Dielectric Strength Tests
A dielectric strength test, commonly called a
"dielectric withstand", "high potential", or "hipot"
test, is a stress test of the insulation of a device
under test (DUT). Such a test applies a voltage
to the DUT that is much higher than normal
operating voltage, typically 1000V AC plus
twice the normal operating voltage. For a
household appliance designed to operate at
120 or 240V AC, the test voltage is therefore
usually about 1250 to 1500V AC.
A DC hipot test can usually be substituted for
an AC hipot test. The best voltage for a DC
hipot is normally higher than the AC test voltage
by a factor of 1.414. A product that would be
tested at 1500V AC would be tested at 2121V
DC.
For double-insulated products, the required test
voltages may be much higher, such as 2500
VAC or even 4000 VAC for a 120 VAC power
tool. The voltage is applied between the operating
circuits and the chassis or ground - the
parts of a product that a consumer might touch
or otherwise come in contact with.
Refer to Figure 5 for typical AC hipot test
setups. The setup for a DC hipot test would be
identical.
The purpose of the test is to make sure that
consumers do not receive an electrical shock
when they use the product, which might be
caused by a breakdown of the electrical insulation.
The test also detects possible defects in design
and workmanship that cause components and
conductors to be too closely spaced. The danger
is that air gaps between conductors or circuit
components may become clogged with
dust, dirt, and other contaminants over time in
typical user environments. If the design spacing
is inadequate, a shock hazard can occur after a
period of use. By subjecting the product to a
very high voltage, the hipot test overstresses
the product to the point that arcing may occur if