Tap and Run splicing

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larryz12302

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New York, Scotia
I've got a 600 amp circuit using pararell 400kcmil AL feeders to a pair of MLO panel boards. I've run out of phiscal breaker space and want to add an additional 250 amp panel. I plan on setting a 6 x 10 x 5' trough under the panelboards and moving the set of pararell feeds from panel "A" to "B" out of the exsisting nipple between the panelboards and running them in the trough so I can tap them to feed the new loadcenter. My question is, do I have to tap BOTH sets of feeders or can I just tap one set of the pararell feeders to the new board? I plan on using 350 kcmil AL for the tap to the new board.The new tap would also be under 10'. Also, would it be over kill to use grounding bushings on the 4" nipples from the panelboards to the trough. This is a 208v- 4 w "Y" system. The measured current on the feeders at the MDP is less than 100 amps per phase.

Thanks for the chance to address this .
Larry Z
 
Re: Tap and Run splicing

Tapping only one set changes the impedance of that set and could cause excessive current in the set with the lower impedance. It would also be a violation of 310.4(5).
Don
 
Re: Tap and Run splicing

Larry:

Did you try getting a sub-feed lug kit from the manufacturer ? I know Siemens and others can get kits that you can add on to existing panelboards.

You might even be able to get a sub-feed breaker kit.
 
Re: Tap and Run splicing

Larry, this has nothing to do with your original question... perhaps I missed some information in the OP but my first question would be is there overcurrent protection for these MLO panelboards or are they all to have a 600 amp rating? The tap conductors as well as the panelboards must have coordinating overcurrent protection. Again, perhaps you have already stated this in your post but I must have missed it.

Pete
 
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