AC Phase detector

How could I build a circuit that dectects if all of the three ac phases (127v) are present? I thought about measuring voltage between AC1+AC2, AC1+AC3 and AC2+AC3, this way it will even detect if the same phase is present on two terminals

Is it the more easy and realiable way?

It must be a compact solution

This will be used to trigger a relay to power a three phase ac motor only when the three phase are present. I know there are such protection devices on the market, but I would embed some other functionalities to a very specific application

Not with an arduino.....

Have you looked at using a 4-channel AC input optocoupler?

Usual arrangement is to use a phase failure relay.

you can connect 3 single phase relay to each phase with neutral and take output from NO to arduino via relay COM. With this arrangements you will get all relays NO connection if all phases are present with respect to neutral and if somehow one phase gets loss its corresponding relay will also loss its NO connection with arduino.

mohit-singh: you can connect 3 single phase relay to each phase with neutral and take output from NO to arduino via relay COM. With this arrangements you will get all relays NO connection if all phases are present with respect to neutral and if somehow one phase gets loss its corresponding relay will also loss its NO connection with arduino.

You are designing for a "Y" connection. I think the OP is designing for a "DELTA" connection for 3-phases.

Paul

3 phase 220VAC wye would be 127VAC line to neutral.

I think this would be as simple as it could get for detecting presence of AC, where loss of voltage in one or more phases, the Arduino input is pulled HIGH. AC voltage at all 3 phases, the Arduino input is switched LOW. Make sure the resistors are rated for 1.6W or higher and have at least 500VAC working voltage rating. LTV-824

|500x188

4 willwork ok especially if all the n/o contacts are seriesed together.