Advantages of 2 Leg Control for 3 Wire, 3 Phase Systems using Burst Fire Control Method

Requirement for 2 Leg Control Method

Burst Fire Control is Acceptable
3 Phase 3 Wire system

2 Leg Control Can Not be used in the following configurations

4 Wire System
3 Wire Inside Delta Wiring Arrangement
Phase Angle Control
Hybrid Phase/Burst Control

5 Main Advantages to 2 Leg Control

High Efficiency/Economical – 33% less losses due to only switching two legs. The load current passes through 4 SCR’s instead of 6.
Lower heat dissipation – Since we are only switching 2 legs, then the heat dissipation if 33% less than switching all three legs
Safety – 3 Lage and 2 Leg Controllers have the same level of safety as both require a mechanical Contactor for safety disconnect. This is a clear requirement for the National Electricity Code since SCR’s are not considered a complete disconnect.
Lower EMC and Harmonics due to having one phase connected at all times. This reduces potential clipping when one phase turns on while there is no return current path. 2 Leg Control generates less noise and harmonics than both 3 Phase Burst and Phase Angle Control

Conclusion

We Highly Recommend the use for 2 Leg Control for Open Delta, or 3 Wire Star applications using Burst Fire control, and in particular in EMC/Harmonics sensitive environments.