The Interface Solution Experts
27
SPA
Site-Programmable RTD &
Thermocouple Limit Alarm Trips
Recommended Ground Wiring
Practices
Moore Industries recommends the following ground
wiring practices:
• Any Moore Industries product in a metal case or
housing should be grounded.
• The protective earth conductor must be connected
to a system safety earth ground before making
other connections.
• All input signals to, and output signals from,
Moore Industries’ products should be wired using
a shielded, twisted pair wiring technique. Shields
should be connected to an earth or safety ground.
• For the best shielding, the shield should be run
all the way from the signal source to the receiving
device. (see Note below)
• The maximum length of unshielded input and
output signal wiring should be 2 inches.
Note:
Some of Moore Industries’ instruments can be
classified as receivers (IPT
2
, IPX
2
, etc.) and some
can be classified as transmitters (TRX, TRY, etc.)
while some are both a receiver and a transmitter
(SPA
2
, HIM, etc). Hence, your shield ground
connections should be appropriate for the type
of signal line being shielded. The shield should
be grounded at the receiver and not at the signal
source.
Contact/Load Suppression
When the instrument relays are used to switch external relay
coil, contactor, solenoid or some other inductive load, large
voltage spikes may be created in nearby cable harnesses.
When excessive, these voltage spikes can disrupt the
operation of all nearby electronics including this product.
Please follow the external relay manufacturer instructions
for their recommended relay coil suppression kits. Inductive
loads should have suppression devices installed on the
relay right across the relay coil itself. Usually this is a
simple diode for dc circuits. AC circuits routinely use an R-C
snubber.
