Electrical Safety & Legal Legislation

[Martin]

Re: Electrical Safety & Legal Legislation

Having now read the IEE Code of Practice (again), it does indeed state 0.3 megohms and a measured touch-current of 0.75 mA apply. In which case I think that those values are quite ridiculous and unworkable and those that carry out PAT testing and such-like should seriously question those regulations.

And what’s all this about?

….. “Note to Table 2” (Note 1 on page 44):-

“Heating and cooking appliances: the earth leakage of appliances with relatively high loaded heating elements could be such that they may be unable to meet the insulation resistance requirements. This may particularly be the case when metal sheathed mineral-insulated elements are used. It may be necessary in some cases to switch on appliances for a period of time to drive off the absorbed moisture before commencing testing……”

Now in my book (still unwritten by the way) is that if it fails at 0.3 megs or lower from a ‘cold test’ then running the appliance in the fervent hope it may give an improved reading is just plain barmy. 🙄

1.0 megohm is also far too high but fortunately these days most RCD based consumer units would blow anyway by then! 🙂

So in conclusion, my ‘rule of thumb and sod the regs’ = 4 megohms or higher and I will disable the appliance until its corrected (or note a warning to the owner on my invoice) 😈

[Brains]

Re: Electrical Safety & Legal Legislation

Martin

I note your conclusions with interest.

I agree with your conclusions about allowing elements to’dry-out’. From what I remember about the ‘early days’, it was common for high power mineral insulated elements to absorb moisture. Running them for about 30 secs allowed them to dry out. Also, if the mineral insulation was kaput, it would trip the fuse/mcb/rcd.

If you look back through the forum, you will see there are many supporters of allowing elements to dry out. Let me say now, I agree with you. If its bad when its cold. Its bad.

Quote ‘1.0 megohm is also far too high (maybe should read low?) but fortunately these days most RCD based consumer units would blow anyway by then! ‘

This could be marginal. This represents 23mA (at 230V) if we assume pure dc resistance. Now depending on loss capacitance of the cables & leakage impedance of the circuits connected to the RCD sub-main switch, you can find that the RCD will trip anywhere from 22mA up to 33mA. Also, keep in mind that appliances are not always connected to RCDs. The Wiring Regs only calls for ground floor socket outlet circuits, external sockets, garages & the like to be connected to an RCD.

RCDs should not be relied upon as primary protection in the majority of cases. RCDs are normally considered as supplementary protection (of course, there exceptions like TT supply configurations etc). Most common protection is EEBAD. So, again, Earth Fault Loop Impedance plays extreme importance in ensuring that fuses & MCBs open within the required time (normally 0.4 secs or 5 secs). Hence my stance in using the appropriate tester instead of the test plugs.

Let me take this opportunity to wish everyone a happy & prosperous new year.

Regards

[squadman]

Re: Electrical Safety & Legal Legislation

When I trained with a Major Manufacturer the insulation testing measurements laid down were Contunity above 1M ohm and Earth Insulation below 1 M ohm . I also know engineers who ride the tools with Manufacturers Service who are currently instructed to perform these measurments at Contunity still at above 1 M ohm and Earth Insulation now being accepted as below 2 M ohm.

Where do the previously mentioned figures of . 2 M ohm or . 3 M ohm fit into this criteria. My concern when testing is to ensure my own safety and that of my clients. Few if any of us are likely to be qualified as electricians and do not profess to be ! likewise the electrician would not be able to perform our role. Therefore my tests ensure that there is an good earth present and that the appliance passes my earth and contunity tests as given.

Any problems with the actual house or site wiring or installation is the responsibilty of the householder. I have been doing this job for the last 17 years during which time I have uncovered mains problems in clients houses some very serious. I once even came across a installation where the whole of the lower house ring was wired up completely wrong! When I advised the owner of this serious problem they advised me that it was nothing that could not be sorted out because they had a qualified Electrician working at the property who happened to be onsite at the time and was working in the lower part of the building topping and tailing one of the consumer units. When I found him and explained my findings he did not believe what I was saying ! However at my insistence he came with me and I showed him that there were indeed problems. He was getting ready to leave for the afternoon having completed his extensive work and I could not believe that he would have left the installation as it was. He actually worked for the regional EELB and was HNC trained !

It may well be that I saved him from something far more serious but I received no thanks from him other that him moaning that he could well be there half the night faultfinding the problem.

It just shows that any checks are better than none ! and my main reasons for placing this whole question in the first place was to try to gain an idea how many of us do these tests ? Seems like a fair few of us do and I would’nt mind betting that a fair few don’t.

[Brains]

Re: Electrical Safety & Legal Legislation

Squadman

Quote’ Where do the previously mentioned figures of . 2 M ohm or . 3 M ohm fit into this criteria. My concern when testing is to ensure my own safety and that of my clients. Few if any of us are likely to be qualified as electricians and do not profess to be ! likewise the electrician would not be able to perform our role. Therefore my tests ensure that there is an good earth present and that the appliance passes my earth and contunity tests as given. ‘ unquote.

The 0.2Mohm value is normally (in fact the wiring regs state 0.25Mohm) taken as a minimum allowable insulation value for a 230V installation. It is recommended that insulation values (for a 230V installation) below 2Mohm are investigated.

Remember that the Earth Fault Loop Impedance values & limits arise from various tables in the Wiring Regulations. As I understand this, the EFLI limiting value is dependent on fuse/mcb type, cables and disconnection times (just to mention a few parameters).

The 0,3Mohm value arises from appliances with elements greater than 3kW(as previously stated in earlier mail).

Hope this helps.

[squadman]

Re: Electrical Safety & Legal Legislation

Thanks Brains

Squadman,

p.s How much detail about our role as domestic appliance engineers does the publication by IEE servicing and testing go into to, i.e is it worth getting a copy ?

[Brains]

Re: Electrical Safety & Legal Legislation

Squadman

I think it is well worth having. Make sure you get the 2nd edition (published 2001). From what I remember its about £25 😕

The Wiring Regs are about £40. The On-site guide is about £20. Both these have data related to Zs (Earth Fault Loop Impedance). It is important to have these limits since if Zs is high the householder will need to have it attended to.

You get all these documents from RS Components or direct from the IEE. Take a look at http://www.iee.org.

AS you are aware, if Zs is high this impacts disconnection time (under fault condition) & could present fire or shock hazards. Alternatively, if you know a friendly electrician & he has Amtech FastTest, he can download ref sheet 1 which has a handy guide of the limiting values for Zs. Use the 80{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} limit (NICEIC recommended) as this will take into account measurement errors etc.

Let me know if you want or need further help.

Have fun!! 🙂

[Author]

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