Safe shutdown of the DC side

Is a DC switch disconnector in the inverter enough?

Find out about and download our brochure on “Surge protection for photovoltaic rooftop systems”.

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String combiner box
Phoenix Contact employee with a tablet

Did you know?

When it comes to the DC switch disconnector, keep in mind the necessary disconnection capacity. In contrast to AC voltage, there is no zero crossing in the case of DC voltage.

There is a high risk of an electric arc in the event of improper shutdown. The same is true if DC connectors are unplugged while under load; this also poses a fire hazard and danger to life.

Safe shutdown of the DC side

Is a DC switch disconnector in the inverter enough?
From a normative point of view, this disconnector is sufficient. But what about the cables to the PV panels? Even when the inverter is disconnected from the DC voltage source by the integrated DC disconnector, these cables remain live. If the inverter is not installed near to the PV panels, the cables are often long. And in many cases, the cables are then laid through the building. In the event of maintenance, repair, or extension work, you cannot disconnect these cables.

The solution is simple: install an additional DC switch disconnector near the PV panels. Ideally together with the surge protection in a string combiner box. Installation is easy. The string combiner box comes ready to connect and has already been tested. And cable installation to the inverter is also easier. It is not necessary to route every string to the inverter. One cable pair per MPP tracker is sufficient.

But what if you can no longer access the DC switch disconnector in the string combiner box, for example, in the event of a fire? Although it is a myth that firefighters will not extinguish fires at homes with a PV system, it should still be possible to shut down the DC cables. Especially if they are routed through the building.

An emergency fireman’s switch, ideally installed directly at the main distribution, enables safe shutdown of the PV cables. When the emergency fireman’s switch is activated, the DC switch disconnector in the string combiner box is shut down by an undervoltage release. It also works reliably in the event of a voltage failure in the emergency switch or in the entire building.

An unintentional and undetected shutdown of the PV system is possible due to the remote shutdown. This happens in the event of brief voltage fluctuations through the undervoltage release. Emergency fireman’s switches with automatic reclosing in the event of unintentional actuation are therefore a good idea. If the voltage is switched off via the emergency fireman’s switch, it goes without saying that it needs to be switched on again manually.

String combiner box for photovoltaic systems up to 1,000 V DC

String combiner box

String combiner box for photovoltaic systems up to 1,000 V DC

For the connection of 2x2 strings. With surge protection (type 1+2), DC fire service switch disconnector with remote access and Push-in connection for the input and output side.