Failed my LABC final inspection

[diy_dude]

I have rewired my house fully with the exception of the consumer unit which was replaced 3 years ago.

Friday was my second LABC visit for a final inspection and sign-off.
He checked the main earth, earthing via gas and water pipes, earth on ring final circuits and RCD disconnect values and times.

The inspector complemented my work as said it was to a high standard, however I failed the inspection because:

1) The RCD in the consumer unit (Square D Dom63R30) tripped at 33ms according to his tester

2) I had not sealed the holes in the top of the CU.

I will replace the RCD when I can find a spare, any idea where to get one from?
When I had the CU replaced he left the holes in the top of the CU unsealed, I cannot get my little finger in them due to the cables. The LABC inspector wants me to seal them with 'something', what something should I use? He suggested silicone sealant.... this seems over the top to me.

Any advice please?

 

[Chri5]

Little Jonny could pour something down it, and rules is rules.

There is a 'finger' test method of old ( a device that looks like a feeler gauge), but in general the holes need to prevent dust, dirt, moisture, liquid and fingers.

Sealant will do or a small hole, with bigger one's there's a chance of the sealant droping straight in to the board.

For those you need to fabricate something, say a piece of plastic sheet and have tight holes with slots and fix that to the top as a cover.

Due to age of a board, with the top damaged I once cut the base off some 25 x 50mm trunking and ended up with a flat piece 45mm x 200mm odd. I then cut the 5 x cable holes with a 10mm hole saw and slotted the holes.
This then gets threaded on to the cable and with some sealant fixed to the CU top. Looked ok and was 500% better than the mess before I worked on it.


What CU make is it? If you post a picture someone will be able to see what alternative replacement RCD's are available .

 

[rebuke]

I haven't got a copy of them to hand, but unless it's changed in the 17th edition, 33ms is a perfectly acceptable trip time (100% of rated tripping current should cause it to trip within 200ms, and if protecting against direct contact a test current of 150ma should cause it to trip within 40ms) - 33ms fits within both of these. These time requirements may have been tightened up in the 17th edition though - I'll check when I can get at my copy (but I'm sure someone will say sooner if that is the case)...

Are you sure it's not 33mA - as if that was the case then assuming it's a 30mA RCD, then failing it makes sense, as thats more than 100% of rated tripping current.

 

[diy_dude]

Damn, I must read my posts back before pressing the submit button.

rebuke, you are indeed correct. It failed at 33mA NOT 33ms. The first time he tested it it would not trip at all. He wiggle the level a bit and got the 33mA trip.

I'll try and get a photo of my CU tonight. I thought I had one online, but I cannot find it now.

 

[jason1958]

First digit of IP rating = ingress protection against solid objects.

Top of enclosure IP4x.
- 4 = Protected against a solid object greater than 1.0mm.
- sphere >1.0mm must not pass thro.

Sides/bottom of enclosure IP2x - 12mm sphere must not pass thro.
- 2 - Protected against a solid object greater than 12.5mm
- sphere >12.5mm must not pass thro.


Hager CU use a piece of adhesive foam tape to solve this problem, MK are nasty in this respect as the top entries are only usable for trunking or you simply mount the CU on batons & use back-entry "like everyone else using MK". MEM might be the best although opinions vary.

 

[Taylortwocities]

I agree, you need a new RCD - test it before you call them back!

You can simply seal the holes with some silicone sealant.

 

[Spark123]

I take it the RCD was tested in isolation?
You can buy Square D stuff from most electrical wholesalers - Rexel Senate and City Electrical Factors do them.

 

[jason1958]

Just noticed this was a Square-D (ie, Merlin Gerin / Schneider).

There has been a recall of their RCBO.
However I am not sure if it also includes RCD.

It may be worth checking with Schneider's website or...
- [email protected]
- 01952 209544

Schneider do answer emails from experience - so I would email.

 

[jason1958]

Oops, cut-n-paste was not complete!

