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Posted By: jsherrard grounding electrode system bus - 02/12/05 08:32 PM
Here's what I have ... an service consisting of (2) 400A, 120/240V, 1ph panels, each being fed with (2) 250kcmil copper per phase and neutral. I have a 4" metal water pipe (more than 10' in contact with earth) and a #5 rebar stubbed out of the footing as my grounding electrodes. I want to set up my grounding electrode system this way ... mount a 1/4" thick x 2" wide x 6" long aluminum bus on the wall above the lay-in ceiling at the service location. A 2/0 copper GEC will run from the 4" water main to the grounding bus. A #4 solid copper GEC will drop down and connection to the rebar. One 1/0 copper GEC will connect from the grounding bus to the neutral bar in each of the (2) 400A panels. (one 1/0 for each panel) The GECs will connect to the bus with standard one-hole lugs bolts to the bus bar. Does anyone see a problem? This seems to be allowed under the new language of 250.64(C)(3) in the '05 NEC. Other than the bus and all connections being accessible, is there any other consideration to look at?
Posted By: shortcircuit Re: grounding electrode system bus - 02/12/05 09:23 PM
The problem I see with your arrangement is that the GEC should be continuous from the grounding electrode(which is the 4" water main) to the grounding terminal bar or bus within the service equipment...250.24(A)(1)

If you were to hit the service equipment first with the GEC and then back to the bus for bonding of other available electrodes, the installation would then be inline with the requirements of 250.64(C)(3)

shortcircuit
Posted By: jsherrard Re: grounding electrode system bus - 02/14/05 01:10 PM
My understanding of the new provision in the '05 code is that the parallel 1/0's from the busbar to the service panels are the unspliced GEC and that all the available grounding electrodes can then be connected to the busbar. Does this make sense?
Posted By: iwire Re: grounding electrode system bus - 02/14/05 02:01 PM
jsherrard

As long as your operating under a permit that was pulled after the 2005 was adopted or the inspector will allow using a 2005 change on an earlier permit it sounds fine.

I am looking at the IAEI 2005 NEC Analysis of Changes and what you describe sounds like exactly what they show.

All you need is a listed connector at the busbar. It is not required to be irreversible.

Shortcircuit

Quote
the GEC should be continuous from the grounding electrode(which is the 4" water main)

The footer is also a grounding electrode not just the water main.

Also keep in mind that this allowance of a grounding bus is new to 2005. [Linked Image]

It is found in 2005 250.64(C)(3)

Bob
Posted By: shortcircuit Re: grounding electrode system bus - 02/15/05 02:23 AM
Iwire ...how does the wording of 250.64(C)(3) allow the GEC to stop at a bus before connecting to the grounded service conductor at the service disconnecting means as specified in 250.24(A)(1)


shortcircuit
Posted By: iwire Re: grounding electrode system bus - 02/15/05 02:42 AM
Shortcircuit, I do not have the 2005 CD-Rom I will try my best to type out (3) & (4) exactly as printed. I have shortened (1) and (2) they are similar to 2002 just laid out different.

2005 NEC
Quote
250.64(C)Grounding conductor(s) shall be installed in one continuous length without a splice or joint except as permitted in (1) through (4):

(1) Addresses splicing with irreversible connections

(2) Addresses Sections of bus bar bolted together

(3) Bonding jumper(s) from grounding electrode(s) and grounding electrode conductor(s) shall be permitted to be connected to an aluminum or copper busbar not less than 6 mm x 50 mm (1/4" x 2").
The busbar shall be securely fastened and shall be installed in an accessible location. Connections shall be made by a listed connector or the exothermic welding process.

(4)Where aluminum busbars are used, the installation will comply with 250.64(A).

Bob
Posted By: iwire Re: grounding electrode system bus - 02/15/05 02:53 AM
This change that allows a grounding bus is not a big change in my opinion. Previously we could use any grounding electrode as a grounding bus.

I could run (and still can) a continuous GEC to building steel or a water pipe etc. Then I could run separate bonding jumpers to as many grounding electrodes as I wanted.

I had a service in a steel frame building about 300' from the water main, I ran a GEC from the service to building steel. Then on the other side of the building I ran a bonding jumper down to the water main this was a major time and matrial savings.

