MCP vs thermal mag breakers

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mshields

mshields

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Boston, MA
I've got a Distribution panelboard feeding a number of motor loads. I've sized the breakers for 175% of FLA (and the cable at 125%). But because this is not an MCC that we're comming from, I'm using thermal mag breakers and not MCP's. My client wants me to provide MCP's because at 65K he contends that they are significantly cheaper.

Can we go with MCP's given the overload protection is at the end of the feeder with the motor? And is there really that much of a cost difference between MCP's and thermal mag breakers?

Thanks,
 
Mike,
MCPs can only be used when part of a listed combination starter.
430.52(C)(3) Instantaneous Trip Circuit Breaker An instantaneous trip circuit breaker shall be used only if adjustable and if part of a listed combination motor controller having coordinated motor overload and short-circuit and ground-fault protection in each conductor, and the setting is adjusted to no more than the value specified in Table 430.52.
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Don
 
Bingo to both of those answers. You will find, if you look carefully, that MCPs are NOT listed by UL, they are what is called "Recognized Components" signified by a backwards UR on the label. This means they CANNOT be used by themselves, they can ONLY be used as a component in an overall listed assembly. No panelboard has been UL listed as an assembly with MCP breakers, so you cannot legally do it.
 
Jraef said:
Bingo to both of those answers. You will find, if you look carefully, that MCPs are NOT listed by UL, they are what is called "Recognized Components" signified by a backwards UR on the label. This means they CANNOT be used by themselves, they can ONLY be used as a component in an overall listed assembly. No panelboard has been UL listed as an assembly with MCP breakers, so you cannot legally do it.
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Not entirely true (and to be difficult), trivia from the Square D Digest: "Mag-Gard circuit breakers are availablewith I-Line construction."

So technically, an equipment manufacturer could use an I-Line panel and still get a UL Listing.:wink:

 
Jim,
What can we use that I-Line breaker for? The only permitted use that I am aware of is as part of a listed combination starter.
Don
 
Don,

Mount the I-Line panel interior only inside of a multi-door enclosure with UL recognized starters. Take this entire assembly to UL for your 508A listing.

Or use them in an old (late 70's early 80's) I-Line motor starter panel. These looked like the traditional QMB fusible style motor starter panel.
 
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