RCBOs
- Thread starter hard-work
- Start date
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Live is always disconnected, the Neutral is only disconnected if the RCBO is a Two Pole device.
The Neutral has to pass through the RCBO in order for the RCBO to compare current on the Neutral with current on the Live and then trip if they are more than 30 mA different due to a fault somewhere on the circuit supplied by the RCBO
I suppose it would be, if one could afford it and could find double-pole RCBOs for the CU in question. Although I think there are some exception, I think that most DP ones are 'double width' at present - which could obviously lead to the need for a pretty 'wide' CU.
With single-pole RCBOs, a neutral-to-earth fault on one circuit will (if large enough in magnitude) lead to the circuit's RCBO tripping but, because that neutral remains connected to the neutrals of other circuits, under some circumstances other RCBOs could also trip.
Kind Regards, John
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On the front of the Rcbo theres usually a schematic wiring diagram, it will as Bernard says likely show it to be Single pole
Not necessarily, there are some obscure faults where disconnecting Live and Neutral is not the best option.
Take the case of the Neutral of circuit A on a double pole RCBO (A) coming into resistive contact with a LIVE from a ciruit (B) that is neither RCBO nor RCD protected.
The RCBO (A) will open but the over current protection MCB on circuit (B) will not operate if the resistive contact does not pass enough current to trip the MCB on (B) Circuit B remains Live
The Neutral of circuit (A) will be pulled up to Live via the resistive contact to the Live of circuit (B)
Very unlikely ( I think ) to occur in a domestic installation.
I can't argue with any of that, but I think that you are (not for the first time
) rather 'scraping the barrel'!! On balance, I think hard-work was right in saying that, if it is practicable and affordable, the advantages of having DP RCBOs would outweigh obscure theoretical 'downsides' such as you describe.
Kind Regards, John
Sometimes it is essential to "scrap the barrel" and then make a decision about whether or not provide for the scrapingsI think that you are (not for the first time
I just looked. A few companies do make DP RCBOs. Not common but readily available. You would probably need a vertical CU, as you see in the USA. Personally I cannot see why RCBOs are not fitted as standard by most sparks. One or two RCDs is just plain naff. Whole banks of circuits can be tripped out which are fault free.
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Twin RCD boards are cheaper, and for many people that is the only consideration.
And yet that 'naff' design causes zero problems for the vast majority of users. You're trying to fix a problem which doesn't exist.
Until the problem occurs of course. Then you have major appliances out because of say a small fault on a lighting circuit. You sound like someone who castigated RCDs when introduced, when many said, "we had no problems so why introduce them?"
You know what? Most safety and security systems will never be used. But when they are, they make a difference. RCBOs are a form of insurance, as are security video cameras.
Faulse economy. Installing all CUs with RCBO is not a great amount of money.
The problem with all-RCD boards is that you don't know if a trip was caused by overcurrent or earth leakage (or even spikes on the supply).
No he doesn't.
Electrical installations are a compromise.
An occurrence can be thought up where doing the opposite would have been beneficial.
I can think of an example where earthing appliances may be dangerous .
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