I'll bite for you  :-)

If the exam question is "Is there a need for arc flash surveys in the UK ?"  Possibly, but I suspect in  a lot of cases not a full survey.

Do realise that the legal base around the UK wiring regs (BS7671 mainly) is not like the USA, and the regs themselves are a standard, but are not a legal requirement generally, although in most cases you need a good reason to go very far off the beaten track, you are allowed to if you can show an equivalent or better standard of safety to that which a regs compliant installation would provide in that particular case. Also a lot of our distribution networks, that is the stuff at higher powers that is mostly under the street, up on poles or in basements, is excluded from coverage under BS7671 at all.

As such for a new measure to be adopted in a permissive system, a better level of explanation is required than where a workforce is used to the imposition of mandates and permits. There is probably a need to educate about the situations where flash burns can be an issue, and corollary, those situations where it cannot. To that end, as part of that  there is a need to translate to and from some things we actually do measure or deduce as  a matter of course when designing a system - I'm thinking that we already look at /know   PSSC (in kA) and disconnection times (ms) and let though energy (joules per ohm)  and all that is needed is a means to put an upper bound on the energy density in joules per m² at the boundary of the arc sphere, or perhaps to deuce the radius of the third degree burn arc sphere where that density falls below 5J/cm²

The other problem we have is a lot of 50-100 year old kit in our higher power distribution networks that we know does not really meet the standards of today anyway, but no-one is going to change it until it fails. It would be good to know in which parts of the systems the current accidents are occurring. I'd not be too surprised if it was this 'legacy' kit that would be largely unaffected by a change of rules.

Mike.

Many thank for the bite... .  Good feedback. 

In the main LV distribution rooms we have charts for all settable protection, which are outputs from grading surveys. This is there to justify the settings and assist if a switch is changed.

We could as a starter make it clear what the actual KA is on a subsequent table for all switches, in essence the closer to the origin the higher the KA .  Then a KA to Cal value/incident energy level table,  Earth loop Zs tests are done at the furthest points to show worst case for disconnection however, this could also be done locally at the outgoing switches to demonstrate a "bolted fault" energy level.

Food for thought.

Cheers.

Steve

I used to work for an American company in the UK which tried to push arc flash protection in the plant. Having compared European control cabinets to American ones I considered the arc flash risk to be very low. IP2X with an open door covers most eventualities. The American designs with open busbars and terminals had a much higher risk of arc flash (and electrocution) to a point where I considered live testing not to be appropriate and installed external test points for the common measurements.

There is also quite a small window where arc flash PPE is useful. At very high energies you are going to get burnt anyway and even in the defined energy range you will just get survivable burns.

Arc flash is best dealt with at source by good design.

we do (usually)  measure PSSC - 'prospective short Circuit current'  - the higher of a phase to neutral or phase to ground or phase to phase case as part of commissioning.
(Though often we actually test P-E and P-N, and double whichever reads larger and assume P-P will never be much more than that )
We could write PSSC and I2t (joules per ohm) on the wall next to each box I suppose. Generally the table of test results  goes with the design documentation and in some establishments it seems that can never be found in a hurry.

Supplies at LV (230 single or 400 3 phase) are rarely more than 16kA at the origin, and fall to sub kA for domestic and small commercial buildings like shops.
Mike

Many thanks for this Mike good feedback...Cheers!

We are both on the same page here, need IP2X standards throughout.  And work on equipment dead.

Many thanks for the reply.

SW1 said:

Also, speaking with various colleagues for the UK , Arc Flash is not mandated/law.  However, more cases are been investigated generally by the HSE, so one could say there have been issues.

Arc flash is a known hazard and as such is subject to the same requirements as any other hazard whether it be shock or working at height for instance. There is an IET fact file on the subject: arc flash fact file and I also wrote a book on the subject called the European Arc Flash Guide. European Arc Flash Guide

The fines are eye watering right now with one company being fined £3.6M for two arc flash accidents, one of which was LV and another for £1M for an LV arc flash. I shared the details on LinkedIn of a fatality in Scotland just last week. Please reach for my book before reaching for heavy duty PPE.

. 

Thanks for linking to that, I found that a nice digestible book. Personally I like the low maths approach and agree with your comment that to use levels based on injury distance of 450mm is a bit arbitrary and will not save the back of your hand or any other body part if it is in or very near the 'event' .  I am however more or less metric ;-) so spend some time converting your caloric formulae to Joules.
Perhaps not in this thread, but if you are OK with the idea it would be useful at some point to have your opinion on the Lee method or better alternatives for situations  outside the readily available test data such as HVDC, or energy limited cases like pulse power capacitor banks that have a huge short term PSSC, no ADS but a definite maximum energy. Do you frequent this forum much ?
Mike

Thank you Mike, for your kind words and in respect of the use of calories rather than joules, I did, very marginally, decide to use calories. This was my explanation from Chapter 4: "This is where the predicted incident energy is calculated to be 5.0J/cm² (1.2 cal/cm²). 1.2 calories per square centimetre is often depicted as the amount of incident energy that one could receive if you were to hold your finger in the hottest part of a match or candle flame for one second. Not to be recommended but it is unlikely that you would receive anything more than mild superficial burns. Whilst the SI unit used (International System of Units) is joules per square centimetre (J/cm²), most of the references to incident energy within this guide will be in calories per square centimetre (cal/cm²) as this unit of measure tends to be universally used for protective measures." I was trying to limit confusion but thank you for your comments.

In respect of your question about Lee equations, (theoretical equations that were developed back in the 1980s by Ralph Lee in the USA) these are often used by software developers for voltages above 15kV but tend to be extremely conservative. As a result, they have been dropped from the latest version of IEEE 1584:2018. There are some alternatives including ArcPro software and ETAP have also provided their own module. However, I understand that other software developers are still using Lee equations. Ralph Lee did provide formulae for blast pressure and in fact, I have used this free tool in the online guide www.ea-guide.com for the purpose of comparison. In my comments, I point out “The Blast Pressure Calculator provides a method to determine and compare blast pressure under relative scenarios. Whilst there is caution about the absolute accuracy in real life situations, it serves as an educational tool and could also highlight extreme danger.”

Sorry for taking some time to get back to you, please PM me about the specifics of other applications that you may have in mind.

Mike

Thank you for that  Mike Frain   I think you may need to set some profile options to receive a PM, the message thing cannot find you as a recipient searching either by name or number - 54a64b2e4c5969a0449a82b1ef1ecf70 It may of course also be me, I do not send that many messages. and this forum messaging SW is not intuitive. Or try ping to me -- I know other folk have managerd that

~mike,