Discuss Type AC RCD with solar inverter in the Electrical Forum area at ElectriciansForums.net

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pc1966

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A friend of mine asked me to look at here PV system as she is not getting any power (and thus money) from it. First real issue is the Aurora inverter has a E031 fault which I suspect is burnt out relays, so I can probably fix that with a big iron and a couple of new relays (at last for another few years).

Other problem she reports is the RCD feeding it frequently trips. It is a 30mA type AC RCD and unfortunately I could not measure the real operating leakage, etc, as the inverter is borked, so I only saw around 0.4mA in its standby/testing IR mode. DC IR results look sane, over 200M for cable and around 10M with the inverter's AC isolator closed.

It is fed via SWA but nobody has bothered to earth the armour deliberately, though far end is in contact with the metal enclosure - sort of!

So I was wondering why it had a 30mA RCD, and on looking at the manual it actually says:

In accordance with article 712.413.1.1.1.2 of Section 712 of IEC Standard 64-8/7, we hereby declare that, because of their construction, ABB inverters do not inject ground fault direct currents.

The use of an AC type circuit breaker with differential thermal magnetic protection with tripping current of 300 mA is advisable so as to prevent false tripping, due to the normal capacitive leakage current of photovoltaic modules.

On the case of systems consisting of multiple inverters connected to a single switch with differential protection, it is recommended to install a device that allows the adjustment of the trip value and timing of intervention.


So my thoughts are to change the 30mA unit to a 300mA delay version and type AC are fairly cheap (as in £60-ish), and to add some SPD as well, so hopefully no more nuisance trips. Now the latest regs say not to use a type AC if there is any risk of DC, but here:
  • It is not even obvious if RCD is needed, given the SWA cable and fixed connections.
  • The manufacturer's instructions explicitly say type AC is OK
Any thoughts?

TL;DR use the depreciated type AC if manufacturer say OK?
 
Yes it is a burnt out relay for sure I had 2 go on a customer after 10years of use, they can be fixed there are a couple of good vids on YouTube!
Seeing as it's fed in SWA then I can't personally see an issue with changing the RCD to 300ma AC, following MI is fine in my book as you have it there in writing so have a defense if something happens.
Although a type A may be better nowadays just in case and probably at the time that inverter was manufactured were either prohibitively expensive or not common!
my customer opted for a new inverters in the end as they had a guarantee for 5 years and were a reasonable price.
Sy
 
Right now we're in the time window when you could proceed with type AC anyway of course.
I can't see why not to use a type A though - it seems to say the DC ground leakage isn't an issue in the above blurb?
I assume the RCD in question is only protecting the PV circuit?
 
Right now we're in the time window when you could proceed with type AC anyway of course.
I can't see why not to use a type A though - it seems to say the DC ground leakage isn't an issue in the above blurb?
Cost really, I can get type AC delay from CEF for around £60 and it matches current install mini-CU, the type A delay ones are a bit more to a lot more.
I assume the RCD in question is only protecting the PV circuit?
Yes, only the PV circuit.

Originally they had the 2.5mm T&E from CU to meter/mini-CU (about 1m) directly off the busbar of the old Wylex board and in to the mini-CU where it has a 20A MCB for OCPD! But I really did not like that so simple change was is another 20A plug-in MCB in the Wylex board feeding it so at least the T&E is safe from serious fire risk.

Yes, I really ought not to be adding to such a board but it seemed like the least-worst option!
 
apologies for hijacking this thread but the forum will not allow me to post a thread. no option offered. my knowledge of solar is that it works in sunlight and not when it's dark. mate has asked me what panels he should get for a canal boat, for battery charging. my first thoughts are to get the Ah rating of his batteries as a starter for 10. any help appreciated.
 
Here are some photos of the burned out Zettler relay:
Type AC RCD with solar inverter relay-1 - EletriciansForums.net

Type AC RCD with solar inverter relay-2 - EletriciansForums.net

The contacts look perfect!

What is burned out is the pin from the steel magnetic frame that the moving contact uses as the path to the PCB. Yup, that is a 30A relay using a 1mm^2 steel pin, so equivalent to 0.125mm^2 or so of copper!!!
 
Update: I picked up a 100mA delay Type A RCD cheaply so that is now in use so original question somewhat academic.

Part of my reasoning was it usually worked on 30mA RCD so 100mA and delay should be plenty of margin, and in the event of direct contact someone probably has a slightly more sporting chance of survival with 100mA trip than 300mA (ramp tested 80mA, trip at In = 271ms).

Not much sun to test it once inverter repaired, etc, (Scotland, 6pm, overcast, so about 40W generated) but when running it was leaking only 2.4mA.

As mentioned earlier, the original installers had not earthed the 3C 4mm SWA armour 'deliberately'. It was sort of connected at the load end via the 3rd core CPC to the inverter, to the metal outdoor box, and metal box happened to be making contact with the gland (but no banjo, etc). So I also used some Earthing nuts at both ends and added CPCs so the inverter now has "high integrity" earthing as well with two separately screwed CPC leads to the CU earth bar.
 
Also to add, the inverter's PCB hole where the burnt out replay pin came from was trashed - the through plating long gone. So for the new relay I wrapped a strand of copper wire (just one of the strand off 1.5mm conduit wire) round the pin and soldered it, then drilled the PCB to about 3mm hole for the "whipped" pin to go through, and then lots of solder on top to try and carry the heat away.

With any luck it will last a few years more!

Type AC RCD with solar inverter soldered-relay-pin - EletriciansForums.net
 

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