In the Jack Fuse Power Port installation manuals and online learning, we state that you can use a NC (normally closed) signal from the FIP to control the fire relay on our Power Port modules. We also state that this signal should not be used in parallel to drive other Power Port fire relays. In this post, we will explore why.
There are two reasons we don’t recommend this method.
- If a technician inadvertently wires any downstream/slave Power Port modules incorrectly and joins an FT- terminal to an FT+ terminal on different Power Port modules, the fire trip can fail to activate and doors will remain locked. This has happened in the real world because the technician believed an NC contact is not polarity conscious. This is normally true (and works for the first module) however once you connect the NC contact to the first Power Port module a voltage is applied to the circuit.
- If multiple power supplies are used either in separate locations or at the same panel then using a paralleled NC fire trip will effectively link the power supplies together. This can cause grounding issues, unexpected voltages, and even damage to cables and equipment.
Remember that even if your system seems to be working, faults may only become apparent during a fire alarm. Future system additions or modifications could also lead to problems if the original configuration has used the NC fire trip in parallel.
The two diagrams above help illustrate the potential problems.
Solution.
A NC signal is the most common form of fire trip provided by the fire contractor. The best way to connect this signal to multiple slave Power Port modules is to use a DC voltage. The first Power Port module accepts the NC signal and provides a tripped voltage to downstream PDMs. See below. Remember to set the fire trip type on each module using JF.
Note: The problem and solution outlined in the post are not exclusive to Jack Fuse Power Port products and could apply to any scenario where an NC signal needs to be duplicated.