zs=ze+(R1+R2)

[Rob69]

Hello.

I would like to know why my measured R1+R2's , measured Ze do not correspond to my measured Zs's in the above formula for all circuits?

I was just doing this for confirmation to proove to myself but it has backfired.

What is the best way to meet the formula with respect to testing circuits and filling in the schedule?

Thanks

 

[Andy™]

Ze & R1R2 do not have parallel paths. Zs does. so is often lower.

 

[choccy]

andy your spot on kidWet Fish

 

[Theorysparky]

Rob

i wouldnt try and make it meet the requirements of the formula

if it is below the required zs values for the circuit config dont worry about it

life is too short

 

[maselec]

Robi wouldnt try and make it meet the requirements of the formula

if it is below the required zs values for the circuit config dont worry about it

life is too short

+1

All you are looking for is that your Zs values are low enough. Measured or calculated methods are both acceptable and 99% of the time won't be the same.

 

[Rob69]

Thanks all.This is for a periodic by the way.

My Zs readings are all below the regs and equal to or below my R1 +R2 readings.

Except on the ring circuit, i got R1+R2 of 0.25 ohms with a max Zs of 0.87,Why?

Can worn sockets inflence these results too and what do i do about it??

With thanks

Rob

 

[paul b b]

Rob, you may be wondering why you would calculate and not measure, one reson would be that measuring a radial may involve working near live parts and the HSAW say that this should be avoided if poss!(yes i know you need to do tjis on a ze, pfc test etc..) another reson may be if your tester trips the rcd so calculated is ok, just note it on the cert.

saying this, if your compitant then i would always measure

 

[professional]

Rob, you may be wondering why you would calculate and not measure, one reson would be that measuring a radial may involve working near live parts and the HSAW say that this should be avoided if poss!(yes i know you need to do tjis on a ze, pfc test etc..) another reson may be if your tester trips the rcd so calculated is ok, just note it on the cert.saying this, if your compitant then i would always measure

Health and Safety DO NOT say that you can not work on live parts!

They state that you must be competent to do so. Unfortunately the Schemes have allowed people who, whilst (supposedly) competent to carry out installation work in domestic premises, may not satisfy the requirements of the Electricity at Work Regulations i.e. that you must be possess adequate knowledge and EXPERIENCE to work on live parts.

THIS is the reason why the NICEIC are peddling their drivel - they are loathe to admit (along with other Scheme operators) that they have deemed totally inexperienced individuals "competent".

Next please! ........

 

[sprocketflup]

Thanks all.This is for a periodic by the way.My Zs readings are all below the regs and equal to or below my R1 +R2 readings.

Except on the ring circuit, i got R1+R2 of 0.25 ohms with a max Zs of 0.87,Why?

Can worn sockets inflence these results too and what do i do about it??

With thanks

Rob

A loose connection can cause high Zs readings I believe

 

[SteveT]

It could be a loose connection/worn socket - more than likely though, this higher reading will indicate a spur on a ring! The resistance of r1+r2 of the spur cable being added to that of the Zs of the 'ring' socket

You will have to open the socket to see - if not a spur then look for other reasons for the high reading:innocent

 

[nicks electrix]

If you are using a test meter with a NO TRIP function for your Zs then you will always get a higher measured value than calculated. With you saying it was on a ring where you got the high reading then there is no doubt it is on an RCD. Then this high reading is expected.

 

[Sidewinder]

Health and Safety DO NOT say that you can not work on live parts!

They state that you must be competent to do so. Unfortunately the Schemes have allowed people who, whilst (supposedly) competent to carry out installation work in domestic premises, may not satisfy the requirements of the Electricity at Work Regulations i.e. that you must be possess adequate knowledge and EXPERIENCE to work on live parts.

THIS is the reason why the NICEIC are peddling their drivel - they are loathe to admit (along with other Scheme operators) that they have deemed totally inexperienced individuals "competent".

Next please! ........

Professional, et al.

HSE do require competence for live working.

The schemes in their clamouring for the cash seem to have ignored certain levels of competence.

HOWEVER the controls on live working go one step further.

One must remember that EAWR89 is Statute Law, that is the law of the land, non compliance is a Criminal Offence and this can be punished by the state and the punishment can include fines & imprisonment.

HSE issue guidance on how they feel one can comply with Statute Law.

These are the HSE L series, AKA Legal series.

Unfortunately there is no such L series guide for EAWR89.

These are Quasi legal documents, they carry more weight in law than do many others.

It is generally accepted that you must achieve or better the requirements in these documents in the event of an issue.

There is however a HSG note, this is formal Guidance, in the case of EAWR there are 2, one is HSG85, the other is HSR25 which is formal guidance on Regulations.

Both of these documents are available as free downloads on the HSE website.

Live working is covered by both, in HSG85 the following is said in para 17:

>>>>>>

Work on or near live conductors should rarely be permitted (regulation 14). Many accidents to electricians, technicians and electrical engineers occur when they are working on equipment that could have been isolated. In most cases, adequate planning and work programming will allow such jobs to be carried out as the Regulations require, ie with the equipment dead. Regulation 14 requires that three conditions are met for live working to be permitted where danger may arise. It is stressed that if just one of those conditions cannot be met, live working cannot be permitted and dead working is necessary. The assessment procedure illustrates this. The conditions are:

• it is unreasonable in all the circumstances for the conductor to be dead; and
  
• it is reasonable in all the circumstances for the person to be at work on or near that conductor while it is live; and
  
• suitable precautions (including, where necessary, the provision of personal protective equipment) have been taken to prevent injury.
  

<<<<<<

This guidance refers to the statute law regulations in EAWR89.

Thus, HSE do allow live working, however, along with competence of the

 

[Andy™]

unfortunately, EAW doesnt make the distinction between live working & live testing. as far as Zs on sockets go, its no more dangerous than plugging something in. lights & others may be a little more difficult, but i still wouldnt class it as 'live working'

 

[Sidewinder]

Andy,

This is quite correct and a point I labour with my colleagues in IOSH many of whom have little idea with regard to electrical works, let alone live working!

This is an anomaly in the regulations, however, live testing is "actually" live working to a certain degree.

I have had this discussion with the chief electrical inspector for HSE in my area, at length we both sat on the local IET committee at the time.

They do understand the difference and are able quite easily to distinguish and ascertain what they consider to be reasonable.

Trust me this guy & his colleagues, were very nice helpful guys, however, they were also VERY knowledgeable in their topic!

 

[tom1]

ok zs is with in the limits great but it should be a figure that you would expect, for instance couple of months back i alterd a cooker circuit, r1 r2 was about 0.8 well in for 32 amp mcb but much higher than i would expect for the length of ther circuit, took off the cooker conection plate and the cpc was not terminated, tightend it up and r1 r2 droped down to about 0.3 ish.

just a simple fix in that case, not saying you should tear the house to bits

 

[Theorysparky]

+1

Fair point but that comes with experience Tom

 

[professional]

Much of this experience should be gained under SUPERVISION.

You can NOT make a spark in a classroom, supervised training is essential.

 

[Voltimax]

It is very common when testing R1+R2 at socket outlets for readings to vary and be very high. As has been said old sockets can be worn, I've tested at sockets before and read in excess of an ohm, yet when removing the front and testing at the terminations the readings been a whole lot lower. It's also worth remembering that readings do vary very slightly even in a perfect ring.

 

[sparkytim]

+1

If you suspect a high reading found, flick socket switch on/off and unplug/plug in tester a few times, this cleans the contacts up a bit and can improve your reading.

 

[Nicky Tesla]

+1If you suspect a high reading found, flick socket switch on/off and unplug/plug in tester a few times, this cleans the contacts up a bit and can improve your reading.

+1

Cooker outlets seem to be the worst for this for some reason. Try testing at the socket, then loosen the socket and test at the terminals, they can be quite different.

One thing though! a guy I know said the the same thing as the op, that it was different with ring ccts. It was because he was taking the continuity readings as R1 R2. I hope he's not doing the same! ?:|