Bonded to building Steel Structure Frame

I need some help here from some of you electrical Gurus’ on this one.
I realize this is far from an HI Sop, but I deal with this everyday.

The question; An existing building built in 1984, steel frame and wood exterior with brick. Added on 8,000 s.q. ft. in 1996.

I added on 8000 more sq. ft. but mechanically bonded by building steel.

New 2,000 amp service added and bonded to the steel structure. All is fine.

Right now, adding another wing, 10,000 sq. ft. with complete isolation from the other building with expansion joints.
The power for the new addition for three 100 amp panels is being fed from the existing building 2,000 amp service.

The new building is not bonded with the rest of the building steel of the existing.

Is this right?

The Electrical Engineer is saying not a problem.
The electrical foreman’s gut feeling that I asked, said it should be bonded steel to steel to mate all the structures together. I feel the same way.
One jumper cadwelded column to column 12" apart will bond the whole complex together back to the Main SwitchGear.

What do you experts believe or think is the right way?

Appreciate any input.

Thanks in advance.

Marcel :slight_smile: :slight_smile:

Cad welding may be overkill but I would certainly bond the building steel segments with a 250.66 sized jumper using listed lugs.

Thanks Greg.


Without too much detail the answer is yes, it needs to be bonded to the exisiting structual steel…if indeed the structual steel is bonded to the GES as it should if structual .

Are the building attached together by chance?

Thanks Paul;

This last addition to the main structure is completly isolated with expansion joints, but there is an area where steel column of one building and the other column are only 12" apart and there is where I think a bonding jumper should be installed, since all the other building are mechanically bond this one should too, no?


Marcel :slight_smile:

Whether or not required by code, IMHO, it is always a good practice to bond metal structures together whenever they are close enough to each other to be be touched simultaneously by a person. Certainly 12" would qualify. It is a very commonly done in industrial settings to make certain different potentials do not exist between structures. With respect to how, I don’t think cadweld is overdoing it as it is the most secure, long-term attachment method and is difficult to remove. 4/0 stranded copper would be to commonly-used conductor size, routed in aluminum conduit in such a way as to avoid likely mechanical damage.

I will agree with Frank’s comment with the bonding termation between the building 4/0 CU will serve just fine and yeah , cadweld is very common useage as the lug/bolt set up as well too.

Merci, Marc

Thanks guys, this just reiforces my exact feeling of how I felt about it and the electrical Contractor will do just that.


Marcel :slight_smile: :slight_smile:

Remember Marcel…since both buildings are sharing a common service as well the bonding of one building should convey to the other…also a good thing to always remember is if the building is to be considered connected to form a single building…again since service or additional service to the same building…the GES must be tied together.

But alas…your GUT was right…you know why…Because you are a good inspector.

Thanks Paul and I appreciate that interpretation.

Talked to the electrical Foreman today about all the help I get on this Board and he replied, you have got yourself a good and usefull tool in your hands.

Unlike the Engineers RFI response. Which is request for information.

His answer was to not worry about it. That is easy to figure why, because he did not call for it and afraid to pay for it and God Bless his soul because he is not going to pay for it and it will be done, (the righteous way) ha. ha.

Thanks again Paul and all the other guys to.

Marcel :slight_smile: :smiley:

Thanks guys, and I took your reccommendations and got it done.
Now the three buildings are all bonded together.

Marcel:) :slight_smile:


The code states that any part of a building that might get energized MUST be bonded.