TT System Questions

[Engineer54]

Threads like this and comments regarding tutors 'skipping over' TT systems prove that training is geared solely towards passing an exam, not to actually provide a student with the basic knowledge needed to work across the variety of systems that an 'electrician' would be expected to be competent to work on.

I personally carry out PIRs for a local authority on the Decent Homes Scheme and the TT installations that I've come across so far have been installed to a very poor standard, a few without any earth electrode at all.

If anything, TT systems should have EXTRA course hours allocated to reflect the total mystery and lack of understanding that many 'electricians' seem to have with TT requirements.

In reality, a copy of BS7671:2008 or even the On-Site Guide provides all that is needed to install a TT system correctly but for whatever reason, the mystery goes on....

I agree with most of what you posted above IQ, but there is very little in my opinion on how to go about installing a working TT system in BS7671. There are many aspects to creating a TT system that if anything, should be far better catered for in the guidance notes they go nowhere near far enough. Those that know about creating TT systems, know there is a great deal more to it, than just bunging/banging a rod in the ground!! Plus the fact they still insist on a totally meaningless max Ra of 200 ohms, which doesn't exactly give any TT system in the UK a fighting chance to begin with!! ...lol!!

 

[topquark]

Ask yourself, what's more likely to fail a TT or a TN based system? TN in case there was any doubt!

 

[Engineer54]

Ask yourself, what's more likely to fail a TT or a TN based system? TN in case there was any doubt!

I theory perhaps, but not in reality, not in what the general consensus of what gets installed these days in the UK that professes to be a TT system!! Most are just a thin short spike, banged into the ground, more often than not in the worst locations possible!! lol!! Most of the year, it's virtually doing absolutly nothing!!! Not that 200 ohms will be doing much anyway...lol!!!

 

[topquark]

I theory perhaps, but not in reality, not in what the general consensus of what gets installed these days in the UK that professes to be a TT system!! Most are just a thin short spike, banged into the ground, more often than not in the worst locations possible!! lol!! Most of the year, it's virtually doing absolutly nothing!!! Not that 200 ohms will be doing much anyway...lol!!!

Well I did mean a properly installed 5/8" system with at least 3 rods and a Ze < 20 Ohms, which (if done properly) should be quite achievable.

 

[yellowvanman]

Heard a story once that a home owner had a sprinkler timed to sprinkle the earth rod every day!

 

[topquark]

heard a story once that a home owner had a sprinkler timed to sprinkle the earth rod every day!

pmsl !

 

[IQ Electrical]

Heard a story once that a home owner had a sprinkler timed to sprinkle the earth rod every day!

It's true, he was electrocuted during a hosepipe ban...

 

[Knobhead]

When I was doing the 17[SUP]th[/SUP] course the lecturer tried to skate around systems involving NER’s (neutral earth resistors), I couldn’t help my self for laughing. I was rotten to him and pushed him in to a subject he hadn’t a clue about.
OK you’re not going to come across them very often, but it doesn’t mean they don’t exist. I’ve had them go wrong, and believe me they caused some head scratching. The biggest problem is that they’re one of those things that just sit there doing their job and so get neglected.

 

[Engineer54]

When I was doing the 17[SUP]th[/SUP] course the lecturer tried to skate around systems involving NER’s (neutral earth resistors), I couldn’t help my self for laughing. I was rotten to him and pushed him in to a subject he hadn’t a clue about.
OK you’re not going to come across them very often, but it doesn’t mean they don’t exist. I’ve had them go wrong, and believe me they caused some head scratching. The biggest problem is that they’re one of those things that just sit there doing their job and so get neglected.

I wonder if many here knows what a NER is, and if they do know, would they know what it is actually doing, let alone where you would most commonly see them in use??

Thou this has nothing to do with TT systems.... lol!!

 

[needasparks]

Nope, got me and many others i would think. Damm, i thought i knew it all.

