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EPO Circuitry

EPO Circuitry

EPO Circuitry

We have been using an EPO circuit for 25 years for laboratory rooms, invented by someone back in the day. It's not good but it works, usually. Sometimes it doesn't.

I attached a diagram of the circuit. Basically, diodes are used to allow for indicating lights when power is ON or when the breaker has tripped. Terminals ST1 and ST2 go out to a shunt trip circuit on a panel main circuit breaker. The voltage on ST1 and ST2 under "normal" circumstances is not zero volts, but rather about 70 volts and goes to 120 volts when an EPO button is pressed.

What happens sometimes is you get chatter from the shunt trip. Sometimes we buy an aux contact with the breaker to put in series with the shunt trip, but if we don't(not an option with all breakers),occasionally the shunt trip coil will chatter from the 70 volts.

What I'm trying to figure out is if changing the specific diodes used could lower the voltage I see on terminals ST1 and ST2 when the circuit is in the "normal" mode.

I also plan to try energizing a solid state 120VAC relay from terminals ST1 and ST2, and then having 120VAC always at one terminal of a dry contact from the relay in the shunt trip circuit. The relay would only energize when the EPO button was pressed.

Can anyone provide any input

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