RCBO: Using when no neutral is present

[kevlarster]

Can an RCBO (Residual Current Detection Circuit Breaker) be used when there is no neutral present? All of the big boys (AB, ABB, Schneider) show connection diagrams that monitor leakage current from Line to Neutral.

I have a 220V 3-phase Delta supply without neutral and am required to use an RCBO (ELCB, combo CB & Leakage detect, etc). I am wondering if the device will function in the manner when it is monitoring between Line and ground. I actually doubt it as the device is intended to measure compare the current in (sum of the Lines) and the current out (return through neutral). Any thoughts or experience that you would like to share?

 

[GoldDigger]

If a breaker is due signed to compare the net current through the three delta conductors to the neutral current (all as vectors), then as a special case it can also compare the net delta current to zero (the neutral current).
In both cases any current not flowing through the breaker will have to travel over an unrelated neutral or through ground/EGC.
If the breaker is simply measuring net delta current in the first place, with current in either neutral or ground indicating a fault, then it will still do that job with no neutral connected.

 

[Jraef]

Before you go too far with this, what is this for? The use of the term "RCBO" means nothing in North America, so it is entirely likely that the machine was designed for use in an IEC country. If that is the case, they would NOT HAVE a Delta power system, so they would not consider the effects of having one. An RCBO is just an RCD (Residual Current Device) + a thermal breaker designed to IEC standards. But because IEC systems would never be Delta, always Y, then it was designed to have the Neutral running through it. Technically, the device could function without running the Neutral through it, but ONLY if the use down stream were completely balanced. So if your machine consists of only 3 phase balanced loads, no problem. But 9 times out of 10, they want an RCD or RCBO device ahead of it because it is a packaged SYSTEM, including some 3 phase and some single phase loads. If that's the case, you re ALREADY in trouble feeding it from a Delta source, because you will not have single phase load capabilities, as an IEC designer would envision them anyway. For them, "230V" means they were expecting a 400V Wye system that is 400V L-L, 230V L-N. You will be feeding it 220V L-L, no N, but inside, it is not evenly distributed (because they would not have had to) and your RCD, without the Neutral to observe, will trip right away.

The solution may require you to use a Delta-Wye transformer ahead of this machine, 220V 3 phase Delta to 400Y230V, then the RCBO on the Y side feed to the machine.