MCC Breaker Notation

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steve66

Senior Member
Location
Illinois
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Engineer
On a set of plans, some of the breakers in a MCC are noted with 150AF/150AT. I know this is 150 amp frame, with a 150 amp trip.

But some of the breakers supplying motor starters have notations like 30/M , or 15/M, or 7/M.

What does that mean? Would a 30/M mean a long time trip of 30 amps, with no magnetic trip?
 

david luchini

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Location
Connecticut
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Engineer
On a set of plans, some of the breakers in a MCC are noted with 150AF/150AT. I know this is 150 amp frame, with a 150 amp trip.

But some of the breakers supplying motor starters have notations like 30/M , or 15/M, or 7/M.

What does that mean? Would a 30/M mean a long time trip of 30 amps, with no magnetic trip?

I would think it would be the opposite...A magnetic only motor circuit protector.
 

jim dungar

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Staff member
Location
Wisconsin
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PE (Retired) - Power Systems
On a set of plans, some of the breakers in a MCC are noted with 150AF/150AT. I know this is 150 amp frame, with a 150 amp trip.

But some of the breakers supplying motor starters have notations like 30/M , or 15/M, or 7/M.

What does that mean? Would a 30/M mean a long time trip of 30 amps, with no magnetic trip?

Some engineers take one manufacturer's terminology, they slightly twist or modify it, and then apply it as if it was an industry standard.

With no other information, I support David's idea that this is meant to designate a Motor Circuit Protector (magnetic only) style breaker. It is similar to a methodology employed by the Square D brand Mag-Gard breakers.

The number would be the nominal full load amps of the breaker.
 
Some engineers take one manufacturer's terminology, they slightly twist or modify it, and then apply it as if it was an industry standard.

With no other information, I support David's idea that this is meant to designate a Motor Circuit Protector (magnetic only) style breaker. It is similar to a methodology employed by the Square D brand Mag-Gard breakers.

The number would be the nominal full load amps of the breaker.

I like the idea - haven't seen it before - wold rather see the adjustable range after the "/" instead of just the "M". But I stopped generating one lines for MCC's and instead of use Excel spreadsheet with Macros that generate the front layout and all other important information, like connected HP/kVA/kW, summary, total inrush, auto OL selection based on FLA, etc. Sortable list, easy to find equipment, even across multiple MCC's.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Magnetic only would make sense, since the long time protection would still be provided by the motor starter overloads.

But if its magnetic only, doesn't that make numbers like "15" or "7" meaningless?

7 wouldn't be any standard circuit breaker size anyway.

So I'm still puzzled.

Steve
 

david luchini

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Connecticut
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Magnetic only would make sense, since the long time protection would still be provided by the motor starter overloads.

But if its magnetic only, doesn't that make numbers like "15" or "7" meaningless?

7 wouldn't be any standard circuit breaker size anyway.

So I'm still puzzled.

Steve

The "7" would be another indicator that this is a magnetic only breaker. For instance, Square D # GJL36007M02 is a Motor Circuit Protector with an Ampere Rating of 7, and an adjustable trip range of 21-77A.

(The Siemens ED63A005 has an ampere rating of 5 and a trip range of 16-54, etc.)
 
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jim dungar

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Location
Wisconsin
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PE (Retired) - Power Systems
But if its magnetic only, doesn't that make numbers like "15" or "7" meaningless?

7 wouldn't be any standard circuit breaker size anyway.

If the breaker has a magnetic trip range of 1.5 to 15 times, wouldn't you need to know the base amount?
Isn't easier to deal with setting a mechanical 'dial' range of 1.5 to 15 times 7amps rather than 0.35 to 15 times 30amps?

There is no NEC proscription against non-standard breaker sizes.
 

steve66

Senior Member
Location
Illinois
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Engineer
It's starting to make sense now.

I guess 7 is an available rating for a motor circuit protector, at least from Square D.
 

jim dungar

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Location
Wisconsin
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PE (Retired) - Power Systems
I guess 7 is an available rating for a motor circuit protector, at least from Square D.
It was.

