RCD problem

donttalktosh · 2025-03-11T16:12:05+0000

Hi,
I am an elderly gentleman so please be gentle with me.

I recently bought and built a large plastic shed and thought it would be nice to turn it into a man cave/sanctuary.
I have dabbled with electrics all my working life as an engineer and have been electrician's mate on many occasions.
So, prior to getting it professionally checked I thought I would do the donkey work and have a go making a start.

I started by taking a spur off my home ring main through the wall (2.5 t&e) to water proof fused switch.
From this I routed 2.5 s w a cable into a small consumer unit in the shed.
This unit has 2 mcbs (1x6amp and 1x16amp).
The rcd is rated at 40amps.
To this I wired 3 plastic double sockets (radial) with 2.5 twin and earth.
When using a socket tester it says all is correct.
When I plug in any thing like a drill or heater the trip goes out immediately.

I just wondered anyone could save my embarrassment before official test

poni · 2025-03-11T17:04:01+0000

hard to say, but check all the connections first, do the lights work with out tripping the RCD?

ProDave · 2025-03-11T18:02:45+0000

Quite likely something like neutral and earth reversed in a socket or a neutral to earth short. Check everything very carefully.

mainline · 2025-03-11T19:56:11+0000

donttalktosh said:
Hi,
I am an elderly gentleman so please be gentle with me.

I recently bought and built a large plastic shed and thought it would be nice to turn it into a man cave/sanctuary.
I have dabbled with electrics all my working life as an engineer and have been electrician's mate on many occasions.
So, prior to getting it professionally checked I thought I would do the donkey work and have a go making a start.

I started by taking a spur off my home ring main through the wall (2.5 t&e) to water proof fused switch.
From this I routed 2.5 s w a cable into a small consumer unit in the shed.
This unit has 2 mcbs (1x6amp and 1x16amp).
The rcd is rated at 40amps.
To this I wired 3 plastic double sockets (radial) with 2.5 twin and earth.
When using a socket tester it says all is correct.
When I plug in any thing like a drill or heater the trip goes out immediately.

I just wondered anyone could save my embarrassment before official test

Your socket tester won't show an N + E reversal.

SPECIAL LOCATION · 2025-03-11T23:01:36+0000

donttalktosh said:
The rcd is rated at 40amps.

The RCD is capable of disconnecting a 40amp load, but it is rated in milliamps.. NOT Amps
It should be 30ma for most domestic circuits. and also should be a "Type A" RCD to comply with current regs..
If not the "person" doing your official test may not consider it compliant.?

Is there not already 30ma RCD protection on the socket circuit you have extended from?

donttalktosh said:
When using a socket tester it says all is correct.

Plug-in socket testers are NOT an industry recognised tool to verify a circuit is wired correctly or is electrically safe..
See best practice document in the following link:
https://www.electricalsafetyfirst.org.uk/media/1205/best-practice-guide-8-issue-2.pdf
So switching on the power and plugging in your tester has not proved "all is correct"

If you had done the correct dead tests... "Continuity" and "Insulation resistance" BEFORE energising the circuit,
then your fault would have been identified prior to attempting any live tests...

donttalktosh said:
I have dabbled with electrics all my working life as an engineer and have been electrician's mate on many occasions.
So, prior to getting it professionally checked I thought I would do the donkey work and have a go making a start.

It sounds to me that the person(s) you were working as a mate to.. were not following industry guidance as per BS7671, for the design, installation and testing of electrical alterations and additions.. ??

Thus you have probably learned some "bad-practice" working methods that are very common amongst the "Builder who knows how to do electrics" brigade! e.g. You NEVER wire an alteration then dive straight into live tests!!

The reality is that you are working with an invisible energy source that you can't hear or smell but can kill a healthy adult in less than a second.. So omitting basic testing, before energising an alteration could endanger yourself or other third-parties who will come into contact with your electrical work.

Dead Tests ALWAYS precede Live Tests, was considered more important than Brown/(Red) is Live and Blue/(Black) is Neutral back in my younger training days!

Do you have access to any other types of electrical test meters other than just a plug-in socket tester?
If not you may have to swallow the embarrassment pill.. (maybe with few beers)..
And get your official tester in to come and sort out what you have done wrong?

Also..
If you have installed a new consumer unit, with new circuits..
Then technically this would come under the requirements of notification to your LABC for Part-P building regulations compliance.. see page 6 of the following Approved document P, Electrical Safety in Dwellings.. "notifiable work"..
https://assets.publishing.service.gov.uk/media/5a802da7ed915d74e622ceed/BR_PDF_AD_P_2013.pdf

So your official tester may raise multiple issues that need addressing with your DIY design & installation?