Details of BS7671:2018 Amendment 1 are here.

Why did the green communities change the term from global warming to climate change?

I'm not sure the term has changed, so much as two different terms describing slightly different things - which one gets used in headlines perhaps changes as per fashion. To me global warming is the nett effect of the planet trapping slightly more energy from the sun than previously. Climate change is the consequence of that - perhaps local warming - perhaps local cooling (if say the gulf stream shifts direction a little and we end up with a climate more appropriate to our latitude) - more frequent and/or violent storms, greater swings in weather patterns (drought vs flood), sea level rise and so on.

 

Simply because the climate DOES change by the second?

Somewhere on the planet it is daytime, somewhere it is night time, somewhere it is raining, somewhere it is snowing, somewhere it is sunny, somewhere it is winter, somewhere it is summer.

No that's still weather, not climate. (possibly other than the day/night thing). The distinctions are meaningful - you wouldn't say that the tides of the sea can't be happening because waves continually move up and down anyway, or land can't be sinking because the tides go up and down.


Sometimes the doomsayers turned out to be right - remember Churchill's predictions before WWII?


   - Andy.

RE: The new Ice Age - more here,

Sun spot activity 11 year cycle. I recall this phenomena from years gone by when I was into radio stuff. You could transmit over great distances every 11 years with relatively little amplification power.

https://astronomynow.com/2015/07/17/diminishing-solar-activity-may-bring-new-ice-age-by-2030/

alanblaby:


Either way, I havent heard of a new ice age coming, rather exactly the opposite, the polar ice shelfs are melting rapidly.

 

The polar ice shelves that are melting rapidly in West  Antarctica, Pine Island and Thwaites, happen to be over active volcanoes which are a more likely cause of melting than global warming:

https://www.nsf.gov/news/news_summ.jsp?cntn_id=295861
https://www.nature.com/articles/s41467-018-04421-3


"Tracing a chemical signature of helium in seawater, an international team of scientists funded by the National Science Foundation (NSF) and the United Kingdom's (U.K.) Natural Environment Research Council (NERC) has discovered a previously unknown volcanic hotspot beneath the massive West Antarctic Ice Sheet (WAIS)."


As this was discovered in 2017-18 it is strange that the BBC failed to mention this in the recent alarmist piece on the 'Doomsday' (Thwaites) glacier.


Best regards


Roger

Is the formula for calculating the maximum neutral current (Im) in Annex A722; A722.1 Neutral current of a three-phase installation, actually correct?


There's an L missing (IL3) and only half of the final multiplication is shown. 


Probably!

What do people make of:

 

Protective conductors and exposed-conductive-parts downstream of a protective device provided for the purposes of (iii), (iv) and (v) shall have no connection to:
(a)any protective conductors or exposed-conductive-parts of any circuit not protected by the same protective device; or
(b)any extraneous-conductive-part.

say I have simple independent extraneous-conductive-parts within reach of the charge point or vehicle - say steel sign posts, bollards, crash barriers or fencing. If I can't bond them to the protected/switched PME earth that's connected to the vehicle, that only seems to leave two options - either bond them to the ordinary (unswitched) PME earth (so they'd be hazardous live in a broken PEN situation) or leave them unbonded (with the associated risks of tingles from the EV or charge point under normal conditions or shocks during faults elsewhere on the system) - nether of which seems ideal.


I can see the issue of bonding extraneous-conductive-parts that could have a hazardous potential on them - e.g. metallic pipework that's also bonded elsewhere - as that would defeat the switching of the c.p.c. under broken PEN conditions - but I think there might be two sides to this coin.


   - Andy.

well, given that you cannot bond exposed blades of grass, or the surface of the flower beds, which are equally touchable and tingly to bare feet, some things are best left to float to local terra-firma potential, and anything planted in it that is short, like a fence post is probably best left alone.

I'm not sure how many of the folk contributing to this advice have ever knelt in semi-live mud and plotted voltage contours around a real electrode, but the field dies off over a distance comparable to the underground length, so most of the surface step voltage is within that radius. You cannot force equipotential over a large area without a mesh or a matrix of electrodes.

well, given that you cannot bond exposed blades of grass, or the surface of the flower beds, which are equally touchable and tingly to bare feet, some things are best left to float to local terra-firma potential, and anything planted in it that is short, like a fence post is probably best left alone.

Agreed - although to  square that with BS 7671's requirements we'd probably need something equivalent to 714.411.3.1.2 in section 722.


Actually that thinking meshes rather well with an approach I suggested for the DPC - which was along the lines of making the earthed metalwork of the EV and charge point practically no more hazardous than a simple piece of metal stuck into the ground. Basically a more stringent version of TT but with 0.2s (or better) disconnection times throughout (no option for 1s), R_A x I_Δn≤25V (rather than 50V) and the electrode in the immediate vicinity of the charge point - all reasonably easy to achieve with a normal 30mA RCD and 200 Ohm rod setup. In that way almost everything is close enough to local earth potential not to be a hazard under any normal or single fault condition so I'd argue no bonding required at all. In highway locations PME'd lampposts etc. shouldn't really be a problem under broken PEN conditions if they have the additional electrodes that DNOs have been specifying for years (one of the few cases where the load is low enough for that approach to be practical) - so we're only left with situations where exposed- or extraneous-conductive-parts connected to larger installations are available to the touch - but that problem was there already and not really anything to do with the EV setup - and experience shows (see reg 714.411.3.1.2 for example) that the risks are very small in practice anyway. Seemingly that wasn't a convincing argument - so if anyone can see the flaws I'd be very interested!

  - Andy.

personally, I;d be happy with that, I note and concur with the 25V maximum exposed voltage instead of 50 instead of 70, why, well , the outdoors is wet, and metal cars are large.


After some digging, it seems the 70V figure comes from a part of IEC 60479-5 that relates to shocks that are only from hand to foot (not one hand on car to another hand on a fence rails), and assumes skin contact areas of 12cm2 or less (if that sounds like a large area, it isn't,  it is a total area of skin a touch over 2 inches by 1- gripping a typical door handle creates a substantially a bigger contact area for all but the most childish hands. Even on a small child a wet footprint is  a larger area)

It is a voltage which may work better for the largest typical bare part of a painted lamp post or traffic lights working in earth return mode on a dry day.


Also statistically there are about 7.5 million lamp posts on the road today *, vs 32 million cars and 4 million vans and half a million lorries. Of course only quarter of a million of those are currently electric, but the car hazard could  become quite a bit more common than the lamp post.


*I agree the lamp posts are slower moving..

I note and concur with the 25V maximum exposed voltage instead of 50 instead of 70

The thinking behind the 25V was that that earth leakage currents can raise a TT earthing system significantly above true Earth potential - so in theory an ordinary TT system could be hovering at anything up to 50V from Earth without the RCD tripping. An adjacent charge point might possibly also be at 50V - but there's no guarantee that the leakage currents are in phase - so you could have 50V x √3 between two adjacent TT systems on different phases - or even 50V x 2 = 100V if they're supplied from different sides of a split-phase supply. Ensuring the RCD trips above 25V was just intended to ensure the touch voltage between any two adjacent point couldn't exceed 50V rather than looking for a lower limit as such.


Of course with a typical 30mA RCD and a 200 Ohms electrode we'd be looking at about 6V per system or 12V max between adjacent points - so in practice it's a lot safer even than that.


  - Andy.