Split load with two RCDs

Dartlec · 13 Jan 2008

Hi,

Can anyone suggest or recommend an insulated CU that has a time delayed 100ma RCD incomer (Or a main switch that can be replaced with such) and then the facility for two separate rcd banks to split the protection across outgoing circuits.

I'm quoting to put in a new board in a TT supplied house, which for now will only supply the kitchen, but the long term plan is to rewire the rest of the house a room at a time and transfer the new circuits to the new board. Bearing in mind the upcoming 17th, it seems sensible to end up with three separate banks of circuits - 1 protected only by the 100ma TD to meet disconnection time, and two banks protected by 30ma to spread the risk of nuisance tripping.

With the introduction of the 17th and the additional requirements for rcd it seems a sensible move and I expected the manufacturers to start bringing out suitable CUs but my brief search doesn't show anything currently available from any of the regular sources.

I can see two other alternatives:

1. Mounting the Time Delay RCD in a separate one way enclosure and connect to a standard split load board, fitted with two RCDs, or

2. using MCBOs

but my first choice is still a suitable single board with rcds, if only for cost issues.

Any thoughts on where I should look?

Regards

Gavin

Lectrician · 13 Jan 2008

If only for cost issues?

You will find a CU with a main switch and two 30mA RCD's is available to order, but be prepared to pay!

A 100mA main RCD with two 30mA splits is not a produced model I believe.......If it was, again, cost is going to be a huge issue.

Dartlec · 13 Jan 2008

Lectrician said:
A 100mA main RCD with two 30mA splits is not a produced model I believe.......If it was, again, cost is going to be a huge issue.

That may well be the case, though I am surprised there is not more call for them, and that the 17th will not increase the call for such things?

I don't see a good reason why the cost should be so much more, we are after all only talking about one extra RCD (two 40A RCDs are not that expensive compared to RCBOs on every circuit) and terminal blocks/busbars that are split into three rather than two.

In fact I could make one up myself if someone made a modular board and the parts available......hmm, have I spotted a gap in the market that will make me a squillionaire?!

It does make me wonder what most people do in a TT installation, especially as a time delayed RCD is not actually that easy to pick up from my local suppliers. Do they just put all socket installations on one RCD and hope that it rarely trips?

Having said that, I am sure many of the TT houses around my patch still have the voltage ELCBs as their sole protection against indirect contact (or fault protection as I must get used to calling it)..

Gavin

RF Lighting · 13 Jan 2008

Normally on TT installations I get / fit a standard insulated split load CU, and wire it as normal, but just swap the main switch for a type S RCD.

Our wholesaler keeps the type S 100mA / 100A RCDs on the shelf.

luminaire · 13 Jan 2008

Could you not use a henley with two sets of tails. One going to a split-load board and the other to a full RCD board?

megawatt · 14 Jan 2008

Normally on TT installations I get / fit a standard insulated split load CU, and wire it as normal, but just swap the main switch for a type S RCD.

So do I, the following is using an MK split load unit ...

MW

ban-all-sheds · 14 Jan 2008

Dartlec said:
Mounting the Time Delay RCD in a separate one way enclosure and connect to a standard split load board, fitted with two RCDs

That will put your 2 30mA RCDs in series - you won't have 2 independent buses - one will be downstream of the first one...

Lectrician · 14 Jan 2008

Dartlec said:
Lectrician said:

A 100mA main RCD with two 30mA splits is not a produced model I believe.......If it was, again, cost is going to be a huge issue.

Click to expand...

That may well be the case, though I am surprised there is not more call for them, and that the 17th will not increase the call for such things?

I don't see a good reason why the cost should be so much more, we are after all only talking about one extra RCD (two 40A RCDs are not that expensive compared to RCBOs on every circuit) and terminal blocks/busbars that are split into three rather than two.

In fact I could make one up myself if someone made a modular board and the parts available......hmm, have I spotted a gap in the market that will make me a squillionaire?!

It does make me wonder what most people do in a TT installation, especially as a time delayed RCD is not actually that easy to pick up from my local suppliers. Do they just put all socket installations on one RCD and hope that it rarely trips?

Having said that, I am sure many of the TT houses around my patch still have the voltage ELCBs as their sole protection against indirect contact (or fault protection as I must get used to calling it)..

Gavin

If you come across a voltage operated ELCB, you must change it as soon as seen - It must be treated the same as no earth to a property.

The boards you want would be rarely used, and the market for them would be very small, hence the lack of stock and therefore price. The most keenly priced split load is the size most commonly used. Thats a standard 10way or 14way split.

If I have to do a TT (and I would first look to PME the install), I would use a standard split loader with main switch, and fit a time delayed 100mA in an enclosure fitted to the tails feeding the board.

I am sure with the 17th, you will soon see prices drop on RCBO's, and may see some new design CU's coming onto the market. I am sure the manufacturers are already investigating the best design.

plugwash · 14 Jan 2008

Lectrician said:
If only for cost issues?

You will find a CU with a main switch and two 30mA RCD's is available to order, but be prepared to pay!

A 100mA main RCD with two 30mA splits is not a produced model I believe.......If it was, again, cost is going to be a huge issue.

MK's largest CU enclosure has three neutral bars so you could build one in it with no trouble.

Jim2287 · 14 Jan 2008

Whats the 100mA RCD for ?

RF Lighting · 14 Jan 2008

Because it is a TT installation, the high impedance of the main earth prevents standard OCPD from automatically disconnecting the supply under earth fault conditions, therefore the use of an RCD is employed to ensure disconnection times are met.

It is a 100mA RCD to prevent nusiance tripping, and time delayed to provide discrimination from the down stream 30mA RCD.

Jim2287 · 14 Jan 2008

sorry i mean, whats Dartlec intending to use it for

ban-all-sheds · 14 Jan 2008

Jim2287 said:
sorry i mean, whats Dartlec intending to use it for

He's quoting to put in a new board in a TT supplied house, which for now will only supply the kitchen, but the long term plan is to rewire the rest of the house a room at a time and transfer the new circuits to the new board. Bearing in mind the upcoming 17th, it seems sensible to him to end up with three separate banks of circuits - 1 protected only by the 100ma TD to meet disconnection time, and two banks protected by 30ma to spread the risk of nuisance tripping.

With the introduction of the 17th and the additional requirements for RCD he thinks it a sensible move and expected the manufacturers to start bringing out suitable CUs but his brief search hasn't show anything currently available from any of the regular sources.

He can see two other alternatives:

1. Mounting the Time Delay RCD in a separate one way enclosure and connect to a standard split load board, fitted with two RCDs, or

2. using MCBOs

but his first choice is still a suitable single board with rcds, if only for cost issues.

Any thoughts on where he should look?

plugwash · 15 Jan 2008

I think the following should do it:

get MKs largest CU enclosure (the one that takes 21 modules total)
get two split load kits.
get appropriate MCBs/RCDs

The split load kit contains cables designed to tap off the busbar and neutral bar for the non-rcd side to feed the RCD side, I can't see any impediment to using two of them to feed two seperate RCD sides.

Jim2287 · 15 Jan 2008

the MK solution sounds good .... i think it works out cheeper to buy another "split load board" rather than the split load kits ? (not sure on inet prices though)

take it that some circuits will not be on the 30mA RCDs and will only be on the 100mA RCD .... so u will actually have 3 banks of circuits, not only 2 banks supplied by the 100mA

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Split load with two RCDs

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