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Ask the Technician

Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer





M Wrote:

I appreciated your article on door holder relays. We have fire doors on our nursery and toddler doors that are held open by magnets. The workers have to "pop" the door off the magnet when church starts. Some of the workers are older and have difficulty closing the door. They have asked if we could install a push button under the magnet that would stop the magnet field when pressed, allowing the door to close. Is there a problem with doing this if we use an auxiliary relay as you stated in your article?

Douglas Krantz Wrote:

Adding a switch to interrupt power to the magnet should not be any problem. As a matter of fact, some manufactures install these buttons on the above-the-door door holders. The worst that can happen by installing the power interrupting switch is that if the switch fails, the door closes.






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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
.