Earthing and supply in Hartlepool
- Thread starter oharaf
- Start date
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Has this property got any protective equipotential bonding in place? If so (hope so!) then it'll share the same incoming (metalic?) supply pipes. If next door has been PME'd and has PEB in place then couldn't that be a reason for such a low Ze?
Gary,
it will contribute. By how much - who knows?
Any conductive material could form part of the TT earth path to the supply.
The lump of lead in the garden will provide an excellent connection to the general mass of earth.
If we are arguing about the effect of bonding on Zs, then Zs should be measured without any bonding in place at all.
There are some that advocate this, but the IET is not one of them.
Surely the point is if the connection via lead, via the mass of earth, via next door's water pipe, via the earth clamp, via the 10mm bonding cable, via the MET and via the supply's neutral, is 0.3ohms - what does that say about the resistance of the general mass of earth? If next door go plastic, what about the other next door, or the house at the back?
Even if next door go plastic, they would have to cut the metallic pipe flush with the wall, or else make the joint outide the property in order to not have the clamp on a metallic portion. In reality, they will make it inside and keep the clamp on the little bit of metal before the joint.
At the end of the day, we have no idea at all what is going on next door. Based on evidence, it's likely to be TT as well (or unearthed).
it will contribute. By how much - who knows?
Any conductive material could form part of the TT earth path to the supply.
The lump of lead in the garden will provide an excellent connection to the general mass of earth.
If we are arguing about the effect of bonding on Zs, then Zs should be measured without any bonding in place at all.
There are some that advocate this, but the IET is not one of them.Surely the point is if the connection via lead, via the mass of earth, via next door's water pipe, via the earth clamp, via the 10mm bonding cable, via the MET and via the supply's neutral, is 0.3ohms - what does that say about the resistance of the general mass of earth? If next door go plastic, what about the other next door, or the house at the back?
Even if next door go plastic, they would have to cut the metallic pipe flush with the wall, or else make the joint outide the property in order to not have the clamp on a metallic portion. In reality, they will make it inside and keep the clamp on the little bit of metal before the joint.
At the end of the day, we have no idea at all what is going on next door. Based on evidence, it's likely to be TT as well (or unearthed).
You hit the nail on the head, we don't know what is going on next door hence we should not be relying on the protective equipotential bonding to provide the earth fault loop impedance path which could be via them for it.
We need to provide our own earthing system which we know is reliable, in the case of a TT system this is normally via an earth electrode and the resulting impedance from this path used to calculate the current which can flow Zs=Ze+(R1+R2) etc. TT systems will almost certainly require RCD protection to all circuits to comply with the 50v rule.
We need to provide our own earthing system which we know is reliable, in the case of a TT system this is normally via an earth electrode and the resulting impedance from this path used to calculate the current which can flow Zs=Ze+(R1+R2) etc. TT systems will almost certainly require RCD protection to all circuits to comply with the 50v rule.
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But the OPs property is TT. This is how TT works. We have no idea what the exact mass of earth path is. Some of it maybe via next door's bonding. Some of it may be via a hundred or a thousand tiny parallel paths. But in any case, it's very unlikely that the major reason for a low impedance earth path is next door's bonding.
An earth rod is installed but was not connected. It was reconnected by the OP. Zs readings 0.3ohms. NEDL will provide a means of earthing to extend PME to the property within 2 months.
With such low Zs, the OPDs can be considered to provide earth fault protection. Certainly well enough for the next 2 months until the major upgrade work is undertaken.
This isn't the final, completed installation so I can't see why people are getting their knickers in a twist.
So, because the installation is not complete, there is no risk at all of a dangerous fault occouring then?
I'd rather play it safe and RCD the whole lot for the time being, just for my own peice of mind if nothing else.
It would certainly make it less likely to electrocute someone in the event of a fault.
Not if it's one of the 3 in 100 that will fail.
And with Zs readings of 0.3ohms...that's better than many TN-S installations.
I assume you've assumed that the customer can swallow all the cost.
Why should the customer pay for an electrician's whimsical appeasement of his conscience and inability to apply soundness of engineering thought in a rational cost/risk/benefit/analysis...
And with Zs readings of 0.3ohms...that's better than many TN-S installations.
I assume you've assumed that the customer can swallow all the cost.
Why should the customer pay for an electrician's whimsical appeasement of his conscience and inability to apply soundness of engineering thought in a rational cost/risk/benefit/analysis...
Making an installation compliant with BS7671, wether as a temporary measure or not is not whimsical.
You are still not understanding the point about parallell paths from the water pipe which could be removed at any time without warning.
