What is a PV Fireman Switch?

Join me as I dive deeper into my Solar system and learn more about how it works in detail and maintain the system as items age/break (everything breaks eventually), so let’s learn about a PV Fireman switch.

Definition of PV Fireman Switch

“Automatically disconnects the DC supply on a Solar PV system when the AC grid supply is interrupted. When installed at the point of cable entry into the premises, this product creates a safe environment for Firefighters.”

So what does this actually mean and what happens if it stops working as expected?

In essence, you can think of the PV Fireman Switch as a DC Relay, that is in the “Normally Open” (NO) position. By default it makes sure that the circuit is open. So when there is no AC power being provided, the switch is in NO position so the voltage from the PV panels will NOT reach your inverter and possibly back-feed. When AC power is provided to the unit, it will close the circuit – “Normally Closed” – and allow the voltage to flow to the inverter and allow the inverter to perform its tasks as normal.

So, why is this needed with on-grid systems?

It is a safety feature. Imagine this scenario, the entity responsible for maintaining the grid and electricity needs to performs works on the grid, so they stop the supply (Hopefully with warning you 😊). Under normal circumstances there would be no voltage on any on the networks, however with Solar PV, many of us can back-feed into the grid and get credits and this is the where the need for this device comes in. If you did NOT follow standards and this device installed, you would now back-feed into the grid and turn the grid live again and risk injuring maintenance staff.

What happens if it “breaks”?

This device consists of electronics and can only handle so much “abuse” (read power trips and power fluctuations), and can fail. Mine did, so what happens now? In essence, your PV panels become irrelevant and the voltage being generated by them is basically dropped to nominal voltage (0-2 V) and the inverter will run only off of batteries or pull power from the grid.

Can I fix it?

The unit is NOT designed to be repaired, it is NOT field replaceable. It is delivered pre-wired and not meant to have items replaced. This ensures that a standard is used. This is my unit that failed and yes it was replaced.

It must be replaced, it is an easy enough job to perform as long as your system is well labelled (which it should be already). It has a label for PV IN and PV OUT and the connection for the AC supply is well marked. Replace your unit and you are up and running again.

Until next time.