OK,
Curious, why does the earth wire need increasing in size?
Curious, why does the earth wire need increasing in size?
Just Moved And Learned What A Tt Earth Is, Some Questions!
- Thread starter curious-one
- Start date
Help Support Talk Electrician Forum:
I never said that. It seemed as if curious-one had a reasonable idea what he was doing but as he is quite happy to leave the installation in a dangerous state it shows that he hasn't.
When it comes down to it, no matter how competent DIYers think they are, they aren't, as has been proved on here time and time and time again.
One DIYer patting the other on the back for leaving a potentially dangerous installation powered up.
curious-one
Active member
Who said it was powered up?
Hi Curious one,
What is supposedly wrong with your existing main earthing conductor?? [The wire to the rod]
john..
What is supposedly wrong with your existing main earthing conductor?? [The wire to the rod]
john..
curious-one
Active member
Hi I was advised by the electrician who tested today that it needed upgrading to 16mm, I haven't done the maths to double check, I don't mind changing it and for the sake of the effort I figure it can't hurt, overkill being underrated and all!
Additionally, the fact I'm online doesn't indicate I have power. I'm a server engineer and one thing I'm not lacking in is UPS and extended runtime packs, if I were to get particularly desperate there is also a 3kw generator in the shed, for heat I have an open fire.
Additionally, the fact I'm online doesn't indicate I have power. I'm a server engineer and one thing I'm not lacking in is UPS and extended runtime packs, if I were to get particularly desperate there is also a 3kw generator in the shed, for heat I have an open fire.
Why do you need a 16mm sq. cpc with a TT system, what will be the fault current that the conductor is required to carry, is this any more than can be carried by say a 2.5mm sq.?
What is the installation method of the earthing conductor?
What is the installation method of the earthing conductor?
curious-one
Active member
The current earthing conductor is run across the loft and then down the internal walls (set in the plaster), then it's been drilled out at the bottom where it connected to the old rod exposed. I've trimmed the discoloured end and put the new rod into an inspection pit and then clamped it, I suspect the recent digging there has knackered it's effectiveness as a location hence running another from it further away tomorrow morning. I'll get the threaded type so I can go deeper at the 2nd location if required, saves keep digging trenches to lay the cable to the next rod!
Curious, why are you ignoring my questions, they are very, very valid to your scenario.
A couple of points,
You have NOT had your earthing tested, your 'electrician' has carried out a totally inappropriate and meaningless test,
Point 2, you shouldn't have your earthing conductor (note, it is NOT a main earthing conductor) buried into the wall on a TT system, completely poor workmanship and/or advice IMHO
Your 'electeician should be able to carry out a couple of quick tests and tell you if you need a deeper rod, or multiples thereof,
I'm not sure he is very conversant with TT system tbh.
You have NOT had your earthing tested, your 'electrician' has carried out a totally inappropriate and meaningless test,
Point 2, you shouldn't have your earthing conductor (note, it is NOT a main earthing conductor) buried into the wall on a TT system, completely poor workmanship and/or advice IMHO
Your 'electeician should be able to carry out a couple of quick tests and tell you if you need a deeper rod, or multiples thereof,
I'm not sure he is very conversant with TT system tbh.
Hi Curious-one,
Pay attention to Sidewinder and his questions..... As he says, they are VERY relevant to what you are doing, and ARE going to save you a lot of hassle!!!!
What size is the existing cable and how is it installed?? is it out in the open, buried, protected against corrosion, mechanically protected....
john..
Pay attention to Sidewinder and his questions..... As he says, they are VERY relevant to what you are doing, and ARE going to save you a lot of hassle!!!!
What size is the existing cable and how is it installed?? is it out in the open, buried, protected against corrosion, mechanically protected....
john..
Last edited by a moderator:
Unless you miss understood your electrician about the 50V thing then he doesn't understand his tester
Generally if a meter shows 50V on a RCD test then it means that the touch voltage has exceeded 50V which is a dangerous situation
Generally if a meter shows 50V on a RCD test then it means that the touch voltage has exceeded 50V which is a dangerous situation
Hi Steps,
Re "main" Late and tired mate!!
Been busy trying to sort out the collection of my new toy!!
http://i1178.photobucket.com/albums/x373/resistance87/Drill.jpg
john..
Re "main" Late and tired mate!!
Been busy trying to sort out the collection of my new toy!!
http://i1178.photobucket.com/albums/x373/resistance87/Drill.jpg
john..
curious-one
Active member
Sorry sidewinder I missed your post in the mass of others. My incoming supply is 60A at 235v, but from what I gather I need to know Ra to calculate the maximum fault current, which it seems I do not having due to the earth not being correctly tested. The largest circuit that is available at the moment is the cooker at 30A (obviously off as stated earlier) but there will be a requirement in the near future for a 40A shower. The fuse board will be upgraded to a CU (by an electrician, I don't have the tools) which will be 30ma rcd and rcbo protected circuits. If I don't need Ra then if someone can link me to the calcs I'll do them immediately, thanks.