 

[alarm man]

I theory perhaps, but not in reality, not in what the general consensus of what gets installed these days in the UK that professes to be a TT system!! Most are just a thin short spike, banged into the ground, more often than not in the worst locations possible!! lol!! Most of the year, it's virtually doing absolutly nothing!!! Not that 200 ohms will be doing much anyway...lol!!!

not necessarily i done one for a family member,2x 5/8 rods which is 8ft of decent copper into the ground with a mash which isnt easy work,conduit run for earth cable, set in a nice earth pit.just a rod in the ground makes it sound wrong..i wasnt allowed to test it because ive not done a di course,and i dont have the test equipment anyway..but it passed at 76ohm

 

[clicon357]

I wonder if many here knows what a NER is, and if they do know, would they know what it is actually doing, let alone where you would most commonly see them in use??

Thou this has nothing to do with TT systems.... lol!!

NER - something to do with ac generating kit from memory and reducing fault current through the star point............?

 

[Engineer54]

NER - something to do with ac generating kit from memory and reducing fault current through the star point............?

Yes, ...That's one of the most commonly seen uses for NER. Normally used on the larger permanently placed stand-by and prime power generator installations...

 

[Engineer54]

not necessarily i done one for a family member,2x 5/8 rods which is 8ft of decent copper into the ground with a mash which isnt easy work,conduit run for earth cable, set in a nice earth pit.just a rod in the ground makes it sound wrong..i wasnt allowed to test it because ive not done a di course,and i dont have the test equipment anyway..but it passed at 76ohm

I'm not saying ''ALL'' UK TT systems are crap, i'm sure there are many decent TT systems in place, created by decent electricians. But from what i have been reading on this and other UK forums, the general practice these days are to bang in a thin short earth rod (if indeed you can call them an earth rod) in the easiest and worst locations you can place a rod. If it's Ra is around 200 ohms, it's a good-un and then happily totally rely on the RCD(s) in the CU for earth fault protection. They probably don't even know that the first metre of that rod will be rendered useless when the ground freezes in winter, or dries out in the summer...

So which system would fail first in these conditions, ...haha, the TT system, every time!!!

 

[alarm man]

I'm not saying ''ALL'' UK TT systems are crap, i'm sure there are many decent TT systems in place, created by decent electricians. But from what i have been reading on this and other UK forums, the general practice these days are to bang in a thin short earth rod (if indeed you can call them an earth rod) in the easiest and worst locations you can place a rod. If it's Ra is around 200 ohms, it's a good-un and then happily totally rely on the RCD(s) in the CU for earth fault protection. They probably don't even know that the first metre of that rod will be rendered useless when the ground freezes in winter, or dries out in the summer...

So which system would fail first in these conditions, ...haha, the TT system, every time!!!

its either that or by the grace of god,a decent rod length should ensure protection all year round,ive never seen any problems in summer or winter,and i know of some farms where the water main freezes under ground so they leave a tap running all day and night,which is a pain when your metered..

 

[telectrix]

should let that tap run over the earth rod then.

 

[alarm man]

should let that tap run over the earth rod then.

it will freeze at the clamp,or in the hose.

 

[Engineer54]

its either that or by the grace of god,a decent rod length should ensure protection all year round,ive never seen any problems in summer or winter,and i know of some farms where the water main freezes under ground so they leave a tap running all day and night,which is a pain when your metered..

There is no problem with rods of any decent depth/length. But these thin short rods that you can't even extend are useless. They should be taken off the market, as there not fit for purpose, full stop!! lol!!

 

[Elmocash]

so ,can I fit an RCD incomer to a localy earthed (rod and structural steel) metalclad board that is fed by an SWA cable, supplied from a bussbar chamber, via a (metalclad) switch/fuse, all SWA, no 'tails' ?

 

[ackbarthestar]

There is no problem with rods of any decent depth/length. But these thin short rods that you can't even extend are useless. They should be taken off the market, as there not fit for purpose, full stop!! lol!!

There are several methods of creating a reliable earth path, assuming that the surrounding resisitvity of the soil is reasonably low.
One method as used by lightning engineers is to use a conductive cement and increase the csa of the earth rod. No need to use anything more than 15mm2 rods with a length of 1.2m.