450 amp service and CT Cabinet 36x 45

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jmsbrush

jmsbrush

Senior Member
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Central Florida
This is a grounding question but please read first!!!I installed a a Ct cabinet yesterday. I had paralle runs of 4/0 going into the cabinet from the green pedistal. I went through my my CT's into a NSI block. I landed my Neutral conductor in a seperate NSI as well. From the NSI Blocks I Fed 3 -150 amp Panels. Now the load side of those panels fed three other MLO panels in the house. I took my grounding electrode conductor from the from a concrete encased electrode and ground rods and I bonded to the ct can 1st then straight to neutral NSI block then bonded my CT rated meter. I fed my three 150 amp panels with 2 hots and a neutral. So here's the question?? In the panels with the 150 breakers, Am required to tighten up the green screw on the neutral bus???? I passed my inspection but im having doubts. PLEASE HELP.
 
It sounds like you are OK just the way you are. The neutral is bonded in the CT cabinet. Tightening the green (bonding) screw would rebond the neutral in the panel which would be a violation. The neutral can only be bonded at one spot.
 
Looks like the CT can is OK.

250.30 Grounding Separately Derived Alternating-Current Systems.
(1) System Bonding Jumper. An unspliced system bonding jumper in compliance with 250.28(A) through (D) that is sized based on the derived phase conductors shall be used to connect the equipment grounding conductors of the separately derived system to the grounded conductor. This connection shall be made at any single point on the separately derived system from the source to the first system disconnecting means or overcurrent device, or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices.
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jmsbrush said:
I took my grounding electrode conductor from the from a concrete encased electrode and ground rods and I bonded to the ct can 1st then straight to neutral NSI block then bonded my CT rated meter. I fed my three 150 amp panels with 2 hots and a neutral.
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What about the ground? Since you grounded the neutral in the CT cabinet, I would think you need to feed the panels with 2 hots, a neutral, and a ground.
 
jmsbrush said:
I fed my three 150 amp panels with 2 hots and a neutral. So here's the question?? In the panels with the 150 breakers, Am required to tighten up the green screw on the neutral bus????
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If, by "tighten up", you mean install a bonding jumper, it depends. The neutrals and EGC's should not be redundantly bonded.

What kind of wiring method is between the CT cabinet and the main-breaker-panel enclosures?
 
from what you stated in your post, I appears that you have not installed any grounding between your ct cabinet and your 150 amp breaker enclosures other than the grounded neutral. If that is the case, you would need to bond those enclosures (normally with the green screw).
As Larry asks, please clarify the wiring from the CT to your breakers.
 
Hey guys, I installed 2 hots and a neutral from the Ct Cabinet to the breakers, #1 copper I believe. So with that being said I would have to tighten the Green bond screws in those panels so that in the case of the event of a ground fault the panels would be protected, In those 150 amp panels with the breakers, the neutral and ground bus are inter connected. That throws me off in my thinking if I already bonded in my CT cabinet. Because you are only supposed to be boned in one spot???
 
Your last sentance is correct, and if I am still understanding the installation correctly, you should have added an equipment grounding conductor from your 150 amp breaker to your MLO panels.
 
A CT cabinet is no handled no differently then a Meter socket or pan.

You bond the neutral to the CT cabinet, run only ungrounded and grounded conductors onto the service then you must bond the service disconnect enclosure as required by the NEC.
 
250.30 Grounding Separately Derived Alternating-Current Systems.
(1) System Bonding Jumper. An unspliced system bonding jumper in compliance with 250.28(A) through (D) that is sized based on the derived phase conductors shall be used to connect the equipment grounding conductors of the separately derived system to the grounded conductor. This connection shall be made at any single point on the separately derived system from the source to the first system disconnecting means or overcurrent device, or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices.
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chris kennedy said:
Looks like the CT can is OK.
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Whooo, I just caught this. Why didn't someone bust me for this? Was it because you guys were being nice?:roll:
 
augie47 said:
Your last sentance is correct, and if I am still understanding the installation correctly, you should have added an equipment grounding conductor from your 150 amp breaker to your MLO panels.
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I did. From the main breaker panels I used S.E.R cable with a ground to my MLO's.
 
iwire said:
A CT cabinet is no handled no differently then a Meter socket or pan.

You bond the neutral to the CT cabinet, run only ungrounded and grounded conductors onto the service then you must bond the service disconnect enclosure as required by the NEC.
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So If I bonded the green screw to the can, would that be considered bonded twice?
 
jmsbrush said:
So If I bonded the green screw to the can, would that be considered bonded twice?
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Yes and no, you should not have a equipment grounding conductor between the CT cabinet and the service disconnect enclosure.

Again think of a typical house service, meter can bonded to neural, two hots and neutral from there to the service disconnect and in that service panel another bond.

This is directly addressed by 250.142(A)(1).

The rule against 'double bonding' really only applies to the load side of the service disconnecting means. :)
 
iwire said:
Yes and no, you should not have a equipment grounding conductor between the CT cabinet and the service disconnect enclosure.

Again think of a typical house service, meter can bonded to neural, two hots and neutral from there to the service disconnect and in that service panel another bond.

This is directly addressed by 250.142(A)(1).

The rule against 'double bonding' really only applies to the load side of the service disconnecting means. :)
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Gotcha, When I get to my job tomorrow I will tighten those green screws! Thank you very much:)
 
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