How are RCD Testers Used and Features to Consider in RCD Testers - aLittleBitOfAll
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How are RCD Testers Used and Features to Consider in RCD Testers

peaktech 2710 Digital RCD Tester

How are RCD Testers Used and Features to Consider in RCD Testers

RCD and appliance testers that have RCD trip features work by simulating current leakage in order to accurately measure the amount of time needed for the appliance or RCD to cut power. The trip time recorded by the tester determines whether the appliance or RCD meets the AS/NZS3760:2010 requirements, which demand the RCD or appliance’s trip time is as low as 40 milliseconds. The most frequently used RCD tests require a trip time test at the rated current of the RCD itself. The fault current needs to be quickly applied by the tester. In most cases, the RCD is sensitive to 30mA, even though in some applications, like medical institutions, 10mA sensitive RCDs may be used. In other cases, variable trip current RCDs are used.

How is an RCD Tester Used?

RCD testing equipment is quite simple to operate. The users of RCD testers, however, still need to be competent and the use of these testers requires the completion of TAFE and other privately run courses that provide competency in testing and tagging. Most testers come with standard Australian 3-pin plug leads allowing them to be plugged into the mains power directly. Then, the power socket or switchboard RCDs can be tripped, generally by choosing the right current and pressing the test button.

You can also check portable RCDs using the same way, but you may also need an isolation transformer. During these test, the RCD tester will apply the fault condition and measure the amount of time it takes to trip the portable RCD. Obviously, the power of the circuits that the RCD protects should be cut and caution must always be exercised. The time measured by the RCD will determine whether the appliance or RCD passed or failed the test.

Some testers come with probes rather than the standard 3-pin plugs. The probes are used in power outlet sockets or switchboards to enable trip time measurement. This is generally used to test 3-phase RCDs. These RCD tests are typically performed by qualified electricians. That being said, if you’re one, consider whether the tester you’re looking at has a 3-pin plug or probes.

Speaking of qualified electricians, many of them test RCDs at the switchboard instead of the power outlet. While this doesn’t check the integrity of the operation of the RCD, it provides a quicker way to test the workings of the RCD. Many testers are designed for this type of operation and come with the appropriate test leads. However, the RCD should still have a category rating of at least CAT-3 for connecting directly onto switchboards.

The category rating is determined by the tester’s ability to be used in different locations within an installation and its ability to withstand electrical transients like voltage spikes and overvoltage. Appliance testers with integrated RCD testing capabilities are usually CAT-2 rated and aren’t suitable for performing switchboard tests. Trying to connect such testers onto a switchboard can damage the equipment and pose a threat to the operator, as it doesn’t feature suitable protection.

KT500 On-site RCD Testing
source: kewtechcorp.com

Features to Consider in RCD Testers

Current Range

Residual current device testers feature a range of tripping currents that can range from 5mA to 500mA, and in some cases, more. Most RCDs are designed to trip at 30mA, though, so the tester must have at least that much range. Fast-trip or half-trip are two common features that you should look for in order to test RCD functions in different conditions.

Tripping Angle

Testers should have an adjustable tripping angle. This metric indicates whether the current is at the 0° crossing point as the current is rising, or a 180° crossing point as the current is falling when the fault is applied. Most testers have both of these angles.

Ramp Current Testing

Ramp current testing is basically a current leakage fault of increasing value being applied. The goal of this test is to check the amount of current at which the RCD will become sensitive to current leakage conditions. Typically, 30mA rated RCDs trip at about 75% of their rated current. So, if the RCD trips at around 15mA, it’s considered oversensitive and potentially faulty. Although this type of testing isn’t necessary under AS/NZS3760:2003, it can be a useful feature to have.

Calibration

Just like all test and measuring equipment, RCD testers need to be checked regularly to make sure they’re working properly. Frequent calibration and verification will ensure you get the right measurements every time. RCD tester calibration should be performed by an authorised party to a recognised standard. The cost of calibration varies, but generally starts at around $100. This is an ongoing cost that should be considered at the time of purchasing your tester. Calibration intervals are determined by the tester’s manufacturer. Typically, calibration is done annually. Tester testing, on the other hand, should be performed every 6 months or so in order to ensure safety and proper working order.

KYORITSU - Digital RCD Tester - 5406 A
source: indiamart.com
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Ian Tompson
iantompsonlee5@gmail.com