Troubleshoot Fire Alarm Ground Faults

Troubleshoot Fire Alarm Ground Faults 

Ground Faults are a big issue. Almost anytime there is a ground fault on a fire alarm system, the panel displays a trouble. Then, no matter what caused the trouble, the trouble has to be fixed. However, the NFPA has an exception to the rules regarding the displaying of ground fault troubles. For all types of pathways for signal or power in building wide fire alarm systems, the rule of thumb for displaying a ground fault trouble goes something like this, "Whenever there is a ground fault, the panel will display a trouble." There is an exception to this rule of thumb. "If the ground fault cannot affect anything else, under any circumstances, then the panel does not have to display a trouble when that particular ground fault occurs."

OK, the NFPA doesn't use these words, but that is the meaning.

What and Where is a Ground Fault?

A ground fault is defined as the unwanted grounding of one or more conducting wires. This can occur in several places. It can happen inside the fire alarm control unit enclosure, metal raceway, ceiling grid, metal junction box, or any other location in which conducting wires and an earth ground source are close in proximity. Ground faults can potentially cause circuits to operate improperly due to the current being “bled” off to ground before making its way to devices. Depending on the circuit type, ground faults must be indicated at the fire alarm control unit. NFPA 72, Chapter 12, Circuits and Pathways (Sections 12.3) will provide useful information. Hopefully the fire alarm system will indicate which circuit has the ground fault condition, making it easier to locate and repair the fault. If it is a system that only alerts you to the presence of a ground fault condition, but not the circuit, then the job will take longer to troubleshoot.

In normal operation, a fire alarm system sends a trouble signal to the fire alarm annunciator (keypad) 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 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.

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 heading off a potential lawsuit (even jail time, if more serious).

Why Does a System Develop a Ground Fault Condition?

There are different reasons why your system may develop a ground fault condition. For example, in newly installed systems, it may have to do with how the conductors were installed in the metal conduit. Sometimes conductors are skinned as they are pulled in the conduit and the copper conductor becomes exposed. If it is not realized that the conductor insulation has been damaged, but the system is otherwise correctly installed and tested, the condition may be evident when the control unit is first powered up. In this case, the problem can be corrected so the Authority Having Jurisdiction (AHJ) will accept the system.

There are times when a ground fault is not apparent when the unit is powered up. For instance, if there is a skinned conductor(s) but it is not in contact with the metal conduit or any metal junction box right away, then the ground fault may not be evident. There is technically no ground fault yet. When the system is tested everything checks out and is accepted by the AHJ. However, at some point later, the problem will show itself. Usually this occurs if the system is subjected to ambient conditions, has settled over time, or undergone some type of movement which causes the skinned conductor to connect with metal.

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.

Use an Ohmmeter

Remember, if fire alarm circuit conductors are in contact with the grounded metal raceway or metal junction boxes, the problem will eventually be found using an ohmmeter. One or more circuit conductors will have continuity between it and a reliable grounding point. Finding the ground fault is only a matter of time and patience — and relatively easy to repair.

Multiple Paths Used

To get a signal from a device in the field to the control panel, or from the control panel to a device in the field, the signal sometimes travels down more than one path. Each path may be classified differently.

A pathway shall be designated as Class A when it performs as follows:

(1) It includes a redundant path.

(2) Operational capability continues past a single open, and the single open fault results in the annunciation of a trouble

signal.

(3) Conditions that affect the intended operation of the path are annunciated as a trouble signal.

(4) Operational capability on metallic conductors is maintained during the application of a single ground fault.

(5) A single ground condition on metallic conductors results in the annunciation of a trouble signal.

A pathway shall be designated as Class B when it performs as follows:

(1) It does not include a redundant path.

(2) Operational capability stops at a single open.

(3) Conditions that affect the intended operation of the path are annunciated as a trouble signal.

(4) Operational capability on metallic conductors is maintained during the application of a single ground fault.

(5) A single ground condition on metallic conductors results in the annunciation of a trouble signal.

A waterflow switch, for instance, starts out on a conventional Class B path to send a signal to an addressable input zone module. The signal is processed in the zone module to make it addressable and then the addressed signal may be sent to the panel on a Class A Signalling Line Circuit (SLC) path.

To turn on the fire horns, the addressed signal is sent from the control panel to another addressable supervised output module on the Class A SLC path. Then the supervised output module sends the signal (power) to the horns using a conventional Class B path.

If there's more than one control panel in the fire alarm system, these same signals could be sent over Class N pathways, which may involve fiber optics as well as CAT(X) wiring.

As a signal travels from the detection device to the panel(s), and from the panel(s) to the fire horns We have to be aware of all the types and Classes of pathways that a signal might travel through.

Regarding any of the Classes of pathways (Class A, B, C, D, E, N, X), we as fire alarm designers, installers, and technicians have to know whether a signal pathway will allow a ground fault to affect the rest of the fire alarm system.

Coupled Pathway

When ground fault troubleshooting, a technician has to understand how various communication paths work in a fire alarm system.

The pathway signals can be divided into two groups: Direct Coupled and Indirect Coupled.

Direct Coupled is electrically connected or hard-wired - There are electrical current carrying copper wires used for transferring data between the electronics in all of the equipment and devices connected to the pathway.