They used to make 3A, 7A, 15A, 30A sizes. Now they make one that has an adjustable nominal rating as well as a magnetic range.
 

templdl

Senior Member
Location
Wisconsin
On a set of plans, some of the breakers in a MCC are noted with 150AF/150AT. I know this is 150 amp frame, with a 150 amp trip.

But some of the breakers supplying motor starters have notations like 30/M , or 15/M, or 7/M.

What does that mean? Would a 30/M mean a long time trip of 30 amps, with no magnetic trip?

Those appear to be the ampacities of MCPs. The #7 for instance will commonly be stamped on the end of the toggle. And it is extremely important that the 7a not be exceeded of there is a strong possibility that you will let the smoke out. As such pat close attention to what you drawings require. Also note that each rating will also have a different adjustable magnetic trip range.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I have been doing some standardization work lately. I thought I would try to be clever and change out some TM breakers in favor of the same breaker but in an IT only version thinking they would cost less.

Imagine my surprise when the TM breakers turned out to be about 20% cheaper.
 

templdl

Senior Member
Location
Wisconsin
I have been doing some standardization work lately. I thought I would try to be clever and change out some TM breakers in favor of the same breaker but in an IT only version thinking they would cost less.

Imagine my surprise when the TM breakers turned out to be about 20% cheaper.

What you are saying is of concern to me. A common TM breaker is UL489 listed stand alone device. A mag only breaker such as an MCP is a reverse UR component listed device which can not be used by itself. As such an MCP c as n not be used to replace a TM Breaker.
MCPs built on a 150 frame start out at 3a max continuous, 5,7,10,15a up to 150a. The ratings as marked on these MCP mag only breakers is just that, a maximum rating which is not to be exceeded. The magnetic element for these breakers consist of essentially a solenoid made of a given size of conductor. Should you exceed the rating of the MCP you will fry the solenoid. With 250a frames and larger the magnetic structure is different and the frame size is the max rating. MCPs also don't lend themselves very well to field test as they will most likely be destroyed when someone attempts to do so.
Also, please don't misunderstand that MCPs cost more to make. Pricing is based upon the functional pricing and the market. The manufacturing cost between an MCP and a TM breaker is really insignificant.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
What you are saying is of concern to me. A common TM breaker is UL489 listed stand alone device. A mag only breaker such as an MCP is a reverse UR component listed device which can not be used by itself. As such an MCP c as n not be used to replace a TM Breaker.
MCPs built on a 150 frame start out at 3a max continuous, 5,7,10,15a up to 150a. The ratings as marked on these MCP mag only breakers is just that, a maximum rating which is not to be exceeded. The magnetic element for these breakers consist of essentially a solenoid made of a given size of conductor. Should you exceed the rating of the MCP you will fry the solenoid. With 250a frames and larger the magnetic structure is different and the frame size is the max rating. MCPs also don't lend themselves very well to field test as they will most likely be destroyed when someone attempts to do so.
Also, please don't misunderstand that MCPs cost more to make. Pricing is based upon the functional pricing and the market. The manufacturing cost between an MCP and a TM breaker is really insignificant.

its for UL508a listed control panels. all motor circuits. in this case for 200 and 250 HP soft starts. I just found the pricing model interesting. another supplier's IT breakers are substantially less for the same frame as a TM breaker. I suppose the marketing geniuses figured out most people can't easily tell what something costs so would assume the IT version was less.
 

templdl

Senior Member
Location
Wisconsin
its for UL508a listed control panels. all motor circuits. in this case for 200 and 250 HP soft starts. I just found the pricing model interesting. another supplier's IT breakers are substantially less for the same frame as a TM breaker. I suppose the marketing geniuses figured out most people can't easily tell what something costs so would assume the IT version was less.

