Debate on Multimotor and Combination Load Equipment

[brother]

There's the new equipment with multimotors (3 of them) and a control center etc.. that is factory wired and the name plate only tells of the FLA, voltage, frequency, the hp of one of the motors. The manufacturer did not follow 2008 430.7(D) (1) that states they should tell YOU what the minimum supply circuit conductor ampacity and the maximum ampere rating of the circuit short-circuit and ground-fault protective device is.

The debate is about the minimum size conductors and size of the overloads (fuses) that should feed this equipment from the final disconnect to the equipment because the name plate on the equipment is 75 FLA total, and the circuit that was ran to it is 80 amps , #4 AWG 80 amp fuses. I believed that it should have the 75 fla X 1.25 =93.75 or 100 amp since we are not certain what the manufacturer did in getting to the FLA, did they or did they not accout for the 125% and what is the amp draw of all the other loads? Even if we did the 3 15 hp 460volt we get 21 X1.25 +21+21=68.25 just for the motors.

I know if it was not a 'factory wired' unit then we would just calculated with the 3 motors at 125% of the largest motor plus 100% of the other motors and the 100% of the other equipment IF we know what amps they pulled.

Called the manufacturer and they say they were not aware of 430.7(D) (1), so they weren't sure what to tell me !!
Ive read both 430.24 and 430.53 Branch circuits and still come up with my same answer to error on the side of caution.

Whats your opinion on this??

 

[infinity]

So the nameplate amperage of 75 amps is the total for the entire piece of equipment?

 

[brother]

So the nameplate amperage of 75 amps is the total for the entire piece of equipment?

yes 75 FLA is what is listed for the whole piece of equipment. But whenever I dealt with FLA I always added the 125%.

By the way, Happy Thanksgiving to everyone!

 

[Smart $]

yes 75 FLA is what is listed for the whole piece of equipment. But whenever I dealt with FLA I always added the 125%.

By the way, Happy Thanksgiving to everyone!

Depending on what the non-motor loads are, it appears the FLA rating is pretty close to what would normally be your MCA.

 

[infinity]

Unless this is a continuous load I would size the branch circuit based on the nameplate rating of 75 amps.

 

[brother]

Unless this is a continuous load I would size the branch circuit based on the nameplate rating of 75 amps.

That's the 'key' answer that makes me 'conservative', the continous load. This unit (or at least some parts of it alternating between motors, pump etc.)will be running for more than 3 hrs. I beleive this should be cause for the continous load 125% add in since manufacturer can't give a straight answer.

 

[Smart $]

That's the 'key' answer that makes me 'conservative', the continous load. This unit (or at least some parts of it alternating between motors, pump etc.)will be running for more than 3 hrs. I beleive this should be cause for the continous load 125% add in since manufacturer can't give a straight answer.

While the unit may operate more than 3 hrs. as a whole, if every component does not operate simultaneously for 3 hrs., the unit does not need to be considered a continuous load. And if the components don't run full on continuously, it seems to me there would be a control panel to house motor starters and other control equipment. Does it have a main ocpd? ...and if so, what is its rating? Just exactly what does it have for control, and what other loads besides the motors are there?

 

[iwire]

I agree with smart about the definition of continuous loads.

Continuous Load. A load where the maximum current is
expected to continue for 3 hours or more.