Tap Rule Multiple Times over

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BZ2005

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As Far I I can tell this situation will meets the NEC...
Does anyone see something that i don't.....
3 large Control panels ganged together left to right. The 1st panel has a 600A main breaker for the incoming feed sized according. In the same panel Installed off of that 600A breaker via 10 foot Tap Rule & Via Free Air Parallel #1's to a Power Distribution block. Distribution feeds about 305 amps of power to SCR controlled heaters individually fused @ 30A with multiple sets of #8 wire. From that same 600A breaker, tap off less than 10ft to feed a 100A and 150A breakers in the other cabinets all still less that 10 feet away . All panels have cable/door disconnect operators.
 

iwire

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Location
Massachusetts
Installed off of that 600A breaker via 10 foot Tap Rule & Via Free Air Parallel #1's to a Power Distribution block.

You cannot use the free air ampacitys, at least some of the terminations will be 75C rated and that will hold you to table 310.16s 75 C column.
 

BZ2005

Member
Makes sense
the wire may be Free-Air "or non contained" but the terminations on the breaker and the Distribution block will not be. Missed this they are defined manufacturer heat build up characteristics 90c rated at 75c because of this

I'll go with parallel 2/0 instead to cover my 300 Amp Possible....
 

Smart $

Esteemed Member
Location
Ohio
Makes sense
the wire may be Free-Air "or non contained" but the terminations on the breaker and the Distribution block will not be. Missed this they are defined manufacturer heat build up characteristics 90c rated at 75c because of this

I'll go with parallel 2/0 instead to cover my 300 Amp Possible....

Are you tapping off the 600A breaker with three different sizes of wire per terminal? Is the lug rated for such?
 

augie47

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Location
Tennessee
Occupation
State Electrical Inspector (Retired) DINOSAUR
assuming this is not "factory wiring" covered by the panel listing, it sounds like a couple of violations.
In the first scenario where you hit the distribution it sounds like you are tapping the tap. Secondly, the 10 ft tap rule states you must terminate in a device (singular). Even if we accept the block, the #8s don't meet the 10x ampacity requirement.
In the second I'm not clear if you have one tap going to two devices, the 100 and the 150 breaker, or if each has its own tap.
 
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BZ2005

Member
What im thinking

What im thinking

Basically, the 600A breaker comes with distribution block lugs 5 wires per phase , basically 2 each to 2/0 the Distribution block devise draws less than 300 amps, this feeders will not extend past the panelboard / enclosure . thus 240.21(b)(1)(4) of the the #8's will not have to meet the 10x ampacity rule because they do not leave the enclosure...

And the the other lugs tap to 100A and 150 a breakers in panels directly left and right of the feeding enclosure do leave the but they do meet the 10 times rule

Also i don't see where the (singular) tap is referenced, they are individual taps (parallel) not taps of taps (series)


thanks
 

BZ2005

Member
What im thinking 2

What im thinking 2

Plus i believe the #8's feed with in the panel should probably be considered branch circuits since they will have secondary protection

2- 2/0 in |distribution block| out #8 fuse devise, #8 Fuse devise ect.
 

Smart $

Esteemed Member
Location
Ohio
...

Also i don't see where the (singular) tap is referenced, they are individual taps (parallel) not taps of taps (series)
You have what, 4 wires per breaker lug... 2 of which parallel to a distribution block, while the other two go to separate ocpds. From what I gather of you posts, all these wires combined do not have an ampacity equal or greater than the ocpd which protects them. Then when you add on top of that that only two terminate in the same device, it makes all the wires connected to the 600A breaker tap conductors. Under the tap rules, a tap conductor must terminate on a single ocpd. Your parallel 2/0's terminate on a distribution block. All load side conductors having an ampacity less than paralleled 2/0's are tapping a tap conductor and not permitted.
 
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