I have a transformer feeding a C.T. can then to the main panel with the first point of disconnect. It is a 120/208 system. With 350kcmil feeders my main grounding electrode conductor connected to the cold water pipe is a 1/O wire, the supplimental ground is a #6 copper. My problem is what is the best way to ground the system right now as it sits between my C.T. can I have my three phase conductors and my neutral. In the C.T. everything is bonded together. Something to me does not seem right with the install. I think in my mind that if the main ground and the ground rod were connected through the panel instead of the C.T. and bonded only at that point with the neutal. Then bring an additional #6 from the panel back to the C.T. can to ground it? Or Does it have to be larger? I would really appreciate the help thanks in advance.
Help!!!!
- Thread starter nathan
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ryan_618
Senior Member
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- Salt Lake City, Utah
Re: Help!!!!
I don't have my book here so bare with me, but I think it is 250.102 or maaybe 250.104 that states that bonding on the line side of the service is to be sized as a grounding electrode conductor as per 250.66. You will need a 1/0 on the CT as it is on the supply side of the service. Hope this helps,
I don't have my book here so bare with me, but I think it is 250.102 or maaybe 250.104 that states that bonding on the line side of the service is to be sized as a grounding electrode conductor as per 250.66. You will need a 1/0 on the CT as it is on the supply side of the service. Hope this helps,
- Location
- Massachusetts
Re: Help!!!!
This sounds like a typical service.
The CT can is grounded by the Neutral coming from the transformer, the neutral lugs in the CT can are solidly mounted to the enclosure. (any that I have seen) the same way as a residential meter socket is grounded.
As you will have the neutral bonded in both cabinets the use of metal raceway will result in neutral current flowing on the raceway.
If I have misunderstood what you are asking I am sorry.
[ November 07, 2003, 06:06 AM: Message edited by: iwire ]
This sounds like a typical service.
The CT can is grounded by the Neutral coming from the transformer, the neutral lugs in the CT can are solidly mounted to the enclosure. (any that I have seen) the same way as a residential meter socket is grounded.
Many on this forum have suggested and it sounds good to me, use PVC between the meter socket or CT cabinet and the service disconnect.
As you will have the neutral bonded in both cabinets the use of metal raceway will result in neutral current flowing on the raceway.
If I have misunderstood what you are asking I am sorry.
[ November 07, 2003, 06:06 AM: Message edited by: iwire ]
- Location
- Massachusetts
Re: Help!!!!
I read your post again and it seems you have done all your grounding and bonding in the CT can and have not bonded at the disconnect.
I have gone that route also, with the blessing of the AHJ to avoid neutral current on the raceway.
But 250.28 requires the bonding to be done in the service disconnect switch.
250.24(A)(1) allows the grounding electrode to be connected in the CT as long as the AHJ considers it a "accessible point"
Having learned from the people here at the forums next time I come across this I will do all grounding and bonding at the main switch and use a non-metallic raceway between the meter socket or CT cabinet and the Service disconnect.
Can you explain your installation in more detail?
I read your post again and it seems you have done all your grounding and bonding in the CT can and have not bonded at the disconnect.
I have gone that route also, with the blessing of the AHJ to avoid neutral current on the raceway.
But 250.28 requires the bonding to be done in the service disconnect switch.
250.24(A)(1) allows the grounding electrode to be connected in the CT as long as the AHJ considers it a "accessible point"
Having learned from the people here at the forums next time I come across this I will do all grounding and bonding at the main switch and use a non-metallic raceway between the meter socket or CT cabinet and the Service disconnect.
Can you explain your installation in more detail?
Re: Help!!!!
250.24(A)(1) requires the connection of the GEC to the grounded service conductor at any accesible point from the load end of the service drop or service lateral to and including the terminal bus to which the grounded service conductor is connected at the service disconnecting means.
Which is to say, the GEC can be bonded to the neutral anywhere on the weatherhead, in the meter enclosure, the CT enclosure or the main panel. The serving utility will usually not permit this connection to be made in the meter enclosure or the CT enclosure, because they seal these up, and thay don't want anyone to cut their seals to check a grounding connection. Which leaves the weatherhead, or the main disconnect. Guess which one we choose.
250.28 deals with the main bonding jumper, which bonds the main panel enclosure(service disconnect) to the neutral and the EGCs, not the GEC. But, the GEC is usually bonded at this point too, because of the previous paragraph.
IMO having the neutral paralleled at the service equipment is not a big deal. The current in the neutral is correspondingly lowered, and any EMF effect is isolated to the service equipment. What are the ill effects? I see none.
250.24(A)(1) requires the connection of the GEC to the grounded service conductor at any accesible point from the load end of the service drop or service lateral to and including the terminal bus to which the grounded service conductor is connected at the service disconnecting means.
Which is to say, the GEC can be bonded to the neutral anywhere on the weatherhead, in the meter enclosure, the CT enclosure or the main panel. The serving utility will usually not permit this connection to be made in the meter enclosure or the CT enclosure, because they seal these up, and thay don't want anyone to cut their seals to check a grounding connection. Which leaves the weatherhead, or the main disconnect. Guess which one we choose.
250.28 deals with the main bonding jumper, which bonds the main panel enclosure(service disconnect) to the neutral and the EGCs, not the GEC. But, the GEC is usually bonded at this point too, because of the previous paragraph.
IMO having the neutral paralleled at the service equipment is not a big deal. The current in the neutral is correspondingly lowered, and any EMF effect is isolated to the service equipment. What are the ill effects? I see none.
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