Adding outlets to basement shop - grounding question

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Old 01-31-06, 12:46 PM
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Question Adding outlets to basement shop - grounding question

New forum member here. I hope I can help others as much as I'm sure some of you will help me. With that being said, I've got a project I need some advice on.

I want to add a couple of 20 amp quad outlet boxes in my shop in the basement. My plan is to install them on the three steel support posts that run down the center of the room holding up the main support beam. The flanges on the bottoms of the posts are bolted in to the concrete floor and the concrete floor was poured on top of heavy duty visqueen (if that matters at all).

I am familiar with the proper wiring requirements for running the romex from the outlets to the breaker panel, etc, and I will be using GFCI setups.

It is an unfinished basement with the standard air ducts, plumbing, gas piping, wiring, etc, and I will be using conduit for the drops from the ceiling joists.

Do I need to install wood backing under the metal junction boxes? If I install the junction boxes directly on the steel posts won't that create a potential grounding problem? Should I be isolating the pole from the junction box or boxing in the poles so that they can't come in contact with metal parts/equipment in the shop or heaven forbid some flooding in the basement?

Thanks.
 
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Old 01-31-06, 12:57 PM
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Welcome, MrDillon.

Originally Posted by MrDillon
Do I need to install wood backing under the metal junction boxes?
Absolutely not.

> If I install the junction boxes directly on the steel posts won't that
> create a potential grounding problem?

No. Grounds do not carry current unless there is a fault.



> Should I be isolating the pole from the junction box or boxing in
> the poles so that they can't come in contact with metal
> parts/equipment in the shop or heaven forbid some flooding
> in the basement?

No, no reason. Just the opposite is true.


You should ground at least one post directly to the panel with #8 or heavier copper.

Likewise, at metal objects must be bonded.
But I am guessing that such bonding might be inherent in the building construction.


If there is a fault, you want a low-resistance fault so that the breaker trips within milliseconds of when the fault occurs.
 
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Old 01-31-06, 01:09 PM
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Originally Posted by bolide
> Should I be isolating the pole from the junction box or boxing in
> the poles so that they can't come in contact with metal
> parts/equipment in the shop or heaven forbid some flooding
> in the basement?

No, no reason. Just the opposite is true.

You should ground at least one post directly to the panel with #8 or heavier copper.

Likewise, all metal objects must be bonded. But I am guessing that such bonding might be inherent in the building construction.

If there is a fault, you want a low-resistance fault so that the breaker trips within milliseconds of when the fault occurs.
Thanks for the welcome, bolide.

I never would have imagined that I would want those posts directly grounded vs. isolated. So any post that I run a direct line to should be directly grounded to the panel, right? I'm not sure if I'll run these three sets of outlets on the same breaker or seperate ones... but they'll probably be seperate so that I don't have to worry about using multiple pieces of equipment at the same time. So I should directly ground all three posts or at least ground them to each other and the center one to the panel?
 
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Old 01-31-06, 01:34 PM
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Are these posts already tied together with other steel parts of the building's framework? Or is each one completely independant of other metal framing components? Was their installation an approved/inspected one?
 
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Old 01-31-06, 01:46 PM
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Originally Posted by MAC702
Are these posts already tied together with other steel parts of the building's framework? Or is each one completely independant of other metal framing components? Was their installation an approved/inspected one?
They are independent of each other, supporting a 18"(?) deep, pressed wood beam. Yes, they were inspected and approved.

When I had the home built the combination electrician/plumber was supposed to install these outlets I'm looking at doing now, but I had him fired a week before the house was finished because I didn't like the quality of his work. ( I found hot water running to a toilet... lol ) There were only a couple of small jobs like this one open so I didn't let the contractor delay my moving in while he searched for another electrician.

Originally Posted by bolide
Likewise, all metal objects must be bonded. But I am guessing that such bonding might be inherent in the building construction.
I forgot to ask what this means? "All metal objects must be bonded".
 

Last edited by MrDillon; 01-31-06 at 01:58 PM.
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Old 01-31-06, 02:04 PM
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Originally Posted by MrDillon
I never would have imagined that I would want those posts directly grounded vs. isolated.
All metallic oxjects like this need to be bonded and grounded.


> So any post that I run a direct line to should be directly grounded to the panel, right?


Not just any post.

Every metal post in your building must be grounded to your grounding electrode system which ultimately ties to your panel, the closer the better.

There are several types of clamps that work for grounding I-beams.
You can drill and tap holes in your poles or whatever.

But good grounding is necessary no matter what.



> So I should directly ground all three posts or at least ground them
> to each other and the center one to the panel?
Yes.

