Final Circuit to Origin?

[westmac]

Hello people,

My company installs a lot of circuits in larger commercial/industrial buildings, we tend to have a lot of trouble gaining access to every sub-main leading to a consumer unit which supplies our new circuit.

My NICEIC inspector was adamant that the installation must be tested all the way back to the origin in every case although just out of my own curiosity I had a look through BS7671. Is it actually a requirement or can you simply collect/test the origin details and test the board to which you have connected?

Thanks.

 

[trebor]

Hello people,

My company installs a lot of circuits in larger commercial/industrial buildings, we tend to have a lot of trouble gaining access to every sub-main leading to a consumer unit which supplies our new circuit.

My NICEIC inspector was adamant that the installation must be tested all the way back to the origin in every case although just out of my own curiosity I had a look through BS7671. Is it actually a requirement or can you simply collect/test the origin details and test the board to which you have connected?

Thanks.

The only tests required are on the new circuit, initial verification, that is insulation,polarity and Zs
inspection of various sub mains for suitability may be required but not tesing, Zs is measured from origin to the poa. if you need Ze and can not turn off supply then estimate from supply type or measure pefc and use ohms law, and show it as a calculated Ze as it will include parallels

 

[malcolmsanford]

Don't you just love the NICEIC, so they expect you on a large commercial complex to shut the entire system down, disconnect the main earh and do a Ze test, for a final circuit installed in a DB baord that might be about 4 subs on .............

Ze; Zdb and Zs

I found this by chance a few years ago and IMO it's is good advice.

 

[IQ Electrical]

Hello people,

My company installs a lot of circuits in larger commercial/industrial buildings, we tend to have a lot of trouble gaining access to every sub-main leading to a consumer unit which supplies our new circuit.

My NICEIC inspector was adamant that the installation must be tested all the way back to the origin in every case although just out of my own curiosity I had a look through BS7671. Is it actually a requirement or can you simply collect/test the origin details and test the board to which you have connected?

Thanks.

To be fair to your assessor (whatever the trade body) he is following the requirements of BS 7671:2008 in that if you are using ADS as your method of fault protection then the details at the origin of the installation should be recorded.

It is then up to you as the inspector to get as much meaningful information as you can given client constraints etc.

I'd rather see a Zdb measurement as close to the origin as possible entered as a Ze value as long as this method and reason was noted on the EIC.

 

[westmac]

To be fair to your assessor (whatever the trade body) he is following the requirements of BS 7671:2008 in that if you are using ADS as your method of fault protection then the details at the origin of the installation should be recorded.

It is then up to you as the inspector to get as much meaningful information as you can given client constraints etc.

I'd rather see a Zdb measurement as close to the origin as possible entered as a Ze value as long as this method and reason was noted on the EIC.

I/We always manage to measure a Zs either very close to the origin or a Ze directly at the origin, we always seem to struggle with testing and certificating every sub-main between this and the final circuit. In some cases we can end up with 11/13 sheets if we fill out a sheet for every sub-main and its supplying distribution board.

Is the general concensus that this is not required, will the details of the origin including measurements/enquired values along with the relevant tests of the final circuit suffice?

 

[Chr!s]

Hello people,

My company installs a lot of circuits in larger commercial/industrial buildings, we tend to have a lot of trouble gaining access to every sub-main leading to a consumer unit which supplies our new circuit.

My NICEIC inspector was adamant that the installation must be tested all the way back to the origin in every case although just out of my own curiosity I had a look through BS7671. Is it actually a requirement or can you simply collect/test the origin details and test the board to which you have connected?

Thanks.

I assume there are sufficient diagrams etc which have allowed you to design the final circuit?

 

[leespeed]

i always ask for the pir of the building surley they have one most readings are on that if its up to date

 

[IQ Electrical]

i always ask for the pir of the building surley they have one most readings are on that if its up to date

And you use those figures and then sign your certificate?

On the rare occasion that we find an existing PIR, the results are normally so 'questionable' that I certainly wouldn't be adopting them into my report/certificate!

 

[leespeed]

what i was saying it gives you a heads up location etc of dbs and so on clever cloggs

 

[malcolmsanford]

The GN 3 advises that the Ze can be obtained by either measurement, calculation or enquiry. In an existing large complex as you guys do, measurement would seem to be nigh on impossible, I would doubt that unless you have specific information from the DNO calculation would be difficult, so the easiest method is to enquiry.

In theory you should be able to contact the supplier and they will tell you, which is OK for perhaps installations that are 10 or less years old, the chances are the supplier will have the Ze. Older than this, and you will be lucky to know if the system is TN-S or TNC-S, more than likely it will not be TT on a comercial system nowadays.

