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

Re#42 - you added these remarks by edit:

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.

after I read your first offering which terminated 'Who pays for the installation of this unnecessary and incorrect RCD?'

Spinlondon - what is up with you? If you don't want to read anything from me select 'ignore'. If you do want to read my stuff and comment on it, then please read it more carefully and quote me correctly including any caveats and provisos I include.

marconi said:

The OP at #12 says the PV installation is on an isolated farm. This being the case is there not a requirement for an RCD with max In 300mA for fire protection; installed at the start of the sub-main to the PV's DB even though SWA is used for the cable run between the inverter and its DB?
For others to clarify.

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That would depend on whether the Farm house is electrically connected to other farm buildings by CPCs or bonding conductors.
The OP states the Earthing system is TN-C-S.
It’s unlikely the Earthing system is continued to any farm buildings which would house livestock.

marconi said:

Re#42 - you added these remarks by edit:

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.

after I read your first offering which terminated 'Who pays for the installation of this unnecessary and incorrect RCD?'

Spinlondon - what is up with you? If you don't want to read anything from me select 'ignore'. If you do want to read my stuff and comment on it, then please read it more carefully and quote me correctly including any caveats and provisos I include.

Click to expand...

I think you need to scroll back and read just what I posted.
I initially asked you whether there was any reason why the RCD couldn't be removed altogether.
Instead of giving any reason why it could not be removed, you cited a source that advised type B RCDs be used.
I asked again and then you wanted my reasons for removing the RCD.

Yes I do sometimes post then edit what I have posted, because sometimes I like to look back and see exactly what has been said on another page.
If I were to look at another page before posting my reply, I would lose all that I have typed and have to start again.
There is also the problem with the website being reloaded, meaning long posts often get lost, so it’s better to post a short post then edit, sometimes having to edit 2 or 3 times.

spinlondon said:

Sunny Boy 3.6kw inverter, not 3.3kw.

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Here is the manual including the info for that invertor, for our reading pleasure .
http://files.sma.de/dl/28329/SB30-50-1AV-40-BE-en-10.pdf
Page 23 here looks much the same info, so if I've understood correctly the RCD (if required) is recommended to be 100mA.

Re #48.
(1) In #26 - you did not ask me specifically you asked everyone who might read this offering. I provided a response which did include (in the reference and in my text) the possibility that an external RCD is not required. You overlooked this.

(2) 'I asked again and then you wanted my reasons for removing the RCD'. I asked sincerely why you thought the RCD could be dispensed with - I found your response thin. I asked you again - if there is offence in the way I asked then point it out to me - to explain in some detail why it is not required. You did not.

(3) You choose to misread (miscomprehend) and then ridicule a way I suggested of investigating the nature of the earth leakage current using a Type AC upfront of the Type B.

I think you are being unnecessarily truculent with me.

http://files.sma.de/dl/7418/RCD-TI-en-43.pdf

SMA Technical Paper - Criteria for Selecting a Residual-Current Devices - Ise of RCD for SUNNY BOY, SUNNY MINI CENTRAL and SUNNY TRIPOWER

Studying the reference in #51 and if the inverter is a Sunny Boy 3600 - to be confirmed by you - then there is galvanic isolation between the dc and ac systems even though it is transformerless in output design. In which case, according to Section 4.1 there is no possibility of dc being fed back into the ac wiring. An externa type A (repeat A) RCD can be used instead of the current Type B 30mA but it must have an delta In of 100mA to cope with operational differential currents (See Section 4.2). The integral Residual Current Monitoring unit provides additional safety (see top of page 9/11).

At Section 3.4 SMA state:

3.4 Additional Protection SMA Solar Technology AG recommends always installing a residual-current device as additional protection in order to achieve the highest possible degree of safety. It can also provide the function of an all-pole disconnecting switch, which is frequently required for other reasons.

There are some calcultions and case studies at Section 5.

South Park - I hope this helps you decide what to do to tackle the nuisance tripping problem.

Providing RCD protection for any power source that is connected in parallel with the grid is not something that should be undertaken lightly.
An RCD which would disconnect the supply from an inverter, generator, transformer, whatever would not necessarily disconnect the grid.
One of the reasons I was querying where the RCD is sited and what it is protecting is because if it is in the wrong place, the part of the installation fed from the grid would still be live and in fault condition.
The Sunny Boy has an in built RCD, so any fault anywhere in the installation should cause it to trip.
However the installation will still be live because it is connected to the grid.
If we were to place another RCD just after where the inverter is connected to the grid, any fault down stream would cause that RCD to trip.
That would just leave the cable from the inverter to where it connects to the grid and the DNO supply cables still live.
If were to place the RCD just before where the inverter cable is connected to the grid, on the grid side any fault in the installation would cause the RCD to trip and also the in build RCD in the inverter.
The only live cables would be the DNO supply cables.

Clear labelling informing users about the two supplies and correct safe isolation procedures are obviously very necessary.

I would consider very carefully the manufacturer’s instructions regarding RCD protection.
This is a German manufacturer and what has been translated might not actually be what they mean.
It may be that they are referring to standard requirements for RCD protection such as socket-outlets, circuits of locations containing baths or showers and for cables concealed in walls.

Why has this turned so difficult. Just because a manufacturer recommends something it does not mean it has to done especially if it contradicts 7671.

So in this instance I would ignore the manufacturers guidance and install as per 7671. So if the installation method dictates a 30mA RCD is required then the answer is no. It cannot be changed to a 100mA one. If the installation method does not require an RCD them yes you can change it to a 100mA one although you would have tonask why have the RCD in the first place.