UMAX030211 Version 1.0.2. Preliminary Documentation – May be subject to change
A-4
Grounding
Protective Earth (PE) must be connected to the grounding stud to reduce the risk
of electric shock. The conductor providing the connection should have a ring lug
and wire larger than or equal to 4 mm
2
(12 AWG). The ring lug should be placed
between the nut and a star washer. (To secure the ground strap, use an 8-32 “K-
LOK” locknut, stainless steel, 3/8” O.D.)
All chassis grounding should go to a single ground point designated for the
machine and all related equipment.
The ground strap that provides a low impedance path for EMI should be a ½ inch
wide, flat, hollow braid, no more than 12 inches long with a suitable sized ring lug
for the module’s grounding lug. It may be used in place of the PE grounding
conductor and would then perform both PE and EMI grounding functions.
Shielding
The CAN wiring should be shielded using a twisted conductor pair. All wire shields
should be terminated externally to the grounding lug on the mounting foot. The
input wires should not be exposed for more than 2 inches (50 mm) without
shielding. Shields can be ac grounded at one end and hard grounded at the
opposite end to improve shielding. If the module is installed in a cabinet, shielded
wiring can be terminated at the cabinet (earth ground), at the entry to the cabinet or
at the module.
CAN Wiring
The CAN port is electrically isolated from all other circuits. The isolation is SELV
rated with respect to product safety requirements. Refer to the CAN specification
for more information.
Use CAN compatible cabling.
Shielded CAN cable is required. The module provides the CAN port shield
connection ac coupled to chassis ground. The chassis ground stud located on the
mounting foot must be tied directly to Earth Ground.
Network Construction
Axiomatic recommends that multi-drop networks be constructed using a “daisy
chain” or “backbone” configuration with short drop lines.
Termination
It is necessary to terminate the network with external termination resistors. The
resistors are 120 Ohm, 0.25W minimum, metal film or similar type. They should be
placed between CAN_H and CAN_L terminals at both ends of the network.
Mounting
Mounting ledges include holes sized for ¼ inch or M6 bolts. The bolt length will be
determined by the end-user’s mounting plate thickness. Typically, ¾ inch (20 mm)
is adequate.
If the module is mounted without an enclosure, it should be mounted vertically with
connectors facing left and right to reduce likelihood of moisture entry.
The CAN wiring is considered intrinsically safe. The power wires are not
considered intrinsically safe and so in hazardous locations, they need to be located
in conduit or conduit trays at all times. The module must be mounted in an
enclosure in hazardous locations for this purpose.
No wire or cable harness should exceed 30 meters in length. The power input
wiring should be limited to 10 meters.
All field wiring should be suitable for the operating temperature range of the
module.
Install the unit with appropriate space available for servicing and for adequate wire
harness access (6 inches or 15 cm) and strain relief (12 inches or 30 cm).
