TT System Questions

[ackbarthestar]

our teacher/tudor told us about it system in 17th edition course, but it was brief, all i know is big resistance and no circuit breakers.... but are monitored am i right

Partially right. Yes the circuits are monitored and protected by O/C devices

You have two fault levels on each final circuit
First fault = monitored and alarmed
Second fault = disconnection of circuit within the times specified in table 41.1

 

[i=p/u]

but he did say, will probably never come across it, but if it is in hospitals etc, theres everychance someday

 

[ackbarthestar]

but he did say, will probably never come across it, but if it is in hospitals etc, theres everychance someday

Yes, as E54 states it appears in all sorts of medical, industrial and ground engineering applications and really should be covered as a completely separate thread since many existing/future electricians are going to come across this method of 'earthing' in parts of large installations.

 

[IQ Electrical]

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....

 

[ackbarthestar]

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 agree with the rest of your post but this statement I feel needs a little boost.
There is not one, or not one that I know of, college in this country that doesn't practice this method of of 'success'. The lecturers tend to verier towards the, 'make sure the student knows what the hell he/she is doing before you let them out of the door'. Managers tend to use a different agenda, fully understandable, mind you! When you see what is stuck up their a***s just before term starts, you'll appreciate the dilemma. - and where is this going ?

 

[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.