Any internet trawl or visit to your local wholesaler will leave you in no doubt that there is definitely no shortage of electrical testing equipment to choose from. Finding out if all circuits are working, if your installation is safe against shock hazards and fire, locating a problem or confirming that everything is as it should be until the next scheduled maintenance visit, these are pieces of information vital to the electrical contractor.
There are numerous things that can be measured, which include voltage, current, resistance, capacitance, power, continuity, phase angle and temperature. Many of these can be logged over time, and can be measured with highly accurate equipment or with simple tools that report absence or presence.
So what instruments are available? !
We’ll start off with the basic voltage detector; there are many models available and they can be split into two fundamental types, two pole contact and non contact.
All voltage detectors will let you know if there is voltage present in the area being tested, and this information, though minimal, is very useful when checking for the absence of voltage for reasons of safety or trouble-shooting.
The two pole contact detectors are supplied with insulated probes to provide safe contact with terminals, most are available to measure a variety of voltage ranges, AC or DC and are priced according to their additional features such as display type, additional test functions and protection levels.
Non-contact tools work by an induced signal and therefore do not require any contact with terminals or other conductive parts. Importantly, they generally do not need a current flowing, or even have a complete circuit to sense the presence of voltage. A variety of models are available and most come in the form of a large pen with a pocket clip, so can easily find a place in your overall or shirt pocket.
But, on the safety front it is very important that these devices are not used to confirm that a circuit is dead.
A step up from the non-contact voltage detectors are two pole voltage indicators; instruments that indicate when there is voltage present at the point being tested and that then display the result in broad thresholds, typically above 50,100,200 or 400V.
But perhaps the easiest way of testing for a live circuit is by using a test lamp of which the John Drummond range are, by far, the most popular. Homemade versions using a domestic light bulb are not a safe alternative and should never be used because when working with electricity safety is paramount.
The importance of proving the tester before and after testing must not be forgotten and there are a number of excellent proving units now available to ensure voltage indicators and test lamps can be fully checked prior to, and immediately after a circuit has been proved.
Manufacturers are increasingly aware of the importance of confirmation by proving devices, and some supply them as bundles, together with voltage testers and lamps, to encourage this routine testing of the indicators every time they are used.
A note about safety!
We can’t emphasise enough the importance of confirming that the appliance or piece of equipment being tested is dead and that there is no possibility of it becoming live during the tests and of course that the test instrument is working.
Contractors are now more commonly put under pressure to carry out live work in areas such as construction sites, critical installations, high cost manufacturing plants and in retail outlets operating around the clock, where power shut downs would result in suspension of vital services or serious financial losses.
Irrespective of these pressures, it’s vital in all possible cases, when it is practicable, that electricians only work on dead circuits and that live working should only be carried out in accordance with the Electrical Safety Council’s Guide and with the provision of suitable protective equipment.
We have already mentioned the importance of using proving units but we also very strongly recommend the use of Lock-off Tag-off systems, essential safety tools for anyone working on circuits or equipment. Lock off devices are a sensible option for lone workers but especially important where there are a number of persons working, in these cases each worker can have their own padlock with its individual, unique key to ensure their safety. There’s no point in proving dead if someone else comes along and restores power without your knowledge. This can be lethal if an electrician is working on a circuit which is suddenly energised or if a worker is cleaning a piece of industrial equipment which suddenly becomes live; and it’s not just the electricians who are vulnerable.
One of the major problems encountered when working on existing sites is the lack of comprehensive circuit labelling. Even in cases where circuits appear to be properly labelled on sites alterations are often made by unqualified or untrained staff and even if the actual changes are safe they are frequently not correctly labelled.
Cable Detectors are particularly useful in retro-fits to easily identify wires which are enclosed within walls, or buried underground; a circuit tracer quickly maps everything without interrupting power or requiring you to uncover anything. Having two parts, a transmitter plugs into a socket, or uses induction for non-contact injection of a signal into the circuit, which a receiver then detects. If you face a complicated unlabelled jumble of wires, they can also be an excellent aid to efficiently identify which is which, without the need for tedious continuity tests.
But the simplest instrument available today is undoubtedly the socket tester which provides a quick and easy way of confirming 13 amp sockets are wired correctly using three bright illuminated LEDs. These simple devices illuminate any circuit-wiring faults and are invaluable for checking sockets in factories, on site installations, or in new-builds.
