Technical Support Articles
Uninterrupted Power Supplies – What are they and how do I test?
An uninterrupted power supply (UPS) is a device that provides power to a load (appliances) when the power supply has been interrupted, generally when it is disconnected or “dropped” by your power supply utility.
The bat-teries, through an inverter provide temporary supply power (230VAC at 50Hz) for the electrical appliance con-nected to the UPS. Many small business and offices utilise UPS’s with com-puter and other IT equipment to pre-vent damage when power is suddenly disconnected and to allow for a “graceful” and controlled shutdown when mains power is lost.
Testing and tagging a UPS in accord-ance with AS/NZS 3760 can be a bit confusing. If you follow these basic steps you can be confident that you have tested it correctly.
The Earth of the UPS must be tested on both the input and output of the UPS. Some UPSs have multiple 230V sockets of which each Earth aperture must be tested separately. Note many good UPS’s will have an earth point (post) located on the back of the UPS. This should make finding a suitable earth for the earth continuity test easy.Most UPSs are surge protected (MOV)which means that an Insulation test of 250V should be performed.
For ‘Best Practice of Testing and Tag-ging’ we recommend that a Leakage current test should be performed on UPSs as most are electronically switched. The UPS will fall under the classification of “Cord extension sets, cord sets, EPODs and PRCDs” & there-fore maximum allowed leakage will be 1 mA
NB: The AS/NZS 3760 states: equipment that must be energized to close or operate a switching device in order to test the insulation, then the leakage current test in accordance with Appendix E (Max Leakage of 5mA) shall be per-formed.
If you wish to test the wiring of the outlet sockets, a typical polarity test will often fail due to the active circuitry. Instead, correct wiring of the outlet sockets can be determined with a socket tester (while the UPS is connect-ed to 230V AC, or with some appliance testers, by powering the appli-ance tester via the UPS (on testers which can identify incorrect wiring of power supply).
Author: Jason Kiekebosch
Is your instrument being used safely?
Nobody likes the smell of burnt electrical components,or the sound or an ominous ‘pop’ from inside your equipment as it is connected to a power source.
Sadly as a test equipment provider it’s something we see too frequently. Often we receive appliance testers and RCD testers returned to us with damage from incorrect connection to an inappropriate power source.
Sometimes the user knows what went wrong, and other times it’s a mystery. It can be caused by a variety of reasons - common scenarios include over voltage damage from power surges and spikes, or accidental connection to more than one live phase during RCD testing at a switchboard.
It's always disappointing to see this, as not only is this type of damage frequently not covered by the manufacturer’s warranty, but the damage to the tester is often extensive. There’s another reason why it should be avoided at all costs — incorrect connection to a power source can also be potentially very dangerous to the user.
It's therefore important to remember that appliancetesters (including those with RCD testing facilities) are typically only designed for connection to single phase power from a power outlet, and normally only carry a CATII rating.
Like most appliance testers, the category rating of Seawards PT300 is CATII. It should only be connected to a 230V AC outlet socket.
So what is a Category Rating and how does it apply to test instruments?
Category ratings are detailed within the standard IEC 61010 - an internationally recognised standard applying to the general requirements of test instruments. They inform users of test instruments, where on an installation the device can be used safely and specify the instruments tolerance to overvoltage conditions.
The CATIII and CATIV markings on this Metrel 3122 RCD and Loop Impedance tester deem the instrument suitable for connection to switchboards and beyond general power outlets.
For example, a CATII device (the category rating applied to most appliance testers) is deemed to be appropriate for use only on single phase, plug in receptacle environments.
In contrast, a dedicated installation tester might be CATIII or CATIV rated, which would indicate that it is suitable for use at switchboard distribution level wiring. You'll also usually see a voltage rating applied to the category eg, CATII 300V.
The voltage rating specifies the transient withstand rating within that category.
As a broad overview, the IEC category ratings specify the following environments for each category.
CAT I — Protected electronic equipment.
CAT II — Single-phase receptacle-connectedloads such as appliances and portable tools.
CAT III — 3-phase distribution including single phase commercial lighting and equipment in fixed locations such as switchgear and polyphase motors.
CAT IV — 3-phase at the utility connection, outdoor conductors, electricity meters, and service entrances.
The correct use of test instruments, category ratings and understanding the limitations of test instruments are all requirements of the legislative Code of Practice 'Managing Electrical Risks in the Workplace'. It's therefore essential that users of instruments are familiar with these ratings and how to safely use test equipment.
Using an the appropriate test instrument for the job will not only help prevent your equipment from sustaining damage, but will also help protect you from injury. If you're unsure of how your instrument can be safely used, contact your test instrument manufacturer or supplier for more information.
Author: James Anderson
Double Insulation Testing
From time to time, we meet customers who misunderstand the correct method for testing double
Surprisingly frequently, test equipment users indicate they are using the wrong method.
The issue seems arise from one common problem—the vast majority of appliance testers will ‘PASS’ a double insulated item— regardless of whether the probe is attached to the metal parts of the appliance or not. In some instances we’ve seen people not use a probe at all.
