AF and AT breaker notation
- Thread starter steve66
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jtester
Senior Member
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- Las Cruces N.M.
Re: AF and AT breaker notation
AF refers to the ampere rating of the breaker frame and AT refers to the breaker trip rating in amps.
AF refers to the ampere rating of the breaker frame and AT refers to the breaker trip rating in amps.
wirenut1980
Senior Member
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- Plainfield, IN
Re: AF and AT breaker notation
Follow up question on this subject...When would you see a breaker with different ampere ratings for the frame and for the trip setting? On an adjustable trip unit? If for something else, for what purpose?
Follow up question on this subject...When would you see a breaker with different ampere ratings for the frame and for the trip setting? On an adjustable trip unit? If for something else, for what purpose?
jtester
Senior Member
- Location
- Las Cruces N.M.
Re: AF and AT breaker notation
Frame rating and trip rating are often different, although often the same. Adjustable breakers certainly are an example. The frame rating is a maximum rating of the based on the design of the particular type of breaker, and the trip rating is some multipler, 1 or less, that the breaker is set to trip at.
This is kinda basic, but it gives you some idea.
Frame rating and trip rating are often different, although often the same. Adjustable breakers certainly are an example. The frame rating is a maximum rating of the based on the design of the particular type of breaker, and the trip rating is some multipler, 1 or less, that the breaker is set to trip at.
This is kinda basic, but it gives you some idea.
- Location
- Mission Viejo, CA
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- Professional Electrical Engineer
Re: AF and AT breaker notation
In NEMA language, "frame" is a reference to the physical size. Where two items have the same "frame-size" they can physically fit interchangeably.
Sometimes the "frame" is common throughout an industry; e.g., all NEMA motors with the same frame size can be intechanged. Sometimes "frame" is unique to the manufacturer;e.g., one manufacturers Molded Case Circuit Breakers, from 15A to 100A would all be the same "frame."
In NEMA language, "frame" is a reference to the physical size. Where two items have the same "frame-size" they can physically fit interchangeably.
Sometimes the "frame" is common throughout an industry; e.g., all NEMA motors with the same frame size can be intechanged. Sometimes "frame" is unique to the manufacturer;e.g., one manufacturers Molded Case Circuit Breakers, from 15A to 100A would all be the same "frame."
wilbur101
Member
Re: AF and AT breaker notation
I normally show the AF/AT designation because breaker manufacturers often have overlapping breaker sizes. If I specify a 150AT breaker, the contractor will purchase the cheapest breaker, maybe a 150AF breaker. The problem lies in if I have specified a wire size that will only fit on a 150AT/250AF breaker. I normally check for this when reviewing shop drawings, but sometimes we don't get them. When the cables can't land on the breaker, the contractor puts in an extra to replace the breaker, which is a problem because the 250AF breaker now won't fit and they need a new panel. Big cost, big delay. Specifying 150AT/250AF should solve this problem (or at least put the responsibility on the contractor.
I normally show the AF/AT designation because breaker manufacturers often have overlapping breaker sizes. If I specify a 150AT breaker, the contractor will purchase the cheapest breaker, maybe a 150AF breaker. The problem lies in if I have specified a wire size that will only fit on a 150AT/250AF breaker. I normally check for this when reviewing shop drawings, but sometimes we don't get them. When the cables can't land on the breaker, the contractor puts in an extra to replace the breaker, which is a problem because the 250AF breaker now won't fit and they need a new panel. Big cost, big delay. Specifying 150AT/250AF should solve this problem (or at least put the responsibility on the contractor.
Re: AF and AT breaker notation
Thanks for the replies. I thought it was something like that, but I wasn't sure what the T and F stood for.
So what frame sizes are standard? Those listed in NEC 240.6(A)? Or are those standard trip ratings? Or both?
Steve
Thanks for the replies. I thought it was something like that, but I wasn't sure what the T and F stood for.
So what frame sizes are standard? Those listed in NEC 240.6(A)? Or are those standard trip ratings? Or both?
Steve
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Re: AF and AT breaker notation
It does not specify the dimensions (frame) nor the trip characteristics of the device.
For most MCCB's the actual physical dimensions of a particular frame size is determined by the manufacturer. That's why they are not generally physically interchangeable in different manufacturer's panels. The primary standardization for frames is so that uniform UL terminal temperature testing may be performed; however, both the NEC and UL recognize "non-standard" ratings. Fuses of the same "Class" and "Rating" generally are interchangable.
Trip ratings are also defined in the product standards with regard to various applications: instantaneous, inverse time, "time-delayed," etc. The trip times vary depending on the definitions.
[ November 17, 2004, 12:17 PM: Message edited by: rbalex ]
That's a very good question. Technically, it is the "constant current for an indefinite time in an ambient of 40C" rating of the devices. This is buried in the product standards (NEMA / UL).
It does not specify the dimensions (frame) nor the trip characteristics of the device.
For most MCCB's the actual physical dimensions of a particular frame size is determined by the manufacturer. That's why they are not generally physically interchangeable in different manufacturer's panels. The primary standardization for frames is so that uniform UL terminal temperature testing may be performed; however, both the NEC and UL recognize "non-standard" ratings. Fuses of the same "Class" and "Rating" generally are interchangable.
Trip ratings are also defined in the product standards with regard to various applications: instantaneous, inverse time, "time-delayed," etc. The trip times vary depending on the definitions.
[ November 17, 2004, 12:17 PM: Message edited by: rbalex ]
Re: AF and AT breaker notation
I trust that this will explain frame sizes. It is ment to be a general overview only.
With regard to industrial breakers frame sizes generally run 100(F), 150(F)to 225a, 250(J), 400(K), 600(L), 800(M), 1200(N), 2000(P),and 2500(P).
The there are non-interchangable and interchangable trips, NIT and IT.
U[ to 150a there are no choices, they are NIT. There are some that are available up to 225a in the 150a frame size.
Frames 250a and larger are available in either NIT and IT. Also, 440a and 600a frames are often times the same size. The 800 and 1200a are also the same size with the 1200a being a greater depth.
There are numerous varieties of the larger 2000a and 2500a breakers.
Breakers sizes 400a and above have electronic trips available with include long and short time delay, adjustable instantaneous, ground fault pick-up and delay etc, with easily changable rating plugs it shange the trip rating withput complete disassembly of the breaker.
I trust that this will explain frame sizes. It is ment to be a general overview only.
With regard to industrial breakers frame sizes generally run 100(F), 150(F)to 225a, 250(J), 400(K), 600(L), 800(M), 1200(N), 2000(P),and 2500(P).
The there are non-interchangable and interchangable trips, NIT and IT.
U[ to 150a there are no choices, they are NIT. There are some that are available up to 225a in the 150a frame size.
Frames 250a and larger are available in either NIT and IT. Also, 440a and 600a frames are often times the same size. The 800 and 1200a are also the same size with the 1200a being a greater depth.
There are numerous varieties of the larger 2000a and 2500a breakers.
Breakers sizes 400a and above have electronic trips available with include long and short time delay, adjustable instantaneous, ground fault pick-up and delay etc, with easily changable rating plugs it shange the trip rating withput complete disassembly of the breaker.
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