Output RCD on an inverter?

[Steve Millington]

I have a modified sine inverter which is providing 240V ac from a 12V SLA battery. There is also a charger connected to charge the battery with a 240V input attached to it.

I have a PCB which will disconnect the inverter from the output socket of the unit when the mains is plugged into it (to power the charger).In this instance, The whole thing becomes a great big mains extension cord! However, what is needed, and how do I implement some sort of fault protection on the inverter's output (when not connected to mains).

Presumably, when not connected to mains, both live and neutral poles from the inverter are floating, so both are just as dangerous as each other. Will an RCD take care of this, even though the device hasn't actually got a physical earth? I know in some situations (e.g. campervans), an actual copper 'earth spike' would be supplied to make a physical 'master earth' connection, however, this application doesn't allow for that unfortunately.

I am really unsure on the legislation that surround this, and am not totally familiar with the different types of RCDs available, so any info would be much appreciated.

Regards

Steve

 

[betwixt]

The 'best' solution is to use an RCD and also add an earth to the neutral side output of the inverter. The earth can be a link to mains earth when plugged in and an earth spike when isolated. You can leave the spike connected when the mains earth is also present.

RCDs will trip under two conditions, the current is exceeded (as marked on the trip's rating) or if an imbalance between the live (phase) wire and the neutral wire current is exceeded (usually about 30mA).
Note that in a domestic power feed, the neutral and earth wires are joined at the transformer (sub-station) so all you need to do is replicate that at your inverter output.

Brian.