65-2640XL-04 M2A Transmitter Operator’s Manual
Chapter 2: Description
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9
M2A Junction Box
The M2A’s cast aluminum junction box protects the terminal PCB and wiring connections made
to the terminal PCB. Use the three 3/4 NPT conduit hubs to wire the remotely installed
combustible gas detector and connect wiring from an external device, typically an RKI controller.
The top hub is shipped with a factory installed and sealed conduit plug to avoid leaks into the
junction box. If necessary, the conduit plug can be removed and the top hub can be used for
wiring.
WARNING: If the top conduit hub is used for wiring, be sure to seal the threads to ensure
water does not enter the junction box. See “Wiring the M2A Transmitter” on
page 17 for complete wiring instructions.
Use the junction box’s two mounting slots to mount the M2A to a vertical surface at the
monitoring site. The window in the cover on the front of the junction box allows you to view the
OLED display and use the magnetic wand to actuate the magnetic control switches so you can
perform non-intrusive calibration. Removing the cover allows you to access the interior of the
junction box.
Detector Junction Box
The detector junction box is intended to be installed remotely from the M2A junction box. The
combustible gas detector is factory installed in the bottom 3/4 NPT conduit hub using a 3/4 x 1/2
NPT reducer. A terminal strip is provided for wiring connections and the detector is factory wired
to one side of this terminal strip. The other side of the terminal strip is for user-supplied wiring to
the detector terminal strip located in the M2A junction box. This wiring should go through the top
3/4 NPT conduit hub. Three spacers installed on the back of the junction box controls the distance
of the junction box from a mounting surface.
Combustible Gas Detector
The combustible gas detector is a catalytic type detector that produces an electrical output that
corresponds to the detection range. It is packaged in a 1/2 NPT nipple with a sintered metal flame
arrestor on one end allowing ambient air to diffuse into the detector. The flame arrestor also
contains any sparks which may occur within the detector. The 1/2 NPT mounting threads at the
top of the detector allow you to mount it into the bottom conduit hub of the junction box. The
junction box conduit hub is 3/4 NPT, so a 3/4 x 1/2 NPT reducer is used to install the combustible
gas detector. A rainshield screws onto the bottom of the detector (flame arrestor end). The
rainshield helps protect the detector from rain and debris in the monitoring environment. Four
color-coded leads extend from the top of the detector. The leads allow you to connect the detector
to the terminal strip.
Calibration Adapter/Splash Guard
A calibration adapter/splash guard is installed on the combustible gas detector. A fitting at the
bottom of the calibration adapter/splash guard allows a length of tubing to be connected for
calibration and routed to a more easily accessible location (near the M2A junction box is optimal
for ease of calibration). The calibration adapter/splash guard also protects the detector from
splashing water or direct water spray.
