mstrlucky74
Senior Member
- Location
- NJ
Is the "rating" of a breaker the frame or trip? If you have 225AF/125AT what "size/amp" breaker is it? I'd refer to it's trip as the "size".
Circuit Breaker Frame & Trip
- Thread starter mstrlucky74
- Start date
- Status
- Location
- Massachusetts
The trip would be the figure that counts as far as protecting conductors and equipment.
The frame just describes what size space it takes up in the panel.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Its rating is 225AF/125AT. Both terms are part of its rating. But if you put it at the origin of a circuit, then that circuit is a 125 amp circuit. Is that what you are looking for?
kwired
Electron manager
- Location
- NE Nebraska
I think that means it is physically the same size as a 225 amp breaker but is a 125 amp trip breaker.
Frame sizes typically are 125 and less, 150-225, 250-400, 450-600...
that is the way I read it
225 Amp Frame
125 Amp Trip (I assume thermal), instant ~12 times that
When I read a spec as the others guys said the frame is 225a but has a 125 amp trip. Usually it is a frame that will take a range of trip units up to 225a. The advantage is that it you spec a 225af and a 125at if you choose to change the ampacity of you circuit you have the opportunity to change the trip to match the new circuit and not the entire breaker.
The older Westinghouse 225af is and LB3225F and you we would order it with an HLB3225T trip installed which could be changed to an HLB3225T trip or HLB3150T, etc trip should you wish to change the ampacity of that circuit.or repurpose the circuit. It you wanted a non interchangable trip try ithe breaker on the oneline we would be specified as NIT, in the case of the 225at it would end up being an LBB3125.
This is just an example as the LB frame has bee superceded. A 225a rated breaker could be supplied as a 125a smaller ftame but the spec writer wanted to usea larger frame for some reason.
rip frame but ithe spec writer wanted to use a 225af
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- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Just to add to what the others said, it also matters a little what TYPE of breaker tyou have. An "MCP" / "Magnetic-Only" / "Instantaneous -Trip" breaker as used in a motor starter is typically NOT shown with a frame size and trip rating because that could get confusing. So they are typically shown with the CONTINUOUS rating of the breaker, and the magnetic Trips will be up to 10X that value. So for example you may see an MCP shown on a one-line diagram as "7A MCP", which means the continuous ampere rating of that breaker is 7A, and the magnetic trips will be adjustable from 300-1000%, so 21 to 70A.
Instant is typically 10 to 12X, every mfr is different.
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- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
One common reason for wanting to use a larger frame size is coordination.
Several of the protective functions of breakers are dependent on the stuff inside of the breaker, like a current sensor or a physical bi-metal. The larger guts mean more fault or inrush current can be tolerated.
For example a 125A trip unit in a 150A frame breaker might have a maximum instantaneous setting of 1500A (about 12X) but a 250A frame device might go up to 2500A (20X)
mstrlucky74
Senior Member
- Location
- NJ
Thanks guys..very helpful.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Yeah, a lot of smart fellers here.
Yes, good points. Technology has come a long ways today. The manufactures have learned how to dr design the smsller breaker frames that can kick butt when it comes to kaic but it is hard to pack the options that electronic trip units in the smaller frames that you can get with the larger frames. But I know that they must be working on it.
kwired
Electron manager
- Location
- NE Nebraska
They can pack a lot of electronics in a small space if they want to, look at how the computer processors keep shrinking but data handling capacity keeps going up.
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