Feeder Tap

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mp73644

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I'm installing a 400 amp 120/240, 3ph panel board. Existing is a 800 amp 120/240, 3ph main distribution feed by parallel 500 mcm. The tap will run approximately 35 ft to 400 amp panel board that resides in an adjacent room. I plan to run 2 1/2" emt and use 250 mcm as tap conductor. Clarity on the tap rules are not always clear and seem to invite there own problems within there definition. Can a smaller tap conductor be used ? and what of the rule not to past through wall?
 
Pierre C Belarge said:
You need to read 240.21(B). There are 5 different conditions for tap rules there. In reading your short description, I believe you do not have the proper conditions to use the tap rules.
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I agree with Pierre, from your description the tap is too long for the conditions.


Also, be sure that you base the size of the EGC between the 800 amp feeder and the 400 amp panel based on the 800 amp feeder.


I plan to run 2 1/2" emt and use 250 mcm as tap conductor
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Two sets of 250 aluminum I assume?
 
iwire said:
I agree with Pierre, from your description the tap is too long for the conditions.


Also, be sure that you base the size of the EGC between the 800 amp feeder and the 400 amp panel based on the 800 amp feeder.




Two sets of 250 aluminum I assume?
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This is correct, I sometimes take it for granted that most people understand this reaquirment in 250.122(G).
 
If the feeders are fused at 400 amp per 500 kcmil parallel feeders on secondary side of disconnect, can you size per 400 amp fuse ?or the overall 800? I will be installing parallel in this application.
Using aluminum at 230 amps if you figure the 1/3 of 800 this is 266 amps?
 
Pierre C Belarge said:
This is correct, I sometimes take it for granted that most people understand this reaquirment in 250.122(G).
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Actually it was always required to do that, but many were not doing it, so 250.122(G) was added to the code.
 
mp73644 said:
I'm installing a 400 amp 120/240, 3ph panel board. Existing is a 800 amp 120/240, 3ph main distribution feed by parallel 500 mcm. The tap will run approximately 35 ft to 400 amp panel board that resides in an adjacent room. I plan to run 2 1/2" emt and use 250 mcm as tap conductor. Clarity on the tap rules are not always clear and seem to invite there own problems within there definition. Can a smaller tap conductor be used ? and what of the rule not to past through wall?
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Why don't you install a breaker in the Main Distribution panel and then install a FEEDER to your sub-panel instead of trying to force this installation into a tap rule.
 
haskindm said:
Why don't you install a breaker in the Main Distribution panel and then install a FEEDER to your sub-panel instead of trying to force this installation into a tap rule.
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Usually the reasons are two fold, cost and available space. There is nothing inherently wrong with using the tap rules.
 
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