Working out which contactor or relay a grower needs.

Power ratings:

- 250W = 1.3 amp
- 400W = 2.4 amp
- 600W = 3.1 amp
- 1000W = 5 amp

(amp rating may vary, check with manufacturer)

The contractor or relay unit should be matched to the power the contractor or relay is used for, so for 4 x 600 Watt ballasts a relay or contactor above 12.4amp with 4 power outlets can be used.

Simply, a relay is cheaper than a contactor - generally. A contactor is used for a higher load.