KMP_772C_B04 Page 3 of 3
772 Series
Pulse Transformers
Murata Power Solutions, Inc. makes no representation that the use of its products in the circuits described herein, or the use of other
technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained herein do not imply
the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifi cations are subject to change without
notice. © 2011 Murata Power Solutions, Inc.
Murata Power Solutions, Inc.
11 Cabot Boulevard, Mansfi eld, MA 02048-1151 U.S.A.
ISO 9001 and 14001 REGISTERED
www.murata-ps.com/support
TECHNICAL NOTES
ISOLATION VOLTAGE
‘Hi Pot Test’, ‘Flash Tested’, ‘Withstand Voltage’, ‘Proof Voltage’, ‘Dielectric Withstand
Voltage’ & ‘Isolation Test Voltage’ are all terms that relate to the same thing, a test
voltage, applied for a specifi ed time, across a component designed to provide electrical
isolation, to verify the integrity of that isolation.
All products in this series are 100% production tested at their stated isolation voltage.
A question commonly asked is, “What is the continuous voltage that can be applied
across the part in normal operation?”
For a part holding no specifi c agency approvals both input and output should normally
be maintained within SELV limits i.e. less than 42.4V peak, or 60VDC. The isolation test
voltage represents a measure of immunity to transient voltages and the part should
never be used as an element of a safety isolation system. The part could be expected
to function correctly with several hundred volts offset applied continuously across the
isolation barrier; but then the circuitry on both sides of the barrier must be regarded
as operating at an unsafe voltage and further isolation/insulation systems must form
a barrier between these circuits and any user-accessible circuitry according to safety
standard requirements.
REPEATED HIGH-VOLTAGE ISOLATION TESTING
It is well known that repeated high-voltage isolation testing of a barrier component
can actually degrade isolation capability, to a lesser or greater degree depending on
materials, construction and environment. This series has toroidal isolation transformers,
with no additional insulation between primary and secondary windings of enameled
wire. While parts can be expected to withstand several times the stated test voltage,
the isolation capability does depend on the wire insulation. Any material, including this
enamel (typically polyurethane) is susceptible to eventual chemical degradation when
subject to very high applied voltages thus implying that the number of tests should be
strictly limited. We therefore strongly advise against repeated high voltage isolation
testing, but if it is absolutely required, that the voltage be reduced by 20% from speci-
fi ed test voltage.
This consideration equally applies to agency recognized parts rated for better than
functional isolation where the wire enamel insulation is always supplemented by a
further insulation system of physical spacing or barriers.
