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Author Topic: RCD Tripping  (Read 1285 times)
Countrypaul
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« Reply #15 on: May 02, 2019, 10:45:52 PM »

I'm not an electricia, but if you change an MCB to an RCBO where that MCB is protected by an RCD won't that just be the equivalent of having and MCB protected by 2 RCDs and if one is stil a 30ma trip and one is a 100ma trip, surely the 30ma will trip first which would mean that replacing the MCB by the RCBO won't solve the problem. Or have I misunderstood something?
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RIT
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« Reply #16 on: May 03, 2019, 01:08:12 AM »

I'm not an electricia, but if you change an MCB to an RCBO where that MCB is protected by an RCD won't that just be the equivalent of having and MCB protected by 2 RCDs and if one is stil a 30ma trip and one is a 100ma trip, surely the 30ma will trip first which would mean that replacing the MCB by the RCBO won't solve the problem. Or have I misunderstood something?

The new configuration of an RCD+MCB or RCBO is independent of the current RCB's, so the CU ends up being an n+1 way CU. So a new neutral bar needs to be set up and most likely some messing about with the Live busbar, all work for a qualified electrician. 
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freddyuk
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« Reply #17 on: May 03, 2019, 05:46:49 AM »

Then someone on here mentioned trying an AB type RCD as we were using the standard A type. The AB type will allow a level of DC influence without tripping and since I bought this and installed it in about 2 minutes there has been no more trips at all. These are the same price as A type so just replace and see what happens.

AB? do you mean type B instead of type A. There are also types AC and F, but these should not be used in an average home setting. This is something I totally forgot to comment on as I've spent the last few weeks reading up on RCBOs and just defaulting to type B.

Yes you are correct I should have put TYPE AC Hager part CDC263UBN £24 so not expensive if it solves this problem. This goes on the output of the inverter which then feeds the main house CU. Then standard A types protect the House loads.This is not an average home setting with the DC element but could you not use the AC type on the solar input into the CU ? Is my solution acceptable as I am protected by both Types?
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RIT
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« Reply #18 on: May 03, 2019, 12:27:37 PM »

Then someone on here mentioned trying an AB type RCD as we were using the standard A type. The AB type will allow a level of DC influence without tripping and since I bought this and installed it in about 2 minutes there has been no more trips at all. These are the same price as A type so just replace and see what happens.

AB? do you mean type B instead of type A. There are also types AC and F, but these should not be used in an average home setting. This is something I totally forgot to comment on as I've spent the last few weeks reading up on RCBOs and just defaulting to type B.

Yes you are correct I should have put TYPE AC Hager part CDC263UBN £24 so not expensive if it solves this problem. This goes on the output of the inverter which then feeds the main house CU. Then standard A types protect the House loads.This is not an average home setting with the DC element but could you not use the AC type on the solar input into the CU ? Is my solution acceptable as I am protected by both Types?

This is where a qualified electrician who understands the exact setup is the only person who can be in a position to say if it was/is acceptable or not. I can just ask even more questions about your setup Smiley such as

   - There is a lower current rated MCB between the inverter and the RCD?
   
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Ted
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« Reply #19 on: May 04, 2019, 11:38:48 AM »

https://www.stroma.com/news/rcd-installation-requirements-guidance

As RIT says, get a qualified electrician.

Ted
(retired qualified electrician)
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freddyuk
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« Reply #20 on: May 04, 2019, 12:28:38 PM »

Qualified electrician has been in yes.
The inverter is fed from the house main RCD then the output of the inverter has an RCD as is required and feeds standard CU for the house loads.
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the blacksmith
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« Reply #21 on: May 11, 2019, 08:08:48 AM »

Just a little update

We have altered the CU by cutting the busbar and fitting a separate RCD & MCB just for the inverter.

Had some heavy rain yesterday  & all seems fine, no nuisance tripping!!   fingers crossed!   

Thank you for all your help & suggestions
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4.2kw & 4.1kw pv array+ immersun
Scruff
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« Reply #22 on: May 11, 2019, 09:35:26 PM »

Is my solution acceptable as I am protected by both Types?

Nope. A type is benignly DC tolerant...but only 6mA So your switch mode power supplies are probably already injecting over-threshold.



As RIT says, get a qualified electrician.

Why? They're all fitting trip curve B RCBOs.  fight
I've yet to see a B-Type in it's rightful place bar the ones I fit.
(any PV/EV Charger CU pics installed by qualified electricians anyone?)


Scruff.
(active not a qualified electrician)


« Last Edit: May 12, 2019, 01:16:39 AM by Scruff » Logged
Scruff
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« Reply #23 on: May 11, 2019, 09:40:50 PM »

Qualified electrician has been in yes.

 hysteria

Did he say AC type was ok?

Didja refer him to ET101:2008
Subsection: 712.411.3.02?

Is your quattro fully isolated from the primary input, did he even ask?
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RIT
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« Reply #24 on: May 12, 2019, 12:12:52 AM »


Why? They're all fitting trip curve B RCBOs.


Why? because they all sign the correct bit of paper to go to the council rather than having the council numpty come round and charge you a high fee for something they have no clue about.

