Shunt trip breakers

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goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
I'm using two (120V trip) 50A shunt trip circuit breakers to disconnect electric ranges in the event of an Ansul dump. The way I see the wiring diagram I can wire the 120V phase trip wires directly to the shunt trip terminals and series in the neutrals through an aux. relay contact to trigger the shunt trip. Is there any reason why I cannot do this (Code wise, ethically, etc.) ?

My reasoning for wanting to do this is that there will be two, multi-contact relays in a separate cabinet that will be used to trigger other functions in the system. Sending one less phase conductor into that relay cabinet is one less potential shock hazard for any non or partially qualified person sticking their hands in there.


http://www.pceca.net/images/stories/shunt_trip_breaker.pdf
 

iwire

Moderator
Staff member
Location
Massachusetts
You can't switch just the neutral.



404.2 Switch Connections.


(B) Grounded Conductors. Switches or circuit breakers shall not disconnect the grounded conductor of a circuit.

Exception: A switch or circuit breaker shall be permitted to disconnect a grounded circuit conductor where all cir-cuit conductors are disconnected simultaneously, or where the device is arranged so that the grounded conductor cannot be disconnected until all the ungrounded conductors of the circuit have been disconnected.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
You can't switch just the neutral.
I can understand that from the standpoint of using a regular switch and and from a safety point of view and I'm not trying to argue that my point is right. However, if you look at the second wiring diagram that Siemens provides "Power from control circuit" it shows the "c" terminal of the shunt-trip breaker wired directly to the ungrounded conductor and the neutral in series with a trip contact. Am I reading this wrong ?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
I can understand that from the standpoint of using a regular switch and and from a safety point of view and I'm not trying to argue that my point is right. However, if you look at the second wiring diagram that Siemens provides "Power from control circuit" it shows the "c" terminal of the shunt-trip breaker wired directly to the ungrounded conductor and the neutral in series with a trip contact. Am I reading this wrong ?

The trip button is on the hot side not the neutral. In diagram #1 the neutral goes directly to the shunt trip coil.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
I think the diagram is confusing due to the fact the 'White Lead' is not the neutral.
Yes, it is confusing. I field tested my method and it works but that doesn't mean it is correct. If I wire in accordance with the first diagram I can run a neutral directly to the "c" terminal of the breaker and then series in the hot through a relay contact and then to the white wire to trip the breaker. If I wire in accordance with the second diagram all I have to do is bring 120V to the trip coil. It doesn't indicate which is hot and which is neutral.

Why didn't they make the trip wire red or blue. It would be much less confusing.:rant:
 

kwired

Electron manager
Location
NE Nebraska
My reasoning for wanting to do this is that there will be two, multi-contact relays in a separate cabinet that will be used to trigger other functions in the system. Sending one less phase conductor into that relay cabinet is one less potential shock hazard for any non or partially qualified person sticking their hands in there.

I don't see having one less ungrounded lessening the shock hazards all that much but do see having switches in grounded conductors increasing shock hazards. Non or partially qualified especially are the ones that will wonder why that white wire got them when they touched it, where if it were not white - they likely treat it as if it is hot - whether it really is or isn't.
 

jap

Senior Member
Occupation
Electrician
I can understand that from the standpoint of using a regular switch and and from a safety point of view and I'm not trying to argue that my point is right. However, if you look at the second wiring diagram that Siemens provides "Power from control circuit" it shows the "c" terminal of the shunt-trip breaker wired directly to the ungrounded conductor and the neutral in series with a trip contact. Am I reading this wrong ?


Your not reading it wrong, but, unless there's more to the picture,,,, the second wiring diagram doesn't signify which is hot and which is neutral.
It just simply indicates 120v.

JAP>
 

iwire

Moderator
Staff member
Location
Massachusetts
Your not reading it wrong, but, unless there's more to the picture,,,, the second wiring diagram doesn't signify which is hot and which is neutral.
It just simply indicates 120v.

