Square D Breaker Plug

[StephenSDH]

We have a switchgear that was ordered with Square D LE breakers. They are a 600A Frame, 250A Sensor, and plugs. Each breaker is not matching up to the sizes we requested. One was an ARP063 (x 0.63) plug giving us 157A when we requested 110A.

I informed the distributor that the plug would need to be changed to match the breaker size that was requested. He called a Square D tech and got back to me that the plug was fine, we just need to adjust down our long term trip setting. I saw in the manual it mentioned the trip was based on the Sensor x Plug x Long Term Setting, which I understand would cause the breaker to trip at a lower current. I can't believe this is correct, becaused it is not fixed at a current rating.

I am unable to find a Square D manual listing the available plug sizes. This is new to me can someone fill me in.

 

[zog]

We have a switchgear that was ordered with Square D LE breakers. They are a 600A Frame, 250A Sensor, and plugs. Each breaker is not matching up to the sizes we requested. One was an ARP063 (x 0.63) plug giving us 157A when we requested 110A.

I informed the distributor that the plug would need to be changed to match the breaker size that was requested. He called a Square D tech and got back to me that the plug was fine, we just need to adjust down our long term trip setting. I saw in the manual it mentioned the trip was based on the Sensor x Plug x Long Term Setting, which I understand would cause the breaker to trip at a lower current. I can't believe this is correct, becaused it is not fixed at a current rating.

That is correct 250x.63 =157.5 so if you set your LTPU to 0.7 you get 110.25A (+/- 7.5%). It is not "fixed", it is an I squared t function and the actual trip occurs at the LTD for a current of 6xP.

 

[StephenSDH]

That is correct 250x.63 =157.5 so if you set your LTPU to 0.7 you get 110.25A (+/- 7.5%). It is not "fixed", it is an I squared t function and the actual trip occurs at the LTD for a current of 6xP.

Does it bother you that it is not fixed? The LTPU has a cover that can be locked, but I have never seen them locked. Just doesn't feel right.

What is the logic of supplying it with a .63 plug instead of a 1.0 plug and setting the LTPU to .45? Do they just try to get you in the ballpark?

 

[zog]

Does it bother you that it is not fixed? The LTPU has a cover that can be locked, but I have never seen them locked. Just doesn't feel right.

What is the logic of supplying it with a .63 plug instead of a 1.0 plug and setting the LTPU to .45? Do they just try to get you in the ballpark?

I am not the guy to ask about OEM's logic.

The real question is why different rating plugs and sensors at all? All of those different settings can easily be programmed into a trip unit, (Many aftermarket ones are), but then they can't sell you replacement sensors and rating plugs when you need to change settings outside the limited range can they?

And about the .45 LTPU, the cheap sensors they use are not accurate below 50% of their ratings, so you typically don't see LTPU settings go below 0.5.

 

[StephenSDH]

I am not the guy to ask about OEM's logic.

The real question is why different rating plugs and sensors at all? All of those different settings can easily be programmed into a trip unit, (Many aftermarket ones are), but then they can't sell you replacement sensors and rating plugs when you need to change settings outside the limited range can they?

And about the .45 LTPU, the cheap sensors they use are not accurate below 50% of their ratings, so you typically don't see LTPU settings go below 0.5.

Really appreciate you clearing it up for me. I have no idea why these breakers were purchased in the first place.