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Contactor and overload Relay

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edetaen01

Electrical
Aug 30, 2012
2
Please can some one advice
i need to connect a 45 kVa lighting transformer to a westin house MCC 600A, incommer 400A and the availabe spare is a 60 A breaker with starter and over load relay how do i connect is it possibele to isloate both the contactor and overload relay and make use of only the breaker ?
Please can some one advice
i need to connect a 45 kVa lighting transformer to a westin house MCC 600A, incommer 400A and the availabe spare is a 60 A breaker with starter and over load relay how do i connect is it possibele to isloate both the contactor and overload relay and make use of only the breaker ?
 
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The type of breaker used in this starter is a Motor Circuit Protector, probably type HMCP. It does not have overload protection since it is meant to be used with the overload of the starter. The only tripping function that is found in this breaker is instantaneous, magnetic, tripping designed to respond to short circuits only.

You can remove the contactor, overload, and MCP breaker from the cubicle and install a standard circuit breaker in their place. The size of the breaker that is required for the 45kVA transformer will depend on your system voltage. If you are not sure of the proper size, consult the transformer manufacturer.
 
If you did not gather it from rhatcher's excellent response, it is ILLEGAL (at least here in the US) for you to use the HMCP breaker that is part of a combination motor starter as a feeder breaker. You must use a Thermal magnetic type circuit breaker. Since it will be the same frame size as the old one already there, the operating mechanism will work if you make sure to match the breaker Series with Eaton. Also pay attention to the Available fault Current and MCC bus bracing, you have to meet or exceed that with the new breaker.

If you don't want to roll your own, you can buy a new replacement MCC feeder bucket from Eaton that will work in that old Westinghouse MCC, they have listed aftermarket buckets for that and would use the newer breakers that will undoubtedly have a higher interrupt capacity.

By the way if it's a 480V MCC, for a 45kVA transformer it would be a 70A breaker anyway and most likely a 60A breaker would nuisance trip on transformer inrush.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)

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Thanks for stepping in with more information jraef. I should have been more specific in my response. I will correct that now.

The HMCP ciruit breaker is specifically designed to be used as a component of a combination starter that includes separate overload protection.

You cannot use a HMCP breaker separately as a feeder breaker to supply a transformer or any other load. This is because the HMCP does not have overload tripping protection. It is actually possible to flow enough continuous current through a HMCP breaker to melt it without the breaker tripping. Of course, the equipment connected downstream can also be destroyed without the HMCP breaker tripping.

When used without separate overload trip protection, the HMCP breaker will allow dangerous levels of current to flow in the circuit that will result in severe equipment damage and the risk of serious personal injury or death.

The easiest and safest solution for edetaen01 is to follow jraef's suggestion. Contact Eaton, provide them with the MCC S.O. number, and purchase a replacement MCC bucket that is fitted with a feeder breaker to supply the transformer. This will ensure that the replacement breaker has the proper interrupting rating to match the MCC specifications. As suggested by jraef, a 70 amp breaker will be required to feed the 45kVA transformer at 480 volts. Other voltages will require different breaker ratings.






 
You would be surprised at how many peope I see using HMCPs as feeder breakers. They can buy them dirt cheap at breaker brokers because there is not as big of an after-market for HMCPs, but the brokers get them in all the time for pennies on the dollar when people strip them out of old motor starters. Almost every time I point it out when I see it, the user shows shock and dismay. I often suspect they know, they are just being cheap and don't like their cheapness being exposed.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)

For the best use of Eng-Tips, please click here -> faq731-376
 
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