MCP Breakers

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djrupprecht

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I am pretty green with all this, but what are the major differences between an MCP breaker and a Thermal Magnetic breaker? I ask because I notice on a couple of single lines I have looked at, MCPs are used with motors hooked up across the line and thermal magnetics are used with VFD run motors. Why is this?

Thanks
 
... and MCPs can only be used in motor starters. They serve as short circuit and ground fault protection. The motor overloads provide overload protection.
 
djrupprecht said:
I am pretty green with all this, but what are the major differences between an MCP breaker and a Thermal Magnetic breaker? I ask because I notice on a couple of single lines I have looked at, MCPs are used with motors hooked up across the line and thermal magnetics are used with VFD run motors. Why is this?

Thanks
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The main reason starter manufacturers use MCPs any more is because they are slightly cheaper for them to buy/supply in bulk. It used to be that they were used because they had adjustable magnetic trip elements, whereas TM breakers had fixed magnetic trips. The average "old school" TM breaker's mag trips were set at 400% of the rating, making them too low for most motor applications, so the adjustability of the MCPs made them more useful. Most modern TM breakers over 125AF now have adjustable mag trips anyway, so there really is no longer an advantage. 100 / 125AF breakers still have this issue however because most of them still do not have adjustable mag trips

Then there's the UL issue. MCPs are not UL listed, they are UL Recognized Components (UR). That means that to use an MCP, you must test the total arrangement as a complete assembly, not just the individual components. So for new devices like VFDs, to use MCPs they would have had to list the VFD, then list it again with an MCP. By using a TM breaker they can list the VFD and say it's OK to use it with any listed TM breaker. It's a little more complex than this of course, but that's the "Reader's Digest" version.
 
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