Sorry just read further, the old cable is chased into the wall and then exits at the bottom.
Sorry just read further, the old cable is chased into the wall and then exits at the bottom.
Last edited by a moderator:
curious,
Your incoming supply is NOT 60A @ 235V, it is 60A @ 230V.
Design calculations are done at nominal, not, measured voltages.
Next, why do you believe that you need a 16mm sq. earthing conductor, and more importantly why does your spark.
I'm not saying that it is not necessary, but why are you looking to use it?
You are going about things in the totally wrong way.
From an Ex-Service Engineer, who actually does this stuff for a living, including the design and consultancy side, on both BS7671 & EN60204-1 amongst others.
Your incoming supply is NOT 60A @ 235V, it is 60A @ 230V.
Design calculations are done at nominal, not, measured voltages.
Next, why do you believe that you need a 16mm sq. earthing conductor, and more importantly why does your spark.
I'm not saying that it is not necessary, but why are you looking to use it?
You are going about things in the totally wrong way.
From an Ex-Service Engineer, who actually does this stuff for a living, including the design and consultancy side, on both BS7671 & EN60204-1 amongst others.
curious-one
Active member
I must confess I didn't quiz the spark on the recommendation, I just took it as advice. Thank you for the info about nominal voltage by the way!
Last edited by a moderator:
you need to get an electrician in,
and quickly, before this bloke you have now does something seriously wrong, like probably fit a metal CU without adequate precautions,
I do hope he was intending to use DP RCBOs,,,,,,
sorry to state the obvious, but he seems more like an installer rather than a real electrician, he is seriously out of his depth, thinking he can test even Ze at a socket is madness, firstly, everything should be dead to test Ze, as all the earths MUST be disconnected from the supply earth, in your case, the rod, thereby leaving you with NO earth and a potentially lethal voltage flowing down it, or any other earth connected to it,
he is a NUMPTY of the highest order, did he walk funny and wear a stetson?
and quickly, before this bloke you have now does something seriously wrong, like probably fit a metal CU without adequate precautions,
I do hope he was intending to use DP RCBOs,,,,,,
sorry to state the obvious, but he seems more like an installer rather than a real electrician, he is seriously out of his depth, thinking he can test even Ze at a socket is madness, firstly, everything should be dead to test Ze, as all the earths MUST be disconnected from the supply earth, in your case, the rod, thereby leaving you with NO earth and a potentially lethal voltage flowing down it, or any other earth connected to it,
he is a NUMPTY of the highest order, did he walk funny and wear a stetson?
Doc Hudson
Moderator
- Joined
- Oct 21, 2008
- Messages
- 5,620
- Reaction score
- 230
There are tables in the regulations that give the resistance values of standard copper conductors. (2.5mm2 is 7.41miliohms per metre 16.0mm2 is 1.15miliohms per meter)
so if you compare 2.5mm2 & 16mm2 CSA you are talking of a difference of something around 0.062ohms per 10m length. So even with a long run from your CU to the rod the difference in actual resistance value will have negligible effect upon the overall earth loop impedance path back via the rod. The Ra of the rod itself will be the biggest governing factor. Unless you are getting your rod down below 10ohms the fault current via a direct short Live to Earth is not going to be a major issue for a piece of 2.5mm2 CSA. and assuming your RCD is operating correctly then the power will be disconnected in a very short time well before the earth has to carry much current. There may be some other factors that require increased CSA and mechanical protection to the cable, but a TT does not need a 16mm earth by default. It would be interesting to know the reasons why your electrician recommends 16.0mm2
Doc H.
so if you compare 2.5mm2 & 16mm2 CSA you are talking of a difference of something around 0.062ohms per 10m length. So even with a long run from your CU to the rod the difference in actual resistance value will have negligible effect upon the overall earth loop impedance path back via the rod. The Ra of the rod itself will be the biggest governing factor. Unless you are getting your rod down below 10ohms the fault current via a direct short Live to Earth is not going to be a major issue for a piece of 2.5mm2 CSA. and assuming your RCD is operating correctly then the power will be disconnected in a very short time well before the earth has to carry much current. There may be some other factors that require increased CSA and mechanical protection to the cable, but a TT does not need a 16mm earth by default. It would be interesting to know the reasons why your electrician recommends 16.0mm2
Doc H.
Last edited by a moderator:
Similar threads
- Locked
