We have recently updated our guidance on contactors for use with the newly launched external transfer switch in combination with gensets solution. Please see the details below:

Previously, we recommended using only the Schneider LC1G3304 TeSys 400A contactor for these systems, due to possible variations in the closing and opening times across different brands and models.

Following further testing, we are pleased to announce that any standard contactor will meet the required timing requirements.

External transfer switch systems with gensets can now use any (common) contactor, allowing for more accessible, flexible, and cost-effective solutions.

The MultiPlus-II External Transfer Switch manual will be updated soon.

GX genset start/stop with cooldown for the most seamless changeover

For a completely seamless transfer, we recommend to use the genset start/stop features in our GX devices, including its cooldown feature.

How does that work?

After the system receives the signal to stop the genset, the inverter will first take over the load. And only thereafter, and after the configured cooldown time, the genset will be stopped. As a result the exact opening time of contactor is irrelevant. The transfer will be entirely seamless, 0 ms.

The alternative, stopping the genset, and letting the inverter initiate the transfer only after it detects the incoming voltage and/frequency to move outside the acceptable window, will always result in a less seamless transfer. No matter how fast the contactor is.

Detailed information on the GX genset start/stop features, along with direct integration into DSE, ComAp and other start/stop controllers, can be found in Chapter 17 of the GX manual.