What is a Ground Fault?
In a fire alarm system, a Ground Fault is an electrical leakage to ground. When it is installed, the system shouldn't have any ground faults. A ground fault occurs in a building, though, when something changes to the wiring: either from poor installation practices or from damage to the system.
Example of a bad installation not showing up as a ground fault until years after being installed. A wire strapped to a threaded rod will only show small marks from the threads after a few days. The insulation will be part way penetrated after months. The insulation will be penetrated all the way through by the threads after years of being compressed by the wire tie. This becomes a ground fault and the ground fault is hard to find if it's above what is now a hard ceiling.
By Douglas Krantz
With the exception of the ground fault circuitry inside the fire alarm control panel (FACP) itself, the wiring
for fire alarm systems has no connection to ground. Any connection conducting electricity to ground is causing a ground fault condition.
Ground faults are common; they can and do occur in almost any kind of fire alarm system. For the technician, fixing a ground fault is easy; finding it in the first place
is the headache. Sometimes even following the wire
Ground faults are the result of:
- Poorly installed systems with shiners (bare copper showing) -- Overly stripped wires, and split or damaged insulation can result in a ground fault, especially if too many wires are inside the box to properly close it.
- Pinched wires in a box -- These soft ground faults often don't show up until days, weeks, months, or even years after installation.
- Water leaking on the wiring or on a device -- These soft ground faults can be in the ceiling, walls or floors; they can be in a device, in a j-box, in conduit, or underground in metal or PVC conduit.
- Damage during remodeling or construction -- Those doing demolition or construction might not notice the fire alarm wiring or devices, or might not care.
- Damage to the insulation after the fire alarm system is installed -- These ground faults can be caused by the wire falling on a sharp ceiling grid, a forklift knocking a device off the wall or ceiling, a door holder damaged as a door is slammed against it, or just plain poor installation practices (a wire tightly tied to a threaded rod is one of my favorites).
- Faulty ground fault circuitry within the fire alarm panel itself -- Inside the panel, either the panel itself may be ground faulting or the panel indicates false ground faults.
Single Ground Fault
Just to be factual, there is no problem with a single ground fault on any fire alarm system. It's just that the technician answering the phone off-site can't tell if it's only a single ground fault, more than one ground fault, or, in the near future, if more ground faults are imminent that will partially impair the system, completely disable the system, or cause false alarms. The ground fault light on the panel just doesn't say.
When to Fix a Ground Fault
Sooner or later, a ground fault has to be fixed. Some technicians might put off troubleshooting until the next business day if there are no other trouble conditions on the panel. However, depending on what causes the ground fault, waiting may be questionable. If any other troubles show on the panel, the troubles, and the ground fault, need to be fixed right away.
Having serviced fire alarm systems for nearly 20, Douglas Krantz has compiled his knowledge of the causes of Ground Faults and how to reliably detect them into the book Make It Work - Hunting Ground Faults
. The book shows the three types of ground fault, what equipment should be used with each type of ground fault, and how to locate those hard-to-find ground faults.
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