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Fire Alarm -- Maintenance

Ground Fault Progression of a wire tied to a threaded rod
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.
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer


What is a Ground Fault?

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 is difficult.

Causes

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.


More Articles

How Does One Find a Soft Ground Fault? -- Normally, we think of resistance like that of a resistor. The amount of resistance is built-in; no matter what voltage is used to drive the electrical... Read More

Why Do Ground Faults Keep Happening in Some Buildings? -- Someone on a condominium board wrote about recurring ground fault issues with his building. Some of the other board members... Read More

Can Fire Alarm Fiber be Run in the Same Conduit as BMS? -- Can fire fiber riser be run in the same riser conduit with BMS? We only have one riser conduit for both. The engineers are saying we need two separate conduits, your thoughts? Read More

It's the Volunteer Firefighter that Reads the Panel -- I suppose it was used because the technician programming the fire alarm system was totally familiar with the acronym AFA and what it means... Read More

PDF Book PDF of Make It Work - Conventional Fire Alarm Systems


Douglas Krantz

Describing How It Works
facpdoug@douglaskrantz.com

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Electrical Flow


On this website, most references to electrical flow are to the movement of electrons.

Here, electron movement is generally used because it is the electrons that are actually moving. To explain the effects of magnetic forces, the movement of electrons is best.

Conventional current flow, positive charges that appear to be moving in the circuit, will be specified when it is used. The positive electrical forces are not actually moving -- as the electrons are coming and going on an atom, the electrical forces are just loosing or gaining strength. The forces appear to be moving from one atom to the next, but the percieved movement is actually just a result of electron movement. This perceived movement is traveling at a consistent speed, usually around two-thirds the speed of light. To explain the effects of electrostatic forces, the movement of positive charges (conventional current) is best.

See the explanation on which way electricity flows at www.douglaskrantz.com/
ElecElectricalFlow.html
.