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Home / Technical Articles / 4 test instruments most frequently used by electricians

Testing an electrical installation

The test instruments and test leads used by the electrician for testing an electrical installation must meet all the requirements of the relevant regulations. The HSE has published Guidance Notes GS 38 (download below) for test equipment used by electricians.

4 test instruments most frequently used by electricians
4 test instruments most frequently used by electricians

The IEE Regulations (BS 7671) also specify the test voltage or current required to carry out particular tests satisfactorily.

All test equipment must be chosen to comply with the relevant parts of BS EN 61557. All testing must, therefore, be carried out using an ‘approved’ test instrument if the test results are to be valid.

The test instrument must also carry a calibration certificate, otherwise the recorded results may be void. Calibration certificates usually last for a year.

Test instruments must, therefore, be tested and recalibrated each year by an approved supplier. This will maintain the accuracy of the instrument to an acceptable level, usually within 2% of the true value.

Download Guidance Note GS38 (Electrical test equipment for use on low voltage electrical systems) //

Download Guide

Modern digital test instruments are reasonably robust, but to maintain them in good working order they must be treated with care. An approved test instrument costs equally as much as a good-quality camera. It should, therefore, receive the same care and consideration.

Let us now look at the requirements of four often used test meters //

  1. Continuity tester
  2. Insulation resistance tester
  3. Earth fault loop impedance tester
  4. RCD tester

1. Continuity tester

To measure accurately the resistance of the conductors in an electrical installation we must use an instrument which is capable of producing an open circuit voltage of between 4 and 24V AC or DC, and deliver a short-circuit current of not less than 200 mA (Regulation 612.2.1).

The functions of continuity testing and insulation resistance testing are usually combined in one test instrument.

Fluke T2 Voltage and Continuity Tester
Fluke T2 Voltage and Continuity Tester (photo credit:

Go back to Test Instruments ↑

2. Insulation resistance tester

The test instrument must be capable of detecting insulation leakage between live conductors and between live conductors and earth.

To do this and comply with Regulation 612.3 the test instrument must be capable of producing a test voltage of 250, 500 or 1000 V and deliver an output current of not less than 1 mA at its normal voltage.

Megger MIT330 Insulation and Continuity Tester
Megger MIT330 Insulation and Continuity Tester (Insulation testing can be performed at selectable test voltages of 250, 500 and 1000V with a built-in insulation limit alarm from 0.01MΩ to 999MΩ.)

Go back to Test Instruments ↑

3. Earth fault loop impedance tester

The test instrument must be capable of delivering fault currents as high as 25A for up to 40ms using the supply voltage. During the test, the instrument does an Ohm’s law calculation and displays the test result as a resistance reading.

Go back to Test Instruments ↑

4. RCD tester

Where circuits are protected by an RCD (residual current device) we must carry out a test to ensure that the device will operate very quickly under fault conditions and within the time limits set by the IEE Regulations. The instrument must, therefore, simulate a fault and measure the time taken for the RCD to operate.

The instrument is, therefore, calibrated to give a reading measured in milliseconds to an in-service accuracy of 10%.

Go back to Test Instruments ↑

Investment //

If you purchase good-quality ‘approved’ test instruments and leads from specialist manufacturers they will meet all the Regulations and Standards and therefore give valid test results.

However, to carry out all the tests required by the IEE Regulations will require a number of test instruments and this will represent a major capital investment in the region of USD 1000.

Instrument calibration

Historically, many electrical contractors have had test instruments calibrated on an annual basis. The instrument would be sent away to a calibration house and it would arrive back, some time later, with a certificate stating the date of calibration, the time period for which the certificate would be valid along with the findings of the assessment in the form of a table of results.

The certificate would state that the instrument was within calibration parameters at that time only. It certainly could not guarantee that the instrument would still be fit for purpose at any time after that.

What can go wrong with test instruments?

Problems with test instruments are not always immediately obvious so it is important that any irregularities are discovered as early as possible.

