Klein outlet tester and multimeter gave different voltage measurements

[FloridaGuy]

I needed to wire a lamp circuit on a dimmer to a flush mount outlet box so I could access a hidden LED strip light by loosening an entire panel, unplugging the LED driver, and removing the panel for service etc. I got the job done and tested the outlet with a Klein outlet tester. I was surprised to see 108 v. I was concerned that I had a poor neutral connection and checked the wiring all the way to the outlet fixture with my multimeter and had 118 v. I checked the outlet with the multimeter and got 118 v, but the Klein still gave 108v. The dimmer is a forward-phase type and was full on. I am speculating that, even full on, the dimmer was "trimming" the sine wave slightly causing the Klein to show 108 v. But the fact that the multimeter showed 118 v indicates that these two instruments measure AC voltage differently. I should add that both instruments show 118 v when I test a regular outlet on the same breaker. Is my specuation correct? Thanks for your help!

 

[Avo Mk8]

Speculation that the dimmer is 'trimming' the waveform at its 'full-on' setting is likely correct.

Your multimeter might be a "True RMS" model, whereas the outlet tester might just give its version of RMS, (or the other way round), in which case you would expect them to give different readings.

There was a similar query here last year (relating to current rather than voltage):

J

Thread 'Perplexing amp reading from different multimeters'

Dec 29, 2024

Hello everyone, I'm new to the forum. Thank you for allowing me to join. I am a DIY'er, I've been doing much of my own wiring for years, but I know my limits.

I have three digital multimeters: a Klein CL-800, a Southwire 21550T (both clamp-style), and a Fluke T5-600, which is an open-end tester. I had an issue in my Morton building, so I tested the amperage on one leg of the subpanel. Using the Klein and Southwire, they read 7.5 amps, but using the Fluke, it read 4.2 amps. That's quite a spread. Does anyone have any idea why there would be such a large discrepancy in the reading? I...

• JackCW
• amp different reading
• Replies: 3
• Forum: USA Electrical Forum

You might be interested in this:

View: https://www.youtube.com/watch?v=PHixK2d_uZU

 

[littlespark]

It may be that one device is calibrated, and much more accurate than a simple diy multimeter.

The dimmer will not be a simple voltage reducer like they used to be with filament lamps…. They’re more electronic now, which can give different readings according to what voltage the tester itself gives out.

 

[FloridaGuy]

Speculation that the dimmer is 'trimming' the waveform at its 'full-on' setting is likely correct.

Your multimeter might be a "True RMS" model, whereas the outlet tester might just give its version of RMS, (or the other way round), in which case you would expect them to give different readings.

There was a similar query here last year (relating to current rather than voltage):

J

Thread 'Perplexing amp reading from different multimeters'

Dec 29, 2024

Hello everyone, I'm new to the forum. Thank you for allowing me to join. I am a DIY'er, I've been doing much of my own wiring for years, but I know my limits.

I have three digital multimeters: a Klein CL-800, a Southwire 21550T (both clamp-style), and a Fluke T5-600, which is an open-end tester. I had an issue in my Morton building, so I tested the amperage on one leg of the subpanel. Using the Klein and Southwire, they read 7.5 amps, but using the Fluke, it read 4.2 amps. That's quite a spread. Does anyone have any idea why there would be such a large discrepancy in the reading? I...

• JackCW
• amp different reading
• Replies: 3
• Forum: USA Electrical Forum

You might be interested in this:

View: https://www.youtube.com/watch?v=PHixK2d_uZU

Thanks for your insights and the video on true RMS measurements. Interesting stuff!

 

[FloridaGuy]

It may be that one device is calibrated, and much more accurate than a simple diy multimeter.

The dimmer will not be a simple voltage reducer like they used to be with filament lamps…. They’re more electronic now, which can give different readings according to what voltage the tester itself gives out.

Thanks for your information! I'll check the specs on the two instruments.