Hi There

I am quoting an installation of 2 2000MW Emergency Generators from Cummings.

It is my first time dealing with high AMP feeders.

The system is 480/277 V. with aluminum conductors in raceway which type is not specified because

is out of the my specific project's scope I mean doing by others.

I received the electrical drawings with the information which include the in-line diagram

for the generators, the feeder towards each EMSB ( Emergency Switch board), and from both EMSB to many ATS ( Automatic Transfer switch) down steam for feed different emergency loads.

The drawing include a table with a list of different capacity CB and its corresponding AWG for feeders.

More exactly the table specify Circuit Breaker Amps, # sets , and # of wires for each sett plus the AWG for grounding conductor.

For example let's take one of those listed feeders:

For 700 A CB we have 2 sets of 3-600 Kcmil plus 1 600Kcmil for Neutral. plus 1 #3/0 grounding conductor.

Among the notes included with the feeder table there is the following:

In total there are 12 feeders towards its respective ATS. Most of those feeders runs are in average 600 feet and have a tag "V" doing reference to the above note.

Here

Let's take the case of one of the feeders: 1600 A running 810 feet.

They specify 6 sets of 3-400 Kcmil, 1_400Kmil for Neutral and 1 350Kcmil for grounding.

I got that for

Should I conclude that the Feeder table is for 100 feet run?

Let's take again the example feeder

For 700 A CB we have 2 sets of 3-600 Kcmil plus 1 600Kcmil for Neutral. plus 1 #3/0 grounding conductor.

If I look up on the table 250.122(B) NEC 2011 I found that for Aluminum 3/0 conductor the corresponding CB should be 800A.

This is 100 A more than the 700 A feeder.

How should I interpret this?

I would appreciate so much son help on this and Thank you all.

I am quoting an installation of 2 2000MW Emergency Generators from Cummings.

It is my first time dealing with high AMP feeders.

The system is 480/277 V. with aluminum conductors in raceway which type is not specified because

is out of the my specific project's scope I mean doing by others.

I received the electrical drawings with the information which include the in-line diagram

for the generators, the feeder towards each EMSB ( Emergency Switch board), and from both EMSB to many ATS ( Automatic Transfer switch) down steam for feed different emergency loads.

The drawing include a table with a list of different capacity CB and its corresponding AWG for feeders.

More exactly the table specify Circuit Breaker Amps, # sets , and # of wires for each sett plus the AWG for grounding conductor.

For example let's take one of those listed feeders:

For 700 A CB we have 2 sets of 3-600 Kcmil plus 1 600Kcmil for Neutral. plus 1 #3/0 grounding conductor.

Among the notes included with the feeder table there is the following:

*Subscript "V" denotes an oversized feeder due to voltage drop. Increase equipment grounding conductor size per requirements of 250.122 (B)*In total there are 12 feeders towards its respective ATS. Most of those feeders runs are in average 600 feet and have a tag "V" doing reference to the above note.

Here

**is my first question**: Is that table valid for 100' runs or it is already updated for long runs?Let's take the case of one of the feeders: 1600 A running 810 feet.

They specify 6 sets of 3-400 Kcmil, 1_400Kmil for Neutral and 1 350Kcmil for grounding.

I got that for

**one set**, 480 v , four conductor in parallel (Phases and Neutral), PVC conduit(it's assumed), temperature 102 F deg then the voltage drop is 7.3 %. Is my calculation correct?Should I conclude that the Feeder table is for 100 feet run?

**My 2th question**is regarding the equipment grounding conductor and table 250.122 BLet's take again the example feeder

For 700 A CB we have 2 sets of 3-600 Kcmil plus 1 600Kcmil for Neutral. plus 1 #3/0 grounding conductor.

If I look up on the table 250.122(B) NEC 2011 I found that for Aluminum 3/0 conductor the corresponding CB should be 800A.

This is 100 A more than the 700 A feeder.

How should I interpret this?

I would appreciate so much son help on this and Thank you all.

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