Here is a graphic from the 2002 NEC handbook that illustrates the possibilities.

[Linked Image]

[This message has been edited by iwire (edited 02-14-2005).]
Posted By: shortcircuit Re: grounding electrode system bus - 02/15/05 11:14 AM
Iwire...I fully agree with all you said about bondind onto the GEC...

But in jsherrard's 1st post he describes " a copper 2/0 GEC will run from the 4" water main to the grounding bus"..."then a 1/0 copper GEC will connect from the bus to neutral bar of each of the 400 amp panels"

This arrangement is not in concert with the requirement of 250.24(A)(1)...See exhibit 250.8 in the 2002 NEC for some other options for the GEC connection at a premises supplied AC service.

This requirement is also illustrated in the exsample that you have posted.

2005 250.64(C)(3) just adds the option of using a bus for interconnecting (bonding) all available electrodes.This bus may also be used to connect taps to other service equipment as allowed by 230.40 exception #2

shortcircuit
Posted By: iwire Re: grounding electrode system bus - 02/15/05 11:31 PM
Shortcircuit I don't know what to say.

I gave you the code as written, IMO it is quite clear.

Quote
(3) Bonding jumper(s) from grounding electrode(s) and grounding electrode conductor(s) shall be permitted to be connected to an aluminum or copper busbar not less than 6 mm x 50 mm (1/4" x 2").
The busbar shall be securely fastened and shall be installed in an accessible location. Connections shall be made by a listed connector or the exothermic welding process.


I took a picture of the 2005 IAEI Analysis of changes that illustrates this new code section. Sorry for the low quality.

[Linked Image]

Bob




[This message has been edited by iwire (edited 02-15-2005).]
Posted By: iwire Re: grounding electrode system bus - 02/15/05 11:43 PM
Here is another one from the 2005 IAEI Analysis of changes.


[Linked Image]
Posted By: shortcircuit Re: grounding electrode system bus - 02/16/05 12:46 AM
Iwire...I see those pictures do point out this change very clearly....although there are no sizes established in the pictures.

Would the jumper from the bus to the grounded service conductor in the service equipment have to be the same size as the GEC, which is based on the size of the largest ungrounded service-entrance conductor?

jsherrard's description in his post has a 1/0 connecting to each panel which is smaller than the GEC which is 2/0 from the bus to the electrodes.

shortcircuit
Posted By: iwire Re: grounding electrode system bus - 02/16/05 01:16 AM
That is a good observation one I also noticed but he is correct.

He has a 800 amp service consisting of two 400 amp panels.

The GEC tap from each panel to the grounding bus is based on only the service conductors feeding the panel it comes from.

Now the bonding jumper from the grounding bus to the water main has to be sized on the total service conductor size.

This is covered by 250.64(D)

Considering the conductors from the panel to the grounding bus are called GEC Taps and the conductors from the grounding bus to the electrodes are called bonding jumpers, the only GEC in his installation may be the grounding bus itself.

Bob



[This message has been edited by iwire (edited 02-15-2005).]
Posted By: shortcircuit Re: grounding electrode system bus - 02/16/05 10:18 AM
Ok... I read 250.64(D)...which allows this arrangement.

But...would these taps to the 400 amp panels be of sufficent size to handle the ground-fault current that may be available from utility source?

Wouldn't the size of the main ungrounded service-entrance conductors(or equivalent size) in jsherrad's (which is a 1000 circular mills) and the neutral be capable of ground-fault current greater those taps can handle?

I thought that table 250.66 bases the size of the GEC according to the largest ungrounded service-entrance conductor for this reason [Linked Image]

shortcircuit
Posted By: iwire Re: grounding electrode system bus - 02/16/05 10:39 AM
I am in a hurry and I will get back to this.

Short answer is the GEC for one particular panel only has to handle what the service conductors feeding that particular panel can supply.

Bob
Posted By: XpertEngineer1 Re: grounding electrode system bus - 08/23/21 06:55 AM
In electrical control panels, busbar (Bus bar) is a aluminium/copper strip or bar. This busbar is installed inside the panel with the help of insulators and colour coded via coloured shrinkable sleeves. Busbar can be installed in Panels, Busducts, busbar chambers for locally transmission and distribution of power.
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