The problems with a PV install include

 - Many inverters such as just about the whole SMA range do not need an RCD fitted (so type is a none issue).
 - There is an expectation that all circuits in a home will be protected by an RCB device (This is where the expectation of type B comes from as it is the default choice and as noted many inverters do not need a specified (or any) type).
 - The rules and regs do not yet seem to recognize the fact that the PV inverter is an energy source rather than an energy sink.
 
At some point, someone will be killed by drilling into a PV circuit and the inquest will note that the installed RCD/RCBO protected the wrong end of the circuit as it remained live for 4-5 seconds as that is the expected shutdown time of a G83/1-2 inverter once grid connection is lost. Then there will be a requirement for all inverters to have RCB/RCBO features built-in or at least an RCD/RCBO placed within a very short distance of the inverter. During this inquest, it will be best to be able to point your finger at a qualified electrician and the council and say that you know nothing.

Quote
(any PV/EV Charger CU pics installed by qualified electricians anyone?)

With the messing about I am getting from my supplier over upgrading my tails and having an isolation switch installed I am guessing a few weeks after hell freezes over and the devil buys himself some ice skates.
« Last Edit: May 12, 2019, 12:24:02 AM by RIT » Logged

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Scruff
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« Reply #25 on: May 12, 2019, 12:24:48 AM »

- Many inverters such as just about the whole SMA range do not need an RCD fitted (so type is a none issue).

Go on!

- There is an expectation that all circuits in a home will be protected by an RCB device (This is where the expectation of type B comes from as it is the default choice and as noted many inverters do not need a specified (or any) type).

What has expectations got to do with scientific logic and controlled repeatability?

No I think high-frequency inverters are pretty shoddy compared to low frequency when you include the cost of a £400 circuit breaker, they wouldn't sell if they advertised the fact.
Light-weight...who cares I'm not lifting it, cheaper to make...more expensive to protect against, lower surge, more fragile... Roll Eyes
Transformer design is better.

- The rules and regs do not yet seem to recognize the fact that the PV inverter is an energy source rather than an energy sink.

They state B-Type RCDs are required for non-isolated inverters in black and white.
18th Edition Uk & 4th Edition Éire
 

At some point, someone will be killed by drilling into a PV circuit and the inquest will note that the installed RCD/RCBO protected the wrong end of the circuit as it remained live for 4-5 seconds as that is the expected shutdown time of a G83/1-2 inverter once grid connection is lost.

I think we ought to stop protecting idiots from themselves.

it will be best to be able to point your finger at a qualified electrician and the council and say that you know nothing.

I would advise just doing it right in the first place and cease and desist vouching for unknowables.
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RIT
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« Reply #26 on: May 12, 2019, 02:54:35 AM »

- Many inverters such as just about the whole SMA range do not need an RCD fitted (so type is a none issue).

Go on!

I know the document - it is the recommendations for when you decide to use an RCD/RCBO It does not state that one has to be installed - that is something for the country regs. You will find the more up to date version at

     https://files.sma.de/dl/7418/RCD-TI-en-44.pdf

- The rules and regs do not yet seem to recognize the fact that the PV inverter is an energy source rather than an energy sink.

They state B-Type RCDs are required for non-isolated inverters in black and white.
18th Edition Uk & 4th Edition Éire

No, the regs state that
 - For the purposes of isolation that a PV system should be considered as a load.
 - Regulation 522.6.x stipulates requirements for circuit cable protection and an RCD or RCBO is valid protection - so would be running armoured cable.
 - Regulation 712.411.3.2.2.1.2 of BS 7671 stipulates that the RCD (when required) shall be of Type B in the case of a PV installation.

So as I stated the regs consider the PV inverter a sink/load rather than a source and there are NO UK regs that state all PV inverters must be connected via an RCD - it depends on the cabling requirements and the type of inverter (DC/AC isolation issue for example).
I may have missed a reg as I do not have access to the original document, but this is a common thread across the internet between qualified electricians as the '(when required)' part complicates the regs.

At some point, someone will be killed by drilling into a PV circuit and the inquest will note that the installed RCD/RCBO protected the wrong end of the circuit as it remained live for 4-5 seconds as that is the expected shutdown time of a G83/1-2 inverter once grid connection is lost.

I think we ought to stop protecting idiots from themselves.

But that would kill off the whole industry that has built up since the rules and regs started to turn into a modern-day version of war and peace.

it will be best to be able to point your finger at a qualified electrician and the council and say that you know nothing.

I would advise just doing it right in the first place and cease and desist vouching for unknowables.
[/quote]

Your view of doing it right can be different from the next person, hence the whole point of getting a signature at the end of the day to force the installer to stand by their choices in a court of law if needed.
« Last Edit: May 12, 2019, 02:59:54 AM by RIT » Logged

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Scruff
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« Reply #27 on: May 12, 2019, 12:20:37 PM »

I take when required to mean when there is other than zero direct path between the DC and AC in standard operation and fail safely so. This is done with transformers.
« Last Edit: May 13, 2019, 02:18:34 AM by Scruff » Logged
Scruff
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« Reply #28 on: May 13, 2019, 02:31:37 AM »




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