65-2640RK-05-04 M2A Transmitter Operator’s Manual
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 16 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. A ground boss near the top conduit hub provides an external earth ground
connection.
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 flame arrestor guard is located at
the bottom of the detector and is permanently bonded to the detector housing. The flame
arrestor guard protects the flame arrestor from impact damage. 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.
