IE
TEST & Measurement
Proximity Testers – Friend or Foe
By Chris Halliday, Electrical Consulting and Training
Proximity testers are an
inexpensive piece of test
equipment. They have been
called unreliable by some
but many electricians rely on
them. Who is right? In what
situations do these testers
come into their own? What
precautions
are
needed
when using them?
P
roximity testers are known by many
names – test stick, test pencil, glow
meter, sniffer, etc. They are relied
on by many electricians for proving the
electricity supply is off before working deenergised. They are inexpensive, easy to
use and small enough to fit neatly in an
electrician’s top pocket.
Proving de-energised is important to
ensure compliance with the legislation and
codes, as we must now work de-energised
in the majority of situations, but most
importantly to ensure that it is in fact safe
to work.
The voltage or more correctly the electric
field produced by the voltage is measured
using capacitive coupling. If you remember
that a capacitor is two metallic plates
separated by an insulator or dielectric, then
you have the basis for understanding how
proximity testers work.
The live metallic component such as
a live wire is the first plate and the other
plate is inside the tester. The operator or
person holding the tester also forms a direct
circuit or by capacitive coupling to ground
if isolated from ground e.g. by shoes or
carpet. The sensing circuit of the tester then
detects that there is a capacitive voltage
and initiates a signal to show that there is
voltage present.
You can prove this by placing a proximity
tester on an insulated table next to a ‘live’
power cord or outlet. The tester will alarm
while your holding it but will turn off when
you remove your hand.
Therefore, the proximity tester may not
work if the operator is isolated from ground.
Various Options Available
Proximity testers come in all shapes and
sizes with various options available. Most
come with some visual indication of the
presence of voltage. Visual indication is
often in the form of a constant red light
or some have flashing LEDs. Some vibrate,
whilst others make a squawking noise
or some use a combination of flashing,
vibrating and squawking e.g. MEET
MS-47VH. This model even flashes and
squawks at a greater rate once the voltage
gets above a certain level.
Proximity Testers – many electricians rely on them
but should they?
Some experts say that proximity testers
are “inherently unreliable” and should not
be used for testing purposes. But is this
right?
Before using any piece of equipment it is
important to read the operating instructions
and to understand how that piece of
equipment works. The same is true for
proximity testers. So how do they work?
Proximity Tester Operation
Proximity testers do one job – detect the
presence of voltage. They do this by non
contact means i.e. without a metallic test
probe touching the apparatus or wire that
is being tested for voltage.
18
The SAGAB Volt Stick Pro 12 has a recessed tip
where the wire being tested must be placed –
this increases the selectivity and reduces the risk
of false indication.
Industrial Electrix
Some monitor the voltage continuously
whilst others need to have a button or test
switch pushed. Some have testing tips that
allow them to be pushed into socket outlets
whilst others have a blunt nose.
Some testers, such as the Fluke 1AC-A II,
have an indication that the batteries are
becoming flat and even have a self-test
feature for visually confirming battery status,
system integrity, and power-on. The status is
satisfactory if the tester double flashes every
2 seconds during normal operation.
It pays to read the specification for your
tester and see the voltage range that the
tester will detect within. Many test between
about 50V and 600V A.C. whilst others
may test as low as 5V. Some testers have an
adjustment to alter the sensitivity of the test
voltage measured. Some also measure the
current level using the electromagnetic field
generated by the current flowing in the wire
e.g. TopTronic T475.
The Amprobe
(KWIK-I-E) has a
LED display in a bar
graph with each LED
illuminating for a step
rise in voltage of
6 volts.
The IP rating should also be considered
when purchasing a proximity tester. Most
are not ‘waterproof’ and will be damaged if
immersed or severely wet.
The type of battery and expected battery
life should also be considered. Some use AAA
batteries whilst others may use ‘watch’ type
batteries which can be quite fiddly to install.
The battery life for continuous operation
for one brand specifies approximately 200
hours.
Quite a few makes and models specify
that they will operate from 50 Hz to 500 Hz,
but all are to be only used for a.c. voltages.
Some such as the MEET MS-47VH
even double as TV/Monitor radiation and
microwave testers. The safety Category
Rating should also be considered and makes
and models vary up to CAT IV 1000V.
Things to Watch Out For
As mentioned previously, the proximity tester
may not work if the operator is isolated from
ground.
Continued page 20 4
January-March 2011
IE
TEST & Measurement
Continued from page 18
It is therefore best to prove the tester using a
known voltage in the location where the tests
are to be performed i.e. proving the operator
has adequate capacitive coupling to ground.
