Testing Zs?? i cant remember!?? help

[kevin1234]

hello

you see when you do the Zs test, and on the top of the NICEIC, schedule of test results for the installation part at the top right hand corner it has asks for the Zs, and maximum prospective Fault current, i always thought that Zs is the whole system that has to be test, but yet the book says you have isolate the supply and the earth to do the test and the test is done on the incoming terminals i thought that this test is Ze for external part???

then when you go to do the test results for each circuit, and it asks for the Zs again, that means it is for the the whole circuit doesnt it??and does the Zs value here have to be the same as the one in supply in the supply characteristics??

could somebody please explain the difference between the two of them please im lost

 

[Zambezi]

Ze = external efli - taken from the supply with the main switch open (off) and the earthing conductor disconnected.
Zs is the taken from the furtherest point on the circuit Zs = Ze + (R1+R2)

I am not with NICEIC and I don't have any of their certs so can't comment on what needs to go where.

 

[kevin1234]

Ye thats how i know it as being but what i dont understand is why does it say on the NICEIC Certificates on the top right corner Zs at the distrubution board and does the value have to be the same as the values recorded at the furthest away point on each circuit???

i only thought that Ze is measured at the board Not Zs so why does it ask for it on that certificate.

 

[ericmark]

Ze = impedance which is external to the installation. In theory given by the provider.
Zs = earth fault loop impedance and there is nothing to state where measure so.

Ze can be called Zs but Zs can't be called Ze.

I would agree we normally consider the first point where we have access to measure Zs on an installation as being Ze.

But you most also consider electric other than in the home. So as a contractor for firm A my first point may be no where near where the power enters the installation and if I enter the reading I get as power enters the board as Ze then when firm B is given my results and has access to more of the installation they will record a different reading for Ze so once one moves away from domestic then not using the term Ze does make some sense.

 

[kevin1234]

so when they are asking for the Zs value at the supply on the NICEIC cert, does that really just mean the Ze value of the supply coming or what

 

[holmslaw]

..

 

[kevin1234]

ye, so say for a house and this was the case would the the Zs value asked for on the NICEIC cert at the top right hand corner would that mean, really the Ze of the supply coming into the house, and would put this in the Zs box, but the value here wouldnt be the same out in the circuits when i record the result for the circuits would it?

 

[Zambezi]

Without seeing an NICEIC cert I can only guess that they want you to put the Ze (or the Zs if it was a sub-main) in the top box and then the measured Zs for the individual circuits would be recorded in the Zs boxes lower down on the form.

 

[kevin1234]

Ye, would the measured value Zs out in the circuits would this be the same as the value recorded at the mains or not???

 

[Zambezi]

No. One is measured at the CU the others are measured at the furtherest point of the individual circuits.
Are you registered with the NICEIC?

 

[kevin1234]

ah right i see what you mean , so why do they ask for 2 Zs readings then, one at the mains incomer and the out going circuits????

No i aint registered i used 2 work for a sparky company but they let me go,

and i am just wondering about this as i cant remember it

 

[Zambezi]

The first Zs is actually the Ze
The second Zs is the Ze+(R1+R2)
They are not the same thing.

 

[kevin1234]

ah right so they dont have to be compared then??

and to do the Zs at the incoming part do you just turn off the supply an disconnect the earth ye?

 

[Zambezi]

ah right so they dont have to be compared then??

and to do the Zs at the incoming part do you just turn off the supply an disconnect the earth ye?

Yes and yes

 

[ElectricDunc]

What sort of NIC certificates are you trying to fill in Kev? I hope they're green ones if your not an NIC member. I'm guessing here but are you looking at the section on the top of the schedule of test results which asks for a Zs, PSC and RCD readings? If this is the case make note of the part above it which states 'to be completed only if the distribution board is not connected directly to the origin of the installation'. So if you have only one consumer unit in the property on test where the tails come straight from the meter in to the consumer unit you leave that section blank. If your referring to something else tell me the certificate reference (eg ICN2) and i'll tell you exactly where your getting confused.