Electrical Room Ground Bus

JoeStillman

Senior Member
Location
West Chester, PA
I've surveyed many old-fashioned electrical rooms with ground bus mounted to the wall all around the room. I never understood why that was done that way. Is anybody still doing this? And why?

I like to specify a grounding electrode collector bus that is external to the service entrance, but that's just 2 ft of 4" x 1/4" copper. Why run it all around the room?
 

kwired

Electron manager
Location
NE Nebraska
I've surveyed many old-fashioned electrical rooms with ground bus mounted to the wall all around the room. I never understood why that was done that way. Is anybody still doing this? And why?

I like to specify a grounding electrode collector bus that is external to the service entrance, but that's just 2 ft of 4" x 1/4" copper. Why run it all around the room?
Gives designer or even owner a good feeling inside, sort of like audiophiles wanting oxygen free cables for their sound equipment.
 

powerpete69

Senior Member
Location
Northeast, Ohio
Occupation
XXX
I've surveyed many old-fashioned electrical rooms with ground bus mounted to the wall all around the room. I never understood why that was done that way. Is anybody still doing this? And why?

I like to specify a grounding electrode collector bus that is external to the service entrance, but that's just 2 ft of 4" x 1/4" copper. Why run it all around the room?
If you were to run that bus all the way around the room, you can easily ground any load by tightening a screw down on it. Very convenient I suppose.
If you run a bare ground wire all the way around the room, you can also add grounds to it but now you need a grounding clamp (barely tougher) or perhaps the drawings specify that you would need to CAD weld (definitely tougher)
It's not code to run the ground bus mounted all the way around the room, but if its already there, fantastic.
You can certainly connect all the grounds from the room into the small 2 feet of 4" of 1/4" copper, but it may be more cost effective to just run a ground wire all the way around the room and clamp on to each load from there. I think there is some flexibility here.
 

petersonra

Senior Member
Some things are/were just done for no really good reason.

Like running a wire type EGC inside of a rigid metal conduit.

I once had an engineering firm specify that all enclosures had to have provision for a 2/0 (or maybe it was 4/0 - was a long time ago) ground wire connection both incoming and outgoing. I tried to get them to allow an exception for small junction boxes. I had a bunch of them that were like 4 X 6 inches. No deal. I ended up having two large mechanical ground lugs installed on each junction box. The lugs were almost as big as the boxes.
 

mshields

Senior Member
Location
Boston, MA
I endevour NOT to be one of those engineers by always listening and respecting the guys who do the actual installing. Yours is a different expertise that ought to be viewed as compliments ours. What arrogance to have you bring this impractical and pointless design to their attention and for them still to insist on it. No doubt he was one of those guys who thinks a couple of letters after his name gives him a kind of electrical infallibility.
 

tom baker

First Chief Moderator
Staff member
Could these installations be done before the adoption of 277/280 Y in the 70's? before that there was delta and ungrounded delta, so maybe it was a way to easily 'ground' equipment
Mike Holt has a good story about this type of work, were its done for no reason other than thats the way we've done it.
Probably the best example is ground rods at metal street light poles
 

kwired

Electron manager
Location
NE Nebraska
Some things are/were just done for no really good reason.

Like running a wire type EGC inside of a rigid metal conduit.

I once had an engineering firm specify that all enclosures had to have provision for a 2/0 (or maybe it was 4/0 - was a long time ago) ground wire connection both incoming and outgoing. I tried to get them to allow an exception for small junction boxes. I had a bunch of them that were like 4 X 6 inches. No deal. I ended up having two large mechanical ground lugs installed on each junction box. The lugs were almost as big as the boxes.
And you probably entered that box with only 1/2 or 3/4 raceways, like you were going to pull 2/0 through that?

First of all if you are running any 2/0 conductors you are going to be in that 6 or 8 times the raceway diameter range as a minimum dimension for the box. (We need the slaping forehead emoticon that was on the old forum inserted here)
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
I've surveyed many old-fashioned electrical rooms with ground bus mounted to the wall all around the room. I never understood why that was done that way. Is anybody still doing this? And why?

I like to specify a grounding electrode collector bus that is external to the service entrance, but that's just 2 ft of 4" x 1/4" copper. Why run it all around the room?
Was the ground bus around the room mounted up high near the ceiling or was it down low and more accessable? Sometimes they have a "halo" ground ring up high on the wall for lightning protection, and it's used mostly to bond metal objects and metal parts of the building structure.
 

JoeStillman

Senior Member
Location
West Chester, PA
Was the ground bus around the room mounted up high near the ceiling or was it down low and more accessable? Sometimes they have a "halo" ground ring up high on the wall for lightning protection, and it's used mostly to bond metal objects and metal parts of the building structure.
Usually, it's down low.

The reason I asked is because it's still a thing in the AIA Masterspec;

Masterspec section 260526 said:
E. Grounding Bus: Install in electrical equipment rooms, in rooms housing service equipment, and elsewhere as indicated.
1. Install bus horizontally, on insulated spacers 2 inches (50 mm) minimum from wall, 6 inches (150 mm) above finished floor unless otherwise indicated.
2. Where indicated on both sides of doorways, route bus up to top of door frame, across top of doorway, and down; connect to horizontal bus.
 

petersonra

Senior Member
And you probably entered that box with only 1/2 or 3/4 raceways, like you were going to pull 2/0 through that?

First of all if you are running any 2/0 conductors you are going to be in that 6 or 8 times the raceway diameter range as a minimum dimension for the box. (We need the slaping forehead emoticon that was on the old forum inserted here)
Off the top of my head, I do not recall if the lugs were inside of the box or on the outside. They might have been on the outside. I do recall they made us put two similar size lugs on the skid of every piece of equipment too. I never did quite figure out what the thinking was.

No way for me to know where the ground wire was going to come in anyway so I think I just had them put all the lugs for the equipment on the front. Or maybe the back. Its a good bet if I had them installed on the front of the equipment the ground wire came in from the back, and vice versa.

Why they could not supply their own ground lugs escaped me.
 
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