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#60278 - 12/27/05 08:12 AM 250.30(A)(4)
goodwill Offline

Registered: 08/23/04
Posts: 53
Loc: Madison, WI, USA
hi all, I'm about tackle a project and could use some advice. in my facility, we have multiple transformers that I will be grounding to one Grounding Electrode Conductor in an old 5 story building. In reading the NEC and the handbook, I have a pretty good idea of how I will be going about the install. (except the taps) the code offers 3 options. is there a listed connector you could suggest using? there is limited space in the riser closet, but that is where it will be tapped. I would like room for easy expansion in the future..(i.e., more transformers), so is the best option for me to use a listed connection to some type of busbar? if you've done this type of installation before, please offer any tips or links. thanks.

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#60279 - 12/27/05 03:30 PM Re: 250.30(A)(4)
ShockMe77 Offline

Registered: 06/11/05
Posts: 823
Loc: Rahway, New Jersey
Hmm. I've never done the work you are describing but I'll take a stab at it anyhow. I believe the 2005 NEC says that 3/0 copper should be the common grounding electrode conductor size for a multiple story building. You'll also need to use a split-bolt connector to tap off the common conductor to each sub-panel location. But I'm sure you already knew this.

If I am wrong about any of this, feel free to correct me.

Good luck!

#60280 - 12/27/05 04:39 PM Re: 250.30(A)(4)
codewarrior Offline

Registered: 12/26/05
Posts: 17
Loc: Camden,New Jersey
Hi new from South Jersey ,what type of construction is your building if it is steel contruction You can look up article 250.52, it allows You to use the building steel structure if it follows 1 of the 4 requirements?
I hope this helps,any corrections or opinions appreciated

#60281 - 01/26/06 09:54 AM Re: 250.30(A)(4)
goodwill Offline

Registered: 08/23/04
Posts: 53
Loc: Madison, WI, USA
thanks for the comments, guys. just to update, after talking it over, I chose the method of bonding each transformer to nearest building steel, and bonding building steel to the incoming water line. thanks again.

#60282 - 01/26/06 11:35 AM Re: 250.30(A)(4)
mshaw Offline

Registered: 01/11/06
Posts: 45
Loc: Fairborn, Oh, USA
I have never tackeled that one but I thought that each transformer needs to be treated as a stand alone installation, meaning you could not use a common electrode. Building steel is one good option a few points to ponder as codewarrior said. I have multipal transformers in my facilities each treated as a stand alone unit. They put off a lot! of heat so keep that in mind when you do your install and future expansion options. I have several electrical rooms that I am looking hard at adding some form of additional ventilation to cool the area. Also if there is a load factor noise is a consideration as well. Put them on a load and they will hummmm right along and drive clients nuts.

#60283 - 01/26/06 12:06 PM Re: 250.30(A)(4)
electure Offline


Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
Take a look at 250.30 (A)(3) for tapping a common grounding electrode conductor.

Also see 250.30(A)(2)b re: Multiple Separately Derived Systems and sizing the GEC

[This message has been edited by electure (edited 01-26-2006).]

#60284 - 01/26/06 03:14 PM Re: 250.30(A)(4)
Dnkldorf Offline

Registered: 12/12/04
Posts: 1091
Loc: nowhere usa
mshaw, if your transformers are putting off alot of heat, and are loud as you state, you could have the wrong transformers for the application....

Transformers do put off heat, but that and the noise can be dealt with, using a different transformers...



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