Solar Energy Systems installation UK - lack of skills

However far more important is how to relate available energy, or rather rate of delivery, into a safe arc radius to avoid instant sun-tan or worse being basted with molten metal, and then to either limit access for body parts, or the energy available during fault, so that the two never coincide. By the time you are talking about needing buckets of sand, if you are in earnest, you are already on the wrong side of a how to design things safely.

M.

(Who is very much not afraid of 3 phases either 400 or 690, when properly fused and in suitable containment, or indeed higher voltages too, but with rather more caveats. )

and anyone who has tried it will tell you that 3 car batteries strike up far better but to go easy anyway, as it does them no good at all. A few minutes non stop welding can heat the battery acid to a temperature that does irreversible damage. On the very rare occasion it is needed, I prefer to see the batteries put in a ditch or on the other side of something solid like  a vehicle, so if one does boil and vent, the scope for injury is limited, and not all on-line videos show sensible behaviour - but that is not just about welding.
It is quite a good thing to know how to do however.

Mike.

gkenyon said:

Anything more than a few (<5) amperes at 12 V or more is enough to draw an arc, and 1-2 amperes is enough to sustain it

More homework needed here old chap. FYI you cant sustain an arc flash at 12 V. You will get a spark but you cant develop a sustained arc (at STP) below a certain voltage.  This is ca 20Vdc.  A welder will tell you that you can only weld with 2 car batteries 24Vdc or more  YT vids are there.

Rob Tes said:

anything >50vdc is way outside my comfort zone

From experience, I'm more worried about DC current than DC voltage. Anything more than a few (<5) amperes at 12 V or more is enough to draw an arc, and 1-2 amperes is enough to sustain it. At 5 V DC, more current is needed ... but not too much to be honest.

Shock isn't the issue, fire, burns and arc flash can be problematic.

I can't disagree with some of the other points that you make.

For domestic installations, anything >50vdc is way outside my comfort zone, but thats my personal prejudice .  Aside from shock hazard,  my concern is that switchgear/fusible links etc are notoriously suspect for circuit protection under load/fault interruption.  Properly authenticated circuit breakers (as per Siemens NF) are very expensive. The Main circuit breaker with AIC 5kA can be ca £1000 for the levels you are referring to.  I was astonished to see a well known US brand which supplies a complete solar kit down to the inverter mains outlet use a rotary cam switch (typically seen on electrical panels) as a circuit breaker between the panels and the Inverter  (no internal arc quench in that design).

At least with ELV systems you can keep the methods of last resort to hand on a shelf by the distribution board - namely a proper set of cable cutters, leather gloves, welder goggles and a plant mister bottle to spray water on an arc flash fire.  But I am old school as were fire buckets with sand.

I have the same fear of 3 phase power and wouldnt trust any old tradesman installing that system (at least it has full industrial design system credentials behind it so I would need a professional design practice to provide  detailed installation drgs and BOM. The tradesman installer has to follow the drg to the letter and not be left to fumble his own interpretations on the back of an envelope (Ive seen this approach)

IMHO the approach to Solar systems is very slap dash and careless, no site installation drgs, BOM, cable run iso

Maybe the sorry tales of fast track installations reported on various Forums has given me a jaundiced view (I hate Roofers)

Rob Tes said:

Surely this doesnt apply to ELV <50V systems? 

Just to clarify, most solar PV systems are not ELV. Typical operating voltages for small domestic systems are ~600-800Vdc, up to utility installations with open circuit voltages of 1500Vdc. Operating currents are of the order 10-20A, depending on configuration, obviously more if anything is in parallel (or if the modules are in reverse current due to mismatch or fault)

It is also worth noting that solar PV installations rely on the measure of double or reinforced insulation, with class II equipment and insulation monitoring devices.

The conductors, at least for sections on the array itself, should be fine wire flexible (cl5) stranded tinned conductors under that insulation, in the most part because anything on the array will be subject to frequent thermal cycling and wind movement.

The connections will also be exposed to a wide range of temperatures (in the UK behind a panel could expect an ambient temperature from -15°C to +70°C with daily swings), are likely to see high degrees of moisture and are likely to be difficult to