Question on TT main RCD

[067256]

Hi there,
Have installed a new circuit for a bathroom heater (3Kw)
TT system, old style wlyex rewirable DB. Earth rod reading 126 ohms, so ok with that. Bonding fine.
Main RCD on incomer did not trip out when tested...its 1 of those old style crabtree 60a ones with a yellow test button. Shall i replace with a 100Ma or 30Ma?
Just a bit concerned that when i have fitted the new RCD it may pick up 'other faults'
Thanks.

 

[067256]

Many thanks for all your advise......i do get the feeling that some of you think i am 'wet between the ears' just coming out of my time. And i admit that i should of done further investigation beforehand, but i am here now and asking for advise. We are not all perfect.
For me now it's about completing the job to a safe conclusion. I shall replace the VOELCB and look at getting the EFLI reading to less than 100 as possible. It does confuse me though that the OSG (page 43) states 200 Ohm in black and white and no mention of 100 ohm or instability.
Hence my very first comment.
Thanks again.

 

[Guest123]

I wasn't having a pop, just wanted to make sure the severity of the condition was understood.

 

[067256]

Lenny,
Thank-you for your time on this issue. One other question, i remember from my 'college days' that an earth rod reading can change many times due to weather etc.....i shall take another reading tomorrow. What if the reading tomorrow was now below 100???
Is the installation, on sign off only as good as the day you tested and did the work?

 

[Des 56]

It does confuse me though that the OSG (page 43) states 200 Ohm in black and white and no mention of 100 ohm or instability.


As yoiu know,the on site guide is produced by the people who make the regulations
The Niceic like to think they can make regulations

 

[trev]

Who is the client? If it's a friend or family member you're going to have a much easier ride on this one
What thoughts have you given to notification? The work IS notifiable no ifs or but. You might have your CPS sorted but wee have no way of knowing
Is there someone near you who would be willing to "Hold your hand" while you get yourself out of the brown stuff

 

[tony mc]

Maybe your client could have the earthing converted to PME its worth having a look at that if it is possible!!

 

[trev]

A PME conversion would be costly and slow to be installed though. 5/8 rods would be about the same price and could be installed tomorrow if the wholesalers have them

 

[tony mc]

Totally agree as the premises needs to be made safe ASAP !

 

[trev]

A question the op needs to ask his client is how much cash do you have spare just now

 

[Engineer54]

It does confuse me though that the OSG (page 43) states 200 Ohm in black and white and no mention of 100 ohm or instability.


As yoiu know,the on site guide is produced by the people who make the regulations
The Niceic like to think they can make regulations

But sad to say, in this case, they are closer to being correct than the OSG. That 200 ohm max is in dire need of revision, it's a totally pointless number!!

067256,

As been advised it would be better to get some extend able 5/8'' rod's and go deep, your after as low a Ra as you can get. if you do have a go, ...make sure you are at least the total length of the combined rods away from the existing rod. You can then link the 2 positions together. Remember. Depth equals stability as well as lower Ra values...

 

[Engineer54]

A PME conversion would be costly and slow to be installed though. 5/8 rods would be about the same price and could be installed tomorrow if the wholesalers have them

I would ALWAYS advise conversion to a PME connection when and where it is available, than relying on a TT system, especially in the UK...

 

[Deleted member 19807]

200 Ohms may be ok if thats the worst its ever going to get, you have to consider if you will still be getting the same reading when there has been no rain for a couple of months and its hot, so drying out the ground. You are not just trying to achive a number you are installing kit that will be safe after you have left and until the next test, maybe 10 years down the line.

 

[067256]

Hello again,
Explained to the client (it's a friend of a friend) the severity of the problem and they were happy to get the problem sorted. So this morning i got 2 x 14mm earth rods from the wholesalers, just incase 1 4 foot rod was'nt enough!
DAMM it was HARD, HARD work.... but got both rods driven into the ground and the result was a new reading of 42.8 Ohms.
Fitted new 63a 30Ma rcd and trips out at 18.1ms (1x) and 12.9ms (5x)
This is going to be my Part P assessment job. Should of picked a different job but hey, there you go. I can explain to the assessor the problems i found and how i addressed them. Was going to go with Elecsa, but chose Napit in the end. Any ideas on how these peolpe are???
Thanks again.

 

[Engineer54]

Hello again,
Explained to the client (it's a friend of a friend) the severity of the problem and they were happy to get the problem sorted. So this morning i got 2 x 14mm earth rods from the wholesalers, just incase 1 4 foot rod was'nt enough!
DAMM it was HARD, HARD work.... but got both rods driven into the ground and the result was a new reading of 42.8 Ohms.
Fitted new 63a 30Ma rcd and trips out at 18.1ms (1x) and 12.9ms (5x)
This is going to be my Part P assessment job. Should of picked a different job but hey, there you go. I can explain to the assessor the problems i found and how i addressed them. Was going to go with Elecsa, but chose Napit in the end. Any ideas on how these peolpe are???
Thanks again.

Did you couple them together to go deep, or did you drive them in separately??

 

[067256]

coupled together.