bonding jumper size

[stew]

600 amp service in a C.T. enclosure with 4 main service panels mounted below. 3@200 amp and the 4th at 225. Using 2 500 mcm al per phase for service conductors. 4/0 al to the 200 panels and 250 mcm al to the 225 panel # 2 al egc from all the service panels. PPVC between the C.T. can and service disconnects. How do I properly size the bonding jumper between the C. T. can and the services? Am I required to use the 250.66 tables for this which woulod result in a 4/0 al jumper? Or is there another way to calculate this?

[ August 02, 2004, 03:11 PM: Message edited by: stew ]

 

[stew]

Re: bonding jumper size

nobody seems to want to tackle this eh? Guess I will just use 4/0 and forget it.

 

[don_resqcapt19]

Re: bonding jumper size

Stew,

How do I properly size the bonding jumper between the C. T. can and the services?

You don't install a bonding jumper here. The grounded conductor is required by 250.28. The grounded conductor bonds both the CT enclosure and the service enclosures.
Don

 

[stew]

Re: bonding jumper size

Don in this configuration the c.t can is mounted above the service disconnects. The grounded conductor is then bonded at each service disconnect per 250.28. As there are no disconnects in the ct enclosure I dont believe the grounded conductor should be bonded within this enclosure. That I believe would be a violation of the parallel path rule becuase you would have 2 points of bond in different enclosures with pvc in between.Same thing as bonding the neutral in a meter can and also bonding in the service disconnect although we all do it all the time and none ever gets cited and usually the run is so short that it doesnt matter. Even though this type of bond is done all the time I have never thought it was proper to do so by the pararle path rule.
I did not want to create that parralel path with the pvc in between but I did want to bond the ct can to the common ground created in the disconnect enclosures per 250.4(A)(3).I felt that this was the proper way to do it but maybe I am mistaken?

[ August 02, 2004, 11:11 PM: Message edited by: stew ]

 

[tom baker]

Re: bonding jumper size

Bonding in the CT can is no different than bonding the neutal in a meter base. The code recognizes there is a parallel path. The CT cans I install have a ct mounting base, then then a bonding jumper is run to the CT can sized per 250.66.

 

[don_resqcapt19]

Re: bonding jumper size

Stew,

That I believe would be a violation of the parallel path rule becuase you would have 2 points of bond in different enclosures with pvc in between.

With PVC raceways where is the parallel path? Take a look at 250.142(A). The grounded conductor is used for all grounding and bonding on the line side of the service disconnects.
Don

 

[stew]

Re: bonding jumper size

I gues i am thinking the paralle path is if the ct base were grounded in the can and the nuetral is bonded again in the disconnects ther would be paralle paths from each disconnect back to the main lug in the ct can. This ct bas hase no provision for a neutral bond unless an additional lug is stacked upon the 4 baarell stack lug that is already being used for the connection to the disconnects. poco doesnt wnt additional lugs stacked on the bus for some reason. I guess I could just run a 4/0 al from the bonding lug in the ct can to the first disconnect and then all would be interconnected.

[ August 03, 2004, 11:04 AM: Message edited by: stew ]

 

[hornetd]

Re: bonding jumper size

Originally posted by stew:
600 amp service in a C.T. enclosure with 4 main service panels mounted below. 3@200 amp and the 4th at 225. Using 2 500 mcm al per phase for service conductors. 4/0 al to the 200 panels and 250 mcm al to the 225 panel # 2 al egc from all the service panels. PPVC between the C.T. can and service disconnects. How do I properly size the bonding jumper between the C. T. can and the services? Am I required to use the 250.66 tables for this which woulod result in a 4/0 al jumper? Or is there another way to calculate this?

Unless this is the service for a mansion how can you use 4/0 aluminum for two hundred amperes. In anything but residential services and feeders the ampacity of 4/0 Al is 180 amperes if all of the terminations are listed for use at 75? C. Using the 75? C column in table Table 310.16 I also get only 205 amperes for the 250 mcm Al. Did you manage to find 90? C terminations?
--
Tom Horne