3 Phase, 460 Volt, Vessel Heater MOCP

[Darick]

The company I work for is supplying an MCC for various equipment. One of the pieces of equipment is a 100KW, 3 phase, 460V immersion heater (tank or Vessel heater) with an FLA of 126 Amps. The MCC bucket provided for the heater comes with an On/Off contactor, a 250 Amp Breaker and a Current sensing device that allows the PLC to monitor the branch circuit current and turn the contactor off if the current rises to an alarm level. I am referencing article 427.57 for the MOCP and it turns me back to article 210.3 and 210.23. I cannot find anything that tells me the Max overcurrent protection rating for the heater... only that the branch circuit must be sized for the overcurrent device. I have two questions, 1.) Is there a MOCP rating for a Vessel Heater and 2.) can a branch circuit be sized to the current limit set in the PLC, that controls the on/off contactor?

 

[don_resqcapt19]

I don't see Article 427 as applying to this installation. I see this as covered by 425 and I don't see anything in Article 425 that would permit that installation. In my opinion the branch circuit conductors must have an ampacity equal to or greater than the rating of the breaker.

In addition the the rule in 425.22(B) requires that load to be subdivided at not more than 48 amps, per heating circuit, or with some restrictions not more than 120 amps.

Unless less the PLC control is listed as an OCPD, that does not count.

 

[petersonra]

I think it is probably article 427 but since the requirements are about the same it probably does not matter much. I agree with the rest of Don's comments though.