Interrupting Capacity of Combination Starter

Ask the manufacturer. And then maybe ask UL.

It probably will. What is of real interest is whether or not it will survive the experience sufficiently well to enable its correct operation on subsequent occasions.

How did the telephone call with the equipment manufacturer go, then?

What is a MCP?

The OP explained that in parentheses: motor circuit protection. (More usually rendered as "protector")

MCP - Definition by AcronymFinder

Check the data sheets carefully for the fault ratings (including their stated durations which is very important) as the proper ratings should be in there to allow you to match the two together. Both must be greater than your prospective fault current or the equipment most likely won't be suitable.

Also check your realistic expected fault currents (worst case) and upstream protection settings, perhaps your prospective fault current is not as high as you think.

"what justification that I could give"?

Tell them you have no clue what you are doing.

I see this in your future:

Unfortunately, it will likely be some poor electrician who suffers the consequences of your incompetence.

Get some competent help, and the code book, and then call your suppliers and ask them for advice.

UL will not offer any technical advice.

Here is how this works. Circuit breakers are designed and listed for a particular interrupting capacity in mind, let's say 65kAIC. They will be tested under that condition and if it passes by itself, they list it that way, but EVERY breaker they sell with that rating is expected to survive that level of fault current, regardless of everything else used in its circuit. So any additional contribution that other devices MIGHT be able to contribute to the process are required to be ignored, because on the surface the listing of the breaker has to stand alone. So because of this, even if the breaker passed at 65kA, they may list it at 35kA and sell it at a lower price and higher volume to end users and OEMs, who will accept the responsibility of doing the extra engineering considerations of how it is used. If they want to take on a little more risk and list it at 65kAIC, they want to get paid for that since the volume will be lower, so they sell the EXACT SAME breaker as 65kAIC for a higher price to get the label that says that. If you want a higher rating, such as 100kAIC, the design of the breaker is often significantly different and volume is significantly lower. So expect to pay a lot more for that.

Now, when the breaker manufacturer wants to sell that lower rated breaker in a series combination string of THEIR OWN other components such as starters, they will often take on the added risk in order to increase their total sale. Plus THEY are in control of the exact design criteria in that series string. So even though the breaker SAYS it is the 35kAIC version , THEY know it will pass in the 65kA string test. In fact in some cases they even pass at 100kA (Rockwell) using the same breaker. An important part of this is that the series MUST be testested by UL together, no simple filing of paperwork.

Friend,

The components chosen will have their own labeled interrupting capacity. When the components are assembled into an MCC bucket then the lowest rated component sets the rating of the assembly unless the assembly of components has been tested and labeled for a higher capacity. The wording of your question leaves some ambiguity, but if this is a factory-assembled combination starter then the label on the bucket would apply even though the MCP appears to have a lower rating.

--JMM

Hi JMM. Thanks for your input. So I could assume now that the combination starter, though MCP is 35KAIC, theoretically, it can clear the Fault of say...55KAIC (for as long that it was UL Tested).

"Assume: it makes an ass out of u and me." - Anon.

If in doubt, consult a local Electrical Engineer.

They won't be calling you "Sparky" for nothing. When you concern for electric safety ceases, you become an endangered species.

The MCP is 35KAIC which means it is suitable for use with the higher rated 65KAIC MCC cubicle motor starter. Does that make sense? But is the MCC rated for the upper fault current values available in the feeder circuit? You need to consult with your 70E code book, and really think about this.

NEVER EVER put say a 70KAIC MCP in a 65KAIC rated enclosure. It will blow the doors off it during a fault interruption, and spray everyone walking by with hot copper liquid, and also the intensely 5000 C hot copper vapor cloud.

^{The MCP is 35KAIC which means it is suitable for use with the higher rated 65KAIC MCC cubicle motor starter. Does that make sense? But is the MCC rated for the upper fault current values available in the feeder circuit? You need to consult with your 70E code book, and really think about this.}

^{NEVER EVER put say a 70KAIC MCP in a 65KAIC rated enclosure. It will blow the doors off it during a fault interruption, and spray everyone walking by with hot copper liquid, and also the intensely 5000 C hot copper vapor cloud.}

Huh? Are you being facetious? (fecetious)