Multiple motors by one starter

[Mila15]

A client with no spare MCC capacity needs to add a spare motor. The only option available is to use the same starter for two motors (main and spare). I was thinking of using a transfer switch so that only one motor can be operated at one time. Does NEC article 430.87 which states that: "Each motor shall be provided with an individual controller" limits that solution? Does that article apply if a transfer switch is to be used?

P.S. Non of the exceptions listed in the acticle apply to our situation

 

[jraef]

No, it's fine. That's a perfectly legitimate use of a double throw switch. Normal and standby. Just make sure the switch is motor rated for the size of motor you have, because sooner or later, SOMEONE will switch it under load.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[davidbeach]

But it won't help if the problem that takes out the main motor is the single starter.

 

[jraef]

Very true. It only helps when the problem is the motor or machine itself.

Also, make your users aware of one possible glitch. If motor 1 gets overloaded and trips the OL relay, then they use the transfer switch to change to motor 2, the OL relay does not know that motor is cold and may nuisance trip right away again.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[Mila15]

Good points davidbeach and jraef. It might be a good idea to change OL relay to electronic type (if possible). But I'll let them know that they won't have complete redundancy, especially if the problem is at either the starter or the switch.

 

[jraef]

You could change your MCC bucket to a feeder CB, then hang two starters on the wall. In fact, you could buy what's called a "Duplex" panel which will have the two starters plus an alternator relay so that the wear and tear on the two motors is kept relatively even.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[crshears]

Hi jraef,

Although i like your approach, the OP stated the need was to have a main and a spare motor; your suggestion might not meet Mila15's requirements...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[melspuds]

Hi Mila15
The best thing to do with a transfer switch from opening under load conditions, is install on the switch handle, a set of interlocks that open the starter holding circuit. The interlock opens before the power switch opens. Most transfer switches that as an option.
Good luck,
Dave