MCC disconnects don't match up to circuit breaker, install shunt trip
MCC disconnects don't match up to circuit breaker, install shunt trip
(OP)
We are replacing some power feeders to some new custom equipment. The design calls for changing out the existing 2P 480v circuit breakers with 100a 3 pole breakers at the MCC. The selected circuit breakers do not match up with the disconnect mechanism on the door. And they are a different brand. The existing breakers range from 100a to 350a and each one located in a full section of MCC. The existing breakers are different physical sizes.
This would work ok if we rendered that disconnect on the MCC inoperable and made the operator open the MCC door to turn off the power. The power would rarely ever be cut off and the receiving end of the feeders have disconnects. Or we could try to fabricate a new piece to get the mechanism to work.
I thought also about installing a shunt trip in the new breakers and leaving the old ones in place and running that through a control circuit. Turn off the power at the disconnect switch it turns off the existing circuit breaker that circuit breaker shunt trips the new breaker.
Is this way too much rigmarole or a reasonable design?
This would work ok if we rendered that disconnect on the MCC inoperable and made the operator open the MCC door to turn off the power. The power would rarely ever be cut off and the receiving end of the feeders have disconnects. Or we could try to fabricate a new piece to get the mechanism to work.
I thought also about installing a shunt trip in the new breakers and leaving the old ones in place and running that through a control circuit. Turn off the power at the disconnect switch it turns off the existing circuit breaker that circuit breaker shunt trips the new breaker.
Is this way too much rigmarole or a reasonable design?






RE: MCC disconnects don't match up to circuit breaker, install shunt trip
RE: MCC disconnects don't match up to circuit breaker, install shunt trip
Using the existing breaker as a control switch for a shunt trip would not be acceptable for use in Lockout/Tagout procedures. Control switches are not acceptable disconnecting means. See OSHA Std 1910.147.
RE: MCC disconnects don't match up to circuit breaker, install shunt trip
I'm not sure how small a trip unit you can put in the frame sizes. I'm looking into that too.
It also looks like the existing 2P breakers are the same physical size as their 3P relative. Is there actually a set of power contacts in a two pole breaker and just not the terminals on the top and bottom? Can you retrofit a 2P breaker and make it into a 3P?
jghrist - The only thing in the entire full MCC section will be this breaker, everything else is being gutted. There is no exposed bus. I also considered just getting a standard enclosed breaker with a side disconnect and mounting it to the back panel. Would that be acceptable? Just a thought on the shunt trip...you torpedoed that one pretty good.
RE: MCC disconnects don't match up to circuit breaker, install shunt trip
A better alternative to your complex shunt trip rigamarole would be to finish gutting that box and put in a full height back panel in each unit, then mount the breakers and use a rotary through-door mechanism for them that interlocks with the door. You will likely need to fill the openings left by the old operating mechanisms, but that's why they make steel plates and rivets...
As to the 2P vs 3P, most NEMA design breakers do not know or care if one pole is used or not, but some IEC breakers might give you nuisance trips when near full load if one pole is left with no power flow. You will have to ask the specific breaker mfr or look in the instructions. If it is sensitive to phase loss, you will see the instructions tell you to loop one pole back to the 3rd so that all 3 have power flow through them.
"Will work for (the memory of) salami"
RE: MCC disconnects don't match up to circuit breaker, install shunt trip
They don't make the breaker that's there anymore. So we are going to have to adapt it to the existing holes.
I like the rotary through the door switch alternative.
RE: MCC disconnects don't match up to circuit breaker, install shunt trip
RE: MCC disconnects don't match up to circuit breaker, install shunt trip
Otherwise, if all else is being removed and replaced then use a rotary handle with whatever breaker you like as jraef has suggested.
RE: MCC disconnects don't match up to circuit breaker, install shunt trip