What's tripping my RCD?

[Solarexploits]

So I've recently installed a new Powland off grid inverter. It has the ability to charge the 48V lead acid battery bank at 48v which i can set to use overnight on the off peak tariff. I've got it all basically setup - see pic & everything works fine, panels charge batteries, inverter works perfectly, but when I connect the inverter to the mains (not charging, just connect the supply in via a 3 pin plug) recognises the iinput to the inverter, but after just a few seconds throws the RCD out on the supply from the inverter to the house circuits. 

I already have suspicions as to where the fault lies, but am no expert when it comes to exactly how the RCD recognises a fault, hoping someone here with more knowledge can help

 

If you look at the setup pic you will see high on the wall I have a switch which can switch feeds either from the inverter or from the mains to certain circuits, hence when batts are running low, or no sun, I can switch some of the drain off from the inverter. Within the switch the earth from the inverter & the household mains earth are connected. I'm intending to fiot an earth rod, but not yet done & at present rely on the incoming mains earth - I'm guessing the fault lies here, but what do I do to correct it?

 

I have seen an image from a FB solar group - see second image - which suggests the neutral & earth from inverter should be connected (same way incoming mains neutral has direct connection to earth), is that likely to fix the issue, but if earth & neutral should be connected that way, why would that not already be done within the inverter?

 

Any help suggestions much appreciated b4 I start disconnecting/connecting things until it's fixed - having the overnight charge facility would be a massive boost for the batteries 

[TonyT]

The RCD and mcb are wired incorrectly and the earth shouldn’t be tied at the neutral on the RCD

best get a sparky in!

[ProDave]

Don't connect earth like that, you will probably upset most of the house circuits and they will be tripping RCD's as you will have created another parallel path for the neutral.

 

Try disconnecting the battery input from the inverter, and connect JUST the mains of the inverter. does that still trip the RCD?

[Radian]

1 hour ago, Solarexploits said:

I have seen an image from a FB solar group - see second image - which suggests the neutral & earth from inverter should be connected (same way incoming mains neutral has direct connection to earth), is that likely to fix the issue, but if earth & neutral should be connected that way, why would that not already be done within the inverter?

That looks like a schematic for a fully off-grid PV system to me. Perhaps you should draw a schematic for your setup.

[Solarexploits]

3 hours ago, TonyT said:

The RCD and mcb are wired incorrectly and the earth shouldn’t be tied at the neutral on the RCD

best get a sparky in!

Don't think you've understood the post. The 2nd image was for reference - that's not how my system is wired

[ProDave]

6 minutes ago, Solarexploits said:

Don't think you've understood the post. The 2nd image was for reference - that's not how my system is wired

Post a schematic of how it is wired?

[Solarexploits]

3 hours ago, ProDave said:

Don't connect earth like that, you will probably upset most of the house circuits and they will be tripping RCD's as you will have created another parallel path for the neutral.

 

Try disconnecting the battery input from the inverter, and connect JUST the mains of the inverter. does that still trip the RCD?

 

It seemed bizarre to me too - until I thought about how household wiring is connected, there are various different types of mains earth setups & I certainly don't understand them all, I'm not a sparky, but where my mains enters the house the main earth terminal is connected directly to the negative at the main fuses, that negative line is also tied to earth at various points along its length from the sub station to your home

 

If I disconnect the battery then the inverter will be off, I'd need to recheck instructions, but IIRC it tells you to connect battery first b4 mains hookup, in hindsight I should have checked the system worked with mains b4 adding the switch that switches some outputs from inverter to mains - wonderful thing hindsight .......

[ProDave]

1 minute ago, Solarexploits said:

If I disconnect the battery then the inverter will be off, I'd need to recheck instructions, but IIRC it tells you to connect battery first b4 mains hookup, in hindsight I should have checked the system worked with mains b4 adding the switch that switches some outputs from inverter to mains - wonderful thing hindsight .......

In that case disconnect (both terminals) whatever is charging the battery so you have JUST battery and inverter and let us know if that trips.

 

If it is a transformerless inverter then any earth leakage in the DC side will trip the rcd on the ac side.

[Solarexploits]

48 minutes ago, ProDave said:

Post a schematic of how it is wired?

 

I've attached a dreadful schematic below, unfortunately had no colours available to make it more obvious, must buy myself a new set of crayons!

 

However in drawing it I think I may have answered my own Q. What I've not put onto the schematic as it was simply getting too crowded, is that the switch from Inverter to mains switches ONLY the live cable, the neutral & earth cables from the inverter to the main consumer unit are connected earth to earth, neutral to neutral at that point. Now, presumably I should be able to connect the 2 earths, as they are already connected at the inverter, but I'm guessing the problem is that the 2  negatives, one from main consumer unit & one from the inverter consumer unit need to be kept separate, in other words I need a double pole switch?

 

 

[ProDave]

30 minutes ago, Solarexploits said:

but I'm guessing the problem is that the 2  negatives, one from main consumer unit & one from the inverter consumer unit need to be kept separate, in other words I need a double pole switch?

It's neutral not negative.

 

Yes you do need a proper 2 pole changeover switch, that will be your problem.

[Solarexploits]

2 hours ago, ProDave said:

It's neutral not negative.

 

Yes you do need a proper 2 pole changeover switch, that will be your problem.

 

Sorry, I know they are neutrals, I'm more used to DC & think of everything as +ve & -ve.

 

So to confirm that's the cause I just need to disconnect the connection from the consumer unit & retest? 

[Temp]

8 hours ago, Solarexploits said:

already have suspicions as to where the fault lies, but am no expert when it comes to exactly how the RCD recognises a fault, hoping someone here with more knowledge can help

 

RCD work by comparing the Live and Neutral currents. If there is a difference they trip because that implies a "leak" somewhere. Eg Where did the electricity go if it didn't return via the neutral?  You could use a similar idea to detect central heating leaks. If the boiler flow and return aren't the same there must be a leak.

 

A common problem occurs when two circuits have their neutrals connected together so the current from the live of one RCD can return to the neutral of another. Sometimes the problem only shows up when a high current load is switched on or off.

 

 

 

[Solarexploits]

Just for info, I disconnected the neutral from the consumer unit, everything now works as it should - thanks for the assistance, sometimes just talking things thro' & thinking about them halps a lot - saved me time in guessing what was likley to be wrong 7 hot the nail on the head first time, just need a double pole switch now!