Feeder Sizing

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Alwayslearningelec

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The feeds sized from xfrmr to 1200a board are obviously incorrect as 600's good for only 475A? Should be multiple sets.
 

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Yes, it calls for three sets of 600 kcmil so you have 1260 amps of conductor and is code compliant.

The grounding conductor shown as 3/0 is really a supply side bonding jumper and is too small. 3/0 is 167kcmil, but this circuit requires the supply side bonding jumper to have an area 12.5% of the ungrounded conductors. That would require the use of a 250 kcmil supply side bonding jumper. It appears that the designer used Table 250.122, but that only applies on the load side of an OCPD. This is on the secondary of a transformer and Table 250.102(C) applies.

There are additional problems unless all of the conductors are in a common raceway such as a wireway or cable tray.
If there are 3 conduits, each conduit would require three 600 kcmil ungrounded conductors, one 400 kcmil grounded (neutral) conductor, and one 1/0 supply side bonding jumper.
 
don_resqcapt19 said:
Yes, it calls for three sets of 600 kcmil so you have 1260 amps of conductor and is code compliant.

The grounding conductor shown as 3/0 is really a supply side bonding jumper and is too small. 3/0 is 167kcmil, but this circuit requires the supply side bonding jumper to have an area 12.5% of the ungrounded conductors. That would require the use of a 250 kcmil supply side bonding jumper. It appears that the designer used Table 250.122, but that only applies on the load side of an OCPD. This is on the secondary of a transformer and Table 250.102(C) applies.

There are additional problems unless all of the conductors are in a common raceway such as a wireway or cable tray.
If there are 3 conduits, each conduit would require three 600 kcmil ungrounded conductors, one 400 kcmil grounded (neutral) conductor, and one 1/0 supply side bonding jumper.
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It doesn't call for (3) sets. It calls for one set w/ (3) hots for each phase.
 
don_resqcapt19 said:
Three sets = three hots per phase. Three hots per phase has an ampacity of 1260 amps without any ampacity adjustment or correction.
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I read it as 3#600MCM+2#600MCM Neutral.... To me... that means (3) #600mcm, one for each phase. Typically when we write plans... we say "3 sets: (4) 600MCM". I'm with the OP that they didn't write the conductor requirements properly. The OP should go back to designers and get the correction.
 
Rock86 said:
I read it as 3#600MCM+2#600MCM Neutral.... To me... that means (3) #600mcm, one for each phase. Typically when we write plans... we say "3 sets: (4) 600MCM". I'm with the OP that they didn't write the conductor requirements properly. The OP should go back to designers and get the correction.
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Most drawings I worked with would look like this where they wanted 3 sets...it was rare to spell out "sets" on the drawings I worked with.
 
Rock86 said:
by why do they only use 2 neutrals?
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The transformer is a K-13 transformer. It looks like they are requiring a 200% neutral. Which would mean that they aren't requiring multiple sets for the feeder. It looks like there are some issues with that feeder that an RFI would clarify.
 
infinity said:
Yes a simple (3)- in front of the 600 would make it correct. The " GND" is a SSBJ and could be smaller a #1/0 is sufficient.
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It could be a 1/0 if the sets are in multiple raceways. If the sets are in a wireway or a cable tray, it would be 250 kcmil.
 
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