Does BS7671 call for you to install two RCDs in series incase you have fitted one of the 3% which may fail?
So why would it be any different with this installation.
You do it you way, I'll do it mine.
P.S. I don't beleive those RCD statistics for 1 second.
Of the thousands of RCDs I have tested over the years, the failure rate is much, much, much lower than 3%
You are still not understanding the point about parallell paths from the water pipe which could be removed at any time without warning.
Does BS7671 call for you to install two RCDs in series incase you have fitted one of the 3% which may fail?
So why would it be any different with this installation.
You do it you way, I'll do it mine.
P.S. I don't beleive those RCD statistics for 1 second.
Of the thousands of RCDs I have tested over the years, the failure rate is much, much, much lower than 3%
If you're going to use the parallel paths argument, please be so kind as to define ALL the paths and the contribution they make to the earth fault loop impedance. Then perhaps we can start eliminating them one at time to determine their exact influence.
By your reckoning, TT should be banned or else tested every 24 hours to be sure it's still performing and that none of the dozens, or hundreds, or thousands of possible parallel paths haven't been removed.
Is this how you normally treat TT?
I'm not arguing about the use of RCDs. But there still to be plenty of people who think they are a fail-safe, bullet proof guarantee of safety. As you've correctl agreed, RCD use comes with risk.
They say an E-Type Jag is a cover for inadequate manhood. Over-engineering, flapping about minute nuances of risk could be said to be a cover for inadequate ability to design.
Yes, you do it your way. I hope you're customers enjoy the unneccessarily expensive invoices you give them.
By your reckoning, TT should be banned or else tested every 24 hours to be sure it's still performing and that none of the dozens, or hundreds, or thousands of possible parallel paths haven't been removed.
Is this how you normally treat TT?
I'm not arguing about the use of RCDs. But there still to be plenty of people who think they are a fail-safe, bullet proof guarantee of safety. As you've correctl agreed, RCD use comes with risk.
They say an E-Type Jag is a cover for inadequate manhood. Over-engineering, flapping about minute nuances of risk could be said to be a cover for inadequate ability to design.
Yes, you do it your way. I hope you're customers enjoy the unneccessarily expensive invoices you give them.
I'm not saying you are going to get away from parallel paths caused by other premises via the general mass of earth, however I do find it difficult to believe that an earth electrode will have a Ze of 0.3 ohms, the path being via the general mass of earth, wether it be a pipe or a stake. A low reading like this would lead me to believe that the path is directly via another premises via a metal conductor. If it is a metal conductor then you need to assess the risk of this becoming disconnected.
Or you can do as we are taught, for a TT system is normally to sink a rod, measure the Ze and add it to R1+R2.
Or you can do as we are taught, for a TT system is normally to sink a rod, measure the Ze and add it to R1+R2.
I think some of the latecomers should read the OP and carry on from there. Look at the before photos, read what action the OP took and what action will be taken in a few weeks.
I predicted a reading of 0.1 to 0.3ohms for the lump of lead. Not a guess, I've seen it so so so many times before.
What I find hard to swallow is the obsession with the belief that only Ra matters and not Zs and that the excellent readings can only come via one property next door.
Can ayone point me to where in BS7671 that the route via the mass of earth is defined?
I predicted a reading of 0.1 to 0.3ohms for the lump of lead. Not a guess, I've seen it so so so many times before.
What I find hard to swallow is the obsession with the belief that only Ra matters and not Zs and that the excellent readings can only come via one property next door.
Can ayone point me to where in BS7671 that the route via the mass of earth is defined?
Ze you mean? It is the earth fault loop impedance external to the property.
If you look at figure 2.5 on page 34 of BS7671:2008 it says for a TT system: All exposed-conductive-parts of an installation are connected to an earth electrode which is electrically independant of the source earth. There is also a picture.
I'm a bit cautious when I see such a low reading - I have had to put in 3m long rods before in order to get a reading sub 100 ohms!
If you look at figure 2.5 on page 34 of BS7671:2008 it says for a TT system: All exposed-conductive-parts of an installation are connected to an earth electrode which is electrically independant of the source earth. There is also a picture.
I'm a bit cautious when I see such a low reading - I have had to put in 3m long rods before in order to get a reading sub 100 ohms!
Yes but did you have very large lump of lead to take advantage of -albeit temporarily - plus a genuine earth rod.
Parallel paths affect Zs on TT, TNS and TNCS.
As I said before, there are some who reckon Zs should be measured with bonding disconnected - the IET is not one of them.
Parallel paths affect Zs on TT, TNS and TNCS.
As I said before, there are some who reckon Zs should be measured with bonding disconnected - the IET is not one of them.
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