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SA20 Shock
Section SA20 effective April 13, 1993
SA20.1 A marine converter or inverter that has been subjected to the vibration test in Section SA19,
Vibration, shall withstand 5000 impacts of 10 g peak with a duration of 20 – 25 milliseconds – measured
at the zero reference line of the half-sine wave shock pulse – without structural damage to the mounting
means or the enclosure that might result in:
a) An increase in the risk of fire, electric shock, or injury to persons;
b) A reduction of spacings to a value less than the minimum specified in Spacings, Section 28;
or
c) Exposure of a live part.
The intended operation of the marine converter or inverter shall not be impaired and the converter or
inverter shall comply with the requirements in SA19.4 upon completion of the test.
Exception: A marine converter or inverter that is marked for use on a vessel more than 65 feet (19.8 m)
long in accordance with SA25.7.
SA20.2 The marine converter or inverter is to be mounted as intended on a rigid test fixture secured to
the shock table. The converter or inverter need not be operable during the test.
SA21 Ignition Protection
Section SA21 effective April 13, 1993
SA21.1 A marine converter or inverter intended for use in an area in which ignition-protected equipment
is required shall operate in an explosive mixture of propane and air as described in (a) – (e) without
igniting the mixture. Each potential ignition source, including individual components such as a switch or a
relay that is considered to be a potential source of ignition, is to be operated 50 times. Either the device
contacts or a spark plug shall be provided to produce a positive arc for ignition of the gas mixture in the
enclosure under test.
a) The propane and air mixture is to be drawn into a component containing a source of ignition
by copper tubing connected to a vacuum pump outside the chamber. Copper tubing having an
inside diameter of 0.061 ±0.0071 inch (1.55 ±0.18 mm) and a length of at least 6 inches (152
mm) is to be used as a flame arrester and to reduce the effect of an increase in volume of the
enclosure of the device under test. All joints are to be gas tight and are to withstand 50 internal
explosions.
b) If a component does not have gaps or seams to permit gas to enter it when a vacuum is
applied, a separate copper tube having an inside diameter of 0.061 ±0.007 inch and a length of
6 inches is to be fitted to the enclosure and the free end is to be open to the explosion
chamber.
c) Means are to be provided to indicate positively that an explosion has occurred within the
enclosure when the spark plug is fired or the ignition source is activated. This may be by sound,
monitoring the pressure in the gas pick-up tube, or pressure changes in the explosion chamber.
OCTOBER 15, 2004UL 458SA14
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