240.21 Three panelboards from one disconnect, no mains

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mn_voyageur

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I recently saw an installation with one disconnect feeding three panelboards. (208) None of the panel boards had main circuit breakers.

I suggested to install double-pole C-H BR breakers and reverse feed them.

I understand 240.21 to indicate that the feeders had to land on single breakers. (No landing the wires on lugs.)

MarkN
 
mn_voyageur said:
I recently saw an installation with one disconnect feeding three panelboards. (208) None of the panel boards had main circuit breakers.

I suggested to install double-pole C-H BR breakers and reverse feed them.

I understand 240.21 to indicate that the feeders had to land on single breakers. (No landing the wires on lugs.)

MarkN
Click to expand...

How were the panels being fed from the disconnect? Did the disconnect have OCPD? Did they have triple lugs?
Give us a little more info.
 
Fused disconnect with a single feeder (+/-100') to a Distribution Block.

Distribution block feeds individual panels.

The three panels are within 30' of the PDB.

MarkN
 
ptonsparky: What difference would it make, whether they are in the same building?

240.21(1) - Does not apply, since the feeder is greater than 10'
240.21(B)(2)(2) states that conductors must land on a single breaker.
240.21(B)(3) - Does not apply, since the feeder does not supply a transformer.
240.21(B)(4) - Does not apply, since this is not a high bay.
240.21(B)(5)(2) states that conductors must land on a single breaker.

Am I missing something?

MarkN
 
No, the taps are identical. Even if we feed a panel, each panel has to be properly rated. Let's say that we are feeding three 100 Amp panels from a 200 Amp disconnect. 4/0 is sufficient, but the 100 Amp panels are improperly fed, correct?

I was taught that the panels either required a main breaker, or they had to be fed from a breaker/disconnect.

I see no exception for the panels to be fed from one disconnect/breaker.

MarkN
 
mn_voyageur said:
No, the taps are identical. Even if we feed a panel, each panel has to be properly rated. Let's say that we are feeding three 100 Amp panels from a 200 Amp disconnect. 4/0 is sufficient, but the 100 Amp panels are improperly fed, correct?

I was taught that the panels either required a main breaker, or they had to be fed from a breaker/disconnect.

I see no exception for the panels to be fed from one disconnect/breaker.

MarkN
Click to expand...

You failed to note that in the original post, as long as the panels and wire are rated higher than the ocp, there is no issue, one could be 200 amp, the second 800 amp and the third 400 amp. As long as the ocp is 200 amps or less, there is not a problem.
 
mn_voyageur said:
No, the taps are identical.
Click to expand...
If each panel feeder is identically sized (i.e. rated) as the feeder trunk, there are no taps and 240.21 does not apply.

mn_voyageur said:
Even if we feed a panel, each panel has to be properly rated. Let's say that we are feeding three 100 Amp panels from a 200 Amp disconnect. 4/0 is sufficient, but the 100 Amp panels are improperly fed, correct?
Click to expand...
Correct. If the panel rating is less than the OCPD protecting its feeder, then an MCB would be required.


mn_voyageur said:
I was taught that the panels either required a main breaker, or they had to be fed from a breaker/disconnect.

I see no exception for the panels to be fed from one disconnect/breaker.
Click to expand...
The requirements [408.30, 408.36] state all panelboards shall have a rating not less than the minimum feeder capacity required for the calculated load and a panelboard shall be protected by an overcurrent protective device having a rating not greater than that of the panelboard. This overcurrent protective device shall be located within or at any point on the supply side of the panelboard.

While the exceptions mention individual protection, the general requirements do not.
 
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