# how to size feeders



## garfield (Jul 30, 2009)

I have 2-200 amp mains in 2 panels with feed through lugs. I am wanting to use those lugs to feed 2/0 copper to a new control panel with 2 distribution blocks and 7 manual motor protectors. (there will also be contactors interlocking etc) They would be 30 hp motors set at 37 amps each...4 on one set of feeders and and 3 on the other. Can I use the amp settings of the manual motor protectors added together and the tap rules to size my wire? 40+40+40+40+10 (for 25% of largest motor) =170 and my settings add up to 148 amps. 2/0 is 175 in the 75 degree column. Thoughts?


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## MDShunk (Jan 7, 2007)

Absolutely. I think you've got solid code to back you up on that also.


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## tates1882 (Sep 3, 2010)

garfield said:


> I have 2-200 amp mains in 2 panels with feed through lugs. I am wanting to use those lugs to feed 2/0 copper to a new control panel with 2 distribution blocks and 7 manual motor protectors. (there will also be contactors interlocking etc) They would be 30 hp motors set at 37 amps each...4 on one set of feeders and and 3 on the other. Can I use the amp settings of the manual motor protectors added together and the tap rules to size my wire? 40+40+40+40+10 (for 25% of largest motor) =170 and my settings add up to 148 amps. 2/0 is 175 in the 75 degree column. Thoughts?


 maybe use 3/0, reason because you are using feed thru protect at 200 amps, the new feeders would also need to be sized for the ocpd not the calculated load. If you use 2/0 then it would fall under taps and you can only have 6 discos togetherness, you have 7. Also being adjustable motor protectors the calc would need to be for max that they "could" draw.


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## telsa (May 22, 2015)

While you're Code worthy with the OP...

Wouldn't you be happier setting twin sub-panels (MLO) and running 3/0? 

Have you ever checked out the Meltric stuff?


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## Dennis Alwon (May 9, 2009)

tates1882 said:


> maybe use 3/0, reason because you are using feed thru protect at 200 amps, the new feeders would also need to be sized for the ocpd not the calculated load. If you use 2/0 then it would fall under taps and you can only have 6 discos togetherness, you have 7. Also being adjustable motor protectors the calc would need to be for max that they "could" draw.


I agree that 2/0 is not compliant. You need 3/0 for a 200 amp panel especially since this does not appear to be residential but even if it were a residence you need 3/0 because the panel does not carry the load of the entire dwelling.


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## Dennis Alwon (May 9, 2009)

Your feeder must be sized to the overcurrent protective device at the panel since you are using feed thru lugs. A conductor must be protected at the source


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## Cow (Jan 16, 2008)

You can't tap a tap. The undersized 2/0 from the 200 amp panel is a tap and may be compliant by itself if you met the tap rules. But, as soon as you hit a distribution block and made several more taps off of it, you would be in violation. 

The simplest solution most likely would be to run 3/0 copper to your dist. blocks.


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## garfield (Jul 30, 2009)

Cow said:


> You can't tap a tap. The undersized 2/0 from the 200 amp panel is a tap and may be compliant by itself if you met the tap rules. But, as soon as you hit a distribution block and made several more taps off of it, you would be in violation.
> 
> The simplest solution most likely would be to run 3/0 copper to your dist. blocks.


From the distribution block it would be going only inside a 3x3 control panel to the manual motor protectors which are the protection sized for the 8 gauge wire from the distribution block to the manual motor protectors.


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## Pete m. (Nov 19, 2011)

What would be the length of the 2/0 conductors you are proposing to use? Actual wire length not raceway.

Pete


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## Pete m. (Nov 19, 2011)

Also, it sounds like you are feeding an Industrial Control Panel - article 409. There are rules there for sizing the circuit feeding it that you would have to meet.

Pete


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## telsa (May 22, 2015)

Cow said:


> You can't tap a tap. The undersized 2/0 from the 200 amp panel is a tap and may be compliant by itself if you met the tap rules. But, as soon as you hit a distribution block and made several more taps off of it, you would be in violation.
> 
> The simplest solution most likely would be to run 3/0 copper to your dist. blocks.


Sure you can.

It's just that the worst, most restrictive, distances would apply: the ten-foot rule.

For the calculation, the smallest conductor and the maximum length would be used... in sum: the ten-foot rule.

%%%

As posted above, it'd be far wiser to just set two sub-panels and stay with 3/0. Downsizing to 2/0 saves you -- what ? Peanuts.

It's a CLEANER scheme -- and beyond reproach.

I totally fail to see the appeal of distribution blocks. To work 'cold' you'd be required to kill the panel -- really BOTH panels -- as you're bringing these taps into the same enclosure... something that I don't find appealing at all.

With twin sub-panels, it's no biggie to kill power with dedicated breakers to this or that motor circuit.... by its self. 

Your budget can't be THAT tight. 

Distribution blocks, and such, are to be expected inside complex machinery... They are inappropriate ( impractical ) for this application -- even when you can meet Code.


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## Cow (Jan 16, 2008)

You're mistaken Telsa, a 2/0 copper on a 200 amp breaker is a tap. That same 2/0 feeding a dist. block and more taps is a code violation. Here's a little cut and paste from an '02 EC&M magazine outlining the tap rule:

_"you must understand that a tap conductor isn't permitted to supply another tap conductor. In other words, you can't make a tap from a tap."_

http://ecmweb.com/code-basics/understanding-rules-feeder-taps


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