Carlo Gavazzi RM1A48D50 50 A 480 Vac Solid State Relay

A zero-switching 50 A industrial solid state relay for 480 Vac loads

The Carlo Gavazzi RM1A48D50 is an industrial single-phase solid state relay with an anti-parallel thyristor output and zero-cross switching. It switches resistive, inductive and capacitive loads up to 50 A rms at 480 V ac, is controlled by a 4 to 32 V dc signal, and includes an LED status indicator and a built-in varistor against transients.

Solid state relays have no moving contacts, so they are suited to heating elements, furnaces, lighting banks and other loads that switch often. The RM1 family uses direct copper bonding (DCB) technology, a housing free of moulding mass, self-lifting terminals and a clip-on IP20 cover. The ordering key decodes as RM (relay), 1 (one pole), A (zero switching), 48 (480 V ac), D (control 4-32 Vdc), 50 (50 A).

Technical specifications

Applying the relay correctly

A solid state relay dissipates heat in the thyristor, so the current rating only holds with a suitable heatsink. The datasheet includes a power dissipation curve and a table of required heatsink thermal resistance versus load current and ambient temperature: at 50 A the required heatsink thermal resistance is about 1.03 C/W at 20 C and falls to around 0.20 C/W at 70 C. Always apply heatsink compound, keep the ambient temperature below the stated limit and leave airflow around the heatsink.

Zero switching turns the relay on when the sine wave crosses zero and off when the current crosses zero, which reduces electrical noise for resistive loads such as heaters. The datasheet states that the instant-on RM1B version with a DC control input can be used for phase control. The D control input accepts 4 to 32 V dc, which suits PLC and controller outputs directly; the A-input versions (20 to 280 V ac, 22 to 48 V dc) have different part numbers.

Selection notes

Select the current rating with margin for the inrush of the load (lamps and some heaters draw several times the running current) and protect the relay with a semiconductor fuse sized to the I2t value. The datasheet notes that conducted radio interference may require mains filters in some applications. Fix the relay to the heatsink with the mounting screws (M5) at the datasheet torque of 1.5 to 2.0 Nm, since a loose fit raises the junction temperature. Other ratings (25, 75, 100 A) and voltages (230, 400, 600 V) are part of the same family.

Documents and quotation

The attached RM1A/RM1B datasheet lists every model in the family together with the heatsink tables, EMC data, wiring and dimensions. When requesting a price for the RM1A48D50, tell us the load type and current, the supply voltage, the control signal and the heatsink or cabinet temperature. See also Contactors and Overload Relays and the ABB AF09 three-pole contactor for loads that suit electromechanical switching.