Best practices

If cables are old they should be rewired at the time can add a spur otherwise  wiring can be sort circuit, existing Rccd can use 

MrJack96: 
It’s a hard one as I don’t want to end up going round locking every thing off but if it’s potentially dangerous really it needs sorting I see it a lot on old motor circuits with old contractors that and an extra bit of resistance to our zs values!! What working practices do you guys usually work to? Thanks for your help guys!!

B.S. 7671 covers commercial and industrial premises etc. 110.1.1

B.S. 7671's rules for the design, erection and verification so as to provide for SAFETY and PROPER FUNCTIONING for the intended use. 120.1 (Caps mine).

131.1 covers  requirements to provide for the SAFETY OF PERSONS, LIVESTOCK AND PROPERTY AGAINST DANGERS AND DAMAGE WHICH MAY ARISE IN THE REASONABLE USE OF THE ELECTRICAL INSTALLATION.

So are you mainly concerned about the earthing of the machines/circuits and the automatic disconnection times due to a L.-E. fault? Is shock risk you main concern?

Z.

Just because you have a higher Zs and a lower IR than BS7671 permits doesn’t necessarily mean that the arrangement is dangerous. Agree entirely however, that it is prudent to comply with our national standard.

To me,  the question is very much one of how much danger really arises.

Consider these examples,   

1) a defective earth to a building with lots of folk in it all using portable appliances, (imagine a computer studies annex to a school ) 

and 

2) A situation with the same fault, but with no users and equipment where even if it fails in the most impressive way possible, there is no  or very little, electrical risk to life, but a nasty consequence to a false trip  (imagine perhaps a locked brick outhouse shed with sewage pumps in or something in it). 

In the former example, the odds that if the ADS is ever needed to fulfill it's purpose, someone, maybe many people,  will be on the wire at the time.  Meeting disconnection times and keeping touch voltages down is then paramount.

In the latter case you could probably have a live pump body for a week and so long as it kept on pumping, no-one would notice.  But you'd need to be aware if you unlocked the door that it may  not be as safe as it appeared, so boots & gloves perhaps.

So if the kit is running but not meeting the regs - do you label it in some way  as operational but with a known fault ?

Now BS7671 apply the same Zs (and therefore ADS operation time) to both, but  there is a world of difference between the severity of outcomes, and to quote Matilda “and  that's not right” Perhaps less strongly, it is not a balanced approach to the real risk.

Very tellingly, the DNOs have a very different set of rules, because in their case leaving the power on if at all possible is the more desirable case compared to turning it off - so they do not even isolate to do cable joints and cut-out replacements, if they can avoid it, and they won't blink at a 1megohm insulation resistance, or even 100k  in a long run of existing cable.

I venture to suggest that some types of installation could be safely treated in a more DNO like way, and even perhaps allowed to run to catastrophic failure with a known minor fault,  without troubling the scorers, so long as access to the possible dangerous bits is limited to folk who understand the risk and know what to look out for.

Whats not acceptable is exposing the ‘ordinary person’ who may be in flip flops and have a weak heart.

Mike.

"We're told we have to do as we're told but surely
Sometimes you have to be a little bit naughty."

Matilda again…

MrJack96: 
Thanks for your input guys I was just concerned about liability if it was to go wrong. I know the Likely hood of a fault on said motor causing harm to someone would be little due to the site being maned by one person. But wasn’t sure if the implications of me knowing it’s faulty and reinstating.

The limited number of people involved does not provide any excuse for safety breaches. What about visitors if the main maintenance person is away?

Z.

In what way is an IR fail a safety breach ? in the sense of how does it hurt a person? 

If you have a higher than target Zs, how high, and what does the ADS operating  time become?

Who is at risk is very much a factor, not in the regs perhaps but in the world of the HSE. 

Suitably trained / qualified personnel are after all allowed to work with things live and covers off, if the situation can be shown to require it.

And if the trained maintenance guy is off, you don't give his keys to someone who has no idea what they are doing - not just  electrical - it could be risk of entrapment in confined spaces, working at height , nasty atmospheres in wells or pits,  any amount of training  and qualifications, depending on the situation.

Now I am not advocating a gung-ho approach to safety, but it is important to be able to grade the risk of leaving something on versus the risk of power being removed.

Mike.

The example I had was a motor circuit feed by 100amp bs88-2 fuses the Zdb was 0.20ohms and the R1+R2 was 0.28   ohms the cable from the panel to the local isolator uses the SWA as an earth. was in a situation where I refused to switch it on as it Doesn’t comply but Was seen as being a Jobs worth. 

That R1+R2 seems a little high unless it is a very long circuit. Table 41.4 gives 0.42 s for a 100 A BS 88-2 fuse at 5 s disconnection time. Table 41.2 does not go to 100 A. Not a country mile out and I think advise rather than refuse to re-energise. Perhaps a supplementary CPC is required?