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Fire Alarm -- Installation

I have a question on how something works.
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer







I have a Question

Question. Can phone lines, fire alarm cables, and 120-240 cables be put together in an outdoor back box?

Signed E

Reply

Besides the legal aspects, fire and safety issues, there's the interference problem.

The voltages and currents from the 120-240 volt cables will be cross-talking to the low voltage cables. How much cross talk is produced will be affected by the actual currents in the high voltage cable, how tight they are to the low voltage cables, and the distance they are running together. The tolerance to this interference is a great issue, and depends on the signals used in the low voltage cable.

Unless you are prepared for major problems from all these issues down the road, I wouldn't recommend it under any circumstances.

Douglas Krantz


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


Douglas Krantz

Describing How It Works
facpdoug@douglaskrantz.com

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Articles

How Does Class A Fire Alarm Wiring Work?-- Fire alarm systems save lives and protect property. Fire alarm systems also break down because... Read More

Just What Is a Signaling Line Circuit (SLC)? -- The SLC (Signaling Line Circuit) is another way of saying Data and Power Circuit. Along with added power to run the sub-computers and their input and output circuits, it's a computer data-buss ... Read More

How is a Buffer Relay Wired Into a Door Holder Circuit? -- Like a door stop, a door holder keeps a fire door open. When smoke is detected, the door holder releases, allowing the door to shut. The door holder looks simple and innocuous enough... Read More

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

Can a Magnet Really be Used to Test a Smoke Detector? -- Smoke detectors usually have two ways of being tested. Smoke (smoke particles in the air, or some sort of canned smoke), and magnets (the activation of an internal magnetic... Read More



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
.