 01:00 PM: Message edited by: iwire ]
 
Re: How to Ground a Residential Sub-Panel

If a neutral opens on that sub panel the unbalanced voltage will be on the frame and anything else grounded to it.This could be anything from 0 to 120 volts.Way too dangerious
 
Re: How to Ground a Residential Sub-Panel

Sorry Bob I missed your intent. Yes losing a neutral at a sub will cause allot more damage and could even cause a fire like you said there is no bond to the water system so the unbalance will be much greater than the main service with this bond.
 
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