Direct Coupled pathways would be:

·        The Signaling Line Circuit (SLC)

·        Upload & Download System Control and Power Loops (Four Wires - Plus, Minus, Send to Devices, Receive from Devices)

·        RS485 circuit

·        RS232 Circuit

·        Power Circuit (like for door holders, detectors, control circuits)

·        Any other pathway that use copper wires, Like wet contact AHU Tripping, Damper operation control, Door Handling unit, solenoid activation ….. etc.

Indirect Coupled is not electrically connected or hard wired - There is no electrical connection between any of the electronic equipment or devices.

Indirect Coupled pathways would be:

·        Radio Frequency (RF) Coupled like Wireless

·        Magnetically Coupled (Transformer Coupled) like CAT(x)

·        Optically Coupled like Fiber Optics

·        Any other pathway that use copper wires, Like dry contact or through NO/NC AHU Tripping, Damper operation control, PA Activation, Access Control Deactivation….. etc.

Continuity Test

The difference between Direct Coupled and Indirect Coupled is electrical continuity. It's not normally used in a fire alarm system, but a plain old light-bulb-and-battery continuity tester can often be used to check whether or not a pathway is Direct or Indirect Coupled.

No, don't do this, this is a mental test or a theory test of the pathway. Use an imaginary continuity checker because a real checker has a possibility of unforeseen damage. Connect your imaginary continuity checker to the positive wires at each end of the pathway, or connect your imaginary continuity checker to the negative wires at each end of the pathway.

If the data-path can turn on the light, the entire pathway is Direct Coupled, if the data-path can't turn on the light, the pathway is Indirect Coupled, at least at some point.

Troubleshooting

Troubleshooting ground faults isn’t much different than troubleshooting any other electrical fault. Use a systematic approach to isolate the problem. In most cases there will be one or more conductors, or even whole circuits, that have made contact with a grounded piece of metal. Always keep in mind when it comes to fire alarm control units indicating a ground fault condition – sometimes a ground fault indication has absolutely nothing to with a grounded circuit. Every now and then there could be another reason — and that reason might be a little unusual – electrically speaking!

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 loop cables, 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.

By bourn this issue need to counter and workout till it’s not gone.

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 a certified commercial fire alarm company or electrical contractor in your area.

Experience Sharing

There are times when a ground fault indication on the control unit has nothing to do with a grounded circuit. The following is happening with SSA Integrate Engineer.

A fire alarm system with an intermittent ground fault condition had been giving us fits for two weeks. This was an older conventional system and did not indicate where the ground fault was. In the middle of trying to figure out which circuit had the problem the ground fault indication would go away. This made troubleshooting the problem even more difficult. We inspected and tested each field circuit looking for any indication of a ground fault and found nothing. We inspected inside the junction boxes for bad or damaged conductors. We looked for moisture in the conduit. We still found nothing. Then we even tried to narrow it down to a certain time of the day, but there was no consistent time of the day for the problem.

After two weeks, I happened to remove one of the batteries to clean the enclosure. I noticed there was a wet spot and paint had peeled up leaving a small area of bare metal. I checked the bottom of the battery. The battery had a tiny crack and was leaking a small amount of electrolytic fluid. The fluid would contact the bare metal. There was a complete circuit from the battery charger – through the battery – to the leaky fluid – to the grounded enclosure, which created a ground fault condition. We cleaned it up, replaced both batteries and did not have another issue from that fire alarm system. Luckily, we did not replace the control unit circuit board, as that would have not solved the problem. It was by chance that the problem was resolved. 

Another case we want to share, customer reported Ground Fault trouble showing in there FACP. Standalone FACP with 3 Loop System no Graphic software no BMS connectivity. Our Engineer visit and find out once loop 2 cable are opened Ground fault is removed. Now team just splitting the circuit into sections or areas until we narrow down the ground. And ultimately found the ground is coming from the fire alarm cable between two devices, simply we replace the cable.

Another case our engineer found pinching the insulation makes certain spots thinner. Even though the insulation is blocking most electrical current, you could say the insulation is breaking down at that location.

The insulation/voltage threshold is lower at that location on the wire, and the electrical current flowing through the insulation at that point can be the cause of the fire alarm panel detecting a ground fault.

Another case our engineer found Rubbing the insulation on a sharp edge. It happened during installation of cooper cable. Initial time it not effected in loop line. It is the cause of a lowered insulation/voltage threshold. Even though the insulation is still covering the copper, it is thinner at that point and the voltage required to push electrons through the insulation is lowered.

Another case our engineer found Water at lower voltages is an insulator; water at higher voltages is a conductor. The voltage/insulation threshold of water is greater for distilled water (very high voltage) than it is for dirty water (salt, chemicals, just plain dirt in the water).

Water in building wiring (it's not supposed to be there, but it gets there anyway) usually has an insulation/voltage threshold of about 7 to 9 volts.

On GST brand fire alarm control panel, on board one jumper is there to disable Ground Fault. Just open jumper to not showing Ground fault in Panel Display.

On Edwards or Notifier or Simplex, all are UL & FM listed panel. They don’t have such option to avoid ground fault.