Shunt trip breaker question

[robertd]

I have a shunt trip question. I do residential work and don't normally install them.
I'm installing a subpanel in the HOs new amateur radio station. After I roughed in the subpanel and EMT for the feeder the HO requested an emergency power off switch. I can't get a shunt trip main for the small QO panel I roughed in, so I got a shunt trip breaker for the GE panel feeding the new subpanel. I plan on putting 2 #12 THHNs in the EMT for the shunt trip along with the feeder and taking power from one of the branch circuits in the subpanel. Since the shunt trip wires aren't normally energized they don't count as current caring conductors, so they only count for conduit fill not derating, correct?

Thanks
Robert

 

[benaround]

Robert,

I don't have a code reference, but I can't see a problem with what you are doing.

 

[LarryFine]

Bob, welcome to the forum! :smile:

Not only does that sound okay, you could even use #14 with no problem, as the shunt-trip requires very little current, and then only for a moment.

It's also good that you supply the shunt-trip from the load panel, since many, if not most shunt-trips can't withstand continuous coil energization.

As an aside, the shunt-trip can receive its neutral connection at the supply panel, and you'd only have to run a single conductor along with the feeder.

 

[iwire]

since many, if not most shunt-trips can't withstand continuous coil energizing.

I know you had some bad luck with at least one, perhaps a stuck internal switch?

But I have my doubts that any modern shunt breaker could not tolerate a continuous signal. To design it otherwise would be an incredibly poor choice by the manufacturer. No different then mechanically held lighting contators.:smile:

 

[LarryFine]

I know you had some bad luck with at least one, perhaps a stuck internal switch?

No, the original had aux. contacts that had not been connected. :roll: The two black wires for the coil were used (obviously), but the three for the aux. contacts (blach, white, and red) were still coiled up and taped from the factory.

This was a 225a breaker that protected a single panel within the switchgear stacks. Had the shunt-trip circuit been supplied by a breaker in the same panel it protected, the aux. contacts would not have been needed.

The reason the original shunt-trip burned was an emergency button I traced out was pushed in and latched (and had to be rotated to pop back out) nobody else discovered. I connected the contacts when I installed the replacement.

But I have my doubts that any modern shunt breaker could not tolerate a continuous signal. To design it otherwise would be an incredibly poor choice by the manufacturer. No different then mechanically held lighting contators.:smile:

The original did have a sticker that said the coil was not rated for continuous energization, probably because it was rated for anwyhere from 120 through 277v, so it obviously expected a short-duration trip voltage.

 

[neutral]

Bob, welcome to the forum! :smile:

Not only does that sound okay, you could even use #14 with no problem, as the shunt-trip requires very little current, and then only for a moment.

It's also good that you supply the shunt-trip from the load panel, since many, if not most shunt-trips can't withstand continuous coil energization.

As an aside, the shunt-trip can receive its neutral connection at the supply panel, and you'd only have to run a single conductor along with the feeder.

I have worked with shunt trip breakers on a lot of industrial machines and control panels and all of them were connected using power applied to the trip coil. That makes it a fail safe operation, if you lose control power or a safety interlock is opened the breaker will trip. If you wire it so you need voltage to trip the breaker and you lose power then you can?t trip the breaker with the E-Stop button. You would have to manually trip the breaker, which is not recommended for a shunt trip breaker.

 

[iwire]

I have worked with shunt trip breakers on a lot of industrial machines and control panels and all of them were connected using power applied to the trip coil. That makes it a fail safe operation, if you lose control power or a safety interlock is opened the breaker will trip.

That is an under voltage shunt trip and is not commonly used around here. (At least in my experience)

All the shunt trip breakers I have worked with trip when power is applied.


It would certainly depend on what type of application your using it for.

I typically use shunt trips for killing kitchen equipment under hoods upon activation of the fire suppression system. Another application is the feeders to elevators but they seem to be doing away with that.

 

[neutral]

That is an under voltage shunt trip and is not commonly used around here. (At least in my experience)

All the shunt trip breakers I have worked with trip when power is applied.


It would certainly depend on what type of application your using it for.

I typically use shunt trips for killing kitchen equipment under hoods upon activation of the fire suppression system. Another application is the feeders to elevators but they seem to be doing away with that.

What trips the breaker if you have a loss of power supplying voltage to the trip circuit? too me that wouldn't be a fail safe mode of operation, I suppose things are done the way they are for reasons that we don't always understand.

 

[brian john]

I know you had some bad luck with at least one, perhaps a stuck internal switch?

But I have my doubts that any modern shunt breaker could not tolerate a continuous signal. To design it otherwise would be an incredibly poor choice by the manufacturer. No different then mechanically held lighting contators.:smile:

Many have clearing contacts to de-energize them after opening the CB.
Many large frame shunts cannot handle continous power.

 

[LarryFine]

What trips the breaker if you have a loss of power supplying voltage to the trip circuit?

One could also ask what happens if the exhaust-fan breaker trips when a fire starts.

 

[weressl]

I know you had some bad luck with at least one, perhaps a stuck internal switch?

But I have my doubts that any modern shunt breaker could not tolerate a continuous signal. To design it otherwise would be an incredibly poor choice by the manufacturer. No different then mechanically held lighting contators.:smile:

Your assumption is logical, however reality is different.

