Pv on rcd

[davesparks]

If a fault on the PV cable occurs then the RCD at the inverter operates, thus causing loss of power and inverter shuting down.

But the faulty cable is also connected to the grid supply, so yes the rcd at the inverter will disconnect the inverter but it will not clear the fault

 

[GEOFF S]

But the faulty cable is also connected to the grid supply, so yes the rcd at the inverter will disconnect the inverter but it will not clear the fault

Hi

But the cable will have protection at the other end as i mentioned, 712.434.1, so with the inverter isolated via the RCD, is it any different to any other circuit not needing rcd protection.

Now if we bury the cable less 50mm, and used standard cable, then yes two rcds at each end would be required, but this can be enginered out using swa etc.

Cheers

Cheers

 

[davesparks]

Hi

But the cable will have protection at the other end as i mentioned, 712.434.1, so with the inverter isolated via the RCD, is it any different to any other circuit not needing rcd protection.

Now if we bury the cable less 50mm, and used standard cable, then yes two rcds at each end would be required, but this can be enginered out using swa etc.

Cheers

Cheers

That was the whole point of the damned discussion, what can be done if the PV cable needs rcd protection!
That is exactly the situation I have been saying you would need two RCDs for.

 

[SibertSolar]

Fascinating...

 

[davesparks]

Fascinating...

It's the first really interesting discussion I've seen on here in ages!

 

[Leesparkykent]

I think the easiest way would be to use a reference method that doesn't require additional protection by means of an RCD ;-)

 

[davesparks]

I think the easiest way would be to use a reference method that doesn't require additional protection by means of an RCD ;-)

Yes, I completely agree, but the discussion has been interesting all the same. It's got me thinking about something properly for the first time in ages.

 

[Leesparkykent]

Yes, I completely agree, but the discussion has been interesting all the same. It's got me thinking about something properly for the first time in ages.

Its defiantly something I want to get to the bottom of as no doubt eventually will end up coming across the situation when surveying/doing a board change.

 

[Energetic]

How about approaching this from the other direction, are there any 3.6kW inverters that are compatible with a 30mA RCD? I think Power One used to do a HF transformered version, at a cost. Was there ever an SMA 3600HF? I once emailed them asking for one...

Seems a big hole in the EU market if there isn't one given the ever increasing requirements for RCD protection.

 

[CBR600]

How about approaching this from the other direction, are there any 3.6kW inverters that are compatible with a 30mA RCD? I think Power One used to do a HF transformered version, at a cost. Was there ever an SMA 3600HF? I once emailed them asking for one...

Ginlong Solis state max 20ma DC injection. We use them on 30ma RCD's without tripping issues.

 

[SibertSolar]

First thing, I'll reiterate what several others have already said - for transformerless inverters, always try to "design-out" or mitigate the requirement for an RCD in the first place.

All transformerless inverters will have a degree of inherent leakage current. I think that G83/2 requires that the tested/reported leakage current is no greater than 0.25% of the max AC current. For a 16A/3.68kW (G83 limit) inverter, this equates to 40mA, most decent units will rarely leak more than 5-10mA.

A 30mA RCD can trip from an AC leakage current value greater than 15.1mA (I stand to be corrected on that exact figure though).

As has been stated already, a TypeAC RCD's trip coil will saturate (and never trip under AC ground fault conditions) if any component of the leakage current is pure or pulsed DC. A TypeA RCD will still operate under AC ground fault conditions even if a pulsed DC component of the leakage current is present. It's trip coil will saturate if any pure DC component is present. However, if the amplitude of the pulsed DC leakage current is greater than 6mA then the Type-A RCD cannot be guaranted to operate within its certified scope of operation - this is an important point (can you or the inverter manufacturer guarantee that the 6mA limit will never be exceeded?). A TypeB RCD will operate under AC ground-fault conditions without being compromised by either pulsed or pure DC components of the leakage current.

Hypothetical (but also very real) scenario - TL inverter, requirement for RCD protection under BS 7671 (for whatever reason), TypeAC RCD installed. RCD never "nuisance" trips, just sits there looking pretty. Subsequent AC ground fault occurs (for whatever reason) but the RCD still doesn't trip. Too late to realise that the reason it never "nuisance tripped" is that the trip coil was saturated with DC and became about as useful as a chocolate fireguard. In that scenario, the end customer has been sold/supplied with a circuit protective device that will not operate as intended. It is worse than not fitting an RCD in the first place.

If there is no simple separation (ie, a galvanic transformer) between the DC and AC circuitry within the inverter, and an RCD is required on the AC output of the inverter (due to consideration of BS 7671) then a TypeB RCD is the required solution to provide ADS/ground-fault protection. However, many TL inverter manufacturers certify their product to VDE 100-712 in that it is, by design, unable to inject DC to ground. If the inverter manufacturer states this, then they typically go on to say that if an RCD is required then it need not be a TypeB (ie, a TypeA is ok to use).

There are some transformered inverters still around, although not many. The difference it makes is that, if an RCD is required on the AC circuit, then the inverter alone will not cause nuisance tripping of the RCD, and there is no scenario where a DC leakage current component might compromise the normal function of such an RCD, regardless of what type of RCD is fitted.

Completely agree with the various previous comments/advice about never sharing an existing RCD - a big no-no. "Nuisance tripping" and DC impact on RCD selection/function are two completely different considerations.

Just my tuppence...

 

[davesparks]

How about approaching this from the other direction, are there any 3.6kW inverters that are compatible with a 30mA RCD? I think Power One used to do a HF transformered version, at a cost. Was there ever an SMA 3600HF? I once emailed them asking for one...

Ginlong Solis state max 20ma DC injection. We use them on 30ma RCD's without tripping issues.

And that 20mA DC injection will saturate the RCD coil and prevent it from tripping in any situation if it is not a type B RCD.
So the most likely reason that you have experienced no RCD issues is that the inverter is actively preventing it from tripping, even under a >30mA AC fault.

 

[SibertSolar]

Exactly Davesparks....although, CBR600 didn't explicitly state that it was a TypeAC RCD fitted.....benefit of the doubt and all that...

 

[Deleted member 26818]

The literature for the ABB Trio inverters, state that they do not continuously inject fault current, so type B RCDs are not required.

 

[Gavin A]

All transformerless inverters will have a degree of inherent leakage current. I think that G83/2 requires that the tested/reported leakage current is no greater than 0.25% of the max AC current. For a 16A/3.68kW (G83 limit) inverter, this equates to 40mA, most decent units will rarely leak more than 5-10mA.

dunno like, I seem to quite regularly see 12-15mA leakage on the SMA 3600TLs particularly in winter, though I'm not entirely clear if this is leakage that would show on the AC side or DC side leakage via capacitance to earth, it's always much worse in cold damp conditions so probably the latter.

 

[davesparks]

The literature for the ABB Trio inverters, state that they do not continuously inject fault current, so type B RCDs are not required.

To my suspicious mind that suggests that they do/can inject non-continuous or occasional DC fault currents

 

[Deleted member 26818]

They may well do.
The literature recommends providing RCD protection for the output, and states the differential protection required is A/AC.