2 Apr 10 16:52
Just because Allen Bradley says something does not make it so... You are right, A-B placed the symbol description in a category they called "Overload Relay" on page 5 of that document. But that is an incorrect reference point. As much of a shock as this will be to some people, they messed up!
But if you read further, you will see that the only place they actually show it in a schematic power diagram is on page 13 as part of a Manual Motor Starter.
But they are not the end-all / be-all for the electrical world, especially when it comes to things IEC. That chart is essentially attempting to rationalize a comparison of JIC / NEMA symbols to IEC symbols; useful, but by no means definitive.
Outside of North America, what we would call a "Manual Motor Starter" is just a manual disconnect device with a thermal trip element. Not so for IEC. They can use it as a Motor Protection Switch because the IEC device has all three elements necessary in a motor protection circuit: a Disconnecting means, Motor Overload relay (thermal element) and Short Circuit Protective Device (SCPD), the magnetic trip element. So when people use them in "combination motor starters", they need only add the contactor.
In traditional NEMA controls, no such all-in-one device exists, so we have a separate Disconnect, SCPD (fuses) and Overload Relay (thermal) attached to the contactor. The only variance is that the SCPD can be a Circuit Breaker, which also acts as the disconnect device, and can come with Magnetic-Only trip elements (often called an MCP Breaker) or a regular Thermal-Magnetic Circuit Breaker. When we use a T-M CB in a combination motor starter, the Thermal element in the breaker becomes redundant to the Overload Relay and is generally ignored as it will by design need to be selected at a size too high to protect the motor anyway. Even a Manual Motor Starter in NEMA parlance still needs the SCPD (CB or fuses) ahead of it.
So the reason I went to this length is to point out that you can't really make a direct comparison because it really depends upon how you are planning to put together your IEC motor starter: Disconnect / SCPD + Contactor + OL, or IEC Motor Protective Switch + Contactor. Either way is valid in IEC designs, although those Motor Protective Switches have limited sizes available.
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