3/0, 225A motor feeder???

[Electromatic]

I have an existing pump station that seems to have undersized conductors. The service comes in to a 225A enclosed breaker, over to an ATS, then to a MLO panel. All of the conductors are 3/0Cu. The primary purpose of the system is the two large pump motors and their vacuum pump primers, but given there are also lights and receptacles in the small structure, is there any way the whole service could fall under an Article 430 calculation? It seems to me the 3/0 is undersized for 225A protection unless I'm missing something. Everything has been in place for years, and I can only guess this was just overlooked when inspected.

 

[wwhitney]

is there any way the whole service could fall under an Article 430 calculation?

Yes:

230.90(A) ". . . protection shall be provided by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor. . . .
Exception No. 1: For motor-starting currents, ratings that comply with 430.52, 430.62, and 430.63 shall be permitted."

Cheers, Wayne

 

[Dennis Alwon]

I have an existing pump station that seems to have undersized conductors. The service comes in to a 225A enclosed breaker, over to an ATS, then to a MLO panel. All of the conductors are 3/0Cu. The primary purpose of the system is the two large pump motors and their vacuum pump primers, but given there are also lights and receptacles in the small structure, is there any way the whole service could fall under an Article 430 calculation? It seems to me the 3/0 is undersized for 225A protection unless I'm missing something. Everything has been in place for years, and I can only guess this was just overlooked when inspected.

I suspect the original installer used the 90C column for 3/0 which would have been 225 amps. However, the 75 C column is what should have been used.

 

[infinity]

Yes the #3/0 is too small for 225 amps.

 

[wwhitney]

Yes the #3/0 is too small for 225 amps.

OK, but the calculated load may be 200A or less, with a 225A OCPD allowed per 430.63.

Cheers, Wayne

 

[infinity]

OK, but the calculated load may be 200A or less, with a 225A OCPD allowed per 430.63.

Cheers, Wayne

For a service?

The service comes in to a 225A enclosed breaker, over to an ATS, then to a MLO panel. All of the conductors are 3/0Cu.

 

[wwhitney]

For a service?

Yes, did you read post #2?

Cheers, Wayne

 

[Dennis Alwon]

I don't see 430.63 talk about the service nor do I see that a 225 amp overcurrent protective device is allowed with a smaller conductor.

 

[Electromatic]

It is Wayne's spotting of 230.90 that allows even the service OCPD to be adjusted according to 430 calculations.
Service Equipment -- Overcurrent Protection

230.90(A) ". . . protection shall be provided by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor. . . .
Exception No. 1: For motor-starting currents, ratings that comply with 430.52, 430.62, and 430.63 shall be permitted."

 

[Jraef]

The exception points to rules for BRANCH circuit protection. If that breaker is the ONLY SCPD for this, then yes, it is a branch. If there are other SCPDs in the control panel, then this 225A breaker is a FEEDER and different rules apply. The OP does not state the size of the motors and vacuum pumps or whether they have individual SCPDs and overload relays, or if the lights and receptacles have their own protection. So really, we can’t tell if those exceptions qualify.

 

[wwhitney]

The exception points to rules for BRANCH circuit protection.

No, 430.62 and 430.63 are feeder OCPD rules. They appear in "Part V. Motor Feeder Short-Circuit and Ground-Fault Protection"

Cheers, Wayne