So if your informed that the system is TN-S then you can on the cert where you need the ZE fill in 0.8 and as IQ said you will then in the box marked existing installation note how you got the figure, by enquiry.

It is not perhaps the best method of obtaining a Ze, but by doing your Zdb/Zs throughout the system your ensuring that protection devices will operate within the designated times, and therefore the installation is safe for use.

 

[westmac]

The only tests required are on the new circuit, initial verification, that is insulation,polarity and Zs
inspection of various sub mains for suitability may be required but not tesing, Zs is measured from origin to the poa. if you need Ze and can not turn off supply then estimate from supply type or measure pefc and use ohms law, and show it as a calculated Ze as it will include parallels

I can't find any black & white definition of how far this verification should go though. Do they expect you to check the insulation resitance of any circuits which supply the new circuit somewhere down the line? Also, am I responsible for ensuring that all sub mains which I am utilising are adequately protected in terms of the protective device and the Zs of the circuit in question?

 

[IQ Electrical]

what i was saying it gives you a heads up location etc of dbs and so on clever cloggs

"most readings are on that"

Is what you said....

 

[leespeed]

well said

 

[malcolmsanford]

I can't find any black & white definition of how far this verification should go though. Do they expect you to check the insulation resitance of any circuits which supply the new circuit somewhere down the line? Also, am I responsible for ensuring that all sub mains which I am utilising are adequately protected in terms of the protective device and the Zs of the circuit in question?

You are going to have to take Reg 131.8 as your guidance, in that any additions you do, can only be done if the existing installation is adequate.

Your extra final circuit at whatever DB it is, will be the only work that your EIC, Schedule of Inspection and Results will cover. You are under no obligation is start carrying out IR tests or any other tests on the existing installation, unless you think that the existing installation is not adequate or safe, and if you felt that the existing wasn't safe or adequate then you would not have installed that extra circuit.

As IQ explained and I on your schedule of results in the part marked Ze at origin you can put a value by enquiry as I suggested, or as IQ suggested you take the ZdB/Zs at that board. Either way you should note on the EIC in existing installation what you had done.

 

[westmac]

You are going to have to take Reg 131.8 as your guidance, in that any additions you do, can only be done if the existing installation is adequate.

Your extra final circuit at whatever DB it is, will be the only work that your EIC, Schedule of Inspection and Results will cover. You are under no obligation is start carrying out IR tests or any other tests on the existing installation, unless you think that the existing installation is not adequate or safe, and if you felt that the existing wasn't safe or adequate then you would not have installed that extra circuit.

As IQ explained and I on your schedule of results in the part marked Ze at origin you can put a value by enquiry as I suggested, or as IQ suggested you take the ZdB/Zs at that board. Either way you should note on the EIC in existing installation what you had done.

Thanks very much, very helpful.

 

[Chr!s]

Your adding a new final circuit, so your inspector will be asking the question does it meet the requirements of BS7671.

How have you proved that it meets the requirements for volt drop etc.

Assessment to some degree of the sub circuits will be required unless you have sufficient information to allow otherwise.

Regards Chris

 

[westmac]

I think I am just going to have to make a detailed note on each certificate that I have visually inspected the sub-main circuits the best I can given the constraints of shut downs and access etc.

With reference to regulation 610.1 "Every installation shall, during erection and on completion before being put into service, be inspected and tested to verify, so far as is reasonably practical, that the requirements of the regulations have been met." Could I argue/explain that I have inspected and tested the circuits as far as is reasonably practical by using professional opinion that the sub-main circuits are suitable to use by the final circuit?

The discussion above drifted a little into the origin of supply being the major hurdle, most of this can normally be assertained as said by enquiry. It is mostly the shut down of sub-main circuits which we struggle with.

 

[malcolmsanford]

The bottom line to this is really your call and experience.

If you had a 70mm sub main from a bus bar chamber/ main switch panel going to a TP+N+E DB and the SWA feeding it looked good and on that board there were only 5 final circuits and the highest phase load was 13 amps, and you were asked to fit a new ring final on to it, there is a very good chance that it is not gonig to affect the existing installation so you do the tests on your EIC for your ring final and the Ze if you wish by enquiry.

On the other hand the 70mm is an old SWA, been in use for years, the TP+N+E Db is crammed solid with all sorts on it, with this lone spare way on it, you just manage becasue it is so crowded to clamp a phase, it is jumping all over the place with loads from 50-100 plus amps and they ask you to fit a new circuit, you might want to do a lot more testing and a lot more investigation.

The end of the day it is you that signs things off.