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!!