Grounding

[iwire]

Ampacities of conductors in the typical sense are not of the conductors themselves, but rather that of insulation and connection degradation. With a grounding busbar there is no insulation degradation at issue.

A bus bar does not float in the air without any equipment or conductors connected to it.

There will likely be insulated conductors or equipment connected to any bus bars. Even the insulting mounting feet often used with bus bars have temp rating. The bus bar can not be used in a way that overheats those other components.

 

[Smart $]

A bus bar does not float in the air without any equipment or conductors connected to it.

There will likely be insulated conductors or equipment connected to any bus bars. Even the insulting mounting feet often used with bus bars have temp rating. The bus bar can not be used in a way that overheats those other components.

That's quite correct. I don't believe I wrote anything contrary to that... and in the case of most grounding busbars, there are no insulating mounts at issue either. The proximity to any insulating material will be an issue, but not regarding the ampacity of the grounding busbar.

 

[iwire]

That's quite correct. I don't believe I wrote anything contrary to that...

You without a doubt implied that.

The proximity to any insulating material will be an issue, but not regarding the ampacity of the grounding busbar.

Proximity?

No one said that the GECs in question where bare.

Most of the GECs and EGCs we run are in fact insulated.

It would be a violation to run that bus bar at a higher temp than any of the conductors connected to it.

I have to ask.

Why is this so difficult?

The NEC specified a size 1/4" x 2", there is a reason a size was given and the only logical conclusion is that has to do with the ampacity.

 

[George Stolz]

I have to ask.

Why is this so difficult?

The NEC specified a size 1/4" x 2", there is a reason a size was given and the only logical conclusion is that has to do with the ampacity.

The reasons it's difficult for me to accept as fact are, it's the first time I've thought of it that way, so before I can lock it in as a given in my head I have to explore it from all sides. I don't have a lot of time to think about it, and search on it, so that's why it's been strung out over days for me.

Second, the permutations come into play in my head. Does that dimension include the holes for terminating, or is that in addition to the volume with holes?

Third, does anyone make a grounding busbar that big? I've never seen one (that springs to mind). Does it have holes for terminating 6, or would it be sized for 1/0 to 250 and I'd have to do something to legally terminate a 6 in it? Would it be custom made?

Fourth, If it's not a shelf item, then why was it written into code?

It's not that I doubt what you're saying at all, Bob. My BS-o-meter isn't letting this one through, but it's not because I think you're BS'ing me. What you're saying makes sense.

If you have the time to search for a big busbar like we're talking about, that would speed me up quite a bit - I tried looking last night and didn't have success.

 

[petersonra]

Why is this so difficult?

The NEC specified a size 1/4" x 2", there is a reason a size was given and the only logical conclusion is that has to do with the ampacity.

I don't agree. if ampacity was the issue the wording would have made that clear. I agree with George on this one. The code says 1/4 X 2. It does not give a third dimension, nor does it say which of the two dimensions they are. it can be 1/4 X 2 X anything and meet this requirement.

you cannot make up stuff in the code by saying it is implied.

Now, having said that, what happens if you took a piece of copper foil that was 1/4 X 2. Clearly that does not meet the requirements because it is not bar stock.

But what is the effective difference if I used a 1/4X2X1 piece of bar (legal in your mind) versus a 1/4X1X2 piece of bar (not legal by your reasoning).

 

[iwire]

you cannot make up stuff in the code by saying it is implied.

Now, having said that, what happens if you took a piece of copper foil that was 1/4 X 2. Clearly that does not meet the requirements because it is not bar stock.

But it would be code compliant according to George and yourself as it has the required dimensions.

To me this is so much about nothing.

A bus bar is a conductor.

When the NEC indicates a conductors dimensions it is almost always it's cross section not it's length that is indicated.

 

[winnie]

Bob,

You have a good point that when the NEC specifies conductor cross section, that length is generally not specified. IMHO a 1/4" by 2" bus bar identifies something that is 1/4" thick, 2" wide, and of arbitrary length.

However I think that talking about the 'ampacity' of this 'conductor' is something of a red herring. A 1/4" by 2" bus bar has a cross section of 250 * 2000 * 4/pi = 637kcmil, far larger than the largest required grounding electrode conductor that you've mentioned; additionally the size requirements are the same for aluminium or copper, even though aluminium is a poorer conductor. I suspect that in this case, the size requirement is there for mechanical reasons, not for ampacity reasons.

