Ground Faults: A Fire Alarm Technician’s Worst Nightmare or An Easy Fix? You Decide…
If you deal with commercial fire alarm systems, there may have been a time or two when you’ve come face to face with a trouble on your system known as a ground fault.
I’ve worked with fire alarm technicians in the past that look at ground faults as though they’re about to be sent into one of the bloodiest battles of all time… you should see the look on their faces.
OK, maybe it’s not that bad, but I have heard some moans, groans and complaints come out of the toughest, hardcore technicians when faced with ground faults.
What is a ground fault?
Here’s a simple definition:
A ground fault occurs when one or more electrical components are short circuited to a ground potential. In a fire alarm system, this can occur when an exposed wire or alarm component touches a metal “grounded” object, such as a junction box, ceiling grid, or any other metal object located in a building structure.
In normal operation, a fire alarm system sends a trouble signal to the fire alarm annunciator indicating that there is a ground fault on the system.
If it’s apparent that there truly is a ground, but it is not reporting, either the fire alarm system needs repair or *it has been tampered with by removing a ground jumper on the system.
*Note: On some fire alarm systems, there are jumpers that can be removed to disable ground faults. If this is found to be the case, call for techincal help as soon as possible as this can impede the proper operation of the fire alarm system.
Example: If the ground happens to be on a smoke detector circuit, the system may not go into alarm upon activation of a detector. Disabling ground fault function is not only a potential danger to building inhabitants, but it is also against fire alarm codes to leave a system in this condition.
Why would a technician use the “disable ground” jumper on a fire alarm system?
In most cases, the ground disable jumper is used during troubleshooting procedures to silence the panel’s annunciator while working on the system. The big problem is when a technician, either purposely leaves the jumper on to “repair” the system or accidentally leaves it on when finished troubleshooting.
Over the years, I’ve worked with technicians who think it’s fine to leave this disable feature intact so they can leave early on a Friday after noon and intend on returning the following Monday… Huge Mistake!
There are times when the technician has no control over their routing schedule or they completely forget to return. Besides, if one leaves the system in this condition, the building (and its occupants) are left with a faulty system that can cause a false sense of security. What if there happened to be a real fire and occupants die in a fire?
If you are a technician, find a ground fault, and for some reason can’t make the repairs at the time of your visit, DO NOT disable this feature. Instead, put the opropriate sticker on the fire alarm panel and contact building mamagement authorities immediately.
You’ll sleep better at night and you’ll also be preventing a potential lawsuit if something bad were to happen.
What are the causes of a ground fault?
Sometimes they are caused by poor installation practices, such as attatching wires to all-thread hangers or building structures above ceiling tiles. After being set in place for a period of time, natural vibrations in a building can cause the wires to become worn and eventually touch a ground potential.
Other times grounds can be caused by other trades working in ceilings. If fire alarm wires are pulled or accidentally brazed, this can expose the metal conductors of a circuit causing an unwanted ground or short.
Ground Fault Troubleshooting Tips
Many times, grounds are not solid, so the first thing needed is a good “sensitive” ohm meter that will show very high resistance.
I’ve personally tried using a cheap meter in the past and although the system showed a ground trouble, the meter just didn’t have the high sensitivity settings to show it on the display. One ohm meter I highly recommend and use is the Fluke brand. It’s a little more expensive than ones you’ll find in big box hardware stores, but it’s good money spent.
To locate a good Fluke meter, you can contact your local Grainger’s Store, a good electrical supply dealer, pawn shop, eBay, or even your local area Craigslist (online). What ever you have to do, get one of these meters. It’ll be money worth spent (especially if you are sent to a service call on a Friday at 3PM! :0)
Always assume that there is more than one ground fault when trouble shooting.
Sometimes you’ll come across a fire alarm system that hadn’t been properly serviced for long periods of time. If this is your scenario and it shows a ground fault then there’s a good chance that there is more than one ground fault on the system.
To find a ground fault, the first thing you should do is *remove all wires from the fire alarm control panel. If the ground trouble goes away, then you’ve ruled out the possibility that it is not an internal ground within the control panel.
*Note: If you decide to remove one wire at a time instead of heed my advice (and there’s more than one ground fault), then you may never see the ground trouble go away.
By removing all of the wires, you will rule out that the ground fault is not an internal panel ground. If the ground is internal, then you’ll need to replace the fire control panel or components within the panel.
If the ground does go away, it’s time to break out the ohm meter.
To find a ground, click your meter to the highest continuity setting. Touch one of your meter leads to each conductor (not electrical circuits, of course) while also touching the other lead to a known ground. If installed properly, electrical conduit is a good source to use as a ground reference.
Once you have found a ground, tag it and keep checking. Don’t assume this is the only ground fault.
After you’ve determined the source of the ground, it’s time to start troubleshooting in the field. If you have as-built drawings available (I know it’s rare), visually split the circuit in half and go from there.
For more tips on repairing ground faults on your commercial fire alarm and security systems, please read the other ground fault article we have listed on this website by clicking the text link above.
If you still can’t find the ground fault (or just don’t have the time to do it yourself, contact our service department. Our technicians at Houston Fire Safety will be more than happy to come out and make the necessary repairs to your system.