GENERAL RELAY INFORMATION
We accept no responsibility for injury, loss, or damage of any kind caused by or resulting from improper product assembly, testing, commissioning or use.
Warning! Risk of Electric Shock!
This information concerns kits and modules with relay outputs. TO USE THE RELAY OUTPUTS
SAFELY YOU MUST OBSERVE THE MAXIMUM VOLTAGE AND CURRENT LIMITS QUOTED
IN THE
PRODUCT DOCUMENTATION
(this is because the board design may not be rated to
switch the maximum voltage and current limits printed on the relay itself or specified in the relay
manufacturer’s data sheet).
Controlling mains equipment with relay outputs must be treated with extreme caution. Electric
shocks can cause severe and permanent injury or even death. Construction, installation, testing and commissioning
should only be attempted by suitably qualified persons, or under the supervision of a suitably qualified person. These
products are not suitable for children. Before connecting mains powered equipment to the relay outputs please check
with the relevant authorities in order to ensure compliance with all current safety regulations.
Many areas of the assembly may operate at mains voltage. A suitable isolating enclosure must be used. Exposed screw
terminal blocks on some products must be insulated to prevent contact with exposed metallic parts at mains potential.
Connected equipment should be suitably fused.
You will find relay outputs on many of the kits and modules that we sell. A relay is an electrically
operated on/off switch. The voltage and current limits specified in the product documentation
generally relate to resistive or light inductive loads.
Relay Terminals
Most boards have SPDT (Single Pole Double Throw) style relays. These have three outputs:
C
= Common
NO
= Normally-Open contacts connect the circuit when the relay is activated; the
circuit is disconnected when the relay is inactive. It is also called a Form A
contact or "make" contact.
NC
= Normally-Closed contacts disconnect the circuit when the relay is activated;
the circuit is connected when the relay is inactive. It is also called a Form B
contact or "break" contact.
Connecting the Device you want to Control
You must provide an external power source to the device you want to control. No voltage is present at
the relay terminals (remember it is just a switch). The relay is normally connected in
series
with the
positive (+) power wire of the device you want to control.
In this case, the positive wire from the power source should be connected to Common. Then either
the NO or NC terminal (as appropriate for your purpose) is connected to the positive (+) wire going to
the device you want to control. The negative (-) wire does not connect to the relay at all. It goes
directly from the power source negative output to the device negative (-) terminal.
Typical SPDT Relay Connection Diagrams
Anti-Spark SPDT Relay Connection Diagram
Sometimes the connected equipment can cause arcing across the relay contacts. This must be
corrected by installing a resistor and capacitor (not supplied) between the two contacts of the relay as
shown below. Component values are for 230Vac mains.