That said, I agree that a bar 1/4" thick, 2" wide, and 1/2" long, with a row of holes through the 1/2" by 2" face, and screws in the 1/4" by 2" face, probably does not meet what the CMP intended...though it _may_ meet the requirements of the words written down

-Jon

 

[iwire]

However I think that talking about the 'ampacity' of this 'conductor' is something of a red herring. A 1/4" by 2" bus bar has a cross section of 250 * 2000 * 4/pi = 637kcmil, far larger than the largest required grounding electrode conductor that you've mentioned; additionally the size requirements are the same for aluminium or copper, even though aluminium is a poorer conductor. I suspect that in this case, the size requirement is there for mechanical reasons, not for ampacity reasons.

I don't see it as a red herring I see it as 'keep it simple'.

A buss bar with a cross section of 2" x 1/4" of either material and a large number of holes drilled in it will have an ampacity of at least the conductors connected to it...every time without fail.

If they went the other way with this we would have to calculate the size of the bar and the losses from drilling holes in it.

Much easer to give a one size fits all approach.

The NEC does not have to worry about the size for mechanical reasons as the installer will have to pick a bar large enough to fit all the conductors.

I guess George or I will have to look through the 2005 NEC proposals to see if we can get some more info on this recent addition to the NEC.

 

[benaround]

Just to add, an equipment grounding bar is not a "bus bar" and the code

says "bus bar".

Also I agree 1/4 x 2 bus bar can be any lenght.

George, they do make grounding bars for large conductors, use them on

transformers all the time, still it is not a bus bar!!!

 

[Smart $]

You without a doubt implied that.

I most certainly did not. Can't help if you read it that way!

Proximity?

No one said that the GECs in question where bare.

Most of the GECs and EGCs we run are in fact insulated.

It would be a violation to run that bus bar at a higher temp than any of the conductors connected to it.

Actually I was referring to all dielectric insulation but mostly that of energized conductors, even if the GEC's and EGC's are bare.

I have to ask.

Why is this so difficult?

It's not. You want to keep it simple... but you want everyone to do so in your terms. In your attempts to make it so, you make it more complex.

The NEC specified a size 1/4" x 2", there is a reason a size was given and the only logical conclusion is that has to do with the ampacity.

Not the only logical conclusion. You see it as ampacity. I see it as heat dissipation. But the net effect is they are one and the same.

 

[Smart $]

That said, I agree that a bar 1/4" thick, 2" wide, and 1/2" long, with a row of holes through the 1/2" by 2" face, and screws in the 1/4" by 2" face, probably does not meet what the CMP intended...though it _may_ meet the requirements of the words written down

-Jon

Actually, in order for a cross-sectional dimension specified as 1/4" x 2" to physically be a bar, it would have to be at least 2" long. Anything shorter, and the 2" dimension becomes the length and the cross sectional dimensions would be 1/4" x (something less than 2"). Cross sectional dimensions of any bar are always the smaller of the three.

 

[Smart $]

If you have the time to search for a big busbar like we're talking about, that would speed me up quite a bit - I tried looking last night and didn't have success.

BIG busbar?

Actually the one I linked above is comparatively a small one.

 

[iwire]

BIG busbar?

Actually the one I linked above is comparatively a small one.

Nice link, thanks that is what I have had in my mind, its even close to the dimensions I had mentioned earlier 12" x 2" x 1/4"

 

[George Stolz]

A picture is worth a thousand words.

That makes sense.

So, if you mount that sunuvagun in a subpanel, you'd be good to go.

The wording in that section needs to be revised, IMO.

 

[roger]

We use Harger and also make our own from copper stock, see an example below of a 1/4" x 3" bar we cut from stock.

Roger

 

[mark32]

Hi, I'd like to go back to the original post for a moment because what he describes is identical to the setup at my parent's house. That being, the main is outside with the meter, from there a #4 copper hits a ground rod, 70' away lies the sub-panel in which another #4 copper is run from the grounding bar to the cold water pipe 10' away. Now I'm assuming the contractor determined the water pipe had less than 10' in contact with the ground so instead of running the #4 all the way back to the service, he just came out of the sub-panel which would be bonded to the service via the equipment ground in the SE. The question is, is this water bond code compliant? After reading 250-104(a)(1) I don't believe it is.

 

[George Stolz]

No, I don't think it's compliant by today's code, but I wouldn't sweat it. If your parents lived in a duplex, what was done would be legal (250.104(A)(2)).