240.21 Three panelboards from one disconnect, no mains

[mn_voyageur]

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

 

[Little Bill]

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

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.

 

[mn_voyageur]

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]

If 100 amp fuse with 100 amp wire :to block and to panels, I see nothing wrong. In same bldg?

 

[mn_voyageur]

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

 

[ptonsparky]

Are these taps of different sizes from the block?

Usually each building has a disconnecting means.

 

[mn_voyageur]

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

 

[hillbilly1]

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

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.

 

[Smart $]

No, the taps are identical.

If each panel feeder is identically sized (i.e. rated) as the feeder trunk, there are no taps and 240.21 does not apply.

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?

Correct. If the panel rating is less than the OCPD protecting its feeder, then an MCB would be required.

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.

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.