TT eicr code?

[hoppy]

Hi doing an eicr on a tt system, plastic board, bonding ok! It is a split 16th edition board with 80amp 100m/amp main switch which has the lighting, smokes and boiler on. On the other side is a 63amp 30m/amp rcd protecting sockets, cooker and shower. The Ra is 28 ohms.

anyway my interpretation of the regs is that for the circuits protected only by the main switch rcd that this would still merit a C3 for not be protected to 30m/amp, would you guys agree? Cables buried in walls less than 50mm and not protected via anything!

thanks

craig

 

[Plonker 3]

I would go for a C2, what was the Zs reading on the 100mA RCD protected circuits?

 

[hoppy]

I see what you are saying but even if covered by a 30mA rcd the zs factor is still the same, so circuits protected by a 30m/A rcd would also be a code 2! Haha think I have just answered my own question, C3 it is then!

 

[hoppy]

Zs results were between 4 and 5 ohms for the 100m/A side

 

[Plonker 3]

What is the max permissible Zs reading for a 100mA RCD?

 

[Plonker 3]

Also don't forget the 100mA RCD is for backup to the 30mA RCD should that fail.

 

[Des 56]

Page 15 of this opinion agrees with you http://www.select.org.uk/downloads/BestPracticeGuide4-Issue3.pdf

The installation described appears to be fine for the 16th edition if the 100m/amp is time delayed ?
Comparison with the 17th would indicate a code 3 for the buried cables



100m/amp Rcd 500 ohms

 

[Deleted member 26818]

Interpretation of the Regs. is always a bit of a mine field.
For instance, generally there is no requirement for any circuit, other than those of a location containing a bath or shower to be provided with 30mA RCD protection.
In this particular instance, the requirement is to provide Additional protection for cables concealed in walls, one of the acceptable methods includes the provision of 30mA RCD protection.

 

[SirKit Breaker]

I am not here to argue with you, i haven't seen the job. Does it comply with the requirements in place at the time it was first put into service, if so then you can only recommend C3 for improvements.

Just for info under current regs the usual set up for domestic TT would normally be 100mA RCD Main Switch protecting the whole board, and then 30mA RCD's for final circuits however you choose to configure it using RCD's for banks for MCB's or RCBO's etc. You have to have a maximum of 30mA for additional protection as this ensures that the voltage under fault conditions stays at or below 50V which is the safe touch voltage.

I use the word "Usual" lightly, there are other conditions that may change what i have written.

Cheers…………Howard

 

[D Skelton]

If it's a 100mA type-s up front then for the circuits not protected by the 30mA RCD then its a C2 as they won't meet required disconnection times and a C3 for circuits not having additional protection by 30mA RCD, if its a 100mA up front then it's just a C3 for any circuits that don't have additional protection by 30mA RCD.

 

[SirKit Breaker]

If it's a 100mA type-s up front then for the circuits not protected by the 30mA RCD then its a C2 as they won't meet required disconnection times and a C3 for circuits not having additional protection by 30mA RCD, if its a 100mA up front then it's just a C3 for any circuits that don't have additional protection by 30mA RCD.

Always nice to be enlightened, Cheers.

 

[Deleted member 26818]

As has already been stated, if the installation complied with (and still complies with) the Regulations in force at the time of design. Then there is no justification for a code C2, in this instance.
There is no requirement in the Regulations for existing installations to comply with current Regulations.

 

[D Skelton]

As has already been stated, if the installation complied with (and still complies with) the Regulations in force at the time of design. Then there is no justification for a code C2, in this instance.
There is no requirement in the Regulations for existing installations to comply with current Regulations.

Regardless of whatever regulations it was designed to if the overcurrent protective devices will not disconnect the circuit under fault conditions in the required time then it's a C2. An EICR is always carried out to current regulations.

Would you not code bare live cable not out of reach but in use that was designed to the first edition of the wiring regulations?

 

[hoppy]

Thanks D Skelton, so basically if an upfront 100mA S type is the only rcd protection for the circuits, then your opinion is a C2 as disconnection times wont be met. But if it is a standard 100mA rcd then it is only a C3.
Not questioning you, but if you test the s type rcd and disconnection times are 20ms @ 1 time and 14ms @ 5 times, then surely disconnection times have been met. As BS7671 states a TT disconnection time of 0.2s for final circuits which equates to 200ms.

Anyone any input, i am always looking to learn?

 

[JD6400]

Thanks D Skelton, so basically if an upfront 100mA S type is the only rcd protection for the circuits, then your opinion is a C2 as disconnection times wont be met. But if it is a standard 100mA rcd then it is only a C3.
Not questioning you, but if you test the s type rcd and disconnection times are 20ms @ 1 time and 14ms @ 5 times, then surely disconnection times have been met. As BS7671 states a TT disconnection time of 0.2s for final circuits which equates to 200ms.

Anyone any input, i am always looking to learn?

It is late and I have hit the booze , but firstly why would you x5 a 100mA , let alone an s type and secondly those look like 30mA times and a couple of hundred shy of where I would expect an s type to be ?

Like I say , late in the evening + fire water = possible wrong end of the stick on my part !:svengo: