Magnetic Thermal Trips

[kennyp]

I have a huge dilemma. I have a project I am bidding on and come upon a huge problem. In a Eaton meter center there is a 1200 amp meter socket with a 600 volt 600 amp breaker and 400 amp magnetic trips installed that is not being used. The electrical engineer sent an addendum that says to set the trips at 300 hundred amps for the new service and I don't think that is how it works. I never adjust the trips when I order gear and to tell the truth have never done any research on this until now. The thermal magnetic trips can be adjusted for long or short term overloads and ate also designed for fault currents. You can not dial it to the amperage you want it to protect correct? I have had my supplier try and contact the Eaton rep. for my area today but with the weather so nice he is probably on the beach and never called us back.

 

[Jraef]

I have a huge dilemma. I have a project I am bidding on and come upon a huge problem. In a Eaton meter center there is a 1200 amp meter socket with a 600 volt 600 amp breaker and 400 amp magnetic trips installed that is not being used. The electrical engineer sent an addendum that says to set the trips at 300 hundred amps for the new service and I don't think that is how it works. I never adjust the trips when I order gear and to tell the truth have never done any research on this until now. The thermal magnetic trips can be adjusted for long or short term overloads and ate also designed for fault currents. You can not dial it to the amperage you want it to protect correct? I have had my supplier try and contact the Eaton rep. for my area today but with the weather so nice he is probably on the beach and never called us back.

If you have Long Time and Short Time trips on your breaker, it is not a Thermal-Mag (T-M) breaker, it is an Electronic Trip circuit breaker. The 600A is the frame size, the maximum current that the parts inside can handle. The adjustment dials / dip switches are separate, they are part of the Electronic Trip Unit (ETU) and should provide you with at lease L, S, and I trip settings (Long Time, Short Time and Instantaneous). The Instantaneous is the equivalent of the mag trips found on T-M breakers. Since that Mag Trip dial on T-M breakers is often adjustable, that may be why you are confusing your adjustment dials with being the "magnetic trips". They are not. Long Time is the equivalent of the "thermal" trip in a T-M breaker, Short Time is something that a T-M breaker never has and is provided for the purpose of having better coordination of your trips within the entire system, as performed in a "Coordination Study". That's one of the main reason people use ETU breakers and spend a LOT more money for them.

But to answer your question, YES, you can adjust the trips on ETUs. I don't happen to think whomever told you to do it without understanding the implications is doing the right thing here, but that's just an opinion. From YOUR standpoint however given that you have an ETU, it's at least your responsibility to ask that EE to provide you with the exact settings he wants on all three of the trip dials. Put the onus on him to do his job correctly, or at least get yourself off the hook if a lack of attention to that detail results in costly down time.