Periodic testing of pre - 17th edition installations

kenbax · Oct 12, 2011

Hi, as this is my first post, please forgive me if this question has already been asked.

When carrying out a periodic inspection of a commercial/industrial installation, the earth loop measurements are higher than currently acceptable in the 17th edition regs and are subsequently highlighted in the NICEIC computerised test sheets. If the existing installation was correctly installed to the old 16th edition regulations, surely there must be an allowance made for this when completing the forms. otherwise an installation completed a day prior to the 17th would not be acceptable a day later.

Any comments/answers would be greatly appreciated.

oldtimer · Oct 12, 2011

A lot of people think there is confusion here but alaways remember the 17th edition in not retrospective or in other words you cannot backdate it if you did then we would be in a fine old mess I look at it this way yes the people who sets the standards would like everybody to have their electrical installtion up to date ie RCD safety breaker protectection but they cannot put a gun to your head to do so they have to accept that most installations are what our American cousins would say are Grandaded in or in other words it was installed and coplied to the standard at the time it was done so how do they get around it well you have an old 3036 fuseboard and you want a shower put in ok no probs but now you are midifying or altering the installation so you have to install the shower to the new regs

malcolmsanford · Oct 12, 2011

Are we talking about the Zs values here and the ones highlighted in the tables?

how far are these figures out ? Is there any existing or past test sheets to compare with ?

The 16th edition Zs tables were calculated on 240 volts so that a 20amp BS 88 G fuse in the 17th is 1.77 for the 16th it would have been 1.84 so just 0.07 difference, are you finding this.

Aslo if it is an old site you may find that originally the circuit was designed for say a Genral fuse or a 'B' Type MCB that over the years had been changed to a M or 'C" type

kenbax · Oct 12, 2011

malcolmsanford said:
Are we talking about the Zs values here and the ones highlighted in the tables?

how far are these figures out ? Is there any existing or past test sheets to compare with ?

The 16th edition Zs tables were calculated on 240 volts so that a 20amp BS 88 G fuse in the 17th is 1.77 for the 16th it would have been 1.84 so just 0.07 difference, are you finding this.

Aslo if it is an old site you may find that originally the circuit was designed for say a Genral fuse or a 'B' Type MCB that over the years had been changed to a M or 'C" type

Hi Malcolm, thanks for getting back. Yes it's Zs values that I'm referring to. Readings measured now are just above the allowed maximum but were within the maximum permissible for their respective mcbs at the time of installation.

malcolmsanford · Oct 12, 2011

Well unfortunately I think your between a rock and a hard place here.

As far as the Zs value and the disconnection times normally I would have coded something like that a code 4 as it does not come up to the current regs and that is what the certs are highlighting, and you have to put those values in.

If I were you I'd be advising the client either via the PIR on the section for summary of the installation or in an attached letter/report that they may want to install RCBO's or RCD's and highlight section 415 concerning additional protection.

I think by doing this you will cover yourself regarding you report.