Bi directional RCBOs

[littlespark]

Fitted a new design Proteus board a few weeks ago, and one of there improvements is that all RCBOs are now biderectional, as well as SPD with built in fuse, no need for upfront MCB….

But is the bidirectional RCBO the way everyone is going now?

I understand for specific circuits, ie PV, battery storage and vehicle based battery storage… but what about regular circuits that are only downstream from the consumer unit?


Say you have a lighting circuit on a 6A RCBO and something develops a fault… Could this fault affect any other bidirectional RCBO as it would be detected coming from the busbar side?

Depending how sensitive the 6A is, that it doesn’t trip first.

 

[mainline]

Say you have a lighting circuit on a 6A RCBO and something develops a fault… Could this fault affect any other bidirectional RCBO as it would be detected coming from the busbar side?

What sort of fault are you thinking of, that would be on the bus bar.

 

[littlespark]

Any fault.... on another circuit might (if its own rcbo doesnt trip in time) will come through to the busbar, and may trip another, being sensed on the supply side rather than the load

 

[Pretty Mouth]

Say you have a lighting circuit on a 6A RCBO and something develops a fault… Could this fault affect any other bidirectional RCBO as it would be detected coming from the busbar side?

Won't pretend I'm an expert on this, as I don't do EV chargers, PV etc, so the following is really just guesswork. I'd have thought that if a circuit supplies power to the busbar via an RCD (e.g. solar PV via a bi-directional RCBO), then any fault to earth 'downstream' would cause said RCD to trip (by 'downstream', I mean the busbar and all other attached circuits).

 

[littlespark]

Let’s think of it another way.

Your PV during the day is generating power, sending it through the RCBO onto the busbar, and out onto other circuits.
As such, there is nothing coming from the grid, but may be going out to the grid….

In simple terms, you now have 2 rcbo’s “in series” and very close together. Either could trip if there’s a fault downstream on the non PV circuit.
This is repeated on every circuit.

If it’s the PV rcbo that is a little more sensitive, it will trip first, making you think the fault is there.


Perhaps the PV RCBO should be higher than 30mA, or time delayed. That way you would know which circuit had the fault as it would trip first.

Of course, we can’t do that, because regs would not allow.

 

[richy3333]

Morning.
I think that Proteus RCBO's have always been bidirectional - they just haven't shouted about it. Mention was made in a renewables podcast with them.

I think - and I'm happy to be corrected but if there is PV (not sure about and EV) if the PV is feeding back through into the CU any RCBO's could be affected as the PV will go through its own RCBO and could then pass through any other RCBO protection in the CU.

Under fault conditions of the PV circuit then the PV RCBO would trip (have seen this but not my installation!).

 

[Pretty Mouth]

If it’s the PV rcbo that is a little more sensitive, it will trip first, making you think the fault is there.

After the PV RCBO had tripped, isolating the PV supply to the busbar, the grid supply would take over wouldn't it? So I'd expect the RCBO protecting the faulty circuit to then trip also.

 

[littlespark]

I’m just thinking out loud really….

Ok, what about island mode, when the power is being taken from battery storage, and there is no grid?

I suppose, to us, it doesn’t matter. We might be called to find a fault, and normal testing would discover which circuit it was on.
But was just mulling it over one day in my head.