I would run a continuous #6 or #8 bare solid copper from the panel to the nearest post first and from there to the next post down the line. You can run it along the beam.

If you have nothing but 20A circuits, I think you might be able to just ground each post by drilling and screwing the box to it.

But as soon as you have a 30A breaker for something, you'll need to add the bonding for each pole with something heavier.

Are you in a location at risk of lightning strikes?
 
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Old 01-31-06, 02:25 PM
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Originally Posted by bolide
Every metal post in your building must be grounded to your grounding electrode system which ultimately ties to your panel, the closer the better.

I would run a continuous #6 or #8 bare solid copper from the panel to the nearest post first and from there to the next post down the line. You can run it along the beam.

If you have nothing but 20A circuits, I think you might be able to just ground each post by drilling and screwing the box to it.

But as soon as you have a 30A breaker for something, you'll need to add the bonding for each pole with something heavier.

Are you in a location at risk of lightning strikes?
These three independent posts are the only metal objects of their sort in the house, other than the black iron gas piping. All of the water pipes are CPVC with the exception of about 2' of copper pipe in to and out of the water heater and the tubing in the heat/ac coils of the air handler (circulated hot water heats the A-Coil. The main beam being supported by these posts is wood.

Correction - Most of the breakers are 20 amp, but there are four double pole 30 amp breakers and a double pole 40 amp for the A/C.

When you say "bonded", do you mean grounding?

Would it help if I took a picture to show you what I'm talking about?
 

Last edited by MrDillon; 01-31-06 at 07:11 PM.
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Old 01-31-06, 05:21 PM
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Originally Posted by MrDillon
These three independent posts are the only metal objects of their sort in the house, other than the black iron gas piping.
The pipe needs to be grounded too within the structure - on your side of the meter.



> All of the water pipes are CPVC with the exception of about 2' of copper
> pipe into and out of the water heater and the tubing in the heat/ac coils
> of the air handler (circulated hot water heats the A-Coil.
These should be grounded via the equipment to which they are attached.



> The main beam being supported by these posts is wood.

> Most of the breakers are 15 and 20 amp, but there are double pole
> 20 amp for the A/C units and a double pole 30 amp breaker for the
> generator/welding circuit in the detached garage.

At a minimum, everything must be grounded for 30 amps.



> When you say "bonded", do you mean grounding?

Bonded means electrically connected to each other so that there is 0V potential between them.
Grounded means a lot of things, but ultimately means 0V potential with respect the to earth (ground, dirt, soil).


(0V means less voltage that you can detect - not harmful.)



> Would it help if I took a picture to show you what I'm talking about?

I think I got the idea.
You have metal parts of your building.

NEC Article 250.104 requires that (B) gas pipe and (C) structural steel must be bonded to the service panel.

You probably need to ground with #4 or #6 copper depending on the size of your service entrance conductors.

If you are an risk for lightning, you should use #4 or #2 copper for bonding.
 
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Old 01-31-06, 05:40 PM
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Originally Posted by bolide
Every metal post in your building must be grounded to your grounding electrode system which ultimately ties to your panel, the closer the better.
This is one I've never heard of or seen. Are you saying every lally column that hods up a wood girder must be bonded???
Sorry, I've never done this, nor seen it done, nor do I expect to do it in the future.


Also, be VERY careful bonding gas lines directly to the GES. Many utilities do NOT want this done. It is generally accepted that the ground contained with the circuit conductors feeding gas applainces is an adequate. There is nothing saying that the bond must be sized as a GEC.

250.104 Bonding of Piping Systems and Exposed Structural Steel
(B) Other Metal Piping Where installed in or attached to a building or structure, metal piping system(s), including gas piping, that is likely to become energized shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used. The bonding jumper(s) shall be sized in accordance with 250.122, using the rating of the circuit that is likely to energize the piping system(s). The equipment grounding conductor for the circuit that is likely to energize the piping shall be permitted to serve as the bonding means. The points of attachment of the bonding jumper(s) shall be accessible.
 
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Old 01-31-06, 06:32 PM
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Originally Posted by Speedy Petey
Are you saying every lally column that holds up a wood girder must be bonded???
Exposed structural structural steel not deliberately grounded and at risk of becoming energized.



> be VERY careful bonding gas lines directly to the GES.
> Many utilities do NOT want this done.

On their side of the meter: correct.




> It is generally accepted that the ground contained with the circuit
> conductors feeding gas appliances is an adequate.
Then it is grounded and it must be grounded.
So whether you deliberately ground it elsewhere is irrelevant.

You cannot use it as a GES.



> There is nothing saying that the bond must be sized as a GEC.
Correct.

