Motor Control Circuit

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scaldave

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I need information about Control Circuit Voltage regarding motor starters.
I have found a panel that has 480 3pH motor starters with 440vac coils, I am sure this practice was once acceptable but I believe now that all control circuits need to be 120vac or lower. Is this correct? If so does anyone know where I can find the reference info to back up my position before I bring to managements attention.
Also doesn't motor power voltage have to be in seperate conduit than 120

Thanks,
scaldave
 
Re: Motor Control Circuit

Coil voltage is not a code issue, its is a design issue. the rules are in article 430 part 6.
120V is preferred as it easier to interface to, and safer to trouble shoot. 460 can be used to keep the cost down, as with 120 you need a control transformer. larger starters such as size 5 and above will typically have a 460 volt coil as the inrush is too high for a 120 V source.
Either 120 or 460 can be used, but 120 is the most common.
 
Re: Motor Control Circuit

It is common for the larger starters to have 480v coils because higher voltage, lower current, that is 480v takes 1/4 the current as 1204 coils. It If the pilot devices are within the starter enclosure then there shouldn't be an issue as there should be an interlock that disconnects power before the enclosure can be accessed.
Should the pilot devices be remote than 120v control circuit with a CPT using an interposing relay to energize the coil with 480v can be used. If you go this far then you may consider a 24vac control.
It is quite common today for the larger starters to actually use DC coils with a built in rectifier using 120vac as power. Such devices commonly have an economizer circuit that switches the rectifier from full to 1/2 wave after the contactor pulls in.
 
Re: Motor Control Circuit

for existing control panels built long ago, you may be stuck with 480 volts.

try nfpa 79 electrical standards for industrial machinery article 9.2 (control circuit voltages).
this limits you to 120 volts.
 
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