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 technical 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 is OK to disable this ground reporting feature. Many do it 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 forget to return altogether. 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 appropriate sticker on the fire alarm panel (describing the problem) and contact building management authorities immediately.
You’ll sleep better at night and you’ll also be preventing a potential lawsuit (even jail time) if something bad were to happen.
What are the causes of a ground fault?
Sometimes they are caused by poor installation practices, such as attaching 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 ground faults are intermittent, so the first thing needed is a good volt/ohm meter that will show very high resistance.
I’ve personally tried using a low-budget meter in the past and although the fire 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 or electronics retail stores, but it is good money spent and well worth the investment (especially if you are sent to a service call on a Friday at 3PM).
To locate a good Fluke brand meter, you can find special online deals on Amazon or eBay.
Assume the worst case scenario
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 may be a chance that there is more than one ground fault on the system.
When troubleshooting a ground fault, do this first
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 follow my advice (and there is actually 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, any electrical conduit is a good source to use as a ground reference.
Since you are using a highly sensitive meter, make sure you are not touching or holding any of the exposed wire leads with your fingers or you will skew the results.
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.
Continue splitting the circuit into sections or areas until you narrow down the ground. If you find the ground is coming from the fire alarm cable between two devices, it is sometimes easier to simply replace the cable.
If you are NOT an electrician or a licensed fire alarm technician, DO NOT attempt to make these repairs yourself. Only qualified personnel should make repairs and troubleshoot energized circuits.
If you need further help in resolving fire alarm system issues, please contact our fire alarm service department. We are here to serve you.