Yes, there are wiring diagrams available depending on the kW of the unit. Please view wiring diagram 900686 for FSE40 heaters (https://www.reznor.co.uk/wp-content/uploads/2025/09/900686-FSE-40-Wiring-Schematic-EN-2019-09-Rev1.pdf) and diagram 900687 for FSE60-300 heaters (https://www.reznor.co.uk/wp-content/uploads/2025/09/900687-FSE-60-300-Wiring-Schematic-EN-2019-09-Rev1.pdf).
Is there a wiring diagram available for the FSE warm air heaters ?
Information on wiring diagrams for Reznor products