TT eicr code?

[D Skelton]

If you have a fault where the resistance is between 7660Ω and 2300Ω then the RCD would (probably) not trip in <0.2 s however it is not required to according to BS7671. This would be a similar situation to MCBs that will not trip in the required time if the fault current is low; similarly how do you know and MCB will trip in the time stated, you do not know, you are relying on the manufacturers making them to standard. It is not (in standard situations) safe to test this compliance.

You are quite right, however we still record the disconnection time on a 100mA at 1x and 1x only. This is the disconnection time at its rated current, which is higher than 200ms, therefore it will not comply.

 

[Richard Burns]

You are quite right, however we still record the disconnection time on a 100mA at 1x and 1x only. This is the disconnection time at its rated current, which is higher than 200ms, therefore it will not comply.

There is a difference between the requirements to meet disconnection times and the requirements to test if the RCD functions.
The disconnection times would be met so long as the Zs reading complied.
The 100mA time delayed RCD tripping in >130ms<500ms at Idn shows that it is working.

 

[D Skelton]

Yes, and in a fault, depending on its conditions, the RCD may or may not trip in less that 200ms, that is my only issue.

 

[Richard Burns]

OK I think I am at a loss to explain here.
The disconnection time of 0.2s for a fault of negligible impedance, which is required by the regulations, would be met.
The RCD would not necessarily disconnect in 0.2s under all circumstances but this is not required at all by the regulations.

 

[Engineer54]

If anyone is going to base whether an installation is safe according to the regs at the time of the installation, they would need to know the date of installation, how often are we blessed with this information? Once upon a time fused neutrals were considered a good idea. Its really up to the individual at the time to make an educated assessment of coding required, many amendments are for the better, some have taken a backward step IMHO. I like to base my decisions on worse case scenarios, can't go far wrong then.

If you were experienced, you would/should be able date an installation to a regulations edition, with some accuracy. Unlike today, Regulations didn't change at anywhere near the regularity they do today... Unfortunately we have 17 day whizz kids and electrical trainee's undertaking/conducting EICR's that haven't got a clue what they are looking at, let alone being remotely able to make an educated assessment. Depends on what you mean by ''worst case'', ..if that means assessing a totally improbable scenario, as being possible, what is that saying?? lol!!

 

[Engineer54]

So what was actually wrong with the long standing previous 0.4 second disconnection times?? Which i might add, is still the disconnection time value for many countries around the world, as well as TN ADS systems in the UK!!

 

[stevethesparks]

No matter how experienced one is, you could never always prove that an installation was installed as per requirements at the time.
I've been in this game 42 years this coming June , and I'm still blimim learning!
I like to try and keep up to date, and have many reference books at my side, its great to know they will all be out of date again come next January. You are certainly right about regs not changing like they do today.

 

[D Skelton]

So what was actually wrong with the long standing previous 0.4 second disconnection times?? Which i might add, is still the disconnection time value for many countries around the world, as well as TN ADS systems in the UK!!

I never said anything was wrong with them, just that where an RCD is used for fault protection on a TT system the maximim permitted disconnection time is now 0.2s. Higher than this is considered unsafe by BS7671:2008

 

[Engineer54]

No matter how experienced one is, you could never always prove that an installation was installed as per requirements at the time.
I've been in this game 42 years this coming June , and I'm still blimim learning!
I like to try and keep up to date, and have many reference books at my side, its great to know they will all be out of date again come next January. You are certainly right about regs not changing like they do today.

Then you should have no problem dating an installation to a reg's edition. lol!! I didn't say you shouldn't test, ....testing is the only way you are going to be sure of any findings you make. Now come on, after 42 years in the game, do you really NEED all those installation by numbers OSG's etc??

 

[Engineer54]

I never said anything was wrong with them, just that where an RCD is used for fault protection on a TT system the maximim permitted disconnection time is now 0.2s. Higher than this is considered unsafe by BS7671:2008

Do you get ''deaded'' faster with a TT installation than a TN one then?? Or is it more about ensuring that RCD protection is included into all TT installations to prop up their 200 ohm Ra value?? lol!!:wings: Don't take this post too seriously now will you!! lol!!

 

[D Skelton]

Do you get ''deaded'' faster with a TT installation than a TN one then?? Or is it more about ensuring that RCD protection is included into all TT installations to prop up their 200 ohm Ra value?? lol!!:wings: Don't take this post too seriously now will you!! lol!!

Haha, no of course not, but when the current regulations deem something unsafe, then I will code it appropriately.

 

[stevethesparks]

Then you should have no problem dating an installation to a reg's edition. lol!! I didn't say you shouldn't test, ....testing is the only way you are going to be sure of any findings you make. Now come on, after 42 years in the game, do you really NEED all those installation by numbers OSG's etc??

I'm afraid I do.
Once upon a time, I could quote regs numbers, but i seemed to have developed a type of dyslexia to all those numbers now lol. Too many regs referring to other regs for my liking.
When I update with a 17th edition course, I thought I was boy wonder again, but its all gone to mush again since :-(
I reckon I could still kick some arse installing MICC, making trunking sets that have near enough been banned, and bashing in some conduit with some intricate bends, but having spent most of my career on that side of the industry, I am almost enjoying catching up on the other side of things, and apart from my reference books, find many posts here enlightening.

I do believe when I attended college all those years ago insulation resistance and ring continuity with a wind up megger was about the most testing that happened. It could just be my memory though.

 

[spark 68]

Part of the difficulty of dating an installation accurately (unless it is untouched and pristine), is that it is often a mish mash of different editions, for example it may have been originally installed to say the 12th then re-wired to the 15th, then at some point had the CU updated to the 16th etc..etc.

We can only really have an educated guess, unless there is prior paperwork (lol in domestic).

Where I disagree with Damien is that I would not fail a fully compliant 16th ed install, it is when you start going further back is where more and more problems arise, and the recommendations become more C2 than C3

The 0.4 disconnection time in the 16th was only for S/Os or final circuits which supply portable equipment and handheld class 1 equipment, for other fixed final circuits a disconnection time of not more than 5 seconds was permitted.

In my view the 16th edition is adequately safe, with no more than a C3 in respect to coding, going any further back and you start attracting C2s.

 

[Engineer54]

I'm afraid I do.
Once upon a time, I could quote regs numbers, but i seemed to have developed a type of dyslexia to all those numbers now lol. Too many regs referring to other regs for my liking.
When I update with a 17th edition course, I thought I was boy wonder again, but its all gone to mush again since :-(
I reckon I could still kick some arse installing MICC, making trunking sets that have near enough been banned, and bashing in some conduit with some intricate bends, but having spent most of my career on that side of the industry, I am almost enjoying catching up on the other side of things, and apart from my reference books, find many posts here enlightening.

I do believe when I attended college all those years ago insulation resistance and ring continuity with a wind up megger was about the most testing that happened. It could just be my memory though.

Much of the work i was doing during my training days (industrial manufacturing sector) and after, was testing!! Everything from ELV to MV installations, to systems control, using test equipment that went way way beyond IR and continuity tests.

Like you, i couldn't quote or spurt off Reg numbers, only really ever look at them, if i want a confirmation, or looking at another aspect of what can be done... I know what you mean about memory though!! lol!!

 

[stevethesparks]

Part of the difficulty of dating an installation accurately (unless it is untouched and pristine), is that it is often a mish mash of different editions, for example it may have been originally installed to say the 12th then re-wired to the 15th, then at some point had the CU updated to the 16th etc..etc.

That the bit I was trying to convey, but you have explained it better than I.