Ze / Zs

[Jimmy Boy]

Apologies mods if this doesn't quite fit in this section I think it may.

Problem..

1)

A lot of my maintenance work takes place in a very busy Veterinary hospital, to shut down the hospital to get Ze would be impossible,if I needed to run a new circuit, I believe the regs. state it is an acceptable solution to gain Ze "By enquiry" and add this to my R1+R2 to obtain Zs do you think this is a satisfactory way of working ?

2)

When I did the 2392 recently I was specifically told by the NICEIC that is now NOT acceptable to measure Zs on circuits other than those that you can put a plug top into ie rings/sockets, as the Zs on these types of circuits can be obtained by calculation of Ze+R1+R2, and so conforms more to Electricity at work regs. that states where possible Live work must only be undertaken IF necessary.

I would be interested to hear your views on this and your working practises

ATB Steve

 

[flukey]

never heard its not acceptable, probably means easiest route possible so if youve got your ze and r1r2 work it out, if not test in the usual way

your last sentence answers the question as live working would be necessary in your situation

 

[Guest123]

Obtaining Ze by enquiry is acceptable, although the supplier will more than likely quote the max permitted values for the given earthing system i.e 0.35 & 0.80.


Personaly I always measure Zs on all circuits and will continue to do so regadless of NIC views.

 

[Sparky Ninja]

The advice from the NICEIC is accurate. It refers to Regulation 14.

 

[Sintra]

Apologies mods if this doesn't quite fit in this section I think it may.

Problem..

1)

A lot of my maintenance work takes place in a very busy Veterinary hospital, to shut down the hospital to get Ze would be impossible,if I needed to run a new circuit, I believe the regs. state it is an acceptable solution to gain Ze "By enquiry" and add this to my R1+R2 to obtain Zs do you think this is a satisfactory way of working ?

If you do alot of work in this place then arrange a time when the installation can be shut down and take all your necessary readings and record them for future use then every time you need to issue a cert you have Ze reading etc.

2)

When I did the 2392 recently I was specifically told by the NICEIC that is now NOT acceptable to measure Zs on circuits other than those that you can put a plug top into ie rings/sockets, as the Zs on these types of circuits can be obtained by calculation of Ze+R1+R2, and so conforms more to Electricity at work regs. that states where possible Live work must only be undertaken IF necessary.

Always have tested Zs and always will. Can't see a problem doing this so long as the correct method is used.

I would be interested to hear your views on this and your working practises

ATB Steve

Hope this helps

 

[Jimmy Boy]

Nice one good advice thanks

the problem is I don't usually work on 3 Phase so if I do a shut down which Phase or line do I take a reading from ? Bearing in mind I will be using a two lead Meggar tester

ATB
Steve

 

[Guest123]

All 3.

 

[Jimmy Boy]

Nice one mate

Record the lowest or highest ?

 

[Sintra]

Highest

 

[robsparky1975]

Guidance note 3,very helpfull for all testing

 

[keniff]

would it not be acceptable to take a zs reading then minus your r1+r2 to gain ze? (ze=zs-(r1+r2)) if that makes any sense to anyone..... only prob is if you work it out and its more than the permitted ze you already have made the circuit live!

 

[Sparky Ninja]

would it not be acceptable to take a zs reading then minus your r1+r2 to gain ze? (ze=zs-(r1+r2)) if that makes any sense to anyone..... only prob is if you work it out and its more than the permitted ze you already have made the circuit live!

Theoretically you could for comparison, however the model certificate forms in BRB Appendix 6 state:

(2) by enquiry or by measurement


so calculating it shouldn't be necessary, as enquiry should be carried out in the absence of measurement.

 

[keniff]

Theoretically you could for comparison, however the model certificate forms in BRB Appendix 6 state:

(2) by enquiry or by measurement


so calculating it shouldn't be necessary, as enquiry should be carried out in the absence of measurement.

Yeah good call, as long as the calculation falls under the max ze for the arrangement would be good for piece of mind, as I would think the supplier generally give the max permitted ze

 

[Guest123]

would it not be acceptable to take a zs reading then minus your r1+r2 to gain ze? (ze=zs-(r1+r2)) if that makes any sense to anyone.

Not really as the Zs reading will include the paralell paths of any bonded services into the property so wouldn't be a true reflection.

 

[Jimmy Boy]

Not really as the Zs reading will include the paralell paths of any bonded services into the property so wouldn't be a true reflection.

Good post, neither I guess would it be good practice to remove the parallel paths ie the main bonding as Zs is a live test..

 

[Sintra]

Absolutely not.

 

[Guest123]

No indeed.

 

[keniff]

indeed 3

 

[Jimmy Boy]

Thanks for the replies fella's..Now according to GN3 page 49 Ze is required to be measured for

1) To verify an earth connection

2) To verify that the Ze value is equal to or less than the value determined by the designer and used in design calculations

So can I safely rely on a previous testing report of Ze to enter on my test results or could I be culpable because I haven't verified the earth, bearing in mind the regs say this may be gained by enquiry ?

ATB Steve

 

[nickblake]

as sintra worst case situation