Fitting a 100ma RCD on Solar PV to solve nuisance tripping.

S

South Spark

-
A solar PV system keeps tripping the 30ma B curve RCD (at dawn).

The system is a TNC-S and the cabling to the inverter is surface mounted SWA.

Is there any reason to not swap the 30ma main switch out for a 100ma ?
 
netblindpaul said:
He probably means a B type RCD.
So it’s only tripping when the DC cables polarise at the start of generation?
Click to expand...

Seems so from customer reports. He's been resetting the RCD and the system is working fine after that. Of course dawn is around 5.15 at the moment so he's missing out on a lot of FIT.
 
Would you know if the Sunny Boy is:

a. transformerless?
b. is disconnected from the SWA cable until PV generation starts?

One thing to look at (from netblindpaul#8) is how tightly have the dc cables been clamped around their insulation to any metalwork.

If there is more than one Sunny Boy (I expect so) can you disconnect one in turn and leave the others on-line to see if the problems goes away?
 
I could be wrong but isn't 100ma the minimum recommended assuming it is not required for additional protection.
 
From my research it seems many Sunny Boy inverters are transformerless which means that there is usually no galvanic isolation between the PV dc input and ac output. If you tell me the model number of the inverter I will delve further.

I thought of an experiment you could do which might determine whether the leakage current waveform is ac or dc. At the moment the RCD is type B which can detect the waveforms ac 50Hz, ac 50Hz pulsed, Smooth dc, and ac greater than 50Hz into kHz region - see page 7/21 of:

http://www.doepke.co.uk/download/Techpub-16

The type AC RCD commonly used in Consumer Units can only detect ac 50Hz - it is blind to ac 50Hz pulsed, Smooth dc, and ac greater than 50Hz into kHz region.

What you could try then is inserting a type AC 30mA RCD upstream of the current type B and then observing what happens every morning to the type AC one -does it or does it not trip?

Just an idea for your consideration which might cast a bit more light on the problem by giving information on the waveform of the leakage current (as well as my # 15).
 
Re #24: What you could try then is inserting a type AC 30mA RCD upstream of the current type B and then observing what happens every morning to the type AC one -does it or does it not trip?

I am not suggesting removing the Type B.
 
Answer yourself - I will be interested to read your reasoning.

I have provided a reference which explains why it is right an RCD type B is intalled because there is no dc - ac side galvanic isolation. It may well be the manufacturer of the in-use Sunny Boy inverter says one is not required - one for the OP to clarify - though for me the presence of the type B RCD indicates that the installer has read and abided by the manufacturer's instructions.
 
marconi said:
Answer yourself - I will be interested to read your reasoning.

I have provided a reference which explains why it is right an RCD type B is intalled because there is no dc - ac side galvanic isolation. It may well be the manufacturer of the in-use Sunny Boy inverter says one is not required - one for the OP to clarify - though for me the presence of the type B RCD indicates that the installer has read and abided by the manufacturer's instructions.
Click to expand...
The reference you have provided indicates that where required, B type RCDs should be used. i.e. circuits of locations containing baths or showers, socket-outlets or cables concealed in walls.
There is nothing there stating that the supply to or the output from the inverter requires RCD protection.
The OP says that the RCD protects the circuit to the inverter and that the circuit is wired in SWA.
 
At page 12/20 para (iv) of:

https://www.----------------------------/mediafile/100117576/Best-Practice-Guide-3.pdf

(iv) Where a microgenerator having a d.c. source does not incorporate the equivalent of a transformer providing at least simple separation between the d.c. and a.c. sides, an RCD installed for fault protection by automatic disconnection of supply or for additional protection (I∆n <_ 30 mA) must be of a type that will operate as intended in the presence of d.c. components in the residual current. (This does not apply where it has been established – such as from a specific written statement given by the inverter manufacturer – that the inverter provides galvanic isolation between the d.c. and a.c. sides that prevents it from feeding d.c. current into the electrical installation.) Note. A Type AC RCD will not fulfil the above requirement. Depending on the level and form of d.c. components, an RCD (where required) will need to be of Type A to BS EN 61008 or BS EN 61009, Type B to IEC 62423, or Type F to IEC 62423. However, in the case of a PV power supply installation, Regulation 712.411.3.2.1.2 of BS 7671 stipulates that the RCD (where required) shall be of Type B.
 
marconi said:
At page 12/20 para (iv) of:

https://www.----------------------------/mediafile/100117576/Best-Practice-Guide-3.pdf

(iv) Where a microgenerator having a d.c. source does not incorporate the equivalent of a transformer providing at least simple separation between the d.c. and a.c. sides, an RCD installed for fault protection by automatic disconnection of supply or for additional protection (I∆n <_ 30 mA) must be of a type that will operate as intended in the presence of d.c. components in the residual current. (This does not apply where it has been established – such as from a specific written statement given by the inverter manufacturer – that the inverter provides galvanic isolation between the d.c. and a.c. sides that prevents it from feeding d.c. current into the electrical installation.) Note. A Type AC RCD will not fulfil the above requirement. Depending on the level and form of d.c. components, an RCD (where required) will need to be of Type A to BS EN 61008 or BS EN 61009, Type B to IEC 62423, or Type F to IEC 62423. However, in the case of a PV power supply installation, Regulation 712.411.3.2.1.2 of BS 7671 stipulates that the RCD (where required) shall be of Type B.
Click to expand...
Yep, as I said.
 
Please provide an argument with reasons using your knowledge of electrical engineering, the wiring regulations, awareness of the law for the safe use of electricity and appreciation of the installation in question.
 
marconi said:
Please provide an argument with reasons using your knowledge of electrical engineering, the wiring regulations, awareness of the law for the safe use of electricity and appreciation of the installation in question.
Click to expand...
I’ve asked you why the RCD can’t be removed.
All you’ve done is provided a link to a source which states that any RCD in the installation will have to be a B type.
Something that I am well aware of.
You have not given any reason as to why it can’t be removed.
Now (though you’ve not answered my question), you want me to explain in depth why an RCD is not required.
The simple fact of the matter, is that from the information provided, the RCD is unnecessary, it’s not required as far as BS7671 is concerned and at the moment it is causing a nuisance.

Now your suggestion, is to install an incorrect RCD to see if that will or will not also trip.
So if it trips, what then?
If it doesn’t trip, what then?
Who pays for the installation of this unnecessary and incorrect RCD?
Most of these inverters have inbuilt RCD protection and they also show error codes if there’s a fault.
Having an external RCD, is probably preventing the inverter from logging any fault.
 
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Fitting a 100ma RCD on Solar PV to solve nuisance tripping.
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