2 way switch induced voltage?

[Hellmooth]

Got a 2 way switch that gives 43 volts down one strapper when off, could this be an induced voltage, and if so why isn't it on the other strapper when it is off?

Also voltage at light switch is 250-252v, the light switch was faulty under load so couldn't be switched, when powered down it switches fine, it is rated to 250v, could this cause an issue?

 

[GEOFF S]

Got a 2 way switch that gives 43 volts down one strapper when off, could this be an induced voltage, and if so why isn't it on the other strapper when it is off?

Also voltage at light switch is 250-252v, the light switch was faulty under load so couldn't be switched, when powered down it switches fine, it is rated to 250v, could this cause an issue?

Hi

Yes sounds likely, probably not on other cable due to seperation distance.

Dont see an issue with voltage.

Cheers

 

[Hellmooth]

Hi

Yes sounds likely, probably not on other cable due to seperation distance.

Dont see an issue with voltage.

Cheers

Yeah did think it would be.

I wouldn't think it would be an issue, any ideas why it wouldn't work under load but ok when switched off?

 

[snowhead]

Yeah did think it would be.

I wouldn't think it would be an issue, any ideas why it wouldn't work under load but ok when switched off?

When you say OK when switched off, you mean has continuity?

If so the contacts are so badly burnt they'll allow continuity with the very low current from a meter but break down under any load.

 

[GEOFF S]

Yeah did think it would be.

I wouldn't think it would be an issue, any ideas why it wouldn't work under load but ok when switched off?

Hi

High resistance resulting in heat dissiapitaion, thus affecting switch operation?

Cheers

 

[Farmelectrics]

When you say it shouldn't be a problem it still should be sorted out your aware of it so rectify it. It will be come a problem for someone the next time it's tested cos your meter won't allow you to do dead testing as it will detect a voltage, I've had this once before when trying to do an insulation resistance test my meter wouldn't give me a reading a warning light comes until you detect the induced voltage.

 

[Hellmooth]

I didn't check for continuity, I mean the switch wouldn't move ie was stuck solid with a load on it, when switched off it worked fine.

And Farm I didn't say the induced voltage wasn't a problem, I was replying to Geoff when he said the voltage of 250v wasn't a problem............

Yes an mft won't allow dead test when it detects any voltage.

 

[Farmelectrics]

Not criticizing hellmooth just something I've came across myself years back

 

[Hellmooth]

Yeah I know, was just pointing out it wasn't the induced voltage I was saying wasn't a problem, it was the fact that it was 250v.

 

[Farmelectrics]

High voltages to have up there lol

 

[Farmelectrics]

High voltages you have up there I ment. Ha ha need to proof read my posts first

 

[Hellmooth]

Yeah it is on the higher end!

 

[davesparks]

It's far more likely to be a capacitively coupled voltage rather than induced.
But it's largely irrelevant as it I'll be easily identified either way if you are using the correct test equipment and understand how to interpret the results it gives you.

It is possible that if the switch is failing then there may be putting a high resistance connection in series with the load, acting as a potential divider
, thus presenting 43V at the switch terminal. But again using the appropriate test instrument and understanding the readings given by it will clear the matter up.

A phantom voltage such as this will not interfere with your dead testing due to the fact the circuit will be dead! Theoretically it could be an issue where multiple circuits are in close proximity and some remain energised, but I've yet to come across this being a problem for an MFT.

 

[davesparks]

250V is not high, it is correct. All UK substations are set to output 433/250V, regardless of the nominal voltage fairy stories you read about.

 

[Hellmooth]

The faulty light switch is not related to the 'induced' voltage I must add!

Thanks for the input anyway Davesparks always appreciated, I will look into it further when I can be arsed..........

The reason I noticed it was because the LED bulb I was using was slightly dimmed when off lol

 

[Hellmooth]

Thought it was maybe just the wonders of LED

 

[Hellmooth]

250V is not high, it is correct. All UK substations are set to output 433/250V, regardless of the nominal voltage fairy stories you read about.

And yeah yeah that is the case, I was just putting the high voltage in with the rating of the switch being 250v, thought it may have caused a problem due to a poor switch, was just putting it out there.

 

[7029 dave]

Get your drumond out, phantom voltages will be soon detected with this instrument.

 

[davesparks]

The faulty light switch is not related to the 'induced' voltage I must add!

Thanks for the input anyway Davesparks always appreciated, I will look into it further when I can be arsed..........

The reason I noticed it was because the LED bulb I was using was slightly dimmed when off lol

That suggests to me that the switch was goosed and causing a high resistance to be in series with the lamp when switched off. Capacitive coupling normally manifests as flashing low energy lamps rather than permanent dim illumination.

 

[davesparks]

And yeah yeah that is the case, I was just putting the high voltage in with the rating of the switch being 250v, thought it may have caused a problem due to a poor switch, was just putting it out there.

What problem did you think it might have been causing?

 

[Lucien Nunes]

Got a 2 way switch that gives 43 volts down one strapper when off, could this be an induced voltage, and if so why isn't it on the other strapper when it is off?

Draw the circuit - think about the permutations. However it is wired, one strapper will always be at line potential. What is on the other(s) depends on which ends the PL & SL are connected.

Scheme 1) PL & SL to L1 & L2, all three terminals of both switches strapped
Light off: Strapper 1 at line volts, strapper 2 at or near neutral via SL & load, common wire could be either.
Light on: Both strappers and common at line voltage.

Scheme 2) PL to one com, SL from the other, L1 & L2 strapped
Light off: One strapper at line volts , other at or near neutral via SL & load
Light on: One strapper at line volts, other floating.

I.e. only in the last situation will one of the strappers be floating and likely to show a ghost voltage, unless the load is O/C in which case one strapper will be floating whenever the switches are in an off state.

A switch that physically sticks after being operated under load, has probably got badly pitted contacts. The tiny weld that forms at each operation, especially if the load has high inrush, can interlock the rough surfaces together. I had this on an MEM grid module, that would jam almost solid after switching about 500W of switch-start fluo, but worked normally off-load.

Rated voltages are nominal based on lifespan and safety and in practice the maximum usable voltage depends on the kind of load. A switch specced for 250V will probably switch 500, but with seriously reduced life and poor safety margin and a tendency to flash over with inductive loads. At very light load it might even handle 750.

 

[Midwest]

It's far more likely to be a capacitively coupled voltage rather than induced.

A phantom voltage such as this will not interfere with your dead testing due to the fact the circuit will be dead! Theoretically it could be an issue where multiple circuits are in close proximity and some remain energised, but I've yet to come across this being a problem for an MFT.

I'm gonna have to disagree with you there davesparks, but I know you'll put me right.

On a couple of occasions, my Megger mft (1730) would not conduct continuity tests, because it detected 'voltage'. Complete isolation of the installation, removed 'phantom, ghost, induced' etc voltage, and the MFT functioned correctly.

 

[davesparks]

I'm gonna have to disagree with you there davesparks, but I know you'll put me right.

On a couple of occasions, my Megger mft (1730) would not conduct continuity tests, because it detected 'voltage'. Complete isolation of the installation, removed 'phantom, ghost, induced' etc voltage, and the MFT functioned correctly.

As I said I've never yet had the problem, or at least can't remember it being a problem. That's not to say it can't happen, and from your experience obviously does happen.

Did you try discharging the dead conductors by briefly connecting to earth? I doubt it would make a difference but am curious?

 

[Midwest]

Did you try discharging the dead conductors by briefly connecting to earth? I doubt it would make a difference but am curious?

Have to say I didn't at the time due to my lack of expertise, but we all gain from our experiences. Now know what to think about in those circumstances.