Super Systems 3 Series - Manual (Page 15)

Series 3 Operations Manual
15
Voltage rating
The maximum continuous voltage applied between any of
the following terminals must not exceed 264Vac:
• relay output to logic, dc or sensor connections;
• any connection to ground.
The controller must not be wired to a three phase supply
with an unearthed star connection. Under fault conditions
such a supply could rise above 264Vac with respect to
ground and the product would not be safe.
Conductive pollution
Electrically conductive pollution must be excluded from the
cabinet in which the controller is mounted. For example,
carbon dust is a form of electrically conductive pollution. To
secure a suitable atmosphere in conditions of conductive
pollution, fit an air filter to the air intake of the cabinet.
Where condensation is likely, for example at low
temperatures, include a thermostatically controlled heater in
the cabinet.
This product has been designed to conform to BSEN61010
installation category II, pollution degree 2. These are defined as
follows:
Installation Category II (CAT II)
The rated impulse voltage for equipment on nominal 230V supply
is 2500V.
Pollution Degree 2
Normally only non conductive pollution occurs. Occasionally,
however, a temporary conductivity caused by condensation shall
be expected.
Grounding of the temperature sensor shield
In some installations it is common practice to replace the
temperature sensor while the controller is still powered up.
Under these conditions, as additional protection against
electric shock, we recommend that the shield of the
temperature sensor is grounded. Do not rely on grounding
through the framework of the machine.
Over-temperature protection
When designing any control system it is essential to consider
what will happen if any part of the system should fail. In
temperature control applications the primary danger is that
the heating will remain constantly on. Apart from spoiling
the product, this could damage any process machinery being
controlled, or even cause a fire.
Reasons why the heating might remain constantly on
include:
• the temperature sensor becoming detached from the
process
• thermocouple wiring becoming short circuit;
• the controller failing with its heating output constantly
on
• an external valve or contactor sticking in the heating
condition
• the controller setpoint set too high.
Where damage or injury is possible, we recommend fitting a
separate over-temperature protection unit, with an
independent temperature sensor, which will isolate the
heating circuit.
Please note that the alarm relays within the controller will
not give protection under all failure conditions.
Routing of wires
To minimise the pick-up of electrical noise, the low voltage
DC connections and the sensor input wiring should be routed
away from high-current power cables. Where it is
impractical to do this, use shielded cables with the shield
grounded at both ends. In general keep cable lengths to a
minimum.