This is a single phase service probably with a 315A fuse at the substation which did not operate
Rare but it does happen!!
Working Near Mains Equipment, This Is What Can Happen!
- Thread starter westie101
- Start date
This is a single phase service probably with a 315A fuse at the substation which did not operate
Rare but it does happen!!
Sponsored Links
- Joined
- 11 Jan 2004
- Messages
- 42,762
- Reaction score
- 2,641
- Country
Nasty...
If it can happen, it will happen (sooner or later)!
Does your employer offer English classes to it's employees?
Kind Regards, John
As a matter of interest .... do the regulations under which you operate have a requirement analogous to that of BS7671, such that the loop impedance at the furthest supplied service has to be low enough for the OPD protecting it to operate (in response to a L-E or L-N fault of negligible impedance) within a specified time?
Kind Regards, John
Sponsored Links
Simple answer, no!
This one was actually only about 80m route length from a substation.
At the end of the day with this type of incident there are no absolutes, the fuse may or may not operate, the customer may or may not get injured, the cable may or may not burn open circuit, the cable may or may not end up carrying enough current to burn back or damage the insulation etc.
We like pictures of melted chisels and smoking holes in the ground......
That's obviously all true, but analogous things are equally true within an installation, in relation to which BS7671 does impose requirements in terms of automatic disconnection in response to negligible impedance faults.
Are you saying/implying that you are subject to no regulatory requirements relating to the operation of protective devices in response to faults?
Kind Regards, John
Read ESQCR
All it says
and
But note the words
To design a network to operate as an installation should be is not reasonably practicable, so within the uncertainty of what can occur we have what we have.
As discussed many times there is not a BS7671 equivalent for the DNOs, we are fairly free to set our own and differing parameters to operate our networks as long as we comply with the deliberately vague requirements of legislation. (just as legislation, Part P, does not require strict observance of BS7671, just that safety is ensured. BS7671 is one way of doing this)
All it says
and
But note the words
To design a network to operate as an installation should be is not reasonably practicable, so within the uncertainty of what can occur we have what we have.
As discussed many times there is not a BS7671 equivalent for the DNOs, we are fairly free to set our own and differing parameters to operate our networks as long as we comply with the deliberately vague requirements of legislation. (just as legislation, Part P, does not require strict observance of BS7671, just that safety is ensured. BS7671 is one way of doing this)
OK - so, as you say, pretty vague, and with a let-out if to achieve even that would not be (in whoever's mind!) "reasonably practicable".
Fair enough - but that one has obviously got nothing directly to do with 'electrical safety'.
That's all true but, in practice, in terms of installations, I think one would probably be very hard pressed to successfully argue that one had complied with the legislation (part P) if one had failed to satisfy disconnection times explicitly specified in BS7671, and probably would be 'laughed out of court' if one's explanation for this failure was that it was considered not to be "reasonably practicable" to design/install cable of an adequate CSA to satisfy the BS7671 requirement!
I suspect one thing you may be overlooking is that it is (presumably) generally DNOs, not individual employees of DNOs, who decide on how to interpret and implement ESQCR (and with whom the buck stops as regards deciding what is "reasonably practicable"), which is probably reasonable. However, in terms of installations, most work is undertaken by independent electricians or small companies - and I really don't think it would be reasonable, sensible or workable to have individual electricians (and 'electricians')!, or thousands of small companies, making their own decisions as to, say, what 'disconnection times' were required in order to satisfy Part P. Hence the need for the more specific guidance of omething like BS7671.
Kind Regards, John
Everyone of our Codes of Practice that shows how we should comply is signed by an individual responsible officer. If it goes wrong that officer can be (and has been) arrested and cautioned!
Quite true but that doesn't, in some ways excuse the depth of detail in that document.
True, a bit like the apparently near absolute requirement for split boards in BS7671 isn't it!
Yes, obviously - but although an individual may be responsible (and accountable), the Code of Practice is a corporate one applying to all employees of the DNO, and there's only a tiny handful of DNOs. That's very different from tens of thousands of individual electricians creating their own personal 'Code of Practice' based on their understanding (if they have any!) of what is required to satisfy Part P!
I'm not so sure. Given the very wide spectrum of knowledge/ competence/ experience of electricians (and 'electricians'), which is many cases is probably negligible in comparison with the 'corporate knowledge' of a DNO, I think that some of them probably need as much detail as can be provided!
It is, and is an example of (probably desirable) vagueness. The "apparently near absolute requirement" exists only for those who chose to interpret "avoid danger and minimize inconvenience" and/or "taking into account the hazards that may arise from failure of a single circuit" in that way!
Kind Regards, John
And the Honourable Mention in this year's Darwin Awards goes to....
I hope you bill him for it.
If that were the case, would not one have expected a 315A fuse to have operated fairly smartish (which westie said it didn't)?
Kind Regards, John
Yep from memory of the cable records about 10kA
Nope as often the explosion blows the fault clear to an open circuit, you would be surprised the amount of damage that can be seen and still found to be live. This applies at higher voltages as we've had cases of badly damaged 6.6kV cables still live
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
