RCD adapter query

[raybarrow]

Hi Folks,
I have a twin socket in the house near the rear access to the garden. I only use it for the lawn mower, hedge trimmer. It's not an RCD socket and wondered should be or would a RCD adapter do the job (with the bonus of it being used elsewhere). House was rewired in 2007.
I'm having the electrician in to do a another little job and was wondering if it is a simple matter of changing the 'normal' 13Amp socket top for an RCD top or just go with an RCD adapter. Which is best?
Thoughts please,
Ray.

[Urbandreamer]

Changing the socket is what I would advise unless you need an extension cable for the mower.
I would be confident replacing the socket, if the existing box was deep enough (it should be with a 2007 rewire). It''s not much more difficult than wiring a plug.

I don't recommend putting the entire house on a RCD, but a split system works quite well. We rewired about the same era the plugs etc are on RCD and the lighting not. You might ask an electrician how expensive that would be as a retrofit.

[monabri]

Have a shufty at these RCD Socket plates on offer from Screwfix.

https://www.screwfix.com/c/electrical-l ... -_-rcdplug

Maybe check how deep your existing plug mounting box is? They seem quite easy to fit.

[88V8]

Hi Folks,
I have a twin socket in the house near the rear access to the garden. I only use it for the lawn mower, hedge trimmer. It's not an RCD socket and wondered should be or would a RCD adapter do the job (with the bonus of it being used elsewhere).
I'm having the electrician in to do a another little job and was wondering if it is a simple matter of changing the 'normal' 13Amp socket top for an RCD top or just go with an RCD adapter. Which is best?

I have a plug-in RCD adaptor, not that I ever remember to use it despite having cut the wire a couple of times. The house is on RCBOs so it's a bit superfluous really.

I did put an RCD socket - yes, it's a straight swap - in the cellar to run our sump pump which once tripped the power circuit that also runs the freezer.
The idea was that the RCD being more local would trip first, but testing it by dropping the power lead into water I found the result quite random; sometimes the RCD tripped and not the RCBO, sometimes only the latter and sometimes both.

I would go with the adaptor.

V8

[Itsallaguess]

I did put an RCD socket - yes, it's a straight swap - in the cellar to run our sump pump which once tripped the power circuit that also runs the freezer.

The idea was that the RCD being more local would trip first, but testing it by dropping the power lead into water I found the result quite random; sometimes the RCD tripped and not the RCBO, sometimes only the latter and sometimes both.

Just in case there's any misunderstanding regarding multiple RCD's on the same circuit, it's very important to get what's called the 'selectivity' of the RCD's correct, and this is usually done by careful selection of relevant 'time delay' characteristics of each RCD, and so 'nearest' in a spatial or circuit-sense is not particularly relevant if those time-characteristics have not been taken into account.

As a brief explanation, on a multiple-RCD-circuit, those nearest any particular end-loads, which would be your sump pump in this example, would need to be fed from a local RCD with a much faster tripping sensitivity than the RCD further 'upstream', towards the consumer unit, and the general rule is that any 'upstream' RCD must be at least three times the sensitivity of the next 'downstream' RCD device, as shown in the following diagram, where for the sake of this example, number 1 might represent your consumer unit, and number 3 might represent your end-load sump-pump -



For anyone thinking about using more than one RCD on a single electrical circuit, it's worth taking a look at the following page, which is the source of the above diagram, and which explains the concept of same-circuit RCD selectivity in more detail -

Coordination of residual current protective devices -

https://www.electrical-installation.org/enwiki/Coordination_of_residual_current_protective_devices

Personally, if I were the OP, I'd look to use a portable and temporary RCD solution in this case, with a 30mA high-sensitivity rating, and which can be plugged into the existing socket without creating a more permanent and more expensive fixing, and which can also then be used more flexibly if there's a need for temporary RCD protection elsewhere in the home as well -

Masterplug 13A Fused Plug-Through Active RCD Adaptor (£9.59) -

https://www.screwfix.com/p/masterplug-13a-fused-plug-through-active-rcd-adaptor/63731



Cheers,

Itsallaguess

[bungeejumper]

For outdoor and general DIY purposes, I use an extension reel (40 metre) with an RCD built into its plug. (Similar to https://www.amazon.co.uk/Masterplug-Soc ... B004I5BQ2Y, but longer.) There are now no excuses for 'forgetting' to plug in an adapter before I start work.

BJ

[DrFfybes]

You don't say if the whole house is on an RCD, but at 2007 I would have thought it quite likely (certainly they were commonplace and so probably required in 2008).

If so then, as IAAG has put in detail, the fastes one will teip. However even if you try and get a faster one on the socket, in actual use the one nearest to the supply is the one that goes so the whole board goes out. This is even the case with a split board, where the main incoming is also protected with an RCBO, which detects earth leakage and overcurrent.

Our new board last year has simply an overload circuit breaker on the main feed to the board, then each individual circuit has RCBOs which protect against overload and Earth trips, which means if I shove a drill through a wire only that circuit trips.

