Power source for shunt trip circuit

[barnem1]

Is there any requirement in the NEC that the power supply for a shunt trip circuit must originate from the same panel as the breaker being tripped? If so, please direct me to the correct code article.

 

[davidr43229]

Is there any requirement in the NEC that the power supply for a shunt trip circuit must originate from the same panel as the breaker being tripped?

I don't think so. Let me explain, for elevators the shunt trip signal originates from the fire alarm controller, which usually resides not in the same room, let alone the same panel.

 

[petersonra]

I have been known to use a battery with attached trickle charger.

 

[brian john]

Small plug and play UPS works nicely.

 

[iwire]

Small plug and play UPS works nicely.

Thats a sharp idea, most are capable of sending a battery alarm over a network as well.

Where I am now they use a few of these small units to keep control panels of certain machines powered up.

 

[dbuckley]

Small plug and play UPS works nicely.

Most shunt release systems are installed as some sort of safety reliant system, and I'd not trust an el-cheapo UPS in that situation. Their reliability is simply not up there. Especially if the long term maintenance situation is uncertain, as it often is outside the worlds of fire and elevators etc.

 

[benaround]

Somebody fill me in, the only shunt trip cb's I have installed require 120vac

to trip them off. Sounds like they work on a signal now, is that correct? If

so I'd like to hear the short story. thanks

 

[davidr43229]

Somebody fill me in, the only shunt trip cb's I have installed require 120vac

to trip them off. Sounds like they work on a signal now, is that correct? If

so I'd like to hear the short story. thanks

Most shunt trip operate with a 120 volt signal, you are correct, which require approx 20ma to 50ma (depending upon manufacturer) to activate that shunt trip.
It usually comes from the fire alarm control panel (do you have one?). If not you will need some means of signal (in emergancy situations) of suppling that. Usually a MCT (Motor Control Transformer) taking that 480/277 to 120 volts and a relay. If you need more info Private message me please.
Just my $.02

 

[barnem1]

Is there any requirement in the NEC that the power supply for a shunt trip circuit must originate from the same panel as the breaker being tripped? If so, please direct me to the correct code article.

The reason I ask is that I have designed projects with shunt trips in the past where I did not specify the source, or I pulled power from a separate circuit. If this is indeed a problem, I need to address it in my design approach.

One issue which my fellow engineers have raised is that if you shut off the main breaker in a panel, you would still have energized wires inside the panel, which could be dangerous.

 

[iwire]

A couple of points I see.

Most shunt release systems are installed as some sort of safety reliant system, and I'd not trust an el-cheapo UPS in that situation.

1)That is true, many shunt trips are used as some sort of safety system. But few if any have any form of supervision at all and can most certainly fail without any notice.

Their reliability is simply not up there. Especially if the long term maintenance situation is uncertain, as it often is outside the worlds of fire and elevators etc.

2) I can't see how a UPS would be less reliable than a standard circuit.

I doubt that many plug and play UPS will fail 'off' as long as there is a utility supply.

 

[kc8dxx]

With a shunt trip circuit, three things must happen to trip the breaker. 1) fault detection circuit works, 2) shunt trip power source works, then 3) shunt trip coil works. We've switched over to Undervoltage Release mechanisms because of problems with #2.

The UV coil trips the breaker when power is lost. So now you're down to two things. 1) fault detection circuit works (designed so that voltage on is equipment OK) then 2) UV module de-energizes.

This requires a bootstrap circuit, i.e. another power source that can be turned on while the breaker is off. Power source comes from same panel as the breaker source, but to get to your original question, I am not aware of a code requirement for this.

 

[benaround]

barnem1,

The only time power would be in the shunt cb, is after the saftey control

has changed from it's normal state, so if you turned the main cb off to a

panel there should be no other power in there unless the shunt cb's are

tripped.

I think designating a circuit/ power source at your end is a good idea.

 

[petersonra]

2) I can't see how a UPS would be less reliable than a standard circuit.

I doubt that many plug and play UPS will fail 'off' as long as there is a utility supply.

UPS batteries have to be replaced periodically.

