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Fire Alarm -- Description

Any attempt at having two companies to keep each other honest is at best a questionable practice
Sometimes building owners want service companies to keep each other honest. The trouble with that is neither company is on site when the other is there, and conflict of interest issues prevents either one from looking into what the other is doing. As much as some building owners want, service companies can't watch each other.
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer

Can One Company Really Keep the Other Company In Line?

By Douglas Krantz

I'd like to tell you a story about dishonesty. Not the kind where a vendor knows he is doing wrong, and lies to the owner about it. This is a story about the other kind of dishonesty, the kind where the vendor really thinks he did a good job of installation, but is not honest enough with himself to check whether the system works or not. In other words, the vendor doesn't care.

At an apartment building, the managers thought two companies, one servicing the fire alarm system and medical emergency-call system, and the other providing the off-site monitoring for these systems, would catch each other's mistakes, and keep each other honest.

But can two different vendors working together really keep each other honest?


At this location, when someone pulled the medical emergency-call cord (e-call) in their apartment, the Central Monitoring Station (CMS) received two signals: a medical emergency and a fire alarm.

Upon receiving the signals, the CMS dispatcher would call for both an ambulance and the volunteer fire department. A fire alarm in the building would get the same double response.

This was getting tiring for the fire volunteers and the ambulance people.

The company in charge of monitoring claimed that their equipment was working correctly, and the fire alarm/medical emergency-call service company (us) should fix the problems.

I was sent to fix the recurring false alarm issue.

Finding the Real Problem

The fire alarm system and the e-call system weren't connected together at any point. Using separate wires, they reported their alarms to the communication dialer on separate zone inputs.

To me, it didn't make sense that at the same time two different systems should have the exact same issue, except at their common connection. I needed to know some of the history of the system.

Recent History

The fire alarm system hadn't changed, the medical emergency-call system hadn't changed. On the other hand another company (the monitoring company) had just replaced a very old telephone communicator with a modern communicator.

At first, I couldn't see any problem. After all, this was a brand new dialer, it appeared to be wired correctly, and the other company supposedly tested it.

Inputs on Old vs New Communicators

I thought one dialer was like another dialer, at least as far as their conventional Class B fire alarm input wiring. But the issue still stood: before the dialer change-out, there were no issues with false alarms; after the dialer change-out, there were issues with false alarms.

To me, this was a hint, but with what I knew about fire alarm systems that didn't make sense.

Normally, at least nowadays, zone inputs on conventional fire alarm equipment will react to three sensing levels.
  • Normal - where the zone input is reading current through the end of line resistor
  • Alarm - where the zone input terminals to the fire alarm equipment are shorted together, somewhere along the loop
  • Trouble - where a connection or a zone wire is broken and the supervision current is no longer allowed to pass through the end of line resistor
The new communicator used this method and I thought the old communicator used this method.

Following Wires

Now I had to troubleshoot. I started following wires.

On the alarm output of the e-call system, instead of seeing the usual contact closure to short out the loop, I saw that on alarm the e-call system sent an active 24 volts to the communicator. That didn't make sense.

Continuing to investigate, I followed more wires.

On the alarm output of the fire alarm panel, wired so that on alarm it would send 24 volts to the communicator, I discovered a relay. That really didn't make sense, but now I knew I was onto something.

Both should be closing a contact to short out the loop when they went into alarm; neither one should be sending 24 volts to the dialer.

From this, I concluded that apparently the old communicator wasn't conventional. It required an active 24 volts on its zone input to send an alarm to the Central Monitoring Station (CMS).

Fixing the Communicator

The alarm signals received on the zone inputs on the new communicator were still the active 24 volts. Not a good thing. This 24 volt signal shorted the inputs together inside the new communicator, so it was now sending both signals when either zone received 24 volts.

In other words, the communicator was now faulty.

But I had a problem. Another company had, without our knowledge, replaced the communicator. They should have known what they were dealing with, the method used to activate the old and new communicators were different. They should have tested the installation afterward.

The trouble is I couldn't just fix or replace the communicator; this was another company's warranty issue.


I saw the wiring problem, and called the other company. Their manager didn't believe me and refused to send anyone to correct the system. He wouldn't even look at the problem.

He wasn't honest enough with himself to check it out, and the issue became his word against mine.

The management for the apartment building and the fire marshal wanted answers.


How was I going to explain this?

The only way to explain this was to do what the other company refused to do: demonstrate the cause of the problems.

With the system in test, I took the building manager with me and pulled an e-call cord. Checking signals received by the CMS, I found that that they received both a fire alarm and a medical emergency. I told the manager what the CMS received.

Then, with the manager still watching, I set off a fire alarm, silenced the fire alarms right away, and reset the fire panel. Again, the CMS received both signals. I told this to the building manager.

One Service/Monitoring Company

The apartment building manager saw that I was correct; either system would send both alarm signals through the communicator. She saw that it was the other company's communicator that was having problems.

To keep the whole system working she decided that one company, performing maintenance on the overall system, was better than two.
Was this
Yes   No

She could point her finger at the one company, say "fix it", and it would be fixed.

Because I showed beyond a reasonable doubt where the problems were, she decided our company should maintain the whole fire alarm/e-call/monitoring system.


One company may be better for service on the entire fire alarm system, because if even one of the companies watching each other isn't honest to begin with, neither of the two companies will be able to keep the other honest.


Douglas Krantz

Describing How It Works

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On this website, most references to electrical flow are to the movement of electrons.

Here, electron movement is generally used because it is the electrons that are actually moving. To explain the effects of magnetic forces, the movement of electrons is best.

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