Magnetic Door Holders and Battery Backup with FACU

Dropping Door Holder Power with Loss of AC Voltage

When designing a fire alarm system you may come across the need for magnetic door holders.  There are no codes nation or state wide that require doors to be held open.  With that said, magnetic door holders are used as a convenience to hold doors open during normal operation.  If a customer wants to hold open a door along a non fire rated wall then they can prop it open.  Now if the customer wants doors along a fire rated wall to be held open then they must use fire rated doors and magnetic door holders tied into the building fire alarm system.  Make sure you understand the correct smoke detector spacing for the activation of smoke doors.

I wanted to write this post to assist installers and system designers with a practice that will help eliminate the need for larger fire alarm system back up batteries to achieve 24 hours of standby and 5 or 15 minutes of alarm.  If the building loses 120 VAC power, the fire alarm system must switch over to backup batteries calculated to handle all of the devices tied to the system.  Door holders draw a lot of current and quickly add to the size of batteries required to properly backup a fire alarm system.

Since magnetic door holders perform their intended function with the loss of power, it is common to install a PR-1 interface relay to drop them out in the invent of AC power loss.  Simply power up the PR-1 interface relay with the AC power at the FACP / FACU or RPS (remote power supply) and break the door holder power circuit switch leg through the N.C. (normally closed) contacts on the PR-1 relay.  If the AC power to the FACU or RPS is lost, the PR-1 relay will change state and drop power to the field magnetic door holders.

Keep in mind that magnetic door holders are self supervising so there is no need to install any end of the line power supervision modules.  Just in case that did not make sense, the door holders perform their intended function (close) upon the loss of power.  You would only need to monitor the power at the end of line if the devices on that circuit require power to operate.

Ground Fault found On PAM Relay Leg

Today I had the pleasure of working on a Saturday. It was a service call to track down and locate a ground fault on a Fire Lite FCPS24 NAC power supply. This ground fault is the reason another company felt it was necessary to disconnect the NAC circuit from the main fire control panel to the NAC circuit power supply. Read about here.

We traced out the ground fault on the negative power wire (constant power used for global HVAC shut down) to the rooftop air conditioning units. Upon a close examination of the unit with the ground fault we found that the 120VAC power leg (black) wire on the PAM-1 relay had been pinched in between the 4 S box and cover.

In this case our fire alarm control panel or FCPS24 NAC power supply was powering up the PAM-1 relays. This mean we connected our constant power to the Red (positive) and White (common) wires on the PAM-1 relay. Therefore the black wire is not used. However, the 120VAC lead (black wire) can still transfer a ground fault through the coil.

Always make sure to cap off the black lead and ensure it is not grounded out when using the PAM-1 relay for HVAC shutdown, elevator recall, door holder, etc.

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