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Crouzet EMER8. Programmable Timer

jb101

Just trying to find out if relay output on this timer is volt free. This is an on site application and I’m using 110 volts ac on the coil, and on the input to the Y1  trigger as I know the trigger is related to the coil voltage, and the input to Y1  must be the same as the phase of the coil voltage applied to A1 otherwise you get odd results, even with AC. I want to switch 24 volts AC with the relay contacts, but I note on this application that I am seein a small voltage of 1.5 v  to ground on the terminals. This could just be a bit of internal pickup from the coil ac, but I am a bit curious about it as the application could  be a critical safety issue, and the data sheet for the timer has a diagram that suggests it’s volt free, but doesn’t actually state it. I have used these timers extensively,  but always hitherto with the same voltage on the coil and relay contacts. Anyone confirm these contacts are volt free?

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    I'm not familiar with the model of timer, but generally real relay contacts are "volt free" as they're basically isolated NO/NC/COM contacts.

     

    If you have any doubt as to mains pick-up, perhaps isolate any cabling from the timer except for the power into the timer and measure the voltage over the connections at the rear. If they are truly relay contacts, there shouldn't really be any voltage measurable (aside perhaps a fraction of a millivolt). If it is solid-state relay, then all bets are off as they can have leakages, and sometimes can be damaged by ESD.

     

    If there still is some voltage, you might want to try putting a load resistor and seeing whether it sources any current or check the insulation from primary to relay outputs with an insulation resistance tester to see if it is actually isolated or whether you have other issues (e.g. carbon build-up behind a relay causing tracking, degraded insulation). Despite having a small voltage, depending on what is reading the value and the input impedance, it could be possible that closing the loop through the input impedance drops the stray voltage enough that it won't cause an issue. If it's internally inducted into the cabling, changing the cable routing to cross other cables at 90 degrees and/or using screened cable grounded at one end may well reduce the problem somewhat.

     

    - Gough