Download Hipot testers help you find trouble spots and let you verify your

INSTRUMENTS
KEEP
IT
SAFE
Hipot testers help you find trouble spots and let
you verify your product's electrical safety.
MARTIN ROWE, SENIOR TECHNICAL EDITOR
N
obody wants to build an unsafe product.
To meet safety requirements such as those
published by UL for the US, by CSA for
Canada,and by IEC for Europe and other
areas, you must perform electrical safety
tests on components, cables, and systems
during engineering development and often in production. Components such as transformers and
motors that handle AC mains-level voltages often
need testing for every production unit.
You should perform a variety of safety tests on
your products (Ref. 1, 2), but the most important
electrical safety test is the hipot test, also called a
dielectric-withstand test. In a hipot test, you apply a
high voltage to a product and measure the leakage
current passing through, verifying that the product’s
insulation can withstand high voltages without letting unsafe current pass through to the user.
A hipot test subjects a product to an AC or DC
voltage. In an AC-voltage test, you subject a product to voltages that are at least 1000 VAC greater
than double the normal operating voltage. Class-I
products, those with three-wire AC mains cords
TEST & MEASUREMENT WORLD www.tmworld.com
You can use a hipot tester on engineering prototypes. Courtesy of Clare Instruments.
that operate at 120 VAC, require hipot tests at a
minimum of 1240 V, but the test voltage is typically
between 1250 V and 1500 V; in fact, some national
standards require even higher voltages. Class-II
products, those with two-wire AC cords, need testing at higher voltages, often at 4000 V. Standards
specify the length of time that you must apply the
test voltage to either class, which is typically 60 s.
You can also perform hipot tests with DC voltages. To find the required DC voltage setting for
testing a product, you simply multiply the AC voltage by 1.414. Most standards also require a stepped
test voltage, which allows time for a product’s in-
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INSTRUMENTS
ternal capacitance to
charge. Only after the internal capacitance charges
can you measure the leakage current. If you apply
the test voltage too soon,
the capacitance will cause
the product’s current draw to exceed the
test limit, causing a false-negative result.
The measured current represents the
normally drawn current plus any leakage
currents in the product.
Multiple features
Several companies manufacture hipot
testers, but the features these instruments
offer can vary.Some hipot testers perform
dielectric-withstand tests only.Some perform AC tests only, while others test
products with both AC and DC test volt-
FIGURE 1. Hipot tests often perform
both AC and DC insulation-resistance
tests. Courtesy of QuadTech.
ages. One line of testers from QuadTech
performs AC and DC hipot tests plus
insulation-resistance tests (Figure 1).
Other testers on the market may perform
up to six tests.These multifunction units,
such as the Omnia 8100 series from
Associated Research (Figure 2), are also
called electrical safety analyzers.
FIGURE 2. Multifunction testers, often
called safety analyzers, can perform up
to six electrical safety tests.
Courtesy of Associated Research.
In most applications, you’ll want to automate a test sequence.Generally,you can
program a tester’s sequence from its front
panel. Most testers also offer an IEEE 488
or RS-232 port so you can use a computer to control the tests.
Testers from QuadTech and Associated
Research offer LabView drivers. DITMCO provides software that lets you automate tests through text-based
scripts.The company also offers
a test-programming environment. Some units, such as the
H111 from AEMC, include a
connector that lets you control
the unit from a programmable
controller through I/O pins.
In addition to checking whether an instrument complies with safety regulations, you also need to ensure that instrument cables do not transmit unsafe
currents to users.To test how well an interconnect cable’s insulation can withstand high voltages, you can use either a
bench hipot tester or a dedicated cable
tester.
Companies such as Cabletest, Cirris,
and DIT-MCO manufacture cable testers
that include hipot tests for cables. The
Horizon 1500 from Cabletest, for exam-
Manufacturers of hipot testers
● AEMC Instruments, www.aemc.com
● Associated Research,
www.asresearch.com
● Cabletest, www.cabletest.com
54 APRIL 2005
● DIT-MCO International,
www.ditmco.com
● Educated Design & Development,
www.ProductSafeT.com
● Chroma Systems Solutions,
www.chromausa.com
● Hipotronics, www.hipotronics.com
● Cirris, www.cirris.com
● Omnitester, www.omnitester.com
● Clare Instruments,
www.clareinstruments.com
● QuadTech, www.quadtech.com
● Compliance West USA,
www.compwest.com
● Vitrek, www.vitrek.com
● Instek, www.instek.com
● Slaughter, www.hipot.com
www.tmworld.com TEST & MEASUREMENT WORLD
INSTRUMENTS
ple, can run hipot tests on cable assemblies at voltages up to 1500 VDC and
1067 VAC (Figure 3).
A safe testing environment
Of course, there’s more to hipot testing
than just buying a tester and running
tests. Because hipot testers generate high
voltages, you must carefully design the
test area. For example, hipot testers
should reside in clearly marked, separate
areas so unauthorized staff members
don’t get too close.
The work surface and chair should be
made of nonconducting materials,and the
tester’s safety ground should connect to a
suring the safety of both your customers,
their customers, and your technical staff.
Hipot tests do more than ensure compliance to regulations.They ensure that your
product is safe to use. T&MW
REFERENCES
1. Rowe, Martin, “It’s not safe until it’s
tested,” Test & Measurement World, April
2004. p. 35. www.tmworld.com/archives.
2. The Operator’s Guide to Electrical Safety
Product Testing, Associated Research, Lake
Forest, IL. www.asresearch.com.
3. Rowe, Martin, “Design a Safe Hipot Test
Bench,” Test & Measurement World, April
1999. p. 39. www.tmworld.com/archives.
FIGURE 3. Cable tests often include
hipot tests. Courtesy of Cabletest.
rod driven into the floor.You can force test
operators to keep both hands away from
the product being tested by connecting
special palm switches to the hipot tester’s
interlock terminals—the operator will
have to use both hands to activate the
tester, so it can’t be started accidentally.
A more elaborate way to protect the test
operator is by installing a light curtain, or
an infrared beam, around the test setup.
Whenever a person breaks the beam—
even by extending his or her hands through
it—the beam will open a switch on the
hipot tester that makes the tester unable to
turn on its high voltage. (To learn more
about this and other safety steps, see “Design a Safe Hipot Test Bench,” Ref. 3).
With the right hipot tester and a proper
test setup, you are well on your way to en-
Standards bodies
Canadian Standards Association
(CSA), www.csa.ca
International Electrotechnical Commission (IEC), www.iec.ch
Underwriters Laboratories (UL),
www.ul.com
TEST & MEASUREMENT WORLD www.tmworld.com
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