Just like any other test instrument, it is
important to test your tester before and
after each no-go result to ensure the tester
is operational. Again, a known voltage
source at the testing location is best but
a voltage proving unit could be used.
Capacitive coupling would then be from
one test terminal to the proximity testers,
through the operator to the other test
terminal or from the proximity tester directly
to the other test terminal.
Quality often comes with the price paid
for equipment. A cheaper tester may not be
as reliable as a more expensive make/model.
Like any piece of equipment, maintenance
is likely to be needed at some stage and this
may simply involve replacing batteries or for
more serious problems it is probably better
to simply dispose of proximity testers due to
their cheap purchase price.
One incident involved a proximity
tester where the tester had problems
with the battery connections. The tester
was tested before and after the ‘no-go’
result but these tests indicated the tester
was working effectively. The electrician
subsequently received a near lethal shock.
The investigation revealed that the battery
connections separated due to gravity for the
‘no-go’ test as a different angle was used
for the real test.
Proximity testers cannot work where the
‘live’ wires being tested are shielded, such as
in a metallic conduit or where the cable has
a metallic shield. However, the tester will
measure a voltage if the metallic conduit or
cable screen is ‘live’.
Proximity Testers have inherently high
input impedance due to their design. This
means that they will detect induced and
leakage voltages through high impedance
paths. A classic example is the voltage on
the metallic case of a double insulated
appliance such as a DVD player. The voltage
will be negligible if measured with a low
impedance test device such as test lamps or
a low impedance voltmeter. There is a real
voltage being measured by the proximity
tester, but the voltage is from a high
impedance source.
Rubbing the tester tip on a synthetic shirt
will cause the proximity tester to indicate
a voltage. This is because it is measuring
the variation in the static voltage being
generated. Bumping the tester may cause
the same type of result, so beware of this
‘qwerk’ with proximity testers. Remember
that proximity testers are for testing a.c.
voltages and not d.c.
Watch out for false measurements when
the tester is used in strong magnetic fields
e.g. near overhead powerlines, particularly
Single Wire Earth return systems.
20
These test results are not false indications
as such as there is a real voltage being
measured.
The proximity tester may not read when
the cable being tested is coming out of the
ground and the measurement is being made
near the ground.
The Best Tool
The dangers of arc flash are well known
and the risks must be managed. Because
proximity testers are non-contact, they
assist in minimising the risk of arc flash and
therefore increase safety.
Proximity testers can be the best tool for
some jobs such as:
• Testing network polarity: No other tool
can test polarity as quick as a proximity
tester. The proximity tester is held to
the wires to be tested for polarity.
It will give a positive indication for
the active and ‘no-go’ result for the
neutral. The proximity tester cannot
prove the neutral is actually connected
i.e. prove neutral integrity.
• Meter readers testing metallic
switchboards are safe to open: Meter
readers can be placed at risk when
opening metallic switchboards if the
neutral to the installation is deteriorated
or open circuit. This causes a dangerous
voltage on the switchboard metallic
surround and lid. Proximity testers that
indicate without the need to push a
button are best and can be strapped
to the meter readers handheld meter
reading/recording tool. The meter reader
simply places the tester near and then
against the metal lid of the switchboard
before opening the lid. Ideally the tester
should be checked before and after
each test.
• Finding open circuits in extension cords:
Trace the active from the socket outlet
along the cord with the tester until it
stops indicating. The open circuit in the
extension cord is then identified and can
be repaired.
• Finding a blown bulb in a string of
series Christmas lights: Trace the active
from the socket outlet along the string
of lights with the tester until it stops
indicating. You will then have found
the faulty bulb. This will save oodles
of time compared to pulling each bulb
out and replacing it or testing it with a
resistance meter.
Comparison with Other Test
Equipment
Test Lamps
Test lamps do not indicate until the voltage
is above about 80 volts, depending on the
ambient light at the time, but will give no
indication of the level of voltage (somewhat
similar to many proximity testers).
Industrial Electrix
They will not measure induced voltages
or voltages from high impedance sources
– they will dissipate induced voltages.
Proximity testers will measure such voltages
and will not dissipate them.
Digital Voltmeters
Digital voltmeters, in the main, are high
impedance and will also measure induced
voltages and voltages from high impedance
sources (similar to proximity testers). A low
impedance meter will then be needed to
prove that the voltage is induced or from a
high impedance source. However, in stark
contrast to the proximity tester, a voltmeter
will give a precise indication of the level of
voltage, within its level of accuracy.
