Douglas Krantz - Technical Writer - Describing How It Works

How do I Solve this Ground Fault Problem?

By Douglas Krantz | Maintenance

A ground fault or earth fault is a current leakage to ground. The panel has its own connection and if the panel detects current through its ground connection, the panel assumes that there is a ground fault.

How do I Solve this Ground Fault Problem?

How do I Solve this Ground Fault Problem?

Greetings Douglas,

I have a fault in the fire alarm panel - Earth Leakages.

Please, could you explain this, and show me how to fix this?

Thank You, BE

An Earth Leakage, also known as a Ground Fault, is an electrical leakage or an electrical short in a circuit in the fire alarm system to the grounding system of the building. Once in a while, the ground fault or earth fault is inside the control panel's box-on-the-wall, but far more often the ground fault or earth fault in in a fire alarm circuit outside of the panel, somewhere else in the building.

Your job is to find this earth fault or ground fault, wherever it is in the building, and fix the leakage or short to ground.

Panel's Short or Leakage Detector

The fire alarm panel has it's own ground connection. That way, if there's any current that flows through the panel's ground connection, the panel can assume there's a ground fault.

The panel can detect the earth fault through its own ground connection. If there's any current that goes through the panel's ground connection, the panel detects trouble, and turns on the earth fault or ground fault light.

Use an ohmmeter to detect the ground fault yourself.

The panel may or may not be able to tell you which circuit to look at. Many times, to even figure out which circuit has the earth fault, you will have to guess-and-confirm a circuit, guess-and-confirm another circuit, guess-and-confirm another circuit . . . Keep testing until you find the circuit.

Don't troubleshoot using the ground fault or earth fault light on the front of the panel, it will only confuse you. See:

Can the Ground Fault Light be Used for Troubleshooting?

Looking for the Faulty Circuit

Before disconnecting anything, take plenty of pictures to make sure you will be able to reconnect the system, exactly the way it was.

When you test for earth faults or ground faults, disconnect both wires of a Class B circuit or all four wires of a Class A circuit. Any wires left connected to the panel on the circuit will confuse all the measurements by conducting current through the panel's ground fault detection circuitry.

If there isn't an earth fault or ground fault detected on the circuit, just to avoid the confusion caused by too many wires disconnected at once, reconnect the wires before disconnecting another circuit.

Different Types of Earth Fault or Ground Fault

There are different types of ground or earth faults.


What is a Ground Fault?

The most common type is a Hard Ground Fault. A hard ground fault is a metal-to-metal contact; a hard ground fault is a direct short. To find a hard ground fault, a regular ohmmeter is easy to use.

Other types of ground fault might require better equipment, than just a cheap ohmmeter. If it's more than a simple hard ground fault, you'll have to figure out what to use.


How Does One Find a Soft Ground Fault?

Locating the Trouble

Remember, no matter where you're looking, the building ground system is essentially the same connection: the electrical box that houses the equipment, the metal conduit, the ground pin on an electrical outlet, a structural "I" beam holding up the building, the metal roof deck, even sometimes the grid that holds in the lay-in ceiling tiles.

When looking for a building ground, just stay far away from any fire-sprinkler heads. I've seen way too much water damage from a single sprinkler head that accidently activated.

You have to measure both wires to ground. The devices betweent he wires might prevent the ohmmeter from detecting the short.

When guessing-and-confirming, the whole circuit has to be disconnected from the panel, and tested using an ohmmeter. If the ohmmeter shows a mostly open circuit, check the other wire in the circuit. If that's also an open circuit, reconnect the circuit while comparing the wiring to the pictures you took before disconnecting the circuit.

Once you've found the circuit with the fault, leave the circuit disconnected from the panel while searching for the short to ground, otherwise the panel confuses the search.

Break the circuit by disconnecting the wires, then use the ohmmeter.

As you look for ground faults or earth leakages, you will discover that finding-and-fixing the faults will become easier. Right now though, expect to have to learn patience using the guess-and-confirm method.

Go to a device on the circuit, check there.

If you can figure out where the circuit is running throughout the building, you can use the Divide-and-Conquer" method of deciding where to test or the fault next.

How do you Troubleshoot an Addressable System? Also known as Divide-and-Conquer

Remember, before disconnecting anything, take plenty of pictures to make sure you will be able to reconnect the system, exactly the way it was.

Next Device

Finding an earth fault or ground fault requires opening up the circuit is many places.

Keep breaking the circuit until you find which wire has the ground fault.

If you can find the fault at one of the devices you're working with, great. If not, you might wind up having to "Follow the Wire"


Can Follow-the-Wire Help Troubleshoot?

I can't tell you how many times I've found the trouble with a system because I followed the wire around the building. Often, this low-tech troubleshooting technique saves lots of time.

Ground/Earth Fault Patience

Looking for ground faults and earth faults requires lots of patience. The first time you have to look for one, it may take 6 hours or more time to find the fault.

After finding lots of these kinds of faults, the time required to find the fault will be less as you learn to talk shorter paths to find and fix the fault. For me, most ground faults took 1 to 2 hours to find and fix, sometimes taking as little as 1 / 2 an hour.

Douglas Krantz
Life Safety
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