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I am trying to put up some shelves so am using a Bosch Truvo detector to find hazards in the wall. It appears to be giving inconsistent readings. I have recalibrated the unit according to the manual.

I have recorded a demonstration to show my problem.

https://youtu.be/Tg5TxNcVnLs

Is this user error or is the unit faulty?

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4 Answers 4

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The instructions1 state that,

  • Make sure that you are properly earthed when taking measurements.
    If you are not properly earthed (e.g. by wearing insulating footwear or by standing on a ladder), it will not be possible to locate live cables.
  • Hold the measuring tool by the intended gripping surface (1) only, so as not to influence the measurement.
  • Do not attach any stickers or labels to the sensor area on the rear of the measuring tool.
    Metal labels in particular will affect measuring results.
  • Do not wear gloves when taking measurements and make sure that you are properly earthed.
    If you are not properly earthed, the identification of live wires may be impaired.
  • When taking measurements, avoid devices that emit strong electric, magnetic or electromagnetic fields.
    If possible, deactivate all tools whose radiation could interfere with the measurement and switch off the corresponding functions or tools.

While this is arguably not what one might expect from such a device, the manufacturer have done what is required of them to make the requirements of this device clear. Earthing is likely the most important factor, so try mitigating this with an Earth Bonding Strap and Plug.

  1. Robert Bosch Power Tools GmbH (2021). Truvo. [online] bosch-diy.com, pp.16, 20. Available at: https://www.bosch-diy.com/storage/en-gb/truvo-100039682-original-pdf-364483-en-gb.pdf [Accessed 12 Apr. 2022].

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  • Grounding (earthing) yourself is so important, they say it twice! Funny, thought, that they specify "standing on a ladder". I own several aluminum/aluminium ladders, I wonder if one of those count. :)
    – FreeMan
    Apr 13, 2022 at 17:23
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It is a multidetector.

I have one and it will pick up electric cables as well as nails and screws in the wall.

Used it last week when putting a shelf in my daughter's room and it found a screw in the plasterboard right where I wanted to put a shelf screw. Meant I had to move the shelf screws a bit but avoided an issue.

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    Think the OP's problem is that holding it one way, it shows something there, but holding it another way, it shows nothing there.
    – crip659
    Mar 12, 2022 at 16:45
  • @crip659 so address the OP… I know how to hold mine. Have you got one? And how did your testing go?
    – Solar Mike
    Mar 12, 2022 at 17:14
  • I do not have one, just watched the video that the OP linked to. The video did show two different results depending on how it was held at the same spot. OP is concerned about driving a screw into a wire.
    – crip659
    Mar 12, 2022 at 17:26
  • @SolarMike I know what it is and how it is supposed to work. As crip659 says, I am indeed asking if it is faulty or if the fault lies with the user (me).
    – James Geddes
    Mar 12, 2022 at 17:36
  • You find studs and live wires by scanning side to side, electrical cables are required to be attached to the stud 1-1/4” away from the face. The field produced by a energized cable may be detected several inches away try scanning right to left, some of these us ultrasonic signals to find the stud pushing hard can confuse the electronics again sweep side to side and you will have more consistent results.
    – Ed Beal
    Mar 12, 2022 at 17:41
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Electrical cables should be running vertically, not horizontally, at places where one may want to drill through (in UK at least). Try moving the detector up and down, and side to side, to ascertain which way the cable (if that's what is being detected) goes.

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  • In the US, electric cables are commonly strung across a wall horizontally, especially when wiring several outlets along a wall. We don't run the cable from one outlet, down through the floor (or up to the attic) and back up unless it's a retrofit and there's access from above or below. In new construction it's cheaper to spend time drilling holes and running the wiring horizontally, than it is to spend copper running the wiring up and down. The OP is, however, in the UK according to his profile.
    – FreeMan
    Mar 14, 2022 at 13:54
  • @FreeMan Correct, I am in England
    – James Geddes
    Apr 12, 2022 at 13:32
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Good video accompanying your question and this answer is based on both the question and the video.

You need to carefully read the user manual. It appears from the video that you either have not, or are ignoring significant parts of it.

Specifically, pages 20 and 21 tell you exactly how to hold the device and what to expect if you do not, or if you (for example) hold it with a stick. Page 22 further describes techniques for detecting live cables: detection improved by cables in use, by moisture in walls, by what you wear on your hands and feet, and by the positioning of your hands and feet. Page 23 explains how to recalibrate the instrument if your readings seem suspicious and pages 24 and 25 explain how to diagnose problems such as yours.

The instructions are, as far as instruction manuals go, freakishly thorough, clear, unambiguous, and helpful. I'm certain that if you read and follow all the instructions carefully you'll be successful.

enter image description here

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    A better answer would quote and cite the appropriate sources
    – James Geddes
    Apr 12, 2022 at 13:34
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    I cited the source: the user manual. I do not agree that answers need to include links or quotes from manuals, especially not vanillla manuals like "the user manual", and especially not when entire sections of the manual are relevant. I think, in fact, Questions should include links to manuals and the sections that have been exhausted before coming here to ask for more. There are almost three entire pages of the manual explaining what OP is doing wrong. You want me to quote them???
    – jay613
    Apr 12, 2022 at 14:03
  • Yes, providing a full citation is needed in StackExchange meta.stackexchange.com/a/284971/371745
    – James Geddes
    Apr 12, 2022 at 16:52
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    @jay613 a close vote is a more appropriate way to signal to someone that maybe they should take a look in the instructions rather than a somewhat hostile non-answer (as it was originally, it's toned down a bit now). Thank you for helping people as much as you do, but a little bit of politeness in today's broken world goes a long way.
    – Luke Briggs
    Apr 12, 2022 at 19:45
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    @LukeBriggs Hear, hear. We all need to remember that there are people on the other end of our keyboards.
    – James Geddes
    Apr 13, 2022 at 7:16

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