I have no end of trouble with them failing on me. Even name brand high end units. They are particularly susceptible to fail if you don't set them to shut down before the battery is completely depleted. But for an emergency system, that would be the last thing in the world you would do.

I have almost come to the conclusion they are more trouble than they are worth. Almost.

 

[georgeswe]

Typically the Breakers that I have had shunts on have been in the 277/480 panel and the shunt voltage has been 120v. We have run a 120 circuit over to the fire panel and had a Junction box where we installal a relay that would contol the 120v hot leg then over to the shunt breaker in the 480 pnl. It would depend on what type of a system installed I have even run the 120 circuit thur a NO contact in a ceiling heat sensor. The best bet would be to get a hold of your fire alarm contractor and see what type of a system you have since things liek if the elevator shaft has sprinklers or not.(if the shunt is for an elevator application)

 

[dbuckley]

Theres two basic schemes where shunt breakers are used.

The first is as some sort of an EPO system, where the source of shunt signal is local to and part of the area where power is being fed to. In this type of system the shunt power can come from (loose terms) the same place as the delivered power, because you only need to have power for shunt trip if you have power to be tripped off.

The drawback to this scheme are that you need low ampacity feed for the shunt supply, usually no more than 10A. The risk is the failure of this feed. The best installations of this type I have seen use a pair of parallel breakers locked away behind perspex, so that they can be seen to be on, but not accidentally or maliciously played with. Other systems have used fuses inside the panel.

The other risk in this system is that under failure of the single phase the shunt is powered from (and other phase or phases stay up) you lose the ability to trip the shunt.

The other type of installation is where some control system wants to power off something, often fire or security controlled. I've seen 12V and 24V shunt trips, but not many. Sometimes the shunt trip feed comes in at mains voltage from another "place" supplied by others. I don't like that arrangement, as (a) I worry that the other thing's mains may fail just when you need it to operate the shunt, which is why there are suggestions of UPSs, and (b) its a source of mains power coming into a panel that isn't isolated by the main breaker, so labeling and extra care needed. Much better to work with the control system installer, get a 12V or 24V feed, and use a relay in the local panel to control the mains feed to the shunt trip same as way 1. An ordinary relay (ie not a red safety relay) should be quite adequate, as the whole shunt arrangement shouldn't be used for a safety critical system anyway.

One worry I used to have was that when there were several breakers being shunt tripped simultaneously and the power source for trip came from a circuit supplied through one of those breakers, that there would be some sort of race condition where because the shunt trip power had dropped some breakers would not open. In my experience, and by the word of a man who had designed and implemented many large scale UPS systems switchgear using just this sort of arrangement, it doesn't appear to be the case; all the breakers trip every time, both MCCBs and ACBs.

 

[Jolly]

Elevator shunt trip

Elevator shunt trip

The elevator mechanic informed the electrical contractor that it is required to have shunt trip breaker inside the elevator equipment room,and it is not acceptable to have shunt trip breaker in electrical room and disconnect in elevator equipment room. Is this correct?

 

[davidr43229]

He is correct, additionally that shunt trip breaker has to be selectively coordinated. Simply by installing one might satisify the elevator mechanic, but not the 2002-2005 NEC. Some states disallow shunt trip, Michigan being one of them.
Just my $.02

 

[micromind]

Getting back to the original question, I don't see how the source could possibly be required to be in from the panel it protects. The shunt trips I usually work with are as follows.

1) Switchboards where the main is located within a building. These have the red triangle outside, with a break-glass, pushbutton, switch or whatever. Usually 120ac coils. Some of these sources are a transformer within the gear, (if it's more than 120) and some are a separate circuit in a 120 panel.

2) Diesel generators. Usually the 'panel' where the breaker is located is on the generator end itself, and only contains that breaker. Usually a 12dc or 24dc coil. Usually controlled by some sort of engine and/or generator protection relay mounted elswhere on the unit. Sometimes also a separate switch located adjacent to the EPO on the building.

3) Power plants. There are a myriad of shunt trips here, some are generator protection, some grid-tie protection, and others. Almost all of these are 48dc or 125dc coils, and the DC is almost always batteries and chargers.

I've actually seen very few shunt trips where the coil was powered from the panel it protected.