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- retired electrician
From the UL Guide Information for Combination Motor Controllers (NKJH)
motor rated breakers
- Thread starter LMartin57
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But electrians do, and the OP is an electrian. That was why I said we just speak different languages.
But electrians do, and the OP is an electrian. That was why I said we just speak different languages.
Would this include an MCP on the primary side of a VFD? You would be more inclined to see a TM UL 489 listed breaker there since it would be very doubtful for an MCP to protect a motor circuit on the secondary side of a VFD as a part of a combination motor starter.
petersonra
Senior Member
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- engineer
which has little to do with MCPs as they are recognized as UL508 items I think. Or maybe they are 489 recognized. In any case, they are not listed at all.
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The answer is 'B', UL 489 recognized.
The important thing to remember is that must rely on another device such as the OLR of a starter to protect the MCP from overcurrent as an MCP in completely stupid when it comes the currents that exceed its rating. The MCP can be destroyed.
- Location
- Illinois
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- retired electrician
It has everything to do with the use of MCPs under the rules of the NEC. The NEC says they can only be used as part of a "listed combintation motor controller". The UL Guide information spells out the conditions of use for "listed combintation motor controllers".
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- retired electrician
If the combination of the MCP and the VFD is listed as a "combination motor controller", it would be code compliant.
I am in total agreement with you Don. But the OP didn't establish that which was the basis for my question which remains unanswered. When an MCPs purpose is to protect a motor circuit from a motor L-G are L-L failure by place a VFD in between the MCP and the motor the MCP would most likely not respond to a motor failure?
The VFD probably would provide over current protection for the MCP.
But it would be interesting if what the OP described did have a UL listed combination rating.
petersonra
Senior Member
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- Northern illinois
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- engineer
take a look at the charts provided by schneider for the soft starters. they list both mcp and tm breakers as having UL testing for high sccr for use with specific starters. would UL make a list like that you were not allowed to use?
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Thanks, I see your point for soft starters. What I question is what a mag. only MCP contributes when there is a vfd between the MCP and the motor. What type of protection does the MCP provide for the motor circuit? I can see where the vfd will act as an overload which would provide OL protection for the MCP and the MCP may provide short circuit protection of the vfd but what type of protection would the MCP provide for the motor? I'm just trying to understand what the purpose of the MCP on the line side of a vfd is.
Thanks, I see your point for soft starters. What I question is what a mag. only MCP contributes when there is a vfd between the MCP and the motor. What type of protection does the MCP provide for the motor circuit? I can see where the vfd will act as an overload which would provide OL protection for the MCP and the MCP may provide short circuit protection of the vfd but what type of protection would the MCP provide for the motor? I'm just trying to understand what the purpose of the MCP on the line side of a vfd is.
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- Illinois
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- retired electrician
I am not sure how that complies with the UL White Book information. In my opinion, it would only work if the combination of parts are marked "combination motor controller". If the specific wording does not appear on the equipment or on a list of equipment that can be combined, then I see it as a violation of the rule in the NEC that only permits the MCP to be used as a part of a listed combination motor controller. Maybe that information is found somewhere in the Schneider document, but without that information, it gets a red tag from me.
petersonra
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- Northern illinois
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- engineer
I think you are taking the word "marking" too literally. UL allows such markings to be part of the instructions or on the boxes the parts come in.
petersonra
Senior Member
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- Northern illinois
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- engineer
It provides only SC protection, just as it does in a normal contactor circuit.
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- Wisconsin
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- PE (Retired) - Power Systems
So you would not approve Motor Control Centers that use buckets which contain starters and MCP's?
These individual buckets are not UL Listed as 'combination motor controller' under the UL White book reference you used.
How about control panels listed to UL508, they are not marked as a 'combination motor controller"?
But it isn't a normal contactor circuit. The OP was referring to an VFD, your reference if using a soft start which is in no way a vfd. How can you provide short circuit protection for a motor when the motor is on the load side of a vfd and the MCP on the line side of the vfd? How can an MCP even see a motor fault as it would as being a part of a common combination motor starter consisting of an MCP, contactor, and an OLR?
petersonra
Senior Member
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- Northern illinois
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- engineer
presumably UL has figured this out as many vfds and soft starters have UL listings that allow this combination. there are some things I do not know enough about that I have to accept what others who presumably know more say.
I have even seen a few high SCCR combinations like 65kA where the TM breaker is only rated at 35kAIC. I guess if they test it and it works, it flies with UL.
What you have finally confirmed is the you do have VFDs that do have MCPs of the primary that have a UL listing.
Also, MCPs do not have an interrupting rating as the interrupting rating is dependent upon a combination test as a combination starter which in your case is 65ksic which is a common combination rating. Also, you happen to have a TH
M breaker that is 35kaic. If required the TM breaker could be replaced with TM breaker with a rating of 65kaic.
It doesn't make any sense to me either that an MCP located on the line side of a vfd is able to protect the motor circuit on the load side.
If it is a UL listed then it's allowed.
- Location
- Illinois
- Occupation
- retired electrician
That is true, but a catalog cut page is not enough, and the markings or instructions must state exactly what components are required to be used to create a listed combination motor controller.
- Location
- Illinois
- Occupation
- retired electrician
Then what provision of the code permits the use of the instantaneous trip breaker in a MCC bucket? To me the code is clear that an instantaneous trip breaker can only be used as part of a listed combination motor controller.
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