I’m at a house just now, the guy has decided to go off grid, got a company in to take care of all that side of things. There’s a shed outside with all singing all dancing off grid solar kit (looks like the inside of a space ship!). The company took an SWA supply from there into the property & fitted it into an isolator from which I’ll take rails into the consumer unit. The supply from the shed is protected by an RCBO which is needed as it’s a TT system. I usually fit RCBO’s on all circuits but got me thinking, is there any need to fit RCBO’s in the new consumer unit with the main supply being already RCBO protected. Would it matter if the RCBO’s were fitted or is best practice to fit MCB’s in the consumer unit? First TT system I’ve worked on.
Not worked on TT myself so not entirely sure a main rcd is required… or if it is, it is either time delayed or rated to 250mA as apposed to 30mA for the final circuits.
Seems pointless having 2 x 30mA in series, so to speak.
Seems pointless having 2 x 30mA in series, so to speak.
Depending on the earth resistance of the earth rod, I'd fit a 300mA delayed RCD in the shed and a house CU with all 30mA RCBOs.
A single 30mA RCD in a remote location is not a good idea.
A single 30mA RCD in a remote location is not a good idea.
Good God, two posts jumped in, in front of me while I wrote my post. Don't recall seeing the "another post has been made on this thread. Read it?" warning pop up. Is that a victim of the forum reboot?
May be a false alarm. I've just been contributing to another thread, and this time it did appear.
Not sure what you’re getting at?
Is that adequate protection (300mA) for the supply into the house though, would it not need to be 30mA? Why would the installers not fitted this?
Why wouldn't it be ? Note that the supply end RCD is there only to protect the cable to the CU - not to protect anything downstream. But definitely one of those cases where there's an argument for a non-metallic CU as you then avoid the tiny risk that someone is touching the CU case during the 100ms the upstream RCD takes to clear a fault.
You then use standard 30mA RCD protection on the outgoing circuits from the CU.
Having a 30mA, non-time-delayed RCD in the separate shed is non-compliant in that there is zero attemp to segregate circuits and avoid the hazards from everything going off at once.
That said, I assume the inverter has limited capacity so there is always scope for that tripping out on overload. Which introduces another question - do you have asufficiently high PFC to trip MCBs in the CU ?
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