What is the Difference Between Electricity Flow and Signal or Power Flow?
Electricity Flow is the One-Way movement through a medium like a wire. There has to be two wires so both directions are accounted for. A signal, though, is thought of as power. Power goes from one place to another, like from an outlet to a motor.
By Douglas Krantz
Electricity is the movement of electrons or charges through a wire; signal flow is the transfer of power or energy from one place to another. Electricity may carry signals or power, but signal flow doesn't just use electricity.
Whether we think of electricity as the movement of electrons or as the movement of electrical charges, the electricity is being thought of as something moving through a single wire.
A drawback in this thought is that when we are only thinking of one wire at a time, we think of either electron movement or charge movement. Electricity flows in a circle, or complete circuit. Both the electrons and the charges have to return to the source, or they are going to "pile up" on the load.
If we're thinking of electrons, the source of the electrons will eventually use up all the electrons in the source, and pile all the electrons on the load. If we're thinking of either positive or negative charges, the source of the charges will use up all its charges and pile on the charges on the load.
This single direction thinking does not work. We have to step back and see that there are two wires: one to carry the electrons or charges from the source to the load, and one to carry the electrons or charges from the load back to the source.
With the two-direction travel, one direction on one wire and the other direction on the other wire, we are able to think of a balance between the source and the load.
Signal flow isn't thought of as the movement of electrons or charges in a single wire; signal flow is thought of the transfer of signals or power along a "pair of wires", a wave guide, or even transmitted through the air (or outer space) from one place to another. Signal flow is the transfer of forces.
This transfer of forces can use the electrons or the charges being guided by the pair of wires, low frequency electro-magnetic forces being transmitted and received using "radio waves", high frequency electro-magnetic forces in the visual spectrum transmitted by the sun and picked up by our eyes, or even gravitational waves crossing the universe caused by two black holes colliding.
Electricity versus Signal
What this means for technicians is that we have to think of electricity as one method of transferring signals or power. At the same time, we have to think of the transfer signal or power as what we are doing with the electricity, or radio waves, or light waves, or even gravitational waves.
When we look at a schematic or wiring diagram, we have to think of circuits, but we also have to think of what the circuits do.
Installers can land a wire on terminal A of the source, and terminal 1 of the load, and another wire on terminal 2 of the load and terminal B of the source is a circuit. Sending a signal from terminals A and B on the source to terminals 1 and 2 of the load is what the installers are doing with the electricity.
Circuit Design versus Signal Flow
As fire alarm technicians, we have to work directly with copper wires, fiber optics, or radio waves (RF or wireless), but all the purpose of the wire, fiber, or RF is to transfer signals or power from one place to another.
The rules and codes that we have to follow are concerned with signal flow, but using wires, fiber, and RF is how the signals and power is being transferred from one place to another.
The NFPA and Signal Pathways
The National Fire Protection Association (NFPA) has pretty much given up talking about electricity flowing in wires for their Pathway Classifications.
Now, they are talking about signals flowing from one place to another.