> 250.104 Bonding of Piping Systems and Exposed Structural Steel
> (B) Other Metal Piping Where installed in or attached to a building or
> structure, metal piping system(s), including gas piping, that is
> likely to become energized shall be bonded to the service equipment
> enclosure, the grounded conductor at the service, the grounding
> electrode conductor where of sufficient size, or to the one or more
> grounding electrodes used. The bonding jumper(s) shall be sized in
> accordance with 250.122, using the rating of the circuit that is likely to
> energize the piping system(s).
> The equipment grounding conductor for the circuit that is likely
> to energize the piping shall be permitted to serve as the bonding means.


This is all about piping as I discussed previously.

What about (C) Exposed Structural Steel?
 
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Old 01-31-06, 06:46 PM
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Originally Posted by bolide
On their side of the meter: correct.
Incorrect. I mean on the customer side. My POCO prohibits it. Many do.




Originally Posted by bolide
What about (C) Exposed Structural Steel?
I would not consider a lally column "structural steel", at least in the sense the NEC uses. I guess my inspectors agree.
If you mount a metal recpetacle box to one it becomes bonded by the circuit likely to energize it.
 
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Old 01-31-06, 08:05 PM
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Originally Posted by Speedy Petey
Incorrect. I mean on the customer side. My POCO prohibits it. Many do.
They can't. The NEC (arguably) explicitly required it from 1999-2001.

Originally Posted by NEC Digest
...
However as recommended in the Fine Print Note to 250.104(B), bonding is desirable in order to negate differences in electrical potential between exposed metal surfaces.
...

One further point on this issue is to emphasize that the bonding connections required by the 1999 and 2002 NEC as well as the requirement contained in NFPA 54 are just that - requirements for bonding the gas piping - and are not contrary to 250.52(B) or the requirement in NFPA 54, which prohibit the use of underground metal portions of gas piping as a grounding electrode.

For obvious safety concerns, gas utilities want to prevent their underground piping systems from becoming an electrical conductor for unwanted current. Gas utilities typically electrically isolate their below grade metal piping systems from the systems installed in and on homes and businesses.



> I would not consider a lally column "structural steel", at least in the sense
> the NEC uses.

If you remove them, would the structure collapse?
If so, then it is no stretch to call them structural if they have exposed steel.
They are bolted in - not temporary supports.

(I will buy the argument that they might not be interconnected by the concrete - I guess no rebar or steel mesh, a resistance check would verify this. Less than 25 ohm means to me that they are interconnected.)


> If you mount a metal receptacle box to one it becomes bonded by the circuit likely to energize it.

That's nice and I could go along with it.
However, a steel jack is not "other metal piping" (250.104(B)).
Where is this permission in the NEC for exposed steel that permits use of only the circuit's EGC?

All exposed structural steel that is not intentionally grounded and might become energized shall be intentionally bonded to the system at the specified locations. How likely it is to become energized could be debated.
But it is at ground level and could come into contact with electrical equipment.
 
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Old 01-31-06, 08:15 PM
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Originally Posted by bolide
They can't. The NEC (arguably) explicitly required it from 1999-2001.
What if my area, and/or many others, are not under the direct NEC?
Like I said, many areas prohibit it. No all areas. Many do have ammendments to the NEC.
I am not required to install AFCIs. Are they an NEC requirement?
 
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Old 01-31-06, 08:20 PM
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Originally Posted by Speedy Petey
What if my area, and/or many others, are not under the direct NEC?
And the gas co is the authority having jurisdiction over what you do with the gas lines in your house?

Sure, if they are going to shut off your service, don't directly bond them.
Gas pipes are still bonded indirectly many ways.
If your neutral breaks off, the gas line will be energized exactly the same with or without a direct bond.



> I am not required to install AFCIs. Are they a NEC requirement?
For certain rooms. I think you know this already.
 
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Old 01-31-06, 08:24 PM
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The AFCI question was hypothetical. I thought that was obvious.
I guess you haven't seen my profile.
 
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Old 01-31-06, 08:32 PM
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Originally Posted by bolide
And the gas co is the authority having jurisdiction over what you do with the gas lines in your house?

Sure, if they are going to shut off your service, don't directly bond them.
Gas pipes are still bonded indirectly many ways.
If your neutral breaks off, the gas line will be energized exactly the same with or without a direct bond.
Yes, they are, especially since they are both the gas and electric suppliers.

The second part I don't even get your point, but I'd rather not have an explanation. I think we've hijacked this thread enough.
 
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Old 01-31-06, 08:43 PM
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I think MrDillon has what he needs by now. If not, MrDillon, you can start a new thread.
 
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