Safety When Proving De-energised
The question now is whether it is safe to
prove de-energised using a proximity tester.
The following will help to determine this.
Many powerline workers rely on proximity
testers to prove de-energised to work
on high voltage powerlines. The main
difference is that capacitive coupling to
ground is assured if the circuit is ‘live’ due to
the high voltage being measured.
If most proximity testers start measuring
at around 50 Volts, are voltages of less
than 50 volts dangerous?
IEC/TR 60479-5 provides touch voltage
tables for strong muscular reaction and
ventricular fibrillation. Depending on one’s
philosophy of danger and risk, one could
use the voltage limits for strong muscular
reaction or ventricular fibrillation.
Taking a conservative approach, let’s
use the strong muscular reaction values as
shown in Table 2b from IEC/TR 60479-5.
An electrician is unlikely to be saltwaterwet or water-wet (though could be quite
damp when sweating profusely on a hot
summer day). A shock from hand to hand
is the most likely result if the electrician was
to touch a live wire and receive an electric
shock. Therefore the test instrument used
by an electrician to test de-energised should
read values down as low as 11 volts but this
will depend on circumstances.
Fluke recommend in their paper
“Electrical Testing Safety” that “these little
tools are good for a first test, but should
always be followed up with a direct-contact
meter.” This is a conservative approach and
is probably a wise approach, especially given
that the operator may not be adequately
coupled to ground to ensure effective
operation of the tester.
Direct-contact meters will not work if
the earth or return circuit being measured
is not connected even if they have been
checked before and after use on a known
source or with a proving unit. This test will
show that the ‘live’ wire is de-energised
and safe to work on when this is clearly
not the case.
January-March 2011
IE
Muscular Effects
Current threshold
AC touch voltage thresholds for long duration (V)
mA
Saltwater-wet
Water-wet
Dry
Large
contact
Medium
contact
Small
contact
Large
contact
Medium
contact
Small
contact
Large
contact
Medium
contact
Small
contact
Hand-to-hand
5
5
9
27
7
25
93
11
40
104
Both hands-to-feet
10
5
9
27
7
25
93
11
40
104
Hands-to-seat
5
3
5
13
3
13
46
6
20
52
Table 2b Strong muscular reaction for alternating current 50/60 Hz
There is no ideal or perfect piece of test
equipment and a combination of test
equipment is recommended. In this
case, the use of proximity testers should
be supplemented with measurements
made using a direct-contact meter. Some
multimeters now come with an in-built
proximity tester. This combines the best
features of both instruments – the noncontact and quick test provided by the
proximity tester with the more accurate and
precise measurement of the voltmeter.
Conclusions and
Recommendations
Proximity testers can be an inexpensive and
effective tool to measure voltages within
their operating range. Their non-contact
design makes them attractive to minimise
the risks associated with arc flash. Their
speed of operation, ease of use and small
size makes them an ideal tool for electricians
but the operator must understand how the
tester works, the problems associated with
this tool and the errors that might occur.
They work through capacitive coupling with
the operator becoming part of the capacitive
coupling circuit. They do not provide an
exact measure of the voltage – a voltmeter
will be required for this type of accuracy.
Proximity testers come with various features
and specifications and it will pay to research
and purchase an instrument that will meet
your needs. Most operate between 50-600V
a.c. but it will pay to read the instructions of
the tester to be used.
Proximity testers will give a positive
reading if there is an a.c. voltage present
and the operator is directly or capacitively
coupled to ground. Some proximity testers
operate down to a minimum voltage of
less than 11 volts and those with self-check
functionality are preferred. They can be used
as a first test to prove ‘de-energised’ but
follow up tests should be performed with a
direct-contact meter. It is this combination
of tests that should ensure safety.
In regards to the question about whether
proximity testers are unreliable, many
are manufactured to high standards and
quality. The operator must understand how
the instrument works and the situation it
is to be used in. This is true of any other
type of test instrument and even directcontact meters can provide unreliable
results in certain circumstances. In other
words, there is no ideal or perfect piece of
test equipment for proving de-energised.
Proximity testers are definitely friends
but should be supplemented with the
measurements made using a direct-contact
meter and then decisions need to be made
based on the test results.
Acknowledgement
The author is not responsible for the use
or misuse of information contained in this
paper. We are not linked to any company
that may have their product mentioned or
depicted in the photos in this paper and we
do not necessarily recommend any of these
brands. The use of such photos is to simply
add value to the paper.
To discuss this matter further contact:
chris@elect.com.au
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