HIO16: Connecting to output relays

Note: This document is not yet complete. It may contain inaccuracies.

The output relays on the HIO16 all have a single normally open contact. Connection is via the quick connect tabs on top of the relays.

Because of the possibly high voltages and currents involved, you must observe certain precautions:

• Make sure the wires are led directly away from the tops of the relays, and do not pass close to other parts of any of the SPLat boards. You should also tie the two wires in each pair together to reduce the size of loops (which can radiate magnetically). This will minimise the risk of noise coupling from high powered output circuits back into the HIO16 or the controller. The board has been deliberately laid out with the relays clustered one end, so you can take the relay wires away from the board without passing them over other parts of the board.
• All wiring should be performed by a person qualified to perform such work in your geographic location.
• Observe all local regulations regarding wire gauge, insulation and fusing. Note in particular that there is no fusing on the board, and the regulations in most places mandate fusing at less than the ampere capacity of the interconnecting wiring. That means you must provide external fusing.

The above photo shows how not to wire an output relay. The problems here are:

a) The relay current is flowing through what amounts to a large loop or coil with the board's logic circuitry right in the middle. This maximises the chances of any magnetic fields generated in the wires inducing currents into the board and upsetting the circuitry on the board. Such magnetic fields are generated by the current flowing through the wires.

b) The wires pass low down and close to the board. This maximises the chances of electric fields generated in the wires from radiating into the circuitry on the board and causing problems. Such electric fields are caused by sudden voltage changes in the wires when the relays switch (especially switching off). The voltages induced when switching off a motor can amount to brief "spikes" of thousands of volts with very rapid rise and fall times.

c) The close proximity of the wires to the board also potentially compromise the safety rating of the setup. If they actually touch the components it means you only have the single layer of wire insulation between the high voltage on the relay contacts and the "safe" ELV side.

The above picture shows a better way of doing it. Here the wires from the relay are routed up and away from the board, and the have been tied together to prevent a loop of wire from being formed. In a real situation it would also usually be necessary to physically restrain the wires so they cannot accidentally move and touch the board.