65-2641RK-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 hydrogen 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 hydrogen 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.
Hydrogen Detector
The hydrogen 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 detector has a built in molecular sieve that only allows hydrogen to diffuse into 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 hydrogen
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 hydrogen 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.
