Motor Breakers - HMCP vs Standard Breaker

[TConnolly]

I've got a project underway with six motors on AB SMC-3 soft starters. Generally I have used HMCP type breakers (magnetic only breakers with an adjustable trip point) on motors in the past, but I'm looking at the quote and comparing it to the price of non-adjsutable thermal-mag moulded case breakers and asking myself "why would I spend this extra money?" It adds up in a panel with six motors. (about 3-1/2 times as much).

So what real advantage do I gain, especially since I'm using soft-starters?

 

[burnerman]

Depends if you've got contactors as well as soft starts, if you have then you can use the contactor as the disconnect for an overload situation using the fault relay on the SMC.
Wouldn't like to rely solely on the SMC to disconnect an overloaded motor.

 

[Jim Dungar]

HMCP type breakers only provide motor short circuit protection and must be used with a seperate motor overload device. Typically the magnetic only breakers are only "component recognized" and may only be used with specific magnetic motor starters per most UL listings. If your equipment needs a UL label, check with the manufacturer of the breaker and the soft-start.

 

[TConnolly]

Jim, so I would be better of to go with a standard thermal-mag breaker?

(No skin off my nose, they are cheaper anyways.)

 

[Jim Dungar]

Hey, I usually take the easy way. I always use the device listed in the soft-starter recommended parts list. But I do like to add a shunt trip coil so that a fault in the starter will "trip" the breaker.

 

[JohnW]

With an SMC-3 you can use a magnetic only MCB. The SMC-3 will handle the thermal trip (which is adjustable as well as the trip class).

 

[Jim Dungar]

John is that a UL listed/recognized combination?

 

[JohnW]

I believe so, the type of device I am talking about is a 140M-C or 140M-D MCB. A switch - fuse unit could be used instead. I have fitted 6 SMC-3s to a Bulletin 141A busbar system with 140M-D MCBs, The 140 provides galvanic isolation for each motor and I fitted a main MPCE contactor that switched the feed to the busbars. The feed to the busbars was protected by fuses.