The only time that you have to be concerned about IT breakers is renewal parts as they are packed with combination motor starters. As such they come packaged with other components.
Are you a UL panel shop? If so I see where you would realize the difference in IT and TM pricing as import and when establishing the cost to build a panel.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
its for UL508a listed control panels. all motor circuits. in this case for 200 and 250 HP soft starts. I just found the pricing model interesting. another supplier's IT breakers are substantially less for the same frame as a TM breaker. I suppose the marketing geniuses figured out most people can't easily tell what something costs so would assume the IT version was less.
As he said, the pricing you can get is functional, not cost based. It does cost significantly less to manufacture a mag-only breaker compared to a TM breaker. Here is how the pricing works:

IT breakers have only two valid uses; FACTORY built and tested motor starters that are going to be UL listed as complete assemblies after short circuit withstand testing, and replacements as such. So if you are buying a Mag Only breaker from a mfr, and you are NOT one of their partner mfrs using their breakers, then the ONLY reason you can be buying it is because you are REPLACING one that it already installed. Then since they know that you cannot replace one brand with another, they therefore also know that they can charge you more and get away with it.

It also serves to keep people from buying IT breakers just because they are cheaper and misapplying them. I would see people trying to do that all the time when I worked for Siemens, I would even see it shown in drawings that were stamped by PEs.

Back to the notations, that is an uncommon notation, but I have seen it before and yes it does mean IT (Mag-Only) breakers. The fallacy is, the engineer that put it there was making a pointless notation in that for whatever motor starter they called for, the mfr has NO CHOICE in the sizing of the IT breaker that goes into it, they can ONLY use the size that the starter is specifically UL listed for. So if he picks right, great, but if he picks wrong, he creates a conflict that may need to be addressed via correspondence, a needless waste of everyone's time. I have to deal with this kind of pointless specificity all the time now, bugs the crap out of me.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
IT breakers have only two valid uses; FACTORY built and tested motor starters that are going to be UL listed as complete assemblies after short circuit withstand testing, and replacements as such. So if you are buying a Mag Only breaker from a mfr, and you are NOT one of their partner mfrs using their breakers, then the ONLY reason you can be buying it is because you are REPLACING one that it already installed. Then since they know that you cannot replace one brand with another, they therefore also know that they can charge you more and get away with it.

That is sort of true.

UL considers an assembly built from recognized parts into a listed assembly to be the same as the listed assembly as long as the instructions are followed. So the assembly itself does not have to actually be made at the manufacturer. It can be assembled from the same parts in the field by someone other than the manufacturer.
 

templdl

Senior Member
Location
Wisconsin
That is sort of true.

UL considers an assembly built from recognized parts into a listed assembly to be the same as the listed assembly as long as the instructions are followed. So the assembly itself does not have to actually be made at the manufacturer. It can be assembled from the same parts in the field by someone other than the manufacturer.

But the field assembly is not listed. As such I believe that it will have a max of 5kaic.
With a manufacturer or OEM that is a UL facility assemblies such a enclosed starters, MCCs etc are tested on the enclosure to meet a given UL criteria. Then the rating of the "assembly" is placed on the enclosure.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
But the field assembly is not listed. As such I believe that it will have a max of 5kaic.
With a manufacturer or OEM that is a UL facility assemblies such a enclosed starters, MCCs etc are tested on the enclosure to meet a given UL criteria. Then the rating of the "assembly" is placed on the enclosure.

My understanding is that one can assemble the pieces yourself.

There are instructions that have to be followed, including things like the minimum size of the enclosure.
 

templdl

Senior Member
Location
Wisconsin
My understanding is that one can assemble the pieces yourself.

There are instructions that have to be followed, including things like the minimum size of the enclosure.

Yes you can as the components are available but it would not be a listed assemble. You can not claim over a 5kaic in ding so.
It is important to note that the actual rating of the assembly is when it is tested in an enclosed and the label is often located on the inside on the side of the enclosure as I stated in one of my previous posts..
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Yes you can as the components are available but it would not be a listed assemble. You can not claim over a 5kaic in ding so.
It is important to note that the actual rating of the assembly is when it is tested in an enclosed and the label is often located on the inside on the side of the enclosure as I stated in one of my previous posts..

that is not my understanding from long chats with the product managers that market these things.

there is often a minimum size enclosure specified as part of the instructions.

I have seen a few that the instructions mention it is for ul508a applications, so they could only be assembled into a UL508a listed panel. But not all of them say that.

if what you are saying is true, only an enclosed starter with the label on it would be over 5kA.

by the way, kaic is a rating for the interrupting device such as the CB or fuse. the assembly has a short circuit current rating measured in kA. There is a big difference.
 
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