MCB or RCBO

[Mrjmegson]

Hey guys,

I've been reading a lot about inverters tripping RCDs, and about the value of using an RCBO so everything protected by the RCD if using an MCB doesn't trip out.

What are you thoughts?

MCB after an RCD
MCB before an RCD
RCBO before RCD

Cheers,

Jay

 

[Murdoch]

Pay a spark?

 

[Mrjmegson]

Lol

 

[binky]

Hey guys,

I've been reading a lot about inverters tripping RCDs, and about the value of using an RCBO so everything protected by the RCD if using an MCB doesn't trip out.

What are you thoughts?

MCB after an RCD
MCB before an RCD
RCBO before RCD

Cheers,

Jay

When inverters start up, the AC relay can 'chatter' which is what RCDs don't like. Modern inverters don't seem as prone to this, but I've been fitting solar for a very long time and have encountered this issue on a few jobs. Some inverters also have a lot of earth leakage, upto 300mA for one particular make which I stopped using as a result.

On top of that is a safety issue when the RCD is shared with other circuits. Now, RCDs are to protect people against getting killed when they have done something stupid like run over the lawnmower cable. Your solar system will be on a dedicated cct, so that sort of scenario will never happen, which is why I recommend a MCB as all you need for overload protection and protection from a dead short eg mice have nibbled the cable in the attic.

RCBO and RCD do the same thing, you never fit both on the same cct.

 

[Mrjmegson]

Hey Binky,

Thanks for the reply.

So an MCB on a bus bar with the main switch, like you would an RCBO?

 

[stuboy]

I'd fit an RCBO over an MCB just in case someone did something stupid on the inverter side, yes I know they shouldn't be playing with it butttt! It would stop em possibly dying and protect from an inverter fault.
That is why you shouldn't just wire up an inverter to your house ring main! It switches off much slower than the 20ms ish your RCD protecting it will and therefore is quite likely to kill you in the process. As the old adage goes, it will hurt you the entire time you are dying!
Have a nice day
Cheers
Stu

 

[binky]

Hey Binky,

Thanks for the reply.

So an MCB on a bus bar with the main switch, like you would an RCBO?

Yes.

 

[Mrjmegson]

Cool, that's exactly what I was thinking, although initially I was thinking RCBO, but after reading about all the trips inverters can cause, I thought I'd ask the question.

Cheers Bink, I really appreciate it.