Douglas Krantz - Technical Writer - Describing How It Works
Go to the Fire Alarm Home Page of Douglas Krantz -- Describing How It Works
Go to the Fire Alarm Operation Map Page of Douglas Krantz - Technical Writer
Go to the General Electrical Map Page of Douglas Krantz - Technical Writer
Go to the Fire Alarm Description Map Page of Douglas Krantz - Technical Writer
Go to the Fire Alarm Installing Map Page of Douglas Krantz - Technical Writer
Go to the Fire Alarm Maintaining Map Page of Douglas Krantz - Technical Writer
Go to the Fire Alarm Testing Map Page of Douglas Krantz - Technical Writer
Go to the Fire Suppression Map Page of Douglas Krantz - Technical Writer
Go to the Science Article Map Page of Douglas Krantz - Technical Writer
Go to the Writer Home Page of Douglas Krantz -- Describing How It Works

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

Can More Than One Class A Circuit be in a Conduit?

Signed J N

Answer

How many Class A Circuits are in a single conduit isn't really the issue. The issue is separating the feed part of any Class A Circuit from the return part of the same circuit.

Keep in mind the purpose of Class A isn't so any problem with the wiring can be repaired in a timely manner; the purpose of Class A is to keep the system working before any wiring problems can be repaired - especially if something breaks once the fire hits and starts to degrade the system.

With Class A, like beads on a necklace, all of the devices are daisy chained on the circuit. The panel is where the feed part of daisy chain starts, and the panel is where the return part of the daisy chain ends. This way, both ends of the daisy chain are attached to the panel.

If the daisy chain is broken somewhere in the middle, the panel is still connected to both ends of the daisy chain. The idea is that signals can get to the panel either on the feed side of the daisy chain or the return side.

The feed and return from devices should be separate so whatever breaks one part of the circuit won't be breaking both the feed side of the daisy chain and the return side for any device.

The biggest concern is survivability of a Class A Circuit (in case a wire breaks, can the panel still communicate with the devices). Just keep the feed and return separate, and the rest can be just standard fire alarm wiring practices.

Douglas Krantz





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


Douglas Krantz

Describing How It Works
facpdoug@douglaskrantz.com

View Douglas Krantz's profile on LinkedIn



Short Circuit
Free Subscription
I'll Send You the
Twice-Monthly
Fire Alarm
Newsletter




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
.