JAP>

If you follow the wires you can determine which is neutral.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
If you follow the wires you can determine which is neutral.
I believe you are correct. If you compare both diagrams the (implied) wire tied to one side of the trip coil in the 2nd diagram would be neutral as it is in diagram 1. A simple H & N where it shows 120V would have cleared things up though. So, now I have to install a white wire from the neutral bar to the "c" terminal and then series in a hot wire between the remote trip contact and the white coiled wire of the breaker. Seems clear enough for a simple 2 wire connection.

Speaking from a design standpoint, wouldn't it have made things simpler if the white wire was installed directly to the neutral bar and the trip lead to the "c" terminal ? I'm sure if I called Seimens it would fall on deaf ears.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
It's really a mistake to think that the neutral is less of a shock hazard than the hot wire.

When one of the relays open, it will disconnect the wire inside the relay cabinet from the neutral bus in the panel.

Once that happens, one side of the switch will have the full 120 volts on it. That 120 volts is connected through your load, but most loads aren't going to limit the current below the milliamps required for a severe shock.
 

jap

Senior Member
Occupation
Electrician
I believe you are correct. If you compare both diagrams the (implied) wire tied to one side of the trip coil in the 2nd diagram would be neutral as it is in diagram 1. A simple H & N where it shows 120V would have cleared things up though. So, now I have to install a white wire from the neutral bar to the "c" terminal and then series in a hot wire between the remote trip contact and the white coiled wire of the breaker. Seems clear enough for a simple 2 wire connection.

Speaking from a design standpoint, wouldn't it have made things simpler if the white wire was installed directly to the neutral bar and the trip lead to the "c" terminal ? I'm sure if I called Seimens it would fall on deaf ears.

Things would be less confusing if the trip wire your attaching to from the line side of the coil clearing contact "a" was not white.

JAP>
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
It's really a mistake to think that the neutral is less of a shock hazard than the hot wire.

When one of the relays open, it will disconnect the wire inside the relay cabinet from the neutral bus in the panel.

Once that happens, one side of the switch will have the full 120 volts on it. That 120 volts is connected through your load, but most loads aren't going to limit the current below the milliamps required for a severe shock.
I understand that Steve in a "normal" switch operation. In the case I was citing, the trip wire would be in series through a N/O contact of a relay. It's not a big deal for me to actually series in the hot leg. I just wanted to know if I'd be in violation. I believe my question was answered in previous posts. Thanks for your reply.
 

mtfallsmikey

Senior Member
While on the subject of shunt trips and kitchen equipment, should a shunt trip breaker trip for kitchen equipment when there is a power outage or interruption, not just an Ansul dump? We did a transfer of all building power over to our generators ( not a dedicated life safety generator, but a system that powers everything) the other day for an elevator test, and the breaker tripped when the transfer to generator power was done.
 

kwired

Electron manager
Location
NE Nebraska
While on the subject of shunt trips and kitchen equipment, should a shunt trip breaker trip for kitchen equipment when there is a power outage or interruption, not just an Ansul dump? We did a transfer of all building power over to our generators ( not a dedicated life safety generator, but a system that powers everything) the other day for an elevator test, and the breaker tripped when the transfer to generator power was done.
For something like kitchen equipment fire suppression systems the control contact is maintained and only changes state when the system has a mechanical operation that causes the control switch to close. But if you are depending on control relays or aux contacts on certain equipment that will change state during a power failure you could have some nuisance trip issues, it is all going to depend on if there is control voltage present when such contacts close - even if only for an instant - and careful selection/coordination of such components or design of how they are connected will determine how easy a false trip can happen.
 

mtfallsmikey

Senior Member
Yes, we have had what possibly could have nuisance trips occuring during brief power blips, which were not long enough to cause a transfer to the generators. I will discuss with the FM, is coming back to finish the final occ. inspection
 
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