Frame Rating and Trip Rating

[Electriman]

Hello,

I know my question is pretty simple but I feel I do not have enough knowledge.

As you all know we have magnetic breakers or thermal breakers or thermal magnetic breakers. You all have seen that on one line drawings there are two ratings near the breaker (i.e. 250 AF, 200 AT) and you know that AF represent frame setting and AT represent trip setting. But this only applies to Adjustable breakers. Here is my question:

Can magnetic breakers be adjustable with different AT ratings? I know that we can adjust their instantaneous settings that are related to short circuit protection.

 

[ron]

Magnetic protection (MCP breakers) is only the short circuit protection.

Thermal protection is the AT rating and is never (not that I know of) available in a breaker without the magnetic portion. Motor overloads (heaters) are essentially thermal protection, but not typically in a breaker format.

The AT value needs to be equal to or less than the AF value.

 

[Electriman]

Magnetic protection (MCP breakers) is only the short circuit protection.

Thermal protection is the AT rating and is never (not that I know of) available in a breaker without the magnetic portion. Motor overloads (heaters) are essentially thermal protection, but not typically in a breaker format.

The AT value needs to be equal to or less than the AF value.

Thank you. Is there any way to find out from breaker part number whether or not it is magnetic or thermal magnetic with out looking at the datasheet?

 

[Jraef]

Thank you. Is there any way to find out from breaker part number whether or not it is magnetic or thermal magnetic with out looking at the datasheet?

Depends on the mfr of the breaker. Some have nomenclature that you can figure out with a little effort and experience. But there is no standard for how breaker mfrs catalog numbers are configured, any mfr can do it any way they like.

What is your real concern here? Why do you care how a mag-only breaker is sized or rated? You realize don't you, that neither you, nor even the specifying engineer, can choose what mag-only breaker is used, right? Because their only legal use is as part of a factory assembled, tested and listed combination starter assembly, so once an assembly has been tested and listed, it cannot be changed, meaning that basically you get what you get.

 

[ron]

Depends on the mfr of the breaker. Some have nomenclature that you can figure out with a little effort and experience. But there is no standard for how breaker mfrs catalog numbers are configured, any mfr can do it any way they like.

What is your real concern here? Why do you care how a mag-only breaker is sized or rated? You realize don't you, that neither you, nor even the specifying engineer, can choose what mag-only breaker is used, right? Because their only legal use is as part of a factory assembled, tested and listed combination starter assembly, so once an assembly has been tested and listed, it cannot be changed, meaning that basically you get what you get.

Just as a fun fact, molded case switches, are also mag only (for self protection). They have fixed mag protection settings.

I did see a MCP that had an adjustable mag setting, but I don't think it is wide spread.

 

[Electriman]

Depends on the mfr of the breaker. Some have nomenclature that you can figure out with a little effort and experience. But there is no standard for how breaker mfrs catalog numbers are configured, any mfr can do it any way they like.

What is your real concern here? Why do you care how a mag-only breaker is sized or rated? You realize don't you, that neither you, nor even the specifying engineer, can choose what mag-only breaker is used, right? Because their only legal use is as part of a factory assembled, tested and listed combination starter assembly, so once an assembly has been tested and listed, it cannot be changed, meaning that basically you get what you get.

I agree with you. But since mostly we use Eaton products I wish I could know what each product category represents. For example MCP represents magnetic breakers HKB represents thermal magnetic.

Most of the times a person does not face this issue but you never know you will face problems that you never imagine. It is engineering world and we all have got used to it.

 

[templdl]

Look for TM breakers to provide overload protection. When cable is sized it has been sized to carry the calculated load. Then the cable is protected with a TM breaker.
It would be extremely rare to find a mag only breaker if at all on a one line diagram by themserlves. However, one line diagrams often include motor control. As such they will show a "combination" motor starter the includes a mag only MCP, contactor, as nd an overload relay. If you do see a combination motor starter though pay close attention to the breaker as instead of an MCP it could be a TM breaker which is not very commonly done.
TM breakers are UL listed for use as a stand alone device, MCP/mag only breakers are reverse UL component listed and are not to be used as stand olone devices.