Grounding on Grounded Lug

[fleetfeet]

Not that it's safe or practical, but I was wondering about the consequences of having a grounding wire tied into the neutral bus. My thoughts are that it wouldn't trip the breaker, but it would divert the fault away from the (equipment).

 

[pierre]

Re: Grounding on Grounded Lug

Where in relation to the building is the bus you are talking about located? ... 1st point of disconnect, or downstream of it?

 

[fleetfeet]

Re: Grounding on Grounded Lug

It's a subpanel in the garage, and the lighting ground wire is taken to the neutral bar.

 

[jbwhite]

Re: Grounding on Grounded Lug

Originally posted by fleetfeet:
It's a subpanel in the garage, and the lighting ground wire is taken to the neutral bar.

That would be wrong, but not for the reason you mentioned.

If the neutral were to become open between the sub panel and the main panel the ground wire in question would become a dangerous current carrying conductor. I hope I explained that well.

 

[don_resqcapt19]

Re: Grounding on Grounded Lug

fleetfeet,
Is an EGC run to the panel along with the grounded and ungrounded condcutors?
Don

 

[fleetfeet]

Re: Grounding on Grounded Lug

No...they ran ungrounded and grounded wire (UF) 24 inches down without pipe. I think they intend to have grounding with water after it's run in the spring.

 

[A/A Fuel GTX]

Re: Grounding on Grounded Lug

Originally posted by jbwhite:

Originally posted by fleetfeet:
It's a subpanel in the garage, and the lighting ground wire is taken to the neutral bar.

That would be wrong, but not for the reason you mentioned.

If the neutral were to become open between the sub panel and the main panel the ground wire in question would become a dangerous current carrying conductor. I hope I explained that well.

[ December 12, 2005, 08:05 AM: Message edited by: m73214 ]

 

[A/A Fuel GTX]

Re: Grounding on Grounded Lug

That would be wrong, but not for the reason you mentioned.

If the neutral were to become open between the sub panel and the main panel the ground wire in question would become a dangerous current carrying conductor. I hope I explained that well.
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Couldn't the same be said about the main panel where the neutral and GEC are always tied together? According to 250.32 B (1) & (2) a detached building could be wired either way providing there is no continuous metallic path between the main structure and detached building. I'm assuming a continuous metallic path would be a metallic water pipe or conduit.

 

[charlie b]

Re: Grounding on Grounded Lug

Originally posted by m73214:Couldn't the same be said about the main panel where the neutral and GEC are always tied together?

That is probably highest on the list of things people in this industry (as well as DIY homeowners) most often wonder about. The simple answer is that current is trying to get back to the source, and that once it gets to the main panel, it has achieved that goal. But if you tie neutral and ground at a panel downstream of the main disconnect, other than in accordance with the rules about separate building, then the current will not yet have succeeded in getting back to the source. Therefore, as it looks for its way back to the source, it will find two paths: the neutral (which it should be taking) and the equipment grounding conductors (which it should not be taking).

 

[infinity]

Re: Grounding on Grounded Lug

Originally posted by fleetfeet:
It's a subpanel in the garage, and the lighting ground wire is taken to the neutral bar.

Let me see if I fully understand your setup:

You have a garage with a feeder comprised of a piece of UF cable with 2 insulated and 1 uninsulated conductor within the UF cable.

The insulated conductors are your ungrounded conductors and your bare conductor is your grounded conductor.

You have no equipment grounding conductor.

At the subpanel you have no equipment grounding bar so your EGC from your light fixture is connected to the neutral bar.


Am I close?

 

[fleetfeet]

Re: Grounding on Grounded Lug

That's correct Infin...I am just wondering what the harm is and why this shouldn't be done.

 

[George Stolz]

Re: Grounding on Grounded Lug

You should always adhere to the NEC, whether you think you know the reasoning behind a section or not, for starters. It's been said that "every section, when traced back through a series of events, was brought on by a hazard."

That said, here's one aspect of what happens. You've got a couple violations coming down the pike. When the water pipe comes to the detached building, it will be coming from the same building supplying the electrical to the detached building.

You will want to connect your panel to it.

When you do this, here's what happens: Imagine that light, turned on. He's running a saw, that's on too. He's got the tunes on, overall, he's pulling, say, 16 amps on a phase. There are 16 amps that are supposed to be on the neutral.

When the neutral current reaches the panel, then it goes two ways: you have a parallel path set up.

The resistances determine how many amps flow on each, let's say they're equal. 8 amps are flowing on the water pipe, and 8 on the real neutral.

I've got to get to work, but here's your solution:

Use the white conductor for a neutral. Use the bare conductor for a grounding conductor. Abandon a phase. Chances are, he wouldn't miss it anyway. And it's much, much safer.

Or, when he digs in the water pipe this spring, put in the proper conductors at the same time.