Overcoming RCD discrimination
- Thread starter paul1972
- Start date
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found the answer to the last part..... he earth is secondary in case the neutral is lost. Had a quick read up on RCBOs. Should really have done this some time back.
I kind of feared that answer haha...... the old 2 RCD problem.
Thanks anyway......
I kind of feared that answer haha...... the old 2 RCD problem.
Thanks anyway......
Sorry iof it wasn't clear. It was really the first sentence/paragraph which mattered - and I was agree with endecotp that I have never personally been aware an RCD or RCBO intended for use in a CU whose test button created a simulated 'fault' to earth (even in the case of RCBOs which have a functional earth connection). If the test button does not simulate a fault to earth but, rather (as has every one I've been aware of) sends a small current from L on one side of the RCD/RCBO to N on the other side (thereby creating a current imbalance which trips the device), then it would not cause an upstream RCD to trip.John, Really sorry have read your post several times but cannot quite understand what it is your saying
What I went on to say (in second paragraph) is that the test button of RCD sockets, RCD FCUs and RCD adapters (rather than RCDs/RCBOs intended to be used in/near CUs) does create a simulated fault to earth, and therefore may well trip another upstream RCD. As I said, when this has been discussed here in the past, it has been speculated that the reason for this may be that the test button thereby confirms that an adequate earth is present at the socket, FCU or adapter (as well as testing the RCD, per se) ... a relevant consideration when one is distant from the CU, but not really a relevant consideration for RCDs/RCBOs intended for use in/near a CU.
Is that any clearer?
Kind Regards, John
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Tried everything I could think of to find breakers for the old memshield DB. Think it was memshield 2. If I could have found at breaker to fit then it was always to be my preferred choice as it would have eliminated the Rcd in series problem.
Could not find memsheild 63a, or find compatible components
If I could I would just pull back my armoured cable 10m and reconnect to other board.
Could not find memsheild 63a, or find compatible components
If I could I would just pull back my armoured cable 10m and reconnect to other board.
find breakers for the old memshield DB. Think it was memshield 2. If I could have found at breaker to fit then it was always to be my preferred choice as it would have eliminated the Rcd in series problem.
Could not find memsheild 63a, or find compatible components
I may have one. Do you still need it? 63A might be a C-type
May have an RCBO pod to fit.
I'm surprised you couldn't find them.
Try spelling it "Memshield"
They will probably be branded Eaton now
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Thank you for everyone's help, think I got myself a tad confused reading your posts while eating etc. but having read all the posts again I seem to be able to follow them better now.
2 rcds (or RCBOs) at the same rating is not the best. My understanding, pressing the test button on an RCD or RCBO in a DB downstream (the end) when the RCD/RCBO has the same rating as the RCD upstream (Source) can cause either RCD to see the fault and trip. This I already new but hoped would not happen if honest.
Just to confirm current 17th regs, I assume the easiest fix at this time is to remove all RCBOs in new board and replace with MCBs, thus retaining the RCD protection from the 63A 30mA RCD on the upstream Hager board.
I take on-board an earlier post on the need to upgrade from 16th to 17th regs.
2 rcds (or RCBOs) at the same rating is not the best. My understanding, pressing the test button on an RCD or RCBO in a DB downstream (the end) when the RCD/RCBO has the same rating as the RCD upstream (Source) can cause either RCD to see the fault and trip. This I already new but hoped would not happen if honest.
Just to confirm current 17th regs, I assume the easiest fix at this time is to remove all RCBOs in new board and replace with MCBs, thus retaining the RCD protection from the 63A 30mA RCD on the upstream Hager board.
I take on-board an earlier post on the need to upgrade from 16th to 17th regs.
Wow, will get back to you johnD as need to confirm type of board and current circuit protection inside it. Was going to pop in tomorrow to make sure all was clean and tidy ready for Monday. Forgot my manners lol. Thanks
Can you not just convert the Hager board into a high integrity board? (I think that's the correct term, please correct if I'm wrong.)
By this I mean get some Hager busbar and some Hager tri-rated tails.
