Shunt trip for multiple main services

[mgardner]

I'm working on an electrical design for a multi-family dwelling. To limit the service sizes and apartment feeder lengths, we have designed the system to have three incoming electrical services. The local AHJ has requested that we provide each incoming main service disconnect with a shunt trip in addition to the required plaque.

What controls the shunt trip on each breaker? Can the shunt trip devices 'talk' to each other to know when one of the disconnects has been opened?

Any thoughts on how this set-up works and what I need to indicate on my design documents would be appreciated.

Thanks!

 

[LarryFine]

In all seriousness, I'd ask the inspector. Be up front, that you haven't done it before, and ask what he'll be looking for.

 

[luckylerado]

I would assume that his intention is to provide a means to disconnect all 3 services with one motion. I would say a red mushroom normally open momentary 15 amp push button properly labeled and installed at or near the fire hose connection (providing that it is sprinkled) or at the main entrance that would be used by fire fighters would fit the bill. I would dedicate a 15 or 20 amp circuit to the shunt trip function from the house panel or emergency panel if you have one. Feed the "Kill" switch then hook all the shunt trip devices in parallel so when you close the switch all shunt trip solenoids are energized and open the mains.

It would also be a good idea from a life safety standpoint to either monitor the control voltage with the fire alarm (if you have one) or a buzzer of some kind that will indicate when control voltage is not present or install a UPS because if the service that feeds the control voltage has faulted then pushing the button will not kill the remaining mains.

This may not be what your AHJ has in mind. He may want individual "Kill" switches.

 

[LarryFine]

It would also be a good idea from a life safety standpoint to either monitor the control voltage with the fire alarm (if you have one) or a buzzer of some kind that will indicate when control voltage is not present or install a UPS because if the service that feeds the control voltage has faulted then pushing the button will not kill the remaining mains.

Or, an open-upon-deenergization scheme.

 

[shockin]

I would say a red mushroom normally open momentary 15 amp push button properly labeled

I would want a maintained switch. The reason being (and its a long shot) if for some reason power was lost for a while when the fireman happened to push the button he would expect it to remain off, when in fact it will come back on when power is restored. Long shot I know, but why not use a maintained and eliminate the chance. I would also want one that is only resettable with a key.

 

[steve066]

I don't see any way to keep kids and others from hitting the shunt trip switch. It seems to me that would be a real safety issue. Easy target for praknsters or criminals.

You could put an aux. switch on each breaker that closes when the breaker is open. That switch could shunt trip the other breakers. You will have to find a way to disable the shunt trip circuit in order to reset the breakers.

It all sounds much more complex and confusing that it should be.

IMO, you should find a way to design it to comply with the code, and avoid any "special inspector requests". These will only become maintenance headaches, or code issues that future inspectors might not accept.

You could just run longer feeders, or if its a new building, 2 hour fire walls could be incorporated into the design (if the design doesn't already have that.)

 

[luckylerado]

I would want a maintained switch. The reason being (and its a long shot) if for some reason power was lost for a while when the fireman happened to push the button he would expect it to remain off, when in fact it will come back on when power is restored. Long shot I know, but why not use a maintained and eliminate the chance. I would also want one that is only resettable with a key.

Good point I agree. As far as keeping the kids off of it I would think that it would be acceptable to install the switch behind a tamper proof glass break enclosure similar to a pull station or fire extinguisher might be.