Shunt trips and even solenoid actuators on MV switchgear are only built for momentary energization. The reason is fairly practical. The energy required to unlatch the spring latches is substantial and require a LARGE solenoid to generate that much flux and operate continually. Since the actuation requires a just a short tap, the coil can be designed to operate at a much higher current than it would be able to withstand continuously without burning out. Shunt trips have an integral switch built into them that opens with the breaker opening and the MV breaker solenoids are wired thorough the NO/NC contacts depends on if they are opening or closing coils.

One major name manufacturer had a problem with their MV switches were the TOC switches would not activate and burn the opening coil up. As the result we were not able to open a breaker - it was used as a 15kV motor controller - so you can imagine the stir it caused. Evidently the problem was a manufacturing defect and resulted in a major repair campaign that lasted a while.

 

[hardworkingstiff]

What trips the breaker if you have a loss of power supplying voltage to the trip circuit? too me that wouldn't be a fail safe mode of operation, I suppose things are done the way they are for reasons that we don't always understand.

I also don't care for shunt-trips due to the possibility of control power being lost (accidently disconnected?) and not discovered until the shunt-trip did not work.

 

[Cold Fusion]

What trips the breaker if you have a loss of power supplying voltage to the trip circuit? too me that wouldn't be a fail safe mode of operation, I suppose things are done the way they are for reasons that we don't always understand.

Some might think that if there is no power, then you don't need to trip the breaker - power is already out - right?

cf

 

[Cold Fusion]

I've never seen a shunt trip CB that did not have an integral disconnect in the CB. Yes, I'm sure there are some out there.

CB mfgs also put aux contacts in CBs. So a CB having two shunt trip leads and three aux contacts leads does not mean the CB needs to have an aux contact used as the ST coil disconnect. It may (should) also have a built-in ST coil disconnect as well as the aux contacts.

Unless the mfg literature says the ST coil doesn't have a disconnector - it has one.

If anyone knows of a CB with out an integral provided ST coil disconnector, give us a link - I'd like to see one. If for no other reason that to know what to avoid.:smile:

cf

 

[brother]

Heres a link that someone gave a me awhile ago about Epo's and how/what design might be best for your application, fail safe or no fail safe.

http://www.teal.com/products/App note AN-16.htm

 

[LarryFine]

CB mfgs also put aux contacts in CBs. So a CB having two shunt trip leads and three aux contacts leads does not mean the CB needs to have an aux contact used as the ST coil disconnect. It may (should) also have a built-in ST coil disconnect as well as the aux contacts.

Unless the mfg literature says the ST coil doesn't have a disconnector - it has one.

If anyone knows of a CB with out an integral provided ST coil disconnector, give us a link - I'd like to see one. If for no other reason that to know what to avoid.:smile:

Well, the one I was talking about is a 3p 225a breaker for one of several sub-panels in a switchgear. This panel section supplied the cooking equipment under the hood. The ST is tripped by the fire-suppression system.

The instructions with the replacement clearly show that the aux. contacts can be used either for remote signaling or for breaking the trip current, depending on whether the ST is supplied by a circuit it protects; this one wasn't.

The coil burned up because the original installer failed to realize that the tripping voltage would be continuous, and obviously ignored the instructions to use the aux. contacts (which I found were optional when ordering it.)

I'm fairly sure that branch-circuit-sized ST breakers do have integral contacts in series with the trip coil, but the one I'm talking about clearly did not. I can find out the type tomorrow. I kept it in case I ever need one without the ST.

 

[iwire]

Your assumption is logical, however reality is different.

I disagree.

Shunt trips and even solenoid actuators on MV switchgear are only built for momentary energizing.

Never think anything I say or type has to do with medium voltage equipment, I don't work with it, don't know anything about it. :smile: I forget it even exists, thats power company stuff.

Shunt trips have an integral switch built into them that opens with the breaker opening

Aha now I see, you misunderstood my post, If you follow the conversation Larry and I where having that is exactly what I have been saying to Larry, the shunt trips have internal switches to prevent self destruction. :smile:

I was not saying that the solenoids could be left energized, only that the entire unit could tolerate a continuous signal from my control circuit.

 

[weressl]

Never think anything I say or type has to do with medium voltage equipment, I don't work with it, don't know anything about it. :smile: I forget it even exists, thats power company stuff. .

Electricity is electricity. MV voltage is distribution not just generation and transmission. It is covered in the NEC and since it is an NEC forum it is relevant.

I was not saying that the solenoids could be left energized, only that the entire unit could tolerate a continuous signal from my control circuit.

Properly wired that is the case, unless the disconnecting means fails. The solenoids CAN NOT BE LEFT CONTINUALLY ENERGIZED, but the entire shunt trip unit with the disconnecting contact - rpoperly wired - can receive a continuous signal.

 

[zog]

Electricity is electricity. MV voltage is distribution not just generation and transmission. It is covered in the NEC and since it is an NEC forum it is relevant.

Yeah! See Bob, it's not just me.

 

[zog]

Never think anything I say or type has to do with medium voltage equipment, I don't work with it, don't know anything about it. :smile: I forget it even exists, thats power company stuff.
.

MV is nearly every industrial plant out there.