It is, however, important to understand the limitations of socket testers. They can spot most single wiring faults but combinations of multiple faults can fail to be detected. Furthermore no socket tester can identify if the neutral and earth are reversed. (Think about it for a moment) Also basic socket testers tell you if the earth is connected, they do not tell you the quality of the earth. Only advanced socket testers give an indication of the earth loop impedance. So although useful for a quick check, they are not a substitute for full 17th Edition testing.
For larger industrial installations there will be the need for phase indicators. These devices will quickly and simply prove the presence of all 3 live phases or identify any faults, as well as confirming the sequence of phase rotation.
Now we will move on to the three basic testers which are often now incorporated into a multifunction tester. On dead circuits we need to use an insulation tester to measure both continuity and insulation. Regular measuring of insulation is also a very effective predictive maintenance tool for industrial equipment.
When the circuit is powered up ensuring that the earth loop impedance is sufficiently low is the next step. These days using a variety of technologies most loop testers offer a choice of high current testing, which will trip RCD’s and low current testing, which won’t.
It’s worth knowing that, although on most sites low current testers give good results, different technologies suffer from different problems on a small number of sites, so manufacturers do not generally specify accuracies below 1 ohm.
RCD testers. ! A residual current device (RCD) is designed to isolate power when it detects an imbalance between the active and neutral conductor. These balances are commonly caused by current leakage through earth and RCD testers are designed to ensure that the RCDs are operating correctly and tripping at the speed they should. RCD testers can be used in conjunction with an Earth Leakage Meter in helping to identify appliances or circuits that are causing the RCDs to trip.
Multifunction testers (MFTs) ! have been designed to carry out the different types of 17th Edition testing functions discussed above and have the ability to complete multiple tests using one instrument as opposed to the aggravation of having to switch devices to perform different tests.
More advanced units can include a data logger to provide power analysis, a function for earth resistivity testing and test data storage and downloading facilities.
Although they appear to be the ideal instrument to have in your inventory and most MFTs have a voltage detection function it is very important that complex multi-range products are not used for proving dead.
Portable appliance testers (PAT). ! There are no shortage of these on the market, from simple hand-held “pass or fail” low-cost units to complex instruments, incorporating labelling systems, sophisticated logging and comprehensive reporting. We have at Martindale produced a 96 page guide on PAT testing which is available for purchase through electrical wholesalers. The important thing is that, just as 17th Edition testing checks the electrics throughout the building, Portable Appliance Testers confirm the safety of the appliances plugged into the mains wiring.
Other common instruments are Digital Multimeters (DMM) and Clamp Meters !As the name implies, DMMs offer several different meters in one package. The functionality varies greatly from one manufacturer to another, but most will measure DC voltage, AC voltage, DC current, AC current, resistance, frequency and capacitance. As the features can vary widely, so do the prices. It makes sense to take your time and choose wisely.
Whereas DMMs can only measure current by interrupting the circuit being measured, clamp meters do not require contact with any conductive element and can be held or clamped around the wire. Again there are many offerings on the market, with wide variances of functionality and price.
However, for general electrical work, a recent category of products amalgamates the functions of DMMs and Clamps in a small package. Examples are
Instruments like Martindale’s ET4 and ET5 electrical testers. Both are exceptionally compact units, aimed at making testing more convenient for the contractor. Pocket sized, these units offer a bright dual-display to indicate volts and amps simultaneously, an open-forked jaw allowing it to be pushed over a wire to read the results, and a plug-in temperature probe. It even incorporates an LED light to illuminate the work area and the switches are easy to control even when wearing protective gloves.
Most importantly whatever type of electrical testing equipment you decide on, quality and accuracy are the key factors. As you’d expect with most tools, you tend to get what you pay for. Most high-quality electrical test equipment is available through your usual electrical supply wholesaler and almost everything can be purchased online. Just beware of too-good-to-be-true prices. Choose a manufacturer you know and ensure it’s the “genuine article” and not a rip-off, to obtain reliable and accurate measurements (clearly and fully displayed to the precision you need), with excellent durability and after-sales services.
Need to find out more ? Request a Martindale Toolbox Talk on Safe Isolation.