Transformers

[dnunez]

I have an inspector that is adament about bonding of my XFMR's. He is requesting that we provide both a bond for building steel or UFER as well as cold water bond. After reviewing the code I feel that bonding to any one of these should satisfy this requirement. what do you think?

 

[kentirwin]

Re: Transformers

It could just be a requirement of your particular jurisdiction. I have run into the same thing here in southeastern Virginia.

 

[iwire]

Re: Transformers

The inspector IMO is more or less correct.

There are two things going on, first is the need for a grounding electrode at an SDS, that is covered in 250.30(A)(4)

250.30(A)(4) Grounding Electrode. The grounding electrode shall be as near as practicable to and preferably in the same area as the grounding electrode conductor connection to the system. The grounding electrode shall be the nearest one of the following:

(1)An effectively grounded structural metal member of the structure

(2)An effectively grounded metal water pipe within 1.5 m (5 ft) from the point of entrance into the building

Exception: In industrial and commercial buildings where conditions of maintenance and supervision ensure that only qualified persons service the installation and the entire length of the interior metal water pipe that is being used for the grounding electrode is exposed, the connection shall be permitted at any point on the water pipe system.

(3)Other electrodes as specified by 250.52 where the electrodes specified by 250.30(A)(4)(1) or (A)(4)(2) are not available

Exception to (1), (2), and (3): Where a separately derived system originates in listed equipment suitable for use as service equipment, the grounding electrode used for the service or feeder shall be permitted as the grounding electrode for the separately derived system, provided the grounding electrode conductor from the service or feeder to the grounding electrode is of sufficient size for the separately derived system. Where the equipment ground bus internal to the service equipment is not smaller than the required grounding electrode conductor, the grounding electrode connection for the separately derived system shall be permitted to be made to the bus.

Notice that you must use either building steel or a water pipe whichever is available for a grounding electrode.

Only if neither of those are available can you use other grounding electrodes like uffers or rods.

Now the second issue is bonding to the SDS.

These requirements are spelled out in 250.104(A)(4)

250.104(4) Separately Derived Systems. The grounded conductor of each separately derived system shall be bonded to the nearest available point of the interior metal water piping system(s) in the area served by each separately derived system. This connection shall be made at the same point on the separately derived system where the grounding electrode conductor is connected. Each bonding jumper shall be sized in accordance with Table 250.66.

Exception: A separate water piping bonding jumper shall not be required where the effectively grounded metal frame of a building or structure is used as the grounding electrode for a separately derived system and is bonded to the metallic water piping in the area served by the separately derived system.

The result is this.

If you used building steel or one of the other permitted grounding electrodes (other than the water line) you still need to bond the water line.

[ June 04, 2005, 08:24 AM: Message edited by: iwire ]

 

[pierre]

Re: Transformers

To add to Bob's post, the bonding of the other system (water or steel) does not have to be terminated in the transformer.
Say you used the steel as your electrode, you could run a conductor from the steel to the waterpipe.

 

[dnunez]

Re: Transformers

Thanks Guys

 

[ryan_618]

Re: Transformers

This section bothers me a bit. The two items in question are already required to be bonded for the first (not SDS) system. Once we have used one as the electrode for the SDS, it seems to me that the other is taken care of automatically. Does the installer really have to do anything to satisfy 250.104(D)?

 

[don_resqcapt19]

Re: Transformers

Ryan,
250.104(D) requires a "local" bond.

... The grounded conductor of each separately derived system shall be bonded to the nearest available point of the interior metal water piping system(s) in the area served by each separately derived system. ...

 

[dnunez]

Re: Transformers

Don, The Exception states that "a seperate water piping bonding jumper shall not be required where the effectively grounded metal frame of a building or structure is used as the grounding electrode for a SDS and is bonded to the metallic water piping in the area served by the SDS."

[ June 06, 2005, 05:15 PM: Message edited by: dnunez ]