Neutral to case bond

[dcspector]

I have a 4000 amp MDP on the first level of a high rise. That is the service equipment with MBJ. From there via a 2500 amp switch feeds to 2nd level to a 2500 amp switch board and distributes to other misc. equipment all within the same retail space. I may be having a brain lapse but when I ohm out neutral to frame beyond the service I am getting tone. 250.24(5) is clear as a bell to me, or is my thinking pattern incorrect?

 

[iwire]

I may be having a brain lapse but when I ohm out neutral to frame beyond the service I am getting tone. 250.24(5) is clear as a bell to me, or is my thinking pattern incorrect?

You should have neutral to ground continuity out to the last device supplied by that voltage system.

 

[dcspector]

Bob what confused me was the neutral bonded to the frames of the load side equipment.

 

[iwire]

Bob what confused me was the neutral bonded to the frames of the load side equipment.

Greg I am not sure from you description.

Did you see the bonds or did you just have tone?

 

[JohnJ0906]

Isn't the neutral solidly connected at the 2500 amp sw board, i.e., not switched? So you would read neutral-to-EGC continuity throughout the system, even with no "downstream" connection?

 

[dcspector]

Bob and John,

I think I may be the confused one here which is confusing you....sorry. What I have is the neutral bus and ground bus to frame in the 2500 amp on the 2nd level. This was fed from the 4000 on the first level which is the service. I thought the neutral had to float so to speak in the load side equipment. Maybe I should get out of the elevator code for awhile and get back to NEC...huh?

 

[RUWired]

I thought the neutral had to float so to speak in the load side equipment.

Typically the neutral and grounds are seperated down stream of the service disconnect no matter how large the down stream switch gear is. It's possible that the down stream gear has a built in transformer and the bonding jumper is installed on the secondary of that.