Damage to the instrument

Consider the scenario // A test instrument was calibrated by a calibration house six months ago and is still within the stated 12-month calibration period. It appears to be working well but, unbeknownst to the contractor, five months ago it had a collision with a conduit bender in the back of the firm’s van and is now out of calibration.

Many, many jobs have been tested with this instrument since the incident occurred and, hence, many certificates and forms have been issued. The certificates and forms, of course, are worthless as the test results contained within would not be representative of the installation.

Therefore, it is extremely important that the instrument is regularly assessed.

Prospective fault current test (VIDEO)

References //

  • Advanced Electrical Installation Work by Trevor Linsley (Purchase paperback)
  • Ongoing accuracy of test instruments by Mark Coles

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More Information

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


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  5. Rajesh
    Mar 13, 2020

    Dear Edward, Really nice presentation. & Good stuf with advance instruments.
    General query not related to your site
    1) Is there any criteria of qualified person for Electrical safety audit.
    2) How can I get all IEC / BS related booklets
    3) What Standards are being followed in UAE & related countries.

  6. George Kung'u
    May 10, 2019

    Good work 👍

  7. Mika
    Mar 08, 2019

    This website was really helpful for my school work! I really appreciate the creation of this, plenty of great for my project, a Measurement Portfolio. I thank you ever so much.

  8. Sulliven
    Mar 15, 2018

    ATTN: Whom it may concern

    How are you!We Meigaolan Elec Instrument Corp., which is a dealer of used Test&Measurement equipment in China, which include oscilloscope, digital multimeter, spectrum analyzer, network analyzer, signal generator, wifi &bluetooth tester, covered the brand as KEYSIGHT, R&S, ANRITSU, TEK, FLUKE, LITEPOINT, etc.since 2003. We can sell, buy, rent and repair according to your needs.

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  9. Shubham
    Jul 16, 2017


    I am very much happy with the articles available on portal.

    Sir, please provide the articles on “”CALIBRATION OF ALL INSTRUMENTS USED IN TESTING””, I am having interview in Quality assurance company QA/QC for the post of Foreman.

    Please also give me the tips for interview as per the post.

    Thanking you.

  10. Marc Spruyt
    Feb 20, 2017

    Good stuff Edvard !

    PS: Check the “Get PDF” button
    Does not work on your last publications

  11. Frank Miller
    Dec 15, 2016

    Thank you for writing this article. As I’m also an electrician, and actually have two sets of testing devices, and intentionally have them calibrated six months a part (call it OCD). Yet I still personally find it amusing, although it’s completely valid and understandable, that we need to calibrate our calibration machines. I wonder if those machines need calibration also…

    In any case, thank you for bringing this issue up, and going into depth about testing. I wasn’t going to say anything about the lack of gloves, but I’m glad someone already did.

  12. Brajesh Rajawat
    Jun 27, 2016

    can i work as an electrician in America i have an Electrical engineering diploma India.

  13. Ahmed BOUDAB
    Feb 08, 2016

    Merci beaucoup

  14. Daniel
    Feb 03, 2016

    NO existe un solo vídeo de instrumentos difundido por fabricantes de instrumentos de medición donde prevalezca la seguridad del técnico, como ejemplo revisen el sitio web de ¨Fluke¨, sus videos son exelentes pero la seguridad no es la premisa

    Excelente articulo Edvar

  15. Derek Bailey
    Feb 03, 2016

    I would have liked to use your article to demonstrate several important points in testing installations.
    Every picture demonstrates bad practice.
    No use of insulated gloves
    No use of full face protection
    No use of flame retardant clothing (Last picture dressed in polyester!!!!)
    I know these shots would be fro manufactures literature further compounding the issue.

    Other wise your site is one of the best on the web for its content.

    • Edvard
      Feb 03, 2016

      Couldn’t agree more on you… safety isn’t demonstrated here on pics :) Maybe I focused too much on test devices themselves.

      Good point Derek, thanks!

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