190-01115-01 G3X™/G3X Touch™ Avionics Installation Manual
Rev. AV Page 21-31
21.3.9 Bus Current
Electrical current can be sensed by the G3X system either by Hall Effect current sensors or through the use
of a traditional ammeter shunt.
21.3.9.1 Ammeter Shunt Installation
The UMA 1C4 ammeter shunt included in Garmin sensor kits (Garmin P/N 909-D0000-00) is a 100 Amp/
50 mv shunt. Other ammeter shunts with different specifications can be supported using calibration
adjustments. See Current portion of Appendix H.4.19.3.2
for GDU 37X systems and Section 30.4.32.15
for GDU 4XX systems (Volts 1 and Volts 2 Inputs) for configuration guidance.
General Installation Guidance – The ammeter shunt has two holes in the base for mounting with #10
screws. The current-carrying wires are attached to the large 1/4” lugs, while the current sense wires are
attached through the use of #8 ring terminals.
Figure 21-18 Ammeter Shunt
NOTE
It is important that no metal portion of the shunt touch any other portion of the aircraft or
exposed wiring. Large voltages and current are present in the shunt, and an electrical
short or fire could result from inadvertent contact.
The shunt should be installed in-line with the current being sensed. As noted below, the appropriate wire
should be cut and attached to each of the large ¼” lugs. A 1A fuse or other form of circuit protection must be
installed between the shunt and the applicable GEA 24/GSU 73 inputs to prevent inadvertent damage to the
GEA 24/GSU 73. Connect the two sense wires (attached to the #8 terminals) to the appropriate inputs on
the GEA 24/GSU 73 as referenced in the G3X interconnects in Section 26
through Section 29. If the
ammeter readings are shown with the opposite polarity, check to see if the sense wire connections are
reversed.
An alternator ammeter shunt should be installed inline in the alternator output (“B” terminal). A battery
ammeter shunt should be installed between the battery positive terminal and the battery contactor.
Depending on the location of the alternator or battery relative to its supported electrical bus, it is typically
desirable to install the shunt on the firewall near where the alternator or battery output would normally
penetrate the firewall.
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