Portable Appliance Testers (PAT) and the latest standard (AS/NZS 3760:2003)
Since the introduction of the latest Australian
and New Zealand Standard for In-service safety inspection and
testing of electrical appliances (AS/NZS 3760:2003), there has
been misinformation circulating about the effectiveness and validity
of tests performed using existing Portable Appliance Testers
(PAT). In particular, PATs without the ability to perform a leakage
current test are alleged to be of no further use. This is not
true.
The addition to the standard for leakage current testing1 of
appliances (where an insulation resistance test can not be conducted)
raises the question in the minds of current users: “Is
my existing Portable Appliance Tester still suitable to test
appliances to the latest electrical safety standard?” Essentially
the answer will be “yes,” except in those cases where
an insulation resistance measurement can’t be conducted
and therefore the only alternative is a leakage current test.
People or companies spreading this misinformation are at best
ignorant of the standard’s intent, or at worst, attempting
to increase their sales by misleading potential buyers. By now,
the new standard has been around long enough for reputable sales
organisations to be well aware that the existing PATs are still
suitable for testing most electrical appliances in accordance
with the latest standard.
The following extract is from one such company’s misleading
letter. This has been circulated throughout the market place
via email and posted on websites:
“AS3760:2003 not only ends the use of insulation testers
but also every handheld Pass/Fail tester currently sold on the
market. Most only offer insulation testing and earth continuity,
and no power-up or leakage test!”
Nelson Procter, Project Manager for the Standard’s Committee2 has set the record straight in a letter to the editor of one
such website (the misleading article was subsequently removed).
The following is an extract from that letter:
“The paragraph claiming that hand held testers are barred
makes little sense when matched against the actual provisions
of the Standard. Ever since its 1st edition in 1990 (2003 is
the fifth) the underlying philosophy has been to require the
simplest instrumentation, and the possession of a multimeter
and megger has for many years has been and still is the only
instrumentation required to determine compliance with 3760 for
the vast majority of appliances falling under its scope. The
exception which proves the rule is the full testing of an RCD
which does require a purpose built tester.”
The standard is very clear in its intent to provide a methodology
with which a competent person may use simple instrumentation
to inspect and test electrical equipment connected to the 240V
or 415V electrical supply via a flexible cord. The second paragraph
of the standard’s FOREWORD states: “The philosophy
of the document is to provide an inspection and testing regime
capable of implementation with only simple instrumentation…” Put
simply, any measuring instrument capable of measuring the electrical
parameters required by the standard may be used for testing.
This does not exclude PATs without a leakage current test, just
as it does not exclude multimeters and insulation testers, however
it does mean another method of testing leakage current needs
to be found.
When testing appliance safety, insulation resistance must be
measured. If a resistance measurement can’t be made, then
a leakage current measurement is the only other option. If your
PAT won’t do that, then you have to devise another method3 such as:
1. inserting an ammeter in series with either the protective
earth conductor for a Class I appliance;
2. inserting an ammeter in series with a conductor connected
between the metal parts of a Class II appliance and an earth;
or
3. a clamp meter around either of the conductors as mentioned
above.
Nelson Procter also makes comment on statements made about PATs
being compliant with the standard:
“I am not overly in accord with the reference to appliance
testers that 'comply with 3760.' 3760 is a document
whose bottom line is the electrical safety of the user. It is
NOT a document about Portable Appliance Testers. More correct
would be to make a statement along the lines that such and such
a PAT is able to test your appliance to determine if it complies
with the requirements defined in 3760.”
"Is my Portable Appliance Tester still suitable to test appliances to the latest electrical appliance standard?"
It is important that those people undertaking appliance testing
fully appreciate this point. That is, when conducting electrical
safety testing, it is the appliances under test that require
compliance with AS/NZS 3760. Any measuring instrument (such as
a PAT) used to conduct the tests, must ensure that the parameter
it is measuring is within the tolerances as stated by the standard.
So, for that one instrument, the parameter or parameters it is
capable of measuring may not be all those required by the standard.
The widely used SafeTcheck MkD from TRIO Smartcal is still a very capable PAT and was arguably one of
the best on the market. It is still able to test electrical appliances
and ensure they comply with the current standard in most situations.
TRIO has now introduced the updated SafeTcheck Professional.
This new generation PAT includes many new sophisticated features
including a leakage current test for both Class I and Class II
appliances.
TRIO’s website has details of the new SafeTcheck Professional
and accessories. This new tester is one of the most sophisticated
PATs on the Australian market. It easily tests an appliance’s
leakage current if required. A FAQ sheet outlining a simple method
to test leakage current is also available.
1 See AS/NZS 3760:2003 Page 14, Section 2.3.3.2 Testing of insulation 2 Nelson Procter is Project Manager of the joint Australia/New
Zealand Standards Committee EL-036, responsible for the development
of AS/NZS 3760:2003 In-service safety inspection and testing
of electrical equipment
3 See AS/NZS 3760:2003 Page 22, Appendix B INSULATION TESTING
for detail relating to Insulation Resistance and Leakage Current
testing methods
