Grounding and bonding for equipment in seperate structures

[jaison09]

I am working on a design for an addition to an existing building. The new addition is attached to the existing building but both building steels are not connected. The new addition has a step down transformer (480V to 208/120V) connected to 208V/120V Panel. The primary of the step down transformer is connected to a 480V panel in the existing building. The design is as follows: [70A/3ph 480V circuit] in existing building is connected to 45KVA step down xfmr (grounded with #6G) via [(3)#4, (1)#8G] wire. The xfmr is connected to a 150A panel with [(4)#1/0,(1)#6G]. Is it require for the existing building steel to be mechanically bonded with the new addition steel or since the xfmr is a separately derived system the grounding for the panel is achieved? Please advise. Thank you in advance

 

[ActionDave]

....Is it require for the existing building steel to be mechanically bonded with the new addition steel or since the xfmr is a separately derived system the grounding for the panel is achieved? Please advise. Thank you in advance

Well, you gotta have an equipment grounding conductor along with the 480V hots tied to the case of the transformer in your addition, and there has to be a bond from the XO on the secondary of the transformer to the case of the transformer and to the building steel in the addition, either at the transformer or the first disconnect (250.30) so the two buildings steels are gonna be electrically connected no matter what else you do, unless somebody does something wrong.

 

[petersonra]

I am working on a design for an addition to an existing building. The new addition is attached to the existing building but both building steels are not connected. The new addition has a step down transformer (480V to 208/120V) connected to 208V/120V Panel. The primary of the step down transformer is connected to a 480V panel in the existing building. The design is as follows: [70A/3ph 480V circuit] in existing building is connected to 45KVA step down xfmr (grounded with #6G) via [(3)#4, (1)#8G] wire. The xfmr is connected to a 150A panel with [(4)#1/0,(1)#6G]. Is it require for the existing building steel to be mechanically bonded with the new addition steel or since the xfmr is a separately derived system the grounding for the panel is achieved? Please advise. Thank you in advance

If they are physically attached they may not be "separate" structures. They potentially could be considered so depending on the construction (for instance if a firewall separates them).

If they are the same structure, you have to run a GEC from the new xfmr back to the existing GES. There is nothing that says you cannot also bond to the steel in the new addition, but the GEC from the xfmr has to go to the existing GES.

If the building codes consider the new addition a separate structure, you have to bond all of the GE found in the new structure and the GEC from the transformer goes to that GES. Again there is no prohibition against bonding the GES of the existing structure to the GES of the new structure.

Keep in mind that just because there is steel in a building structure does not mean that steel is considered a GE by the code.

 

[augie47]

Since the units are connected and make it one "building", if the building steel in each section qualifies as a grounding electrode under 250.52(A)(2), then 250.50 would required the two electrodes (sections of building steel) to be bonded together.
I agree with ActionDave that they are connected thru the transformer wiring, however, 250.121 does not allow an equipment grounding conductor to serve as a grounding electrode conductor.
I think a valid call would be to require a conductor or structural member connect the two sections of the building.

(I was typing as petersona posted... hopefully we said the same thing)

 

[petersonra]

(I was typing as petersona posted... hopefully we said the same thing)

I was mostly trying to make the point that depending on the construction the new addition may or may not be a separate structure. That would affect the answer to the OP's question.

My understanding is that you can have two structures that are physically touching that are considered "separate" by the building codes.

 

[augie47]

As I unfortunately tend to do, I might have read something into the OP.
My answer was based on the premiss that the two structures were combined in such a manner that they became one "building" (code-wise). IMO, if that were the case and you ended up with two metal frames that each qualified as a grounding electrode, they would need to be bonded together per 250.50.

 

[petersonra]

As I unfortunately tend to do, I might have read something into the OP.
My answer was based on the premiss that the two structures were combined in such a manner that they became one "building" (code-wise). IMO, if that were the case and you ended up with two metal frames that each qualified as a grounding electrode, they would need to be bonded together per 250.50.

he said something about it being "addition" to the existing building which would seem to make it part of the original structure.

he also said the building steel in the addition was not connected to the building steel in the existing part which seems odd if it is part of the same structure. Some how the whole structure has to be tied together if it is a single structure.