There will be termal element which responds to increase in current by virtue of its own property to get heated up in more than rated current and deflect from the normal position which in turn operate the lever and trips the motor
zero voltage relese there is no device called like that ther are single phase preventers and fuse failure monitors which take care of loss in voltage or one fuse
If I might add, there is a low-voltage trip mechanism (which I have heard called zero voltage tripping, but it doesn't come anywhere near zero volts) that can be added to MSP's (IEC Manual Motor/Starter Protectors.)
Quite a few people are switching from NEMA to IEC style starters because of cost and features. MSP's are like circuit breakers, but in North America, they do not meet UL 489. Which means they can only be used for overload protection and not short-circuit protection. People are using these on top of contactors inplace of other removable heater design overloads.
If the motor starting contactor is electrically held, the holding coil will drop out and release the contactor if the control voltage falls below about 60-70% of rated. If the control voltage is derived from the same source as the motor power source, then the electrically held contactor fulfills a zero voltage release function.
ctolbert - glad to see a new face in the crowd. I've seen some of your posts at motorcontrol.com and looking forward to hearing more.
Can you explain a little bit about the advantage of using MSP if you already have a breaker and a starter with overload? What else do you need? Or does it perform the overload function in place of the starter?
The msp strictly takes the place of an overload unit. It's only advantages over a NEMA overload unit are single-phase protection (as a function of thermal OL), plug-in modules (shunt trip and undervoltage), and cost.
You still have to follow NEC 430... but you can use article 430 53c which allows for "group motor installation" It's up to the user.
