Arduino relay shields arduino a000110 the arduino 4 relays shield is designed as a solution for driving those high power loads that cannot be driven by arduinos digital ios due to current and voltage limits the shield features 4x relays with each relay providing 2 pole changeover contacts no and nc the 2 changeover contacts have been put in parallel in order to increase output current limits the relays are controlled by the following arduino board pins relay 1 arduino pin 4 relay