Circuit Breaker Frame Size

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Grouch1980

Grouch1980

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New York, NY
Hi,
I saw this thread from some time ago:

frame size?

What is meant by frame size for an instantaneous trip circuit breaker, and where does the 3 times 5 times 10 times for low medium high come from. Anyone know where I can read up on this. What the heck is frame size?
forums.mikeholt.com

Post #5 by Jraef explains the frame size of a circuit breaker, where the frame size refers the switch part of the breaker.

What I don't follow is this definition for frame size: The frame size is the designation of the maximum continuous current the breaker can carry.

So if you have a 100 amp circuit breaker, non-continuous rated, the frame size is 80 amps using the definition above? That doesn't make sense.
 
Frame size is not the same as the breaker rating. Frame size is the physical size and configuration of the breaker. A 600 A frame breaker with a 100 A trip will be the same physical size as a 600 A frame breaker with a 600 A trip. Conversely, a 100 A breaker might be a 100 A frame, 225 A frame or a 600 A frame size.
 
David Castor said:
Frame size is not the same as the breaker rating. Frame size is the physical size and configuration of the breaker. A 600 A frame breaker with a 100 A trip will be the same physical size as a 600 A frame breaker with a 600 A trip. Conversely, a 100 A breaker might be a 100 A frame, 225 A frame or a 600 A frame size.
Click to expand...
I understand that. What I don't understand is the continuous rating definition.
 
Grouch1980 said:
Hi,
I saw this thread from some time ago:

frame size?

What is meant by frame size for an instantaneous trip circuit breaker, and where does the 3 times 5 times 10 times for low medium high come from. Anyone know where I can read up on this. What the heck is frame size?
forums.mikeholt.com

Post #5 by Jraef explains the frame size of a circuit breaker, where the frame size refers the switch part of the breaker.

What I don't follow is this definition for frame size: The frame size is the designation of the maximum continuous current the breaker can carry.

So if you have a 100 amp circuit breaker, non-continuous rated, the frame size is 80 amps using the definition above? That doesn't make sense.
Click to expand...
A 100 Amp breaker can carry 100 Amps continuously. The problem is the standard terminals and wire attached to them don't allow for enough heat transfer into the wiring so it MIGHT overheat and trip if used at its maximum capacity for an extended period of time.
 
petersonra said:
A 100 Amp breaker can carry 100 Amps continuously. The problem is the standard terminals and wire attached to them don't allow for enough heat transfer into the wiring so it MIGHT overheat and trip if used at its maximum capacity for an extended period of time.
Click to expand...
I'm not sure that is right. The non continuous rating is due to the real world of breakers being packed with other breakers on either side, and not being in free air.
 
petersonra said:
A 100 Amp breaker can carry 100 Amps continuously. The problem is the standard terminals and wire attached to them don't allow for enough heat transfer into the wiring so it MIGHT overheat and trip if used at its maximum capacity for an extended period of time.
Click to expand...
What about a 100 amp non-continuous rated breaker?
 
A 100 A breaker in open air can carry 100 A continuously (up to the maximum ambient of its listing). When it's put in an enclosure the continuous rating is reduced due the reduced heat dissipation. Not related to frame size. The exception would be a 100% rated assembly that can carry 100% continuously. This is more related to the enclosure than the breaker.
 
electrofelon said:
It looks like you got that definition from post number three in the linked thread. I don't think I would agree with that definition and would leave the word continuous out.
Click to expand...
I see. And it makes more sense not to use it.

I've actually seen the word 'continuous' used in other places. For example, Elite Software has a charting software where you can graph the TCC curves... they also define the breaker frame size using the word 'continuous'... similar to post #3 in the link.

What I'm gathering here is, the word 'continuous' has a different meaning / context when used to define the frame size. They mean continuous in 'open air', and not in a panel.
 
electrofelon said:
It looks like you got that definition from post number three in the linked thread. I don't think I would agree with that definition and would leave the word continuous out.
Click to expand...
....unless we happen to be talking about a continuous rated breaker. If that makes sense.

If we have two breakers that are exactly the same, except one is continuous rated at 100A, and the other is 80% rated at 100A, I would call both a 100A frame size.

In other words, you would NOT say a continuous rated 100A breaker has a 125 frame size.
 
Frame size has nothing to do with the NEC definition of 'continuous'.
A breaker frame size tells you nothing about its tripping characteristics. Frame size deals with the breaker case physical size and the maximum nominal amps of the contacts and other internal parts. This is important because most manufacturers require same frame size breakers to be mounted across from each other in panelboards and switchboards.
 
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