Does 430.28 Apply?

[gcaudill]

I want to install a subpanel off of an existing panel. The subpanel will feed three combination loads.

The existing panel is fed by 3-350mcm feeders per phase. The tap conductors will be 2-250mcm cables per phase, and will be bolted to the existing panel bus bars. The subpanel will be located within 10ft of the existing panel. The subpanel will have a 400A fused disconnect switch and feed three branch circuits that are fused. The fused disconnect and three branch circuit fuse sets are within the subpanel. The three branch circuits vary in length from 50ft to 275ft to each branch combination load. Each combination load is a panel that includes motors and other electrical loads. The panels are adequatly fused and protected with overloads, disconnects, etc.

Assuming that the feeder, tap, and branch conductors are adequate for the connected loads and OCPD's, does 4.28 apply in this situation? Specifically, may I have tap conductors that are atleast 1/3 the ampacity of the feeders without any OCPD between the existing panel and the subpanel (containing the 400A fused disconnect and branch circuit fuses)? For the comination loads, the individual motor fuses, overloads, etc., are actually more than 25ft away from the tap. Only the branch conductor fuses are contained in the subpanel.

 

[DanDel]

Is the 400A fused disconnect switch the Main device for the new panel? Are all the tap conductors terminated there?

 

[gcaudill]

Yes, the tap conductors feed the 400A fused disconnect. That is the disconnect/OCPD on the tap. The branch circuits are fused on the load side of the fused disconnect. The combination loads (motors, fuses, overloads, etc.) are down stream of the circuit fuses.

 

[DanDel]

430.28 is for motor feeder taps that terminate in a branch-circuit device. Your 400A fused switch is not a branch-circuit device.
Why are you asking about motor feeder taps? Shouldn't you be considering 240.21(B)(1) or (2)?

 

[gcaudill]

That's what I was asking. 240.21(F) got me thinking along the lines of 430.28. I thought of the subpanel as the "branch-circuit protective device".

240.21(B)(1) leads me to think that branch circuits leaving the subpanel are okay on the load side of the tap conductor.

But, 240.21(B)(2) leads me to think that the tap as well as the branch circuits must terminate inside the "switchboard, panelboard, disconnecting means, or control devices they supply".

What's your take on this?

 

[dpc]

How do you plan to make the tap? You can't modify the bus in the panel in the field (per UL). You could tap conductors ahead of the panel.

 

[gcaudill]

There are available lug positions on each phase bus.

 

[DanDel]

A subpanel main would not be a branch circuit protective device. A branch circuit is defined as "The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s)." The final overcurrent devices are the feeder(or branch) C/Bs in your subpanel.

I believe 430.28(F) might apply if there was one overcurrent device being fed by the motor feeders and feeding a single motor branch circuit.

240.21(B)(1) requires that "the tap conductors do not extend beyond the switchboard, panelboard, disconnecting means, or control devices they supply", not 240.21(B)(2). Some of the differences are the length of the tap and the necessity in 240.21(B)(2) that the tap conductors "terminate in a single C/B or single set of fuses", etc.
Sounds like 240.21(B)(2) should apply to your situation.

 

[cuky2000]

The enclose Application Guide (Section F1-3), discuss 3 modes of panelboards interconnection:

o Gutter Tap.

o Sub-feed lugs.

o Through-feed lugs.

Check if this could be helpfull for your application.

http://www.cutler-hammer.eaton.com/unsecure/html/catalogs/CAT71.htm