Electrical installation certificates

[wayneward25]

Hi

Im currently doing my 17th edition and ive got a few mock certificates to do.

Im a bit confused on the section that states

particulars of installation referred to in the certificate.

Maximum demand.

surely the maximum demand is determined by the size of the fuse?

and I cannot find any details in the 17th edition book regarding diversity calculations

please help!!!

 

[PrenticeBoyofDerry]

Have you got the on-site-guide
If you have take a look at "Appendix A"
You don't just add all the current ratings of the protective devices up!

 

[wayneward25]

no only got the full 17th book which is a minefield and the iee electricians guide to the building regulations

 

[wayneward25]

theres a few of them onsite guides on amazon which one is it?

 

[PrenticeBoyofDerry]

The green one, same as big green one, the exam you are studying for.
This may help
http://www.tlc-direct.co.uk/Book/6.2.3.htm

 

[PrenticeBoyofDerry]

the iee electricians guide to the building regulations

That should have them in, but looked and can't find them.
Look at the link above and I assume you taking 17th editions because you want to do electrical work, so you will need the OSG!

 

[wayneward25]

yea im gonna get it now thanks

 

[wayneward25]

If it was an existing installation to a domestic property but addition of a new circuit was being added would the maximum demand that they are asking for in the certificate still be that of the complete installation or just the maximum demand of the new circuit that has been added?

 

[flameport]

It's the maximum demand of the installation as a whole - not just the bit you have added.
The point being that you are showing that you have considered both the existing and new loads to ensure you are not exceeding the capacity of the supply.

The fuse size is of little relevance, and in most instances you won't know what the fuse is anyway, since the only way to know would be to remove it and look, which of course would be tampering with DNO equipment.

 

[PrenticeBoyofDerry]

If it was an existing installation to a domestic property but addition of a new circuit was being added would the maximum demand that they are asking for in the certificate still be that of the complete installation or just the maximum demand of the new circuit that has been added?

You would add the new circuit to the total of the existing system, but remember you still apply the percentage factors of the circuits, so if it was new 20A socket radial it would be 40% of that or if lights 66%

 

[wayneward25]

thanks guys I really appreciate it, one final thing how come they dont include the water inside a copper pipe when taking into consideration supplementary bonding???

 

[SparkyTris]

could it be because fresh water is an insulator at 240V?

 

[JohnW2]

could it be because fresh water is an insulator at 240V?

Even if it were sea water, or even strong brine, the copper would win hands down. Do you think he might have actually meant plastic pipe?

Kind Regards, John

 

[SparkyTris]

I thought is said plastic when I read it!

 

[PrenticeBoyofDerry]

thanks guys I really appreciate it, one final thing how come they dont include the water inside a copper pipe when taking into consideration supplementary bonding?

Not sure what you really mean or whether my answer is relevant but I'll answer question as read:
One thing to consider is copper as a conductor is better than water.
The other is, not all copper pipes contain water or service water appliances.
If your question was actual in regards to plastic pipework rather than copper.
Plastic is an insulation material and will create a barrier between any potential electrical contact between the voltage and the water contained within the pipework, should an electrical fault occur.

Yes you may have metallic fittings on appliances that are served by plastic pipes but if the requirements of BS7671 are upheld, any external influences should have been negated.