What happens when someone comes to service your solar powered building, or worse, has to put out a fire or fix a gas leak? The first step is to remove all sources of energy to that location, but it’s not so obvious how to do that when there are solar panels on the rooftop. So, how do you ensure safe power shutdown when solar panels are installed? Add a rapid shutdown switch.
Purpose of rapid shutdown switches
The purpose of rapid shutdown switches is to protect emergency responders, or anyone who needs to work close to the solar panels, from dangerous DC voltages that may exist on the cables going from the solar panels to the Solar Inverter. For example, during an emergency situation a firefighter may have to enter through the roof or another access point that's in close proximity to a cable carrying high voltage DC, which can typically be up to 1000 Volts DC. For comparison, your household plug is typically 110 Volts to 240 Volts. In these cases the Rapid Shutdown Switch is used to disconnect power from the solar panel array on the rooftop and isolate them from the rest of the system. These rapid shutdown switches are required to be located near the utility connection/meter to your house, but the actual disconnection happens on the rooftop too.
On loss of AC power from the Utility, the rapid shutdown will automatically operate to disconnect the solar array from the inverters and quickly discharge any residual energy in the system through the rapid shutdown box. This means electrical safety is ensured between the inverter and the rapid shutdown box.
Rapid shutdown is a requirement of NFPA 70 (United States) and CEC (Canada). Technically speaking, the source output circuits are limited to not more than 30 Volts (Safe) and 240 VA (Low power) within 10 seconds of rapid shutdown initiation, thus allowing yourself, firefighters or service workers to safely work around the system.
Dr Michael Wrinch is a Canadian Functional Safety Professional Engineer and President of Hedgehog Technologies who’ expertise is in design of complex machines.
Collin Doherty is a Canadian design engineer at Hedgehog Technologies. He designs renewable systems.