225amp feeding 150amp disconnect

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inspectorjoe

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Dover, NH USA
you have a 400amp panelboard with various breakers serving loads, one of those breakers is a 225amp breaker with225 amp rated wire 3/0 run to a 200amp disconnect inside the building and then the wiring changes to 150amp wire thru the wall to an outside disconnect (fused) 150amp for HVAC equipment. the question is can you feed the 150amp disconnect from the 225 amp breaker?
 
Here is a section that may help. The issue is 3/0 cu is only good for 200 amps not 225

408.36 Overcurrent Protection. In addition to the requirement
of 408.30, 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.
Exception No. 1: Individual protection shall not be required for a
panelboard used as service equipment with multiple disconnecting
means in accordance with 230.71. In panelboards protected by three or
more main circuit breakers or sets of fuses, the circuit breakers or sets of
fuses shall not supply a second bus structure within the same panelboard
assembly.
Exception No. 2: Individual protection shall not be required for a
panelboard protected on its supply side by two main circuit breakers or
two sets of fuses having a combined rating not greater than that of the
panelboard. A panelboard constructed or wired under this exception
shall not contain more than 42 overcurrent devices. For the purposes of
determining the maximum of 42 overcurrent devices, a 2-pole or a
3-pole circuit breaker shall be considered as two or three overcurrent
devices, respectively.
Exception No. 3: For existing panelboards, individual protection shall
not be required for a panelboard used as service equipment for an individual
residential occupancy.
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inspectorjoe said:
you have a 400amp panelboard with various breakers serving loads, one of those breakers is a 225amp breaker with225 amp rated wire 3/0 run to a 200amp disconnect inside the building and then the wiring changes to 150amp wire thru the wall to an outside disconnect (fused) 150amp for HVAC equipment. the question is can you feed the 150amp disconnect from the 225 amp breaker?
Click to expand...
You cannot feed the 200 amp disconnect with a 225 amp feeder OCPD.
 
Agree. I also note it is for HVAC equipment so we well may have a 240.4(G) situation. Guess we wait on more specifics.
 
If this is feeding HVAC equipment we do need to consider what the MCA and MOCP of the unit is, could be more complicated if feeding multiple units.
 
In addition to the 3/0 being too small to be protected by a 225 amp OCPD, it also appears that the wire size was reduced before it got to the outside fused disconnect. The reduced wire part of the circuit would be a tap and would have to comply with the rules in 240.21(B).

If the 3/0 was run all the way to the fused disconnect, even though it is only 200 amp wire, that would be ok if that run complied with 24021(B).
If not, the 3/0 is too small.
 
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