RCBO recall referred to...
Schneider Electric Limited - RCBO’s:
Merlin Gerin C60, C60X; Square D KQE; SQOR; QOE.
The potentially faulty devices were manufactured from 15th December 2003 to 30th June 2004 inclusive. Products manufactured before and after these dates are unaffected by this alert. Affected products would have been made available for purchase up to the 1st December 2005.

Schneider Electric have become aware of an issue with a component non-conformance on certain Merlin Gerin and Square D RCBO (residual current circuit breaker with overload protection) devices. The component may be found in electrical distribution boards of Merlin Gerin and Square D manufacture. The identified earth leakage circuit protective devices may not trip in accordance with the specification on an earth leakage fault. The circuit protection component of the RCBO’s is unaffected by this Alert.


As I recall an extremely limited number were faulty. Schneider test, if found to be within spec the RCBO is fine and unaffected.


RCD & RCBO are not infallible.
- RCD are mechanical devices
- They can suffer stickion (eg, older Contactum) causing trip times to drift
- They do not like being rough handled, do not chuck them around


ERA Research...
"From research published in Italy, electromechanical RCDs have an average failure rate of 7.1%. If RCDs are tested regularly, this figure falls to 2.8%. RCD reliability is improved if the test button is operated regularly.

From the available evidence, the primary mode of failure on electromechanical RCDs is ingress of fine particles of dust and moisture causing the moving components within the RCDs to stick or to operate more slowly than intended.

Whilst electronic RCD manufacturers claim that their products are more reliable than electromechanical RCDs, ERA has found no evidence to support this claim. Research carried out in the US suggests that the reliability of electronic RCDs may be similar to that of electromechanical
RCDs.

The RCD failures in the US were attributed to the failure of electronic components. The failure rates were higher in cities with high humidity conditions, which may not be relevant to conditions found in the UK.

If you do not test regularly the failure rate is 7.1%.
If you have 14 RCBO in an enclosure there is a very high probability one will drifting outside the permitted test limits (probably time). Unfortunately the failure rate cited by Era says nothing about population size, or age of the device, or ambient/humid/dust conditions. I also think Italians use DP RCBO due to TT supply where supply polarity "can vary" - not checked.


Another bit of (equally useless) information.
- Summary of Published Current Thresholds (in mA) for 60Hz Exposure
- Source - Sutherland et al.
- Startle = 2.2-3.2mA (women)
- Let-go current = 10.5mA (women) 10ma (men)
- Breathing difficulty (respiratory tetanus) = 15mA (women), 23mA (men)
- Respiratory paralysis = 30mA (men)

So do not think 30mA is "not noticeable" or "safe" - 3.2mA will startle.

 

[diy_dude]

Taylortwocities: You say I should test the RCD before I call the LABC back, how should I do this?

He tested it by plugging a test meter into a socket in the kitchen, so no it was not tested in isolation. How would you test one?

 

[rebuke]

You need an RCD tester, these are relatively expensive, so unless you happen to know an electrician who has one they can let you borrow you won't be able to test it yourself (other than using the test button on the front of course)...

 

[Spark123]

Tested in isolation means with no circuits connected to it as these may have an impact on the readings. If nothing else was on power from the RCD though I doubt it will make a massive difference.

 

[ban-all-sheds]

Due to age of a board, with the top damaged I once cut the base off some 25 x 50mm trunking and ended up with a flat piece 45mm x 200mm odd. I then cut the 5 x cable holes with a 10mm hole saw and slotted the holes.
This then gets threaded on to the cable and with some sealant fixed to the CU top. Looked ok and was 500% better than the mess before I worked on it.

Check in Yellow Pages for any company near you that sells uPVC fascias, soffits, window boards etc.

Take a trip down there and see what offcuts and damaged bits they've got in the bins/skips outside....

 

[Stoday]

Blue Tack.

 

[oharaf]

WEETABIX PASTE

I can send my daughter round, she seals and sticks everything with this bloody stuff