40A SSR-40AA AC-AC Single Phase Solid State Relay SSR 40AA Voltage 80-250V AC 220V TO 24-380V AC Output Load High Quality You need choose the correct type (the current and the control Mode) Also a suitable radiator(to dissipate heat of SSR)  is improtant.

Notice:

As the generate heat of SSR is too high,SSR must be loaded on Radiator when the current of load is over 10A.And there are must put the thermal Grease Compound between SSR and Radiator.

In meanwhile, the cooling fan is necessary when the current is over 60A.

The Ratio depend on The kind of loading for your Equipment.

Resistive load: 60%  Inductive load: 30%