Dodgy voltage detector

Hi all
Just bought one of these
https://www.screwfix.com/p/lap-ms8907-voltage-detector-pen/3222g?_requestid (7869
Reviews seemed good only needed it to confirm circuit is off before I cut i nto it. It seems to detect voltage but when I switched the circuit off it s till seems to think there is voltage although the beep / led is not continu ous. I know the socket is off as I had something plugged into it which then went off when I switched the circuit off.
The instructions say that it self tests when you press the power button and indicates ok with a flashing LED. Mine gives a solid green.
Just took it back to Screwfix and tried 3 others and non seem to do the sel f test thing. Brought a new one home to test on the off circuit and same pr oblems.
It seems unlikely that all 4 and dead (maybe a dodgy batch) but now thinkin g maybe I am missing something?
Thanks
Lee.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@yahoo.co.uk wrote:

They use an unsound principle and cannot be relied on. Don't buy
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/12/2017 15:37, Bob Minchin wrote:

I'd be interested to learn more about that.
--
Robin
reply-to address is (intended to be) valid
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sunday, 3 December 2017 16:47:12 UTC, Robin wrote:

they produce false positives and false negatives, relying on one is a hazard
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
If this type is so unreliable what is the safest way to determine if a cable is safe to cut?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sunday, 3 December 2017 17:31:31 UTC, snipped-for-privacy@yahoo.co.uk wrote:

voltmeter
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sun, 3 Dec 2017 09:41:40 -0800 (PST) snipped-for-privacy@gmail.com wrote:

What if there's no neutral, either missing (fault), or unavailable (switch drop)? Possibly no earth either, in the case of a switch drop wired in singles.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

use an extension lead
--
from KT24 in Surrey, England

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
A volt meter will only be useful once you have cut into the cable. In my situation I want to prove that a cable is part of a particular circuit and is off
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
That’s not true if you use a probe that has the equivalent of a pin at the end that you can stick true the insulation.

That sort of probe will do that.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@yahoo.co.uk wrote:

I don't believe you can do that certainly without having a physical connection to the wire involved. I'd certainly not want to rely on something that detects the (weak) radiated field from the wire.
--
Chris Green
·

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sunday, 3 December 2017 21:33:05 UTC, Chris Green wrote:

You can and it's easy enough, but I no of no product that does it.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sunday, 3 December 2017 19:20:36 UTC, snipped-for-privacy@yahoo.co.uk wrote:

You must be using yours differently to what I do
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Use an extension cord to a GPO to get one.

Ditto.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/12/2017 17:41, snipped-for-privacy@gmail.com wrote:

Not exactly "non contract" though is it!
--
Cheers,

John.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 04 Dec 2017 00:10:01 +0000, John Rumm wrote:

I have a Megger that can do this. It beeps when in close proximity to a high voltage. Not sure about the possibility of false positives, though (inductive coupling) I must check it out one day when I can be arsed.
--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Monday, 4 December 2017 00:10:01 UTC, John Rumm wrote:

No. Is that an issue?
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 04/12/2017 05:18, snipped-for-privacy@gmail.com wrote:

Yes! The whole purpose of the volt stick style detector is that it can make an assessment without needing any direct contact to the circuit, and so avoids all the risks associated with that.
Also keep in mind that a false positive reading is equally possible from a high impedance volt meter.
--
Cheers,

John.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Monday, 4 December 2017 10:43:27 UTC, John Rumm wrote:

yes

it creates a bigger risk by misinforming users on occasion that a live cable is dead.

not from a standard multimeter. Especially high impedance ones are a different fish of kettle.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 04/12/2017 12:55, snipped-for-privacy@gmail.com wrote:

You have that back to front. High impedance meters are the norm. Any common digital multimeter will likely have an input impedance in the megohms range, and that is high enough to see capacitively coupled floating conductors as live.
This is why test gear makers specifically make kit for mains test applications that have low or adaptive impedance measurement options to eliminate these spurious readings.
Goo look at the specs for something like a Fluke 114, or 115
--
Cheers,

John.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.