Paul

[88V8]

You don't say if the whole house is on an RCD, but at 2007 I would have thought it quite likely (certainly they were commonplace and so probably required in 2008).
If so then, as IAAG has put in detail, the fastest one will trip. However even if you try and get a faster one on the socket, in actual use the one nearest to the supply is the one that goes so the whole board goes out. This is even the case with a split board, where the main incoming is also protected with an RCBO, which detects earth leakage and overcurrent.
Our new board last year has simply an overload circuit breaker on the main feed to the board, then each individual circuit has RCBOs which protect against overload and Earth trips, which means if I shove a drill through a wire only that circuit trips.

We have RCBOs, which I see from looking this morning are 30Ma, so my pump needs a 10Ma RCD.

Our board has a 100Ma time-delay RCCB as overall protection, and that has never tripped. Until we went to RCBOs it was quite normal for a trivial fault such as a blowing bulb to trip the whole house.

My workaround for the pump... was that when we go away on hols, I plug it into a roundpin socket run off the cellar lights, so it can't trip the power circuit and the freezers and seeing as it's a roundpin, so one is going to plug anything else into it.

V8

[raybarrow]

I think an RCD adapter is the most convenient/versatile way to go.

When the house was rewired the electrician who did it (can't contact him now) put a non-standard double 13 amp socket (with the 'T' shaped earth pin) where the freezer is plugged in. It doesn't have any extra switches, just the normal on/off. Would that have been used just to stop someone unplugging the freezer by mistake and using the socket for something else? It doesn't appear to have any magical powers. I've made myself a small extension non-standard 'T' type to standard socket so I can use the spare socket but wondered if the non-standard socket gives me any advantage other than discouraging the unplugging of the freezer.

Thanks,
Ray.

[raybarrow]

Missed an earlier question - Yes the CU has master RCD switch.
Ray.

[Urbandreamer]

I've made myself a small extension non-standard 'T' type to standard socket so I can use the spare socket but wondered if the non-standard socket gives me any advantage other than discouraging the unplugging of the freezer.

Thanks,
Ray.

I really wouldn't use an extension with it. While the main RCD should work, a earth leakage breaker might not. This type of socket is intended for use with a separate earth than the common one, for sensitive equipment. I suspect that it was not originally used for a freezer.
I found this explanation.
https://www.voltimum.ie/content/non-sta ... aped-earth

If the point was to stop the freezer being unplugged, it could have been hard wired.
ie
https://www.screwfix.com/p/mk-base-13a- ... lsrc=aw.ds

[csearle]

My experience has been that there is no apparent rhyme or reason which RCD will trip when there are more than one in succession. This, regardless of whether they are both 30mA, 100mA, time-delayed or any combination of these. I have very, very often had (and sometimes installed) 100mA time-delayed RCDs to cover TT installations (as required) with 30mA RCDs/RCBOs further downstream only to have the time-delayed ones trip before (and occasionally as well as) the "instantaneous" ones. This often happens even when using my calibrated RCD tester.

From tests that I perform (most days) I know that the 30mA ones are almost universally set to trip at 25mA and usually do so within either 30-40ms (or with some brands 8-10ms).

If I find a selectivity issue (e.g. two 30mA RCDs in series) during a test and inspection I flag it as a code C3 improvement recommended observation.

Chris

[servodude]

My experience has been that there is no apparent rhyme or reason which RCD will trip when there are more than one in succession. This, regardless of whether they are both 30mA, 100mA, time-delayed or any combination of these. I have very, very often had (and sometimes installed) 100mA time-delayed RCDs to cover TT installations (as required) with 30mA RCDs/RCBOs further downstream only to have the time-delayed ones trip before (and occasionally as well as) the "instantaneous" ones. This often happens even when using my calibrated RCD tester.

From tests that I perform (most days) I know that the 30mA ones are almost universally set to trip at 25mA and usually do so within either 30-40ms (or with some brands 8-10ms).

If I find a selectivity issue (e.g. two 30mA RCDs in series) during a test and inspection I flag it as a code C3 improvement recommended observation.

Chris

Does it work like a propagated pulse then?
So for devices in series you'd expect both to see it and them to trip based on where they sat in the margins of the design?

[csearle]

My experience has been that there is no apparent rhyme or reason which RCD will trip when there are more than one in succession. This, regardless of whether they are both 30mA, 100mA, time-delayed or any combination of these. I have very, very often had (and sometimes installed) 100mA time-delayed RCDs to cover TT installations (as required) with 30mA RCDs/RCBOs further downstream only to have the time-delayed ones trip before (and occasionally as well as) the "instantaneous" ones. This often happens even when using my calibrated RCD tester.

From tests that I perform (most days) I know that the 30mA ones are almost universally set to trip at 25mA and usually do so within either 30-40ms (or with some brands 8-10ms).

If I find a selectivity issue (e.g. two 30mA RCDs in series) during a test and inspection I flag it as a code C3 improvement recommended observation.

Chris

Does it work like a propagated pulse then?
So for devices in series you'd expect both to see it and them to trip based on where they sat in the margins of the design?

Well I think so, yes. Also a pulse with a fast risetime on either input can cause them to trip too, even the time delayed ones. Apparently type G are immune to this to some extent (G for Gewitter) although I forked out for one once at a place adjacent to s garage where they had an arc welder and it still experienced nuisance tripping. C.