Breakers with Adjustable Trip

[Jimmy7]

If I'm looking at drawings and I see a breaker that has 200AF/175AT. Am I correct in saying that this breaker has a 200Amp frame and is currently set for a175 Amp trip. Can this breaker be adjusted to a 200 amp trip if needed if it has a 200 AF? Is it possible to tell if a breaker is specified to be adjustable by looking at drawings? Is it when it shows both the AF and AT?

Thank you

 

[augie47]

This thread may help:

Frame/Trip or Load

ATS schedule says 400A and draw out breaker say trip of 300A and frame indicates 400A. You size conductors to the frame or trip setting?

forums.mikeholt.com

 

[infinity]

In that size most likely not adjustable.

 

[steve66]

For most breakers that small, I would expect a 200AF/175AT breaker to be a fixed trip at 175 amps.

If the designer wanted something with an adjustable trip, they would probably note somewhere that they wanted an "adjustable trip", an "electronic trip" or they might use a notation like LSI meaning adjustable Long, Short and Instantaneous settings, or LSIG which would include a ground fault setting, or even just an "L" for long time adjustment.

If it was a larger breaker, it would be more common to include a replaceable trip sensor, like a 800AF/600AT with a 600A sensor that could be replaced. And it would also be more common to include electronic trip settings that offer a variety of adjustment.

Edit: Typing while infinity said it much more concisely.

 

[ATSman]

If I'm looking at drawings and I see a breaker that has 200AF/175AT. Am I correct in saying that this breaker has a 200Amp frame and is currently set for a175 Amp trip. Can this breaker be adjusted to a 200 amp trip if needed if it has a 200 AF? Is it possible to tell if a breaker is specified to be adjustable by looking at drawings? Is it when it shows both the AF and AT?

Thank you

Electrical drawings, single line diagrams in particular, can be like the wild wild west - there are no standards. For instance the symbols used for circuit breakers, transfer switches, etc. can vary from one consulting firm to another. In the case of breaker ratings and trip units, as others have mentioned, the trip rating (LTD) is usually fixed for smaller molded case breakers. However, depending on the breaker manufacturer and model#, the trip unit may be replaceable or the Rating Plug (like a miniature hockey puck screwed into the trip unit) may be replaceable. All this info varies depending on the manufacturer and model# and these details are not usually shown on the 1-Line. You may have better luck looking at the Bill of Materials (BOM) found on the job submittals (if one exists) that lists each component or, if the equipment is already installed, do a job walk.

 

[Carultch]

If I'm looking at drawings and I see a breaker that has 200AF/175AT. Am I correct in saying that this breaker has a 200Amp frame and is currently set for a175 Amp trip. Can this breaker be adjusted to a 200 amp trip if needed if it has a 200 AF? Is it possible to tell if a breaker is specified to be adjustable by looking at drawings? Is it when it shows both the AF and AT?

Thank you

Think of the trip rating as electrical, and the frame size as mechanical.

Manufacturers group their breakers in ranges of trip ratings, such that the breakers of the same product family in the same frame size are built with standardized components. That way, instead of needing 30 different breaker designs for every trip setting, they can simplify their inventory on the product family to perhaps 5 designs, by binning ranges of trip ratings in frame size categories. The lugs, molded-case, switch handle, bus connections, and most other components would be the same across a given frame size. The essential difference would be the trip mechanism calibration.

For thermomagnetic breakers, the trip rating is a fixed value, and you'd have to replace the breaker if you needed a different trip setting.
For electronic trip breakers, which are common in higher amp ratings, there could be the option for an adjustible trip breker, either by replacing the rating plug, or configuring the rating settings on it.

 

[Jraef]

In North America, UL and CSA do not recognize adjustable thermal
trip devices as “circuit breakers” for branch or feeder use. You CAN however use them as “Motor Protection Circuit Breakers” (MPCB) now, meaning they feed just one motor. The only listed feeder/branch circuit breakers that can have adjustable (programmable) trips are those with Electronic Trip Units (ETUs), ostensibly because they would typically be only used in an industrial or large commercial installations “under engineering supervision”. That’s where you would see the “LSI” or “LSIG” designation on drawings.

 

[jim dungar]

In North America, UL and CSA do not recognize adjustable thermal
trip devices as “circuit breakers” for branch or feeder use.

Also, there are UL Listed thermal magnetic breakers which have field replaced/exchangeable trip units. While they are adjustable these style do allow you to change the AT rating of a breaker without having to replace the frame assembly.