RCD - sensitive to L/N swapped?

[matthewriches]

The Multiplus is a clever box of tricks, very good bits of kit. I use them regularly on cruising boats and work boats.

I know how they operate, but what is being portrayed by Vic's comment is that the unit is wired as a series connection.

Whilst the diagram posted may look to be series wired, look carefully and you'll see what it isn't.

The device is inline of the shorepower, yes, but not in series.... You'll actually see that if you input dirty AC at 246V for example, the unit outputs a clean stable 230V plus or minus a few volts.

You need to appreciate the the Victron Multiplus is wired exactly as Vic describes. It synchronises itself to the incoming AC phase so that its output is the same so when needed it takes extra power from the battery - eg. if the shore power can only supply 16 amps and the boat demands 20 amps.

 

[sailinglegend420]

....The device is inline of the shorepower, yes, but not in series.... .

This is only your opinion. I see it as just pointless semantics which only ruins threads.

Put simply the Multiplus is in Series with the shore power as opposed to in Parallel.

Most Inverters are wired in parallel with shore power which is why this is a difficult concept for many who don't know the Multiplus.

 

[lw395]

The aim was to explain, or at least help you understand, why sailinglegend described it as "wired in series", but failed obviously

SHOREPOWER SUPPLY - - - - MULTIPLUS - - - - BOAT AC SYSTEM​

The three items are "in series" , like trucks in a railway train, one after the other

Electrical or electronic components are said to be "in series " when a common current flows through them.
When the Multiplus is operating in shorepower mode it could be argued that a common current flows in the shorepower supply, the Multplus and the boat AC circuit.

I would describe that as a 'cascade' connection, not series.

The Multiplus has a relay in it to ground its neutral output when its mains input is isolated. I think this is programmable, so possibly it is mis-programmed? Or stuck shut. I would say 'broken', but I'd mean 'broken in a permanently 'made' kind of way.
Better to use the correct technical term 'buggered'?

A 'common mode current' in the shore supply would normally mean, in the electronics/EMC industry, a current flowing in the same direction in L and N conductors, as in left to right in both not clockwise/anticlockwise, i.e. exactly the thing that trips a RCD. So this is another unhelpful mis-use of a defined term. I'm not just being pedantic or wishing to pick on anyone, just trying to avoid us all talking at cross purposes.

 

[sailinglegend420]

I would describe that as a 'cascade' connection, not series....

To try and stop the bull.hit that is spoiling this thread I have e-mailed Victron and described my reverse polarity light illuminating with just a 5v Earth/Neutral voltage that I get in old marinas. I hope people aren't still calling this a 'fault'?

I've also asked them what is causing the tripping at 8v or above that now seems to be the thread of this thread.

It doesn't matter what we call the way the Multiplus works, or is wired, it's the principle of why an RCD should trip at 8v not 5v.

 

[lw395]

The principle of an RCD tripping when the neutral is at 8V is that there is a path to ground, (or some other route back to the substation perhaps) which probably should not be there.

The Victron manual seems fairly explicit in its diagram showing N and L disconnected, so ISTM they must be anticipating a potential difference.

Just how much PD you accept between N and E before you call it a 'fault' might be a matter of opinion or various standards. Is there 5v drop on the L too?
Not knowing the exact details of the polarity indicator in question, it's hard to say what to read into it showing a fault, but taken incombination with spurious RCD tripping, I'd be investigating further.
Is there a galvanic isolator and is it showing volts across it?

It might be useful to check the impedance of your wiring.

 

[Lon nan Gruagach]

A few points that have arisen:
Having had a while to think about mains powered LED indicators. There are 2 common power supplies for deriving low power, low voltage from mains. Cheapest (and dirtiest) is a capacitor divider, similar in principal to a resistor divider with 3 significant differences. First, they only work on a.c. Second is that there must be a constant current load otherwise the out put will rise to the input voltage. Finally (and this is where they are really cool [pun intended]) they are very efficient, unlike resistor dividers the "unwanted"voltage is not turned into heat, but returned to the supply on the next 1/4cycle(ish). The other circuit is a buck converter (cheap, very simplistic switched mode power supply).
As a replacement for a neon mains indicator, the latter would be prone, not only glowing dimly at low voltages, but also potentially drawing the full output current from a low voltage input.
As such the latter (buck converter type) may not perform as you might want, and therefore be inappropriate.

Then theres the nomenclature for series vs parallel connection. While parallel might be unambiguous for devices with more than 2 terminals, series is not. In the example above series might mean: supply L -> inverter N[in], inverter L[out] -> device L, device N -> supply N (a bizarre and very unlikely voltage boost set up) or it may be interpreted as per the diagram (far more sensible, but not definitive). Probably best reserve "series" for 2 pin devices. Terms like inline and cascade or pass-through suitable for more than 2 pins...

edit add:

Ohh, and the other thing. Capacitative mains transient suppressors triggering RCDs when the neutral is disconnected (either by wiring fault or reversed polarity supply). Usually these are 3 equal capacitors wired in delta configuration between L, E and N. As far as the RCD is concerned they could be modelled as a single capacitor between the L, N mid point and E. If you disconnect the neutral, that modelled capacitor is effectively between L and E. If such a capacitor is sufficient to generate a fault current, it follows that 2 such devices connected to a correct supply will also trip the RCD. Probably why they arent used so much in modern(ish) domestic equipment.