80A 100mA RCD in Domestic TT installation?

[leascliffe]

Hi,

I am starting out as a domestic installer and would really like some of your advice please??

I went to preview a job today to replace some pendant light fittings. The customer said the CU was replaced in 2010 together with a new earth rod being a TT supply. The overhead lines come into the distributor's fuse, tails out to the meter and just one pair of tails from the meter into an MK insulated C/U. The C/U consists of a 80A 100mA Time delayed RCD as main switch and 10 MCB's. There does not appear to be any other C/U at the property so I was wondering why the original installer went for a time delayed 100mA RCD?

I'm concerned there is no 30mA protection and believe the 100mA time delayed RCD should be swapped for a standard 30mA. Wondered if any of you have experienced the same and agree or disagree? Thanks!

 

[Jay Sparks]

I too am registered with Elecsa, I've just phoned them for advice and also NAPIT who the original installer is registered with. They both have the same complaints procedure laid down by the Government. The customer has to give the original installer opportunity to put it right (A.N. Other contractor cannot correct the original work at this stage). If the contractor does not reply, then a complaint must be sent in writing to the certification body, who will investigate and decide the outcome, in this case it seems the contractor 'could' be struck off, meaning they would struggle to re-register with any other certification body.

The customer is emigrating at the end of this month and intending to let their house, don't think this will be possible while the complaint is ongoing and only 100mA protection in place, oh dear!...

The problem there is, the guy prob won't even care if he can register again coz he will just get a third party to do it, or just not bother notifying!!!! Its a bloody crock of poo!!!




Registration my ---!!!lol

 

[Engineer54]

So how long to you have to allow, for the original installer to put things right?? And how long to completion, after the official written complaint has been registered. It makes you wonder, just how much the safety of an installation or to it's occupants, matters to these scam providers? They beat the safety drum hard enough when it suits them, but when it comes to safety costing THEM money, it then becomes another story altogether!!

As for the original electrician/contractor being struck off, i doubt that very much, and even if he did, would have no trouble signing up with one of the others. I doubt very much that they have any common dialogue between them...

 

[leascliffe]

So how long to you have to allow, for the original installer to put things right?? And how long to completion, after the official written complaint has been registered. It makes you wonder, just how much the safety of an installation or to it's occupants, matters to these scam providers? They beat the safety drum hard enough when it suits them, but when it comes to safety costing THEM money, it then becomes another story altogether!!

As for the original electrician/contractor being struck off, i doubt that very much, and even if he did, would have no trouble signing up with one of the others. I doubt very much that they have any common dialogue between them...

That's what the chap from NAPIT told me....

He said to allow the contractor 15 days to reply to your complaint in writing, if you do not receive a reply, then the customer issues a written complaint to the certification body and they will investigate, anyone's guess how long it could then take to get it resolved. It's probably less stressful for the customer to forget the complaints procedure and just pay another contractor to put it right, the trouble is they'll be out of pocket for 12 RCBO's (being the least disruptive replacement), what are your thoughts on cost for this? I think cheapest MK Sentry RCBO's are about £24each plus certification etc...

 

[Engineer54]

That's what the chap from NAPIT told me....

He said to allow the contractor 15 days to reply to your complaint in writing, if you do not receive a reply, then the customer issues a written complaint to the certification body and they will investigate, anyone's guess how long it could then take to get it resolved. It's probably less stressful for the customer to forget the complaints procedure and just pay another contractor to put it right, the trouble is they'll be out of pocket for 12 RCBO's (being the least disruptive replacement), what are your thoughts on cost for this? I think cheapest MK Sentry RCBO's are about £24each plus certification etc...

No idea on the cost side of things, not being UK resident for a number of years now. I'm sure others here will know and give advice on that side of things...

What was the the rods Ra value on this installation?? Is the earth rod a standard 5/8'' extendable, or one of those short thin twigs they have the cheek to call an earth rod?? A photo or two would be interesting to see!! lol!!

 

[leascliffe]

Thanks . I did check the Ra and surprise, surprise it's 130ohm and I don't think the 'new' rod is extendable either, probably not even 5/8" - I'll be going back to break the news so will try to post a pic or two

 

[Spudnik]

I always thought that the CU had to be all insulated to avoid the 100ma rcd, as its only there to protect the tails.

 

[driverman]

In the past on TT installations.......light circuits with no cpc......100ma time delayed RCD's were used as a main switch / isolator.
But then usually 30ma RCD for skts etc giving discrimination.

 

[Engineer54]

In the past on TT installations.......light circuits with no cpc......100ma time delayed RCD's were used as a main switch / isolator.
But then usually 30ma RCD for skts etc giving discrimination.

Not in 2010, TT installations have required overall 30mA protection for some years now, sockets on TT systems, have required 30mA protection even longer.

 

[leascliffe]

I always thought that the CU had to be all insulated to avoid the 100ma rcd, as its only there to protect the tails.

Seems the 100mA is normally used either upfront followed by 30mA RCD's in a C/U, or if it's in a distribution board powering another C/U with RCBO's elsewhere so that there is discrimination between them. All insulated on TT to avoid the live tails unlikely touching a metal case (before any protection from RCD's)

 

[leascliffe]

Sounds good, it seems the current installation is just wrong, even on the day it was installed in 2010...

..in reply to Engineer54 at #33

 

[Octopus]

Seems the 100mA is normally used either upfront followed by 30mA RCD's in a C/U, or if it's in a distribution board powering another C/U with RCBO's elsewhere so that there is discrimination between them. All insulated on TT to avoid the live tails unlikely touching a metal case (before any protection from RCD's)

Yes metal enclosure, not for a plastic one.

 

[Engineer54]

I always thought that the CU had to be all insulated to avoid the 100ma rcd, as its only there to protect the tails.

I know what your saying, and agree in principle with your above comment. But how many follow the complete recommendations on TT based CU's, like all MCB's/RCBO's being of the DP variety, very few i'd wager...lol!!
Tails into metal-clad CU's used on a TT system, can be more than adequately protected entering the CU by use of a suitable gland or even a suitable grommet/blind grommet. Hell, the tails are insulated and sheathed to start with...

What an upfront 100/300mA S type will achieve on a TT system, is provide an extra/added level of protection to single RCD's covering multiple circuits. The alternative is totally relying on those single RCD's for your earth fault protection. And we all know that RCD's are not the most reliable of protective devices, be they from the high end manufactures, or from budget manufactures...

 

[Engineer54]

Yes metal enclosure, not for a plastic one.

You'd be a fool not too, especially if it was Your house/installation!! lol!!