Bonding Xfmrs on Multi Story Building

[aklb05]

We are currently working on a multi story building. My question is that the plumbing contractor used a combination of stainless steel and copper piping with dielectric unions. If we bond the cold water line, then what happens to the potential between the floors where the stainless is being used? Does the NEC reference such a situation? Can we run a separate conductor up and bond the xfmrs that way in lieu of the water piping or can we bond to water pipes as they were described above?

Thanks

 

[chris kennedy]

We are currently working on a multi story building. My question is that the plumbing contractor used a combination of stainless steel and copper piping with dielectric unions. If we bond the cold water line, then what happens to the potential between the floors where the stainless is being used? Does the NEC reference such a situation?

It does.

250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
(1) Metal Underground Water Pipe. A metal underground water pipe in direct contact with the earth for 3.0 m (10 ft) or more (including any metal well casing bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joints or insulating pipe) to the points of connection of the grounding electrode conductor and the bonding conductors. Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall not be used as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system.
Exception: In industrial, commercial, and institutional buildings or structures where conditions of maintenance and supervision ensure that only qualified persons service the installation, interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall be permitted as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system, provided that the entire length, other than short sections passing perpendicularly through walls, floors, or ceilings, of the interior metal water pipe that is being used for the conductor is exposed.

Can we run a separate conductor up and bond the xfmrs that way in lieu of the water piping or can we bond to water pipes as they were described above?

You can. But this allows you to save money.

250.30(A)(4) Grounding Electrode Conductor, Multiple Separately Derived Systems. Where more than one separately derived system is installed, it shall be permissible to connect a tap from each separately derived system to a common grounding electrode conductor. Each tap conductor shall connect the grounded conductor of the separately derived system to the common grounding electrode conductor. The grounding electrode conductors and taps shall comply with 250.30(A)(4)(a) through (A)(4)(c). This connection shall be made at the same point on the separately derived system where the system bonding jumper is installed.

Welcome to the Forum.

 

[RUWired]

Does the NEC reference such a situation? Can we run a separate conductor up and bond the xfmrs that way in lieu of the water piping or can we bond to water pipes as they were described above?

Thanks

If i can add to Chris's post, 250.104(D)3 also requires the building steel or area water pipes to be bonded to.
Rick