And, there is also frequently a misunderstanding regarding whether a probe must be used during class II leakage testing.
It’s important to remember that when testing a Class II item, if you’re not using a return lead, you’re not actually testing at all!
Class II items are often considered safer by design than earthed appliances. This maybe true, but Class II appliances can still present a lethal hazard if faulty or damaged.
The recent tragic death in NSW of Sheryl Aldeguer suspected to be from Class II mobile phone charger sadly illustrates how dangerous Class II items can be if faulty, or unapproved.
It’s therefore critical to remember that Class II items must be tested according to AS3760.
In basic terms, the Class II test ensures that any accessible metal part on the exterior of the appliance is suitable insulated from the internal live parts of the appliance. The return lead is used to ensure there is no break-down of insulation between the internal live parts, and the exposed metal or conductive parts of the appliance.
Whether a 500V DC insulation test is carried out, or a 240V AC leakage test is carried out, without the earth return lead connected, a measurement cannot be made by the tester—a PASS result will always be achieved— regardless of the safety of the appliance
No return lead = no test
Author: James Anderson
3-Phase Appliance Testing
Many of us have the need to also test and tag 3-phase appliances. But the testing of 3-phase appliances is not as straight forward
at it first might seem.
One of the biggest considerations when testing 3 phase appliances is, how can it be done effectively?
For many single phase earthed appliances, an earth continuity and insulation test is sufficient to test the electrical integrity of the appliance. However, the Australian standard specifies that for appliances that must be energised to be in the 'on' position a currentm leakage test shall be performed. For that reason, many single phase appliances also require a current leakage test. 3-Phase appliances are no different in this respect.
3-Phase appliance 'on' switches
On most 3-phase appliances, contactor relays are used to switch the appliances. Typically, these can only be operated when the appliance is powered. Therefore, 3-phase appliances are more commonly, appliances that must be energised to be in the 'on' position and therefore many would consider that a current leakage test should be performed.
However, testing 3-phase appliances for current leakage is neither straight forward, nor something that can be performed without either costly test equipment or by a non-qualified electrician.
Basic 3-Phase adaptors for appliances testers
Some 3-phase adaptors are available for single phase appliance testers which allow 3-phase appliances to be tested. The normally consist of a single phase plug attached to a 3-phase extension lead socket.
These allow for the earth continuity an insulation of a 3-phase appliance to be tested. However, as previously mentioned, many 3-phase appliances have relays on the power circuits. These adaptors cannot test beyond these circuits so have many limitations.
By using such adaptors, some appliances will not be tested in accordance with AS/NZS3760:2010. These adaptors typically cost about $250.00 - $350.00 + GST. Circuit diagrams are available for those that would like to manufacture their own.
Current leakage 3-Phase adaptors for appliances testers and 3-phase leakage testers
As many 3-phase appliances require a leakage test, 3-phase adaptors exist which allow 3-phase appliances
to be tested using a current leakage test. The adaptor is basically used like an extension lead. The single phase
appliance tester is used to make anearth continuity reading while a measurement of current leakage is measured
using the device while the appliance runs. Theseadaptors can test appliances to check compliance with
AS/NZS3760:2010. However, they tend to be costly devices and you can expect to pay in excess of $800.00 for
such a device.
Other 3-Phase current leakage tests
A 3-phase leakage adaptor is not the only method by which 3-phase appliances can be tested for current leakage. Other methods would include measuring the current present in the earth core while the appliance is running or by using a current leakage current clamp. While both these options are significantly lower in cost, they may not be appropriate for a non-qualified electrician.
Details on testing using these methods can be found in Best Practices Guide to Testing and Tagging.
Insulation and Continuity meters
For those who decide that the Insulation and Continuity testing of their 3-phase appliances is sufficient, an insulation and continuity meter may well be the most versatile and low cost solution available. Not only will this allow the insulation of each conductor to be tested independantly, but it also provides a simple means of testing the polarity of 3-phase extension leads too.
The cost of an insulation and continuity meter maybe even less purchasing a single adaptor lead for a PAT.
Other issues relating to 3-phase equipment
While current leakage testing may be the most thorough method of testing 3-phase equipment, there are still many other issues relating to testing 3-phase equipment effectively. One consideration must be whether it is safe for a run test to be carried out on the equipment. Some 3-phase appliances are not only large but can be dangerous if operated by non authorised personell. It is quite likely that the authorised personnell may not be available at a time when the equipment is required to be tested.
Deciding how to approach 3-Phase Current leakage testing
Questions you'll need to be able to answer before deciding on the most appropriate route forward include:
• Do I want to test 3-phase equipment in accordance with AS/NZS3760:2010
• Is the equipment electronically controlled and switched with relays?
• Do I want to use adaptors in conjunction with an appliance tester?
• Do the sockets and plugs in the workplace use 4 pins or 5 pins?
• What amperage rating are the plugs and sockets, 20A, 32A or something else?
• If current leakage testing, am I authorised to run the 3-phase equipment during a run test?
• Is the 3-phase appliance safe to run during a powered test?
Author: James Anderson