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#77202 - 05/10/01 09:01 PM Tap vs. Ocpd  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,303
This is somewhat of a borrowed Q i thought i'd bring to this forum.

Taps are made , resulting in a conductors served from larger OCPD's, this is primarily addressed in 240-21
(b)feeders
(c)Xformers
(d)service cond.
(e)busway's
(f)motor circuits
(g)genny's

so how would the conductors included in
T310-15(b)(6) or T430-72(b) be defined in light of this?
( or are they meant as d & f ?)

any conjecture, speculation, etc...?
[Linked Image]




[This message has been edited by sparky (edited 05-10-2001).]


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#77203 - 05/11/01 02:30 AM Re: Tap vs. Ocpd  
Scott35  Offline

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Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
Steve,

On the first table [if I am looking at the right one], I would say that the demand on free air feeders would be only high for minute times - not exceeding an hour or so.

On the other table T430-72 (b), I have some referenced notes that came with my 99 NEC, which edits the printed text.

In that note, there's a few points towards values of 400% of 310-17's 60 degree table, plus 300% of 310-16's 60 degree table.

I'm not exactly sure what level of current would cause a #10 cu to fry, but 160 amps would be at least close enough.

Is this going in the direction you were hoping?? [Linked Image]


Scott SET


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#77204 - 05/11/01 06:14 AM Re: Tap vs. Ocpd  
sparky  Offline
Member
Joined: Oct 2000
Posts: 5,303
Thanks Scott!
yes, i find it interesting how the NEC defines protection in given situations. We tend to think in fixed numbers for conductors, yet this is frequently not so. The original Q eluded to just how far one can fanegal this in the NEC

Also the 'tap rules' as they are know, are not only to be smaller wires 'tapped' into larger wires, but also smaller wires directly introduced to larger OCPD's

This , although the end result is the same, creates a little focus on the definitional aspects of the practice.

The only guidance in those terms i have found is 240-3(e)

I just thought i'd throw it out for the BB's thoughts

[Linked Image]



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