In the past three months, I have received eight technical support calls about the same bathroom application. In all cases, they needed a 120 Vac exhaust fan to start when a 277 Vac light fixture was turned on using a single 277 Vac rated wall switch. Two of the individuals had both 120 Vac and 277 Vac power available, while the rest had only 277 Vac available. The remainder of this blog will explain how both control scenarios can be achieved. We will utilize RIB2402B in these examples.
120 Vac and 277 Vac Power Available
The first scenario of having access to both 120 Vac and 277 Vac power is diagramed in Fig. 1 and requires a single Relay in a Box® (RIB®). When the wall switch is in the ON position, the light is powered, and the coil of model RIB2402B is energized. This pulls in the Normally Open (N/O) contact of the relay, allowing 120 Vac power to turn on the fan. When the wall switch is in the OFF position, the light and fan will both turn off. The RIB2402B can switch motor loads up to 1 HP at 120 Vac. For motor loads of 1/3 HP and less, model RIBH1C will meet your needs, and all wire colors and connections will be the same.
277 Vac Only Power Available
The second scenario of having access to only 277 Vac power is shown in Fig. 2. This application requires a single RIB® relay and a 277 to 120 Vac step down transformer. The diagram is essentially the same, but the fan is now being powered by a transformer. In this scenario, the ratings of the fan will dictate which RIB® to use, as well as the size of the transformer needed. Functional Devices offers a variety of 277 to 120 Vac step down transformers with different VA ratings.
This blog only covers some of the many possible variations this application may have. While most scenarios can be realized in a similar manner, there is not a one-size-fits-all solution. If you have any questions, call our Technical Support Team. We are available Monday through Friday, 8AM – 5PM EST. Alternatively, feel free to send us an email.