With some fiddling you may be able to achieve a non-RCD-protected 63A mcb, typically next to the main switch, then RCD 1 and it's circuits, then RCD 2 and it's circuits.
By this I mean get some Hager busbar and some Hager tri-rated tails.
With some fiddling you may be able to achieve a non-RCD-protected 63A mcb, typically next to the main switch, then RCD 1 and it's circuits, then RCD 2 and it's circuits.
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Indeed - but even if they were of different (trip current) ratings, there would be no guarantee that the lower-rated one would trip first. Don't forget that a fault current could be considerably in excess of the trip threshold of either of them
I'm not convinced that, regulations-wise, it would make any difference. Forgetting the issue of what happens when you press test buttons, in either case a fault on any of the circuits from the new CU could take out the upstream Hager's RCD and hence everything else protected by that RCD. Whether it would or would not be compliant with current regulations would depend upon whether you (or whoever) felt that reasonable steps had been taken to "minimise inconvenience" (due to multiple circuits being killed) in the event of a single fault.
Kind Regards, John
Spark-............
This is an option, and I have looked into it. If honest was a little nervy at doing this as although fully qualified... 236 pt1 and 2 the AM2 etc, most of my work for the last 20 years has been maintenance repairs, commercial and industrial. Motors, pumps, catering, and loads more, but the more domestic stuff and design I am rustier than I realised. Who I work for even 'buys in' the 5 year inspections, so getting rustier on testing over time too.
When wife asked for help I kind of jumped at the chance to do 'real' work again, and perhaps approached it wrong and with an attitude of 'it will work' instead of sitting back and looking at the options and issues clearly.
Have a few options now. And learnt a valuable lesson too. Will look at the hager rebuild option too as well as the pulling back of the mains to the mem board, and also (assuming its permissible) changing the contactum rcbos to MCB (last resort).
All said and done, nothing will be done that is unsafe, and nothing will be left untested. Certainly not in a place of young children.
This is an option, and I have looked into it. If honest was a little nervy at doing this as although fully qualified... 236 pt1 and 2 the AM2 etc, most of my work for the last 20 years has been maintenance repairs, commercial and industrial. Motors, pumps, catering, and loads more, but the more domestic stuff and design I am rustier than I realised. Who I work for even 'buys in' the 5 year inspections, so getting rustier on testing over time too.
When wife asked for help I kind of jumped at the chance to do 'real' work again, and perhaps approached it wrong and with an attitude of 'it will work' instead of sitting back and looking at the options and issues clearly.
Have a few options now. And learnt a valuable lesson too. Will look at the hager rebuild option too as well as the pulling back of the mains to the mem board, and also (assuming its permissible) changing the contactum rcbos to MCB (last resort).
All said and done, nothing will be done that is unsafe, and nothing will be left untested. Certainly not in a place of young children.
Sparywright is wright.
You can convert most Hagers into High integrity boards. Post the Hager CU part number if you not sure.
VAT05 is the part number for the additional neutral bus bar (just clips in) and a VAN00 neutral link cable. You might need a short bit of busbar too for the live out from the main switch to the 63A MCB.
You can convert most Hagers into High integrity boards. Post the Hager CU part number if you not sure.
VAT05 is the part number for the additional neutral bus bar (just clips in) and a VAN00 neutral link cable. You might need a short bit of busbar too for the live out from the main switch to the 63A MCB.
Thanks john.
Testing circuits with 2 rcds will be a nightmare for me, should have thought it though a little better.
Will look at other option listed in this thread and as a last resort replace the RCBOs for MCBs in the new board.
Will however install the other circuits 1st as originally intended as interested to see if this happens on all circuits and if needed its only a few seconds to change the protective device.
Testing circuits with 2 rcds will be a nightmare for me, should have thought it though a little better.
Will look at other option listed in this thread and as a last resort replace the RCBOs for MCBs in the new board.
Will however install the other circuits 1st as originally intended as interested to see if this happens on all circuits and if needed its only a few seconds to change the protective device.
Thankyou Taylor, will look into it now. Think I saw the parts in TCLs website
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