65-2640RKSS-04S M2A Transmitter Operator’s Manual
9
M2A Junction Box
The M2A’s stainless steel junction box is dust and weather resistant. The junction box also protects the M2A and
all connections made to it. Use the three 3/4 NPT conduit hubs to wire the remotely installed combustible gas
detector and connect wiring to 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 16 for complete wiring
instructions.
Use the junction box’s two mounting holes 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 stainless steel, corrosion resistant 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. An O-ring seals
the interface between the junction box cover and the junction box base. A locking set screw on the junction box
cover allows you to secure the junction box cover and prevent it from being removed.
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.
Magnetic Wand
The magnetic wand is a short plastic rod with a magnet in one end. It is used to actuate the magnetic control
switches on the control PCB while the junction box cover is still installed so that non-intrusive calibration can be
performed.
