Adjustabel T/M breakers Vs Electronic breakers

[NickParker]

I have been told that adjustable thermal/Magnetic setting is not available in ANSI standard breakers (MCCB). If it is required the solution is electronic type breakers. Is it true?

 

[davidbeach]

Thermal is definitely not adjustable. Sometimes the magnetic (instantaneous) is and sometimes not. Electronic trip units have many options.

 

[jraef]

You can now use MCCBs with adjustable thermal trips in the US as Motor Protector Circuit Breakers (MPCBs), but not as feeders or any other application that is not associated with a motor controller.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[NickParker]

Any reason, why the MCCCB don't have adjustable settings of both T/M in ANSI standards, as IEC MCCBs have it?

 

[NickParker]

Can I understand that ANSI breakers (Non-Electronic Units) have only Interchangeable trip units, but do not have an adjustable trip setting (built-in trip setting that allows the user to change the setting, just by rotating the knob on the front fascia)

 

[davidbeach]

I've never seen an ANSI TM breaker where the T part was adjustable; the M part sure, but not the T part. I'm not familiar with the devices for jraef was referencing above, and I may not agree that they fall under (what I'd consider a) MCCB. Full adjustibility, as I'm familiar with it, requires an electronic trip.

 

[wbd]

I have not seen MCPs with adjustable thermal only instantaneous as the thermal part is done by the overload in the starter.

 

[jraef]

UL-489 for circuit breakers does not accept adjustable trip T/M circuit breakers for anything other than motor control circuits and even that use (MPCB) is a relatively new development because of the flood of IEC breakers coming in and pressure from the suppliers to find a home for them.

UL-489 only accepts ETU breakers with interchangeable and /or programmable long time trips because of a tacit acceptance of the concept that they will only be used in industrial or high end commercial facilities “under engineering supervision”, meaning Bubba the ‘lectrician can’t just willy-nilly walk up to it and “crank ‘er up” if it trips. How realistic that concept is can be debated ad infinitem, but that’s how it is here. As a general rule, UL has a dislike for anything that “relies upon the skill of the installer” when it comes to protection devices, at least outside of the aforementioned “facilities under engineering supervision”, meaning residential and light commercial work where an EE is rarely involved.

I’m not sure when MPCBs were allowed under UL-489, but they have been allowed under UL-508 as a “Manual Motor Starter” since the 1980s at least, when I first started using them. I THINK they may have been added to UL-489 in the early 2000s, maybe even 2010s.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden