Zs testing

[alpha spark]

I'm not been funny but as competent electricians if u can't take a zs u shouldn't be allowed in the trade with all the modern technology with are test equipment these days ie 2 wire zs leads I remember as a apprentice the sparky used to make me take all the zs readings at spurs isolators etc with a 3 wire tester. But that's are job wots next we won't be allowed to go near a fuse board without remotely isolating the worlds gone mad

 

[Zeespark]

Agreed Alpha, H&S gone mad.

AndyGuinness

 

[apprentice87]

Hi all,

The figures given in the OSG [or anywhere else for that matter] are most certainly NOT maximum values at all, they are merely TYPICAL values..... I do not care what the IEE might like to think think, here is what Western Power Distribution have to say on the matter;

"The maximum earth fault loop impedance is used to calculate the available earth fault current within an installation connected at low voltage (below 1000V).

The following values are typical for low voltage installations:

Earthing Type Maximum Earth Fault Loop Impedance

Protective Multiple Earthing (TN-C-S) 0.35 ohms*

Cable Sheath Earth / Separate Continuous Earth Wire (TN-S) 0.8 ohms*

Direct Earth (TT) Dependent on resistance of the customer

 

[shed69]

On the money alpha... No testing live!!!! It's like fixing a car and refusing to start it and test drive it !!!!

 

[kerching]

Out on a limb here, expects to be shot down, appologies in advance yahda yahda yahda...............but, how do you measure Ze without 'doing it live' Measure NOT by enquiry :innocent ...................... :coat

 

[Technician]

Steps picked me up on where I found those values and rightly so.

All I could do was quote my source.

Steps; :Salute

There is no doubt in my mind that live measurement is necessary

and it would be extreme folly to ASSUME that the values quoted

should be applied.

As some contributors have also said, if the person concerned is

not able, competent or confident to perfom live testing he/she

might be well advised to consider their position.

Some say that the DNO's do not always give out accurate values

for Ze and my older mentors all said that when Ze was gained by

enquiry to avoid live working under EAWR, a note should be made

in the report against Ze stating "by enquiry".

With the greatest respect Apprentice 87, read that page.

 

[apprentice87]

Hi Technician,

Yes, I agree with all you say!! especially the bit about

"Some say that the DNO's do not always give out accurate values

for Ze and my older mentors all said that when Ze was gained by

enquiry to avoid live working under EAWR, a note should be made

in the report against Ze stating "by enquiry"

The DNO would tell you anything, just to make you go away, they will just quote the usual .8 or .35 bit. Same as if you ask them about PSCC, they will just tell you 16 KA or 23KA i think it is for "normal" sized three phase supplies. The bit you say about whether you obtained the details by measurement or enquiry is of course also correct.

Please do not think i was having a dig, i just come across like that sometimes...

john...

 

[batty]

well i would think there may be a problem with the existing installation that is causing meter to trip RCD when testing loop if altered circuit is correct.

 

[stoff]

Adcrop 14, most up to date test instruments have a "no-trip" setting, if yours hasn't then perhaps you should think about investing in one to save yourself a lot of problems in future.

Steptoe, I agree with you regarding the use of the term "hard down".

 

[boltonsparky]

Get on your step ladder, tester round your neck, clip a croc clipped lead to the earth/cpc (whatever they're calling it this week) terminal in the ceiling rose, live and neutral (no trip loop) probes/leads into the rose terminals and take your Zs, I really don't see what the problem/hazard is here, and my leads aren't GS38 (more hinderance than a help).

It can even be managed holding the meter with one hand and holding three leads into terminals un croc clipped.

At college we were always told to live test on both, 3 phase and single phase, and heaven forbid they even let us take the cover off the 3 phase board to test without isolating.

 

[Zeespark]

Why not just clip the one lead to the CPC and use a lightmate for the other 2? that way both hands are free to use.

Andy Guinness

 

[pewter]

I am a member of NIC and i have not read anything about calculation been preferred over testing of Zs.

though i admit i do not set out to read all the greatest works. Usually just what they send me.

Regards calculation Vs testing Zs

here is something i have going on at the moment

New build TT.  

Thought i finished testing it, then some new stuff went in a month later.

Ra was slightly different on both days.

there will be a couple extra circuits in a couple months also.

and then i will complete the EIC.

As the Ra will be slightly different again, for the new circuits i will be putting the calculated Zs on the certificate, as the measured value will look incorrect due to the Ra been different.

I wont  be retesting the entire property due to a couple more circuits going in.

 

[Sidewinder]

One MUST remember that Z & R values are measured in two completely different ways.

The only way of ensuring that the circuit will meet the Z requirements in 7671 is by live TESTING, NEVER live WORKING.

 

[steptoe]

I am a member of NIC and i have not read anything about calculation been preferred over testing of Zs.

though i admit i do not set out to read all the greatest works. Usually just what they send me.

Regards calculation Vs testing Zs

here is something i have going on at the moment

New build TT.  

Thought i finished testing it, then some new stuff went in a month later.

Ra was slightly different on both days.

there will be a couple extra circuits in a couple months also.

and then i will complete the EIC.

As the Ra will be slightly different again, for the new circuits i will be putting the calculated Zs on the certificate, as the measured value will look incorrect due to the Ra been different.

I wont  be retesting the entire property due to a couple more circuits going in.

are you actually measuring Ra or Ze ?

Ra shouldnt actually ever change that much if measured correctly,

either that or Im measuring it wrong.  :C

 

[SLIPSHOD & SLAPDASH]

Back to the  OP. Does the boiler work and have you plugged any thing else into the sockets to try them. I also think of hard down as meaning a dead short. What do you mean by,   the tester is set to 30ma as the red is ?

 

[SPECIAL LOCATION]

Back to the  OP. Does the boiler work and have you plugged any thing else into the sockets to try them. I also think of hard down as meaning a dead short. What do you mean by,   the tester is set to 30ma as the red is ?

Back to the OP........

That was posted in 24 Jan 2012.... :B-

think its sorted by now?????

You still suffering jet lag and reacclimatization to this time zone slips???

 

[SLIPSHOD & SLAPDASH]

I blame Boltonsparky for taking almost a year to start this thread up again. 

 

[boltonsparky]

Homer-Simpson-doh.gif

I blame Boltonsparky for taking almost a year to start this thread up again. 

Responsibility accepted, don't know how I came across this thread in the first place but getting my 2013s mixed up with 2012s... it is still early in 2013 yet  :innocent