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What the shunt is going on here?
Shunt Trip Breakers
Situation:
I was recently contacted by an offshore electrician who posed the following situation that I would like to share with you.
"A newly installed shunt trip breaker is no longer functioning as directed, I tested it using the Fire Control Panel several times, it functioned fine the first 6 tests, then nothing"
Definition:
A shunt trip device is an optional accessory in a circuit breaker that mechanically trips the breaker when power is applied to the shunt trip terminals. The power for the shunt trip does not come from within the breaker, so it must be supplied from an external source. Some circuit breakers allow field installation of a shunt trip kit, however others require factory installation when the breaker is ordered. Check the specific breaker type for available AC and DC shunt trip voltage ratings and for the method of installation
Uses:
The shunt trip device located inside a circuit breaker is designed to electro-
The breaker itself, is like any other traditional circuit breaker, if an excessive amount of current flows through the circuit the breaker will activate preventing an over current condition
Based on the situation, I asked for the following information;
1. What is the exact make, model & part number of the shunt trip breaker?
2. Who is the manufacturer and what is the model number of the Fire Control Panel?
Diagnosis:
Based on the information given, the breaker in question has the shunt mechanism installed, but does not have the internal mechanical disconnect switch to protect the coil of the shunt.
The Fire Control Panel does not have the ability to pulse the auxiliary power to the shunt.
$1,600.00 special order, UPS Red, shunt breaker shot. No exchanges or returns.
Solutions:
Most internal shut mechanisms are not intended to have continuous power to the shunt coil, constant power will cause the coil to overhead and eventually fail. This is why the need for the disconnect switch is required.
Not all Fire, and for that matter Gas Detection systems do not have the ability to provide a temporary pulse of power to the shunt mechanism. Some Intelligent Fire & Gas systems do, through programming options or specifically designed control output modules.
When selecting control modules or dry contacts, always be aware of the initial or inrush current required to trip the breaker. Inductive loads are more demanding than resistive loads.
If replacing the breaker or control panel is not an option, a timer relay can be utilized between the systems and breaker, but I am not a big fan of over complicating the design.
Research:
How do I know if my shunt trip breaker has this function?
Following all lock out procedures to prevent electrical shock, disconnect the external wiring from the Fire/Gas Control Panel to the shunt mechanism. Using your ohm meter measure the coil resistance of the shunt mechanism with the breaker in the On position, your meter should display a shorted state between the coil.
Next, with your meter still attached, manually move the breaker to the Off position, your meter should display an open state.
This breaker has the built in special ordered shunt with internal disconnect.
To determine if the Fire/Gas Control Panel is able to send a temporary pulse, It would have to be evaluated on an individual basis depending on the system in operation.
Note:
By design limitations shunt trip breakers are not what is considered Fail Safe, but depending on the systems in place they can be made Fail Supervised. Contact me should you require more info on this.
If you require more information regarding the terms and explanations above, contact me by email or phone for assistance.
The above information is covered in the following Tec Trek class segments: Awareness Training (FG-
For more information regarding training schedules and course curriculum, please visit our Web Site at
or Contact Todd Olivier at (337) 298-
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Email: todd@tectrek.org