RSI Series
DC Ammeter Shunts / Busbar Shunts
300 Amp - 1,200 Amp
TECHNICAL NOTES
Mounting: Shunts should be mounted with manganin resistive blades in a vertical position in order to
promote the free convectional flow of air. If vertical mounting is not practical, forced air cooling or adding
heat sinks to the blocks can reduce the operating temperature. The manganin blades must never exceed
+145°C, otherwise permanent resistance change may occur.
When current of 100A or greater is passing through the shunt, the major portion of heat generated is dis-
sipated by conduction through the shunt terminal blocks into the connecting buss bar or cable. Therefore
it is necessary to insure that good contact is made between the shunt terminal blocks and the conductor
terminals and that the conductors have adequate cross section to keep the temperature of the shunt from
exceeding 145°C ( 125°C recommended ).
If the shunt is mounted in an enclosure, care must be taken to ensure adequate cooling. If the power density
is greater than 1/4 watt per square inch of the enclosure surface for all enclosed devices, additional cooling
must be supplied in the form of air vents or fans.
Shunts also must be installed in a way that protects them from thermal expansion forces produced from
buss bar or short-circuit forces. Flexible wiring may be required in high pulse current, high vibration, or high
temperature applications.
Where possible, all shunts should be mounted on the ground side of the circuit. For circuits above 750VDC,
RS shunts must be mounted on the ground side due to the dielectric strength of the shunt base.
Operating Current Derating: For continuous operation, it is recommended that shunts are not run at more
than two thirds (2/3) the rated current under normal conditions per IEEE standards for DC instrument shunts.
At ambient temperatures above 40°C, the current must be further derated to prevent damage.
Pulse Operation: Shunts that do not need continuous operation and are only exposed to intermittent pulses
can be operated at levels above their rated current for short periods of times. Pulses are limited to the
maximum temperature of the blades not exceeding 145°C ( 125°C recommended ). Many variables such as
ambient temperature, cross section of the current carrying conductors, and pulse duration make calculating
exact values difficult. Shunt size will need to be validated by customer for pulse current and duty cycle on a
case by case basis.
Riedon Inc.
300 Cypress Avenue
Alhambra CA 91801
(626) 284-9901
(626) 284-1704
© Riedon, Inc.
Revised: 201803_002
www.riedon.com
sales@riedon.com