I'm confused about where to bond the neutral to the ground in a couple scenarios. The code appears to allow the bond to be done either at the transformer, or at the first disconnecting means. That means one or the other and not both doesn't it? What if you have a padmount Xfmr, a typical meter, and then a main panelboard? I believe the utility always bonds at the xfmr, but isn't it a requirement to bond at the meter too? And don't most contractors bond at the main panelboard? My understanding was that you only want neutral and ground bonded at one spot. What if you have a pole mount xfmr, a meter with disconnect, and then a main panelboard several hundred feet away? If there is no bond on the polemount xfmr, then would I bond at the meter and at the distant main panelboard? Perhaps there is simply a difference here between what should be done ideally, and what is done in reality! Can someone simplify this for me? Thanks!
Bond at Xfmr, Meter, and/or Main Pnlbd?
- Thread starter psa807
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- Bremerton, Washington
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- Master Electrician
Re: Bond at Xfmr, Meter, and/or Main Pnlbd?
Either location is fine, but the connection to the grounding electrode conductor is done at the same location as the bond. The NEC allows the bond and GEC to be made at different locations, as long as a parallel neutral path is avoided, however I would not do it this way.
For small 5- 15 KVA systems the GEC and bond is normally done at the first disconnecting means.
For large systems > 25 KVA its typically done at the transformer XO terminal.
This is for SDS under section 250.30, which typically do not have a meter. If there is a meter then most likely you are connecting to a utility source of supply and then a different section of Art 250 applies. The main bonding jumper is installed at the service disconnecting means.
[ October 15, 2003, 04:08 PM: Message edited by: tom baker ]
Either location is fine, but the connection to the grounding electrode conductor is done at the same location as the bond. The NEC allows the bond and GEC to be made at different locations, as long as a parallel neutral path is avoided, however I would not do it this way.
For small 5- 15 KVA systems the GEC and bond is normally done at the first disconnecting means.
For large systems > 25 KVA its typically done at the transformer XO terminal.
This is for SDS under section 250.30, which typically do not have a meter. If there is a meter then most likely you are connecting to a utility source of supply and then a different section of Art 250 applies. The main bonding jumper is installed at the service disconnecting means.
[ October 15, 2003, 04:08 PM: Message edited by: tom baker ]
- Location
- Illinois
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- retired electrician
Re: Bond at Xfmr, Meter, and/or Main Pnlbd?
If this is a service, then 250.24(A)(2) says that there will be at least two points of connection to grounding electrodes.
In my area there are normally three points of connection. 1) at the utility transformer, 2) at the meter can (our utility requires that the GEC from a ground rod be terminated in the meter can) and 3) at the service panel where the water pipe or building stell GEC is connected.
Don
[ October 15, 2003, 05:12 PM: Message edited by: don_resqcapt19 ]
If this is a service, then 250.24(A)(2) says that there will be at least two points of connection to grounding electrodes.
In my area there are normally three points of connection. 1) at the utility transformer, 2) at the meter can (our utility requires that the GEC from a ground rod be terminated in the meter can) and 3) at the service panel where the water pipe or building stell GEC is connected.
Don
[ October 15, 2003, 05:12 PM: Message edited by: don_resqcapt19 ]
Re: Bond at Xfmr, Meter, and/or Main Pnlbd?
Thank you! Actually what I have is a PUD pole with transformer supplying a 240V service drop pole with a meter and disconnect, then about 500 feet away I have a main panelboard. The panelboard is attached to the leg of a transmission tower that is well grounded. The load is tower top lighting at a power line river crossing. My problem has been in determining if the code supports the neutral being connected to ground in multiple locations or not. In a substation, with a copper ground grid, I would consider the earth a parallel path, but in this situation, it looks like I should not!
Thank you! Actually what I have is a PUD pole with transformer supplying a 240V service drop pole with a meter and disconnect, then about 500 feet away I have a main panelboard. The panelboard is attached to the leg of a transmission tower that is well grounded. The load is tower top lighting at a power line river crossing. My problem has been in determining if the code supports the neutral being connected to ground in multiple locations or not. In a substation, with a copper ground grid, I would consider the earth a parallel path, but in this situation, it looks like I should not!
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: Bond at Xfmr, Meter, and/or Main Pnlbd?
When I first read your post it seemed you were questioning how to bond a SDS per 250.30. You are really installing a service to a seperate building or structure, per 250.32. The NEC would perfer that the neutral be floated at the remote building or in your case, the main panelboard.
You can still make a neutral to case bond, but I would not.
If you are in Washington State, our state code will not allow a neutral to case bond in a remote building or structure.
When I first read your post it seemed you were questioning how to bond a SDS per 250.30. You are really installing a service to a seperate building or structure, per 250.32. The NEC would perfer that the neutral be floated at the remote building or in your case, the main panelboard.
You can still make a neutral to case bond, but I would not.
If you are in Washington State, our state code will not allow a neutral to case bond in a remote building or structure.
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