Feeder Sizes

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mstrlucky74

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So this is not making sense to me. MC-4 is being fed with4-4” w/ 4 #600 & 1 #4/0 ground from a 1600A switch in the main service gear. MC-7 & 10 are being fed with 4-3-1/2” w/ 4 #500 & 1 #4/0. Seems way oversized or too many parallel setsfor 800amps(MC-4 & MC-7. Agree? Conductors are THHN & Copper. Thanks.
 

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  • Panel Schedule.jpg
    Panel Schedule.jpg
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  • Riser.jpg
    Riser.jpg
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Is that one riser with taps to the three MC boards? If so the 4-500 Kcmil protected at 1600 amps is no good unless the 1600 amp switch has smaller fuses in it. For whatever reason I cannot read your first attachment.
 
I can't read your diagrams either.

It seems to me though that the conductors going to MC7 and MC10 are tap conductors and don't meet the tap rules since they don't terminate on a single set of OCPD.
 
I'm guessing that they reduced the conductor size since the load above the 4th floor is diminished. This will work if they use a 1500 amp OCPD in the main service gear.
 
infinity said:
Is that one riser with taps to the three MC boards? If so the 4-500 Kcmil protected at 1600 amps is no good unless the 1600 amp switch has smaller fuses in it. For whatever reason I cannot read your first attachment.
Click to expand...

Yes it is. Why is it no good?
 
petersonra said:
I can't read your diagrams either.

It seems to me though that the conductors going to MC7 and MC10 are tap conductors and don't meet the tap rules since they don't terminate on a single set of OCPD.
Click to expand...


They are tap conductors. Explain a little further what you mean about not terminating on a single OCPD. Thanks.
 
infinity said:
I'm guessing that they reduced the conductor size since the load above the 4th floor is diminished. This will work if they use a 1500 amp OCPD in the main service gear.
Click to expand...

I'm still confused. Why do we need 4 sets of 3-1/2" with #500's for 800A dist. board? Isn't that way over sized?
 
mstrlucky74 said:
Yes it is. Why is it no good?
Click to expand...


The riser portion consisting of 4 sets of 500 Kcmil does not meet the conditions of the tap rules so the use of a 1600 amp OCPD with conductors that only have an ampacity of 1520 amps is no good.
 
infinity said:
The riser portion consisting of 4 sets of 500 Kcmil does not meet the conditions of the tap rules so the use of a 1600 amp OCPD with conductors that only have an ampacity of 1520 amps is no good.
Click to expand...


What are the tap rule conditions?
 
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240.21(B)(2)

240.21(B)(2) Taps Not over 7.5 m (25 ft) Long. Where the length of the tap conductors does not exceed 7.5 m (25 ft) and the tap conductors comply with all the following:
(1) The ampacity of the tap conductors is not less than one-third of the rating of the overcurrent device protecting the feeder conductors.
(2) The tap conductors terminate in a single circuit breaker or a single set of fuses that limit the load to the ampacity of the tap conductors. This device shall be permitted to supply any number of additional overcurrent devices on its load side.
(3) The tap conductors are protected from physical damage by being enclosed in an approved raceway or by other approved means.
Click to expand...
 
mstrlucky74 said:
Thanks. So back to my other question...aren't those feeders oversized to feed an 800A board?
Click to expand...


Something is missing from this equation. On the riser drawing it appears that the riser is being tapped to feed the 800 amp boards but there must be some missing information. :?

How are the boards connected to the riser?
 
infinity said:
Something is missing from this equation. On the riser drawing it appears that the riser is being tapped to feed the 800 amp boards but there must be some missing information. :?

How are the boards connected to the riser?
Click to expand...

What do you mean how are they connected? Off the taps they are being fed?
 
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