Why would you install MCB for an Earth wire

[swordfish]

I have noticed something unusual in a popular Solar Inverter (SunSynk) installation manual. There is an MCB on the earth wire of the surge protector. Why is that necessary? As far as I'm aware, this goes against all recommendation I've seen for SP installation. What are the reasons behind it and what rating that MCB needs to be? See attached picture below:

[Dylboy]

It may be for diverted neutral currents... Still doing CPD on earthing and surging etc but people have picked up currents in the Earth from broken PEN and leakage currents etc... as said still doing more learning on that matter but thats my initial thought on why an MCB on the earth. As for size I would assume like a 20A or what ever for selectivity breaker but then the KA rating of what ever the SPD can handle and the installtion etc. But it does go against the grain and what I have been taught and learnt over the years so hopefully we can get some clarity on this
Putting a breaker on Earth does not sit well...

Edit:

Actually no idea what size breaker.... why would they want that earth path, if I find a new potential reason will update

Sent from my SM-N960F using Tapatalk

[Derlyn]

That's what is so lekker about this forum. Questions are asked and hopefully we are all wiser after some responses.

Since yesterday I have been searching for a legitimate reason for having that MCB in the earth connection, but have failed.

The closest I came to finding an answer was in one of JW's videos where he says that if the manufacturer specifies MCB protection then so be it.

Maybe this is a question that can be asked on SunSynk's forum.

It does not make any sense, but then again, neither do a lot of other things lately.

Peace out .. Derek

[AndyD]

MCB protection is often used 'on the earth wire' to limit the amount of current through a surge protection device to basically prevent it exploding during a lightning strike or or during the failure of the device, in fact it's often specified as a manufacturer requirement in which case MUST be installed. During a large surge the current flowing through the SPD can exceed its safe maximum, also when they break down with age SPD's often fail in conductive state which can be a fire hazard if that failure current isn't limited. (See CBI instructions on their website require a QA or QF MCB is fitted for example). Some SPD's come with internal fuses and/or thermal runaway protection in which case no supplimentary overcurrent protection is required.... again refer to manufacturers instructions.

In short it's common to see MCB's installed on the path to ground of an SPD but they should never be installed on the path to ground of the CPC of the final circuits.

[Justloadit]

@AndyD The surge arresters we supply, have an internal thermal fuse, and are encased in sand to prevent specifically your description on absorbing surges.