Breaker/contactor power circuit
- Thread starter lquadros
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- Lockport, IL
- Occupation
- Retired Electrical Engineer
The breaker could serve as the controller's disconnecting means, if all the controller's components (including the contactor) are downstream. But in you installation, the contactor will be energized, even with the breaker turned off. Sounds like a dangerous situation to me.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
In operation, not much really.
In reality, I would be very suspect of what the SCCR is for that combination of devices in that order. SCCR (Short Circuit Current Rating) is a requirement of the NEC article 409, "Industrial Control Panels", so it will partly relate to whether or not your AHJ will consider the equipment relevant to that section or not. If the equipment has a UL508A listing on the assembly, he may not take it any further, but you STILL will need to deal with what level of SCCR is shown on that assembly, listed or not.
The reason I bring that up is because IF the mfr of the breaker and contactor have listed them TOGETHER at a high SCCR, then it's almost guaranteed that the listing stipulated that the breaker be AHEAD of the contactor. Most contactors are rated very low all by themselves, they NEED something ahead of them to help protect them. Without that, their SCCR will likely be in the 5,000A level and the SCCR of an un-tested combination of devices can be no higher than the lowest rated device in it. So for instance if you have 25kA available in your facility, and the breaker is rated 35kAIC, that's fine, but if the contactor is only rated 5kA, then the entire thing is rated at 5kA. That then means YOU, the installer, must deal with the fact that the AVAILABLE fault current feeding this panel is limited to no more than 5kA. Might be tough, and/or expensive to accomplish.
- Location
- Illinois
- Occupation
- retired electrician
There still has to be an OCPD on the line side of the stater to provide the short circuit and ground fault protection for the conductors that feed the starter.
Breaker/contactor power circuit
Yes. You are correct. Charlie B. Another thing....generally breaker/contactor manufacturers have series rating studies done with breaker upstream and contactor downstream setup. In case of a short circuit fault, I am not sure how the contactor opening and breaker trip timing will work with each other with a set up that has not been tested. Is this a valid concern?
Yes. You are correct. Charlie B. Another thing....generally breaker/contactor manufacturers have series rating studies done with breaker upstream and contactor downstream setup. In case of a short circuit fault, I am not sure how the contactor opening and breaker trip timing will work with each other with a set up that has not been tested. Is this a valid concern?
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