Using Diodes to Prevent Backfeed in 120V AC Alarm Circuit with SPDT Switches

This is probably an easy question, but I have received a couple of incorrect answers from our company electrical "experts". I have two 120v circuits, each controlled by a SPDT toggle switch. I want to wire in an alarm which would activate when either of the switches is toggled. Problem is that I need to place a "one-way valve" component into the wires from the switchs to the alarm, otherwise when one switch is togles, the current to the alarm backfeeds from the alarm to the untoggled switch terminals. I am told by the company guys to just wire in a rectified diode. However, I thought a rectified diode would not prevent backfeed, just convert ac curent to dc. I would appreciate any suggestions.

Is the alarm powered by the 120VAC? In other words, when a switch is closed, does that supply 120 to both the alarm and whatever is being controlled by the switch?

It sounds like your alarm runs on 120Vac. You’re right, a diode rectifier wouldn’t work for this purpose.

I’d recommend using two 120V relays as an easy approach.

Connect each relay coil from the line (hot) wire, just after each toggle switch, to the neutral wire. Then connect the relay contacts in parallel with each other; from the line wire, before the toggle switches, to the alarm.

"StrykerTECH":http://www.stryker-tech.com/ Engineering Staff

basically confirm it first is it ac or dc voltage .
CASE 1 : AC
if it is ac then diode are of no use u need to have a relay circuit which will turn one at one time to bulgar out
there also devices like SPCO (Single pole changeover) & SPTT (Single Pole Triple Throw)

CASE 2 : DC
in this u can use the diode but in reverse bias
or the best solution is the scr as it can handel heavy voltage and currents , in a pair
its circuit is easy and can be found easily with the automatic night lamps or so

i hope u might have got ur answers if there are more corrections plz let me know thank u.
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