Douglas Krantz - Technical Writer - Describing How It Works

Is it Mandatory to Report a Ground Fault?

By Douglas Krantz | Maintenance

Is it Mandatory to Report a Ground Fault?


Is it Mandatory to Report a Ground Fault?


Greetings Douglas

I have a question regarding detection of a wiring trouble in addressable fire alarm control panel. My question: "Is it mandatory to report ground/earth fault for a fire alarm control panel as per NFPA 72?"

Thank You, AH

Yes, the NFPA 72 Code does address monitoring for ground faults. Keep in mind, though, that the NFPA "Code" is a list of laws. It shows the dos and the don'ts concerning fire protection; it doesn't really go into why there's any do or don't requirements. Still, there has to be reasons for the requirements.

Example of a do or don't requirement in the law: Somewhere in the driving laws of the land is a law that says you are not supposed to drive at a normal driving speed down a crowded downtown sidewalk. That law doesn't say why you're not supposed to drive on the sidewalk, it just says that you're not supposed to drive there.

It's the same way with the NFPA 72 "Code". It doesn't say why ground faults are included when monitoring for integrity, it just says that ground faults are to be included.

Nonetheless, knowing what a ground fault is in the first place would help with understanding why ground faults are included with the monitoring for integrity. An open wire is easy to understand, a single open wire prevents the fire alarm system from fully working. The trouble light and buzzer are turned on with a single open wire.

On the other hand, a single ground fault in a fire alarm system usually doesn't affect the fire alarm system; the fire alarm system will usually still detect fires and warn people of fires. But then again, that's only a single ground fault, or the "First Ground Fault".

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First Ground Fault

The first ground fault in a fire alarm system is exactly like grounding one terminal of a battery in a car. In a car, connecting one terminal of the battery to the chassis ground; the car runs. Because it's normal to ground a car battery that way, there is no trouble and the ground connection does not have to be "fixed".

With a fire alarm system, connecting one wire to the ground of a building is a trouble; the fire alarm system, however, still runs normally. The control panel turns on the ground fault light, and turns on the trouble light and buzzer. The ground fault light, though, is an extra warning light. The extra warning light says "Fixing the Ground Fault Trouble is Very Important".

This single ground connection on a car, and this single ground connection on a fire alarm system is the "First Ground Fault".

Second Ground Fault

DO NOT TRY THIS - TRYING THIS ON A CAR WILL CAUSE AN ARC FLASH, PROBABLY CAUSE A FIRE, AND POSSIBLY CAUSE AN EXPLOSION. YOU CAN EASILY BE INJURED OR KILLED.

The first ground connection is always in a car. If, when using a wrench, you make an accidental electrical connection between a bolt on the chassis and the ungrounded terminal of the battery, you create a second ground connection. This second connection completes the electrical circuit, shorting out the battery. Besides the dangers mentioned earlier, the voltage on the battery drops. During the time the wrench is shorting out the battery, the battery won't be able to power anything.

The first ground connection on the car battery is always supposed to be there. The first ground fault on the fire alarm system should be fixed right away.

If the first ground fault on a fire alarm system is not fixed before a second ground fault occurs, the second ground fault has a 50-50 chance of shorting out something. The second ground fault could:
  • Short out the Initiating Line Circuit (IDC), causing a false alarm

  • Short out the Notification Appliance Circuit (NAC), preventing horns and strobes from being turned on

  • Short out the Signaling Line Circuit (SLC or Addressable Circuit), preventing the system from detecting fires and from sounding the alarm

  • Short out the Auxiliary Power, causing unknown problems


In case of a second ground fault, the fire alarm control panel may have safeguards to prevent total shutdown of the entire fire alarm system, but I wouldn't count on it.

Ground Fault Light

The ground fault light on the panel is an extra warning light. It is saying "Fix the ground fault before another ground fault occurs to shut things down."

Mandate in the Code

I have the 2007 NFPA 72 Code Handbook. It's an old Code book so the Code numbers won't match the ones in the book you have. However, if you look in the index in the back of the book, under the heading "Trouble Signals", sub heading "Installer Conductor Integrity" or "Conductor Integrity", you'll get the approximate location of the Code you're looking for.

In that Code you will see that all equipment and wiring shall be monitored for opens, and also for ground faults. Like the laws that say don't drive on crowded sidewalks, the Code doesn't say why these are to be monitored, the Code only says that these are to be monitored.

Douglas Krantz

facpdoug@douglaskrantz.com
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