Metal building shell

[marshallf3]

I'm working on an old metal building 100' x 200' and none of the metal is in contact with the earth. Of course like most old buildings I run into there's not a grounding rod one even at the service entrance.

From the way I read 250.52 if I properly ground at the service entrance junction box, and if that box is bonded to the metal building I'm OK?

In my opinion, and some may consider this overkill, but on a building that old and that large wouldn't I have an advantage not only adding the required ground at the service entrance but also driving ground rods at each corner of the building and bonding them to the metal shell?

 

[jwelectric]

In my opinion, and some may consider this overkill, but on a building that old and that large wouldn't I have an advantage not only adding the required ground at the service entrance but also driving ground rods at each corner of the building and bonding them to the metal shell?

When you do this you have the metal building part of the electrode system

 

[mdshunk]

I'm not so sure that barn tin is rated for use as a grounding electrode conductor.

 

[wbalsam1]

I'm working on an old metal building 100' x 200' and none of the metal is in contact with the earth. Of course like most old buildings I run into there's not a grounding rod one even at the service entrance.

From the way I read 250.52 if I properly ground at the service entrance junction box, and if that box is bonded to the metal building I'm OK?

In my opinion, and some may consider this overkill, but on a building that old and that large wouldn't I have an advantage not only adding the required ground at the service entrance but also driving ground rods at each corner of the building and bonding them to the metal shell?

I think you would have to tie the ground rods all together into the grounding electrode system and not "hitchhike" thru the building metal sheathing, sidings or veneers. JMO. Seems like too high a resistant path your way.

 

[LarryFine]

I'm working on an old metal building 100' x 200' and none of the metal is in contact with the earth.

Is the framing wood or metal? If metal, is the foundation concrete?

 

[ecirplr]

This brings up another point. During the 50's and forward, aluminum siding became the rage. My father-in-laws house has this application and the siding is not grounded at any point. Most of the older homes utilized SE or "rag" services and the siding was just notched to allow the SE to exit to connect to the overhead sevice. Offering no protection from accidentally nicking the wire and electrfying the exterior. Since the siding is not grounded/bonded this could create a serious safety issue as for I am concerned.

 

[marshallf3]

The framing is welded metal pipe and I beams and yes, it's built on a concrete slab with high stem walls thus no earth contact, All the internal wiring (and there's a ton of it, building's been partially rewired at least once) is in EMT. At one point in time this building was a manufacturing plant and has tons of both single and three phase outlets throughout.

I'll probably check voltage drop differences using a load to compare the difference between the neutral and the ground conductors at various points to verify that all the EMT is still well bonded.

No , I don't expect perfect continuity throughout all the barn tin. It's all screwed to the framing but I'd expect some corrosion throught all the years.

I plan to of course obtain my main ground at the service entrance which, with the EMT, should provide a good ground path to for safety reasons at all the outlets, my main concern is there are a lot of trees at the end of the building opposite the service entrance and a lightning stike to the building at the far end might wreak havoc.

My thoughts are that by grounding the building shell at several locations might help form the building structure into more of an "envelope" and lessen the chance of the energy having to travel all the way through the internals. Should a lightning strike try to travel through 200' of EMT (which would probably be the path of best continuity) my guess is a fair amount of voltage could present itself at the recepticle grounds along the way thus presenting a hazard to anyone operating machinery along the way - not to mention what it could do to some of the sensitive computerized equipment that is going to be used.

 

[petersonra]

I think you are worried about the wrong things. the chance of lightning striking the building is fairly remote in the first place. its been there all this time. Do you see any signs of lightning striking it? What makes you think it is likely to get hit now?

 

[stickboy1375]

Even if lightning did hit the building, you think a ground rod is really going to save the building?

 

[mdshunk]

This brings up another point. During the 50's and forward, aluminum siding became the rage. My father-in-laws house has this application and the siding is not grounded at any point. Most of the older homes utilized SE or "rag" services and the siding was just notched to allow the SE to exit to connect to the overhead sevice. Offering no protection from accidentally nicking the wire and electrfying the exterior. Since the siding is not grounded/bonded this could create a serious safety issue as for I am concerned.

I was involved in one minor house fire in which the service neutral went open, and the siding had arc marks at nearly every place where pieces overlapped. The siding was carrying at least some of the neutral current at that point.

 

[iwire]

Most of the older homes utilized SE or "rag" services and the siding was just notched to allow the SE to exit to connect to the overhead sevice. Offering no protection from accidentally nicking the wire and electrfying the exterior. Since the siding is not grounded/bonded this could create a serious safety issue as for I am concerned.

There is no way that Aluminum siding could be bonded well enough to make it safe with a service conductor fault.