Fitting new CU to TT system and old BS fuse box

[Chris Churchman]

Hi there, new to this site and just after a bit of advice. I am part qualified as a Domestic Electrical Installer and am just waiting for the course to complete my Part P.

I have been asked to install a new Consumer Unit on a TT system in a very old cottage. As seen in the photographs, the current system is the old BS, but I am a little concerned that on examination, the CPS appears to be only 2.5mm where I would have thought it should be 10mm minimum.

Any advice would be greatly received.

Chris

 

[davesparks]

No, Ra for an installation is the combined the resistance to earth of all connected earth electrodes.
Ra is also used with reference to a single electrode.

Testing can be carried out in a number of ways, which generally require an earth resistance tester of some type. The most common method being the 3 wire fall of potential method.
It is possible to obtain an approximation of Ra through use of an earth loop impedance tester where the measured Ze minus half the measured L-N loop impedance is used.

 

[HandySparks]

...It is possible to obtain an approximation of Ra through use of an earth loop impedance tester where the measured Ze minus half the measured L-N loop impedance is used.

And since it's the Ze (& Zs) that really matters with regard to earth fault disconnection times, if you have a supply already on site it's not a bad way of doing it (unless you really need to know an accurate figure for Ra).

 

[Chris Churchman]

YOU are a star! I really appreciate all of this expertise and advice. As you can tell, as much as I am fairly confident in my abilities, there is an awful lot to learn and experience is the greatest of them all. Thank you for all your help.

Kind regards,

Chris

 

[davesparks]

And since it's the Ze (& Zs) that really matters with regard to earth fault disconnection times, if you have a supply already on site it's not a bad way of doing it (unless you really need to know an accurate figure for Ra).

I guess it depends on whether you are happy with an approximation which can be affected by external influences or if you prefer to measure it properly.

 

[davesparks]

YOU are a star! I really appreciate all of this expertise and advice. As you can tell, as much as I am fairly confident in my abilities, there is an awful lot to learn and experience is the greatest of them all. Thank you for all your help.

Kind regards,

Chris

Yes it is clear you need a lot more experience. You are obviously not ready to be working away from your mentor yet. How far through your apprenticeship are you?

 

[Chris Churchman]

Final stages of course and then a weeks practical for the Part P, but it's experience I lack. I have studied in my own time whilst employed elsewhere and not in the electrical industry. Scary times but I intend to take this very slowly and seek help and advice at all times.

 

[davesparks]

So you haven't spent any time working with an experienced electrician?

 

[Andy78]

Final stages of course and then a weeks practical for the Part P, but it's experience I lack. I have studied in my own time whilst employed elsewhere and not in the electrical industry. Scary times but I intend to take this very slowly and seek help and advice at all times.

So you are setting up in business as an electrician with no practical experience ?

 

[Simonslimline]

Final stages of course and then a weeks practical for the Part P, but it's experience I lack. I have studied in my own time whilst employed elsewhere and not in the electrical industry. Scary times but I intend to take this very slowly and seek help and advice at all times.

Can you please explain what this entails?

 

[Simonslimline]

Final stages of course and then a weeks practical for the Part P, but it's experience I lack. I have studied in my own time whilst employed elsewhere and not in the electrical industry. Scary times but I intend to take this very slowly and seek help and advice at all times.

Thats called an apprenticeship!!!

 

[Chris Churchman]

Okay, okay, okay. I know, but you try getting an electrician to take you on, or even get a mediocre job with no previous experience! Believe me, I've tried and I am sick and tired of banging my head against a brick wall.

 

[Leesparkykent]

How longs the entire course out of interest?

 

[HandySparks]

I guess it depends on whether you are happy with an approximation which can be affected by external influences or if you prefer to measure it properly.

Any engineering measurement (including Ra the 'proper' way) will be subject to errors of various sorts and will be affected by external influences. It's your judgement as to whether the errors are significant in each case. In many cases, measurement of Ze will do just fine.

 

[Simonslimline]

Any course that is selling it's unsuspecting candidates Part P practical training is going to be a farce.

Take the recognised route and get proper training IMO.

 

[GMES]

Chris welcome to the forum, out of curiosity what is your background before deciding to become an Electrician, and how long is the course meant to last. The only reason I ask is we see a lot of guys getting sold these short courses with the promise of earning mega money and going straight self employed when the reality can be that the money is not that great and you can end up not qualified, as already been said part p is not a qualification but simply a building regulation.
If you are not confident and qualified you really shouldn't be practising on the public, truth be known you should be looking at a 4-5 year apprenticeship followed by a few more years under an experienced Electrician before going at it on your own.