7W CFL lamps on PLC relay out

[Lancie1]

Trying to switch the grounded leg can lead to problems, and also will cause you to measure erratic and unpredictable voltages-to-ground at the PLC output terminals.

If L2 is your grounded leg and it is connected to COM1 and COM2, then measuring between any COM and any PLC "Y" terminal (with output OFF) means that you are really measuring the voltage through the Output Device connected to that terminal. So this voltage should measure (220 volts minus the voltage drop through the CF Lamp ballast). That explains some of your readings.

I think your PLC outputs are wired backwards.

Our supply voltage is 220 Vac (line-to-line). However, when I tried reading voltage from any PLC output to ground (line-to-ground), I read 100 Vac. This is true even when PLC output is on or off.

Yes, backwards. That is all there is to say about that.

 

[Lancie1]

Ripley,

How about an update? Did you solve the problems?

 

[Bit_Bucket_07]

However, most programmable switch which leaks current are triac, not relay output. Please help me understand this situation.

Most relay outputs feature a snubber circuit which can allow a small bleed current while in the off state.

 

[theripley]

Ripley,

How about an update? Did you solve the problems?

Fortunately or unfortunately, we have a long weekend because its holy week. I may give you an update next week, when we resume to work. BTW, happy easter

 

[shooter]

Inside many relay outputs there are supressors, so they will give some leakage. If output is open, you will see still voltage with a normal meter.
As these lamps only need very little power they try to start when voltage is high enough, giving small flashes of light.

 

[Lancie1]

All true, Shooter.

Also, if the Mitsubishi PLC outputs are wired as shown in Ripley's drawing, then measuring voltage "to ground" results in unexpected readings. Shown here by the 3rd reading, 9 to Y1 will not be 0 as might be expected with Y1 off.

 

[Lancie1]

Fortunately or unfortunately, we have a long weekend because its holy week. I may give you an update next week, when we resume to work. BTW, happy easter

Easter is fog in the rear-view mirror, and so is April Fool's Day. What happened?