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main bonding jumper #8838 04/06/02 05:30 PM
Joined: Jun 2001
Posts: 8
D
dom Offline OP
Junior Member
Can the manufacture supplied bonding strap in a normal 480v delta/120/208v wye transformer be used as the main bonding jumper for the separately derived system? Or must a properly sized bonding jumper be added according to the size of the secondary phase conductors?
Thanks

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Re: main bonding jumper #8839 04/06/02 11:05 PM
Joined: Aug 2001
Posts: 599
N
Nick Offline
Member
The bonding strap that comes on most transformers is to bond the core frame not to act as a MBJ. You need to install a jumper sized by table 250-66 based on the secondary phase conductors from the equipment grounding lugs to the transformer XO.

Re: main bonding jumper #8840 04/07/02 12:27 PM
Joined: Mar 2001
Posts: 2,056
R
Redsy Offline
Member
Nick,
Doesn't the neutral also have to be connected to the Grounding Electrode System?
I have seen quite a few installations that only consisted of a jumper from XO to the transformer housing.
Please comment.

Re: main bonding jumper #8841 04/07/02 01:06 PM
Joined: Aug 2001
Posts: 599
N
Nick Offline
Member
Redsy,
Yes. I always connect the neutral, GEC and bonding jumper at the XO terminal.

Where did they land the neutral?

Re: main bonding jumper #8842 04/07/02 03:29 PM
Joined: Jun 2001
Posts: 8
D
dom Offline OP
Junior Member
I always run my own MBJ from XO to a ground terminal in the xfmr. On smaller wires 1/0 and less I usually install a ground buss (having removed the paint under the buss) in the transformer to connect all the grounding conductors usually 5 or so.
1)MBJ from XO
2)grounding conductor to service equipment
3)grounding conductor routed with primary circuit to transformer
4)water bond conductor
5)GEC
On larger conductors is it ok to use several one or 2 port equipment grounding lugs for the purpose of tying all the grounding conductors together at one point?
Or is it necessary to obtain a ground buss, so the continuity of the grounding conductors isn't dependant on the transformer enclosure?
thank you

Re: main bonding jumper #8843 04/07/02 09:05 PM
Joined: Aug 2001
Posts: 599
N
Nick Offline
Member
It is not a code or listing standard that I know of but it is a good practice. I do that myself whenever possible.

Re: main bonding jumper #8844 04/08/02 07:17 AM
Joined: Mar 2001
Posts: 2,056
R
Redsy Offline
Member
Nick,

The neutral & GEC leave the xfmr enclosure, where they are bonded together, and go to the panelboard. The neutral connects to an insulated neutral bus. However the GC only connects to the panel enclosure. There is no connection to the Grounding Electrode System.
There are at least 3 setups like this at my site.

Dom,
If your GEC is run in your primary conduits, does that mean you have 2 in there? (1 as an EGC for the primary feeders and on 1 larger GEC for the secondary?)

Re: main bonding jumper #8845 04/08/02 06:59 PM
Joined: Jun 2001
Posts: 8
D
dom Offline OP
Junior Member
One EGC routed with the primaries based on the ocpd of the primary circuit.
The GEC connects directly to the ground electrode system in its own raceway, and/or just directly to the ground rod installed below the transformer through the concrete pad.

Re: main bonding jumper #8846 04/08/02 08:40 PM
Joined: Mar 2001
Posts: 2,056
R
Redsy Offline
Member
dom,
Sorry, I misread your list. The reason I questioned it is because there was a previous thread discussing the GEC routed int the primary conduit.
Thanks.

Re: main bonding jumper #8847 04/08/02 10:38 PM
Joined: Jun 2001
Posts: 8
D
dom Offline OP
Junior Member
I've seen the primary equipment ground used as the GEC. I believe that is not permitted by NEC. That could form a long and indefinite path for a completed circuit from a lightning strike or overvoltage to the grounding system.


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