Zs of Lighting circuit via dimmer

[Guest 004]

I am doing some testing of new build flats, when the R1R2 was done , I had a reading of 0.9 ohms. However when I get the Zs once the dimmer has been connected the reading obtained is 150 ohms. Take the dimmer out of circuit, then everything is correct with a reading of just above one ohm.

The DB is a dual RCD board
The MCB is a 6 amp

Thoughts anyone?
Any comments on test sheet?

 

[telectrix]

measure Zs with the dimmer linked out.

 

[Guest 004]

Yes already done that to get a lower reading.

 

[nickblake]

some dimmers have a choke coil the supply goes through it will probabley be this that gives you the higher reading ,test as you have done and tel suggested

 

[mogga]

dimmer linked out deffo

 

[platty1005]

Write in 150 and why in comments box ( dimmer switch)
Calculate Zs as Ze + (R1+R2) write why in comments box
Zs of 150 ohm is OK because of RCD protection
max Zs for 30mA RCD circuits = 1667 ohms
So 150 as measured or Ze + (R1+R2) either will comply

PS equipment vulnerable on test sheet ( RCD's and Dimmer switches)

 

[Draig Coch]

As Nick says there is probably a coil in line when the dimmer is switched on.

The loop tester uses a pulse test wave with probably greater frequency than 50Hz and the switch electronics don't get properly energised so you wouldn't expect a low resistance path through a dimmer. The waveform will change when switching in different ranges or using a different tester that would provide you differing results if you wanted to check. I've seen this before but with an RCD.

Just another way of looking at things is that you could submit calculated Zs (Ze + R1R2) values for that circuit to show compliance, as long as you indicate clearly thats what it is. You can cover yourself by stating the measured value in the observations.

 

[Deleted member 26818]

Dimmers work by varying the resistance.
The greater the resistance, the dimmer the light.

 

[IzzyS]

All the ones I've ever used work by firing an SCR to control the cycle time. Dissipating 200 or 300W through a resistor may cause a few problems in a standard back box. As said, loop it out, but note that there's a dimmer.

 

[Calebp43]

Hey guys I know this thread is over 10 years old but interestingly I was testing today and on the dimmer switch had a R1+r2 Of 0.92 ohms and a Zs of 0.00ohms?? Retested a few times to be sure and always the same. Bypassed the dimmer and got a normal reading then... It was 0.6 ohms or something like that. After reading these comments.im pretty baffled

 

[Lucien Nunes]

The dimmer is a bunch of electronics that corrupt the waveform of current passing through, likely to confuse the tester which is only expecting to see the sine wave of the mains through a length of copper wire. The actual figures will depend on exactly how the electronics in the dimmer behave when subjected to the abnormal conditions created by the tester, and how the tester behaves when subjected to the abnormal conditions created by the dimmer.

Traditional leading-edge types are just a triac with a firing delay circuit, modern trailing edge ones can contain a microprocessor driving an IGBT. Attempting to measure impedance through a tangle of semi-intelligent stuff switching on and off at high speed according to a programme that can't run properly because the tester is not a valid load, is not likely to yield useful results.

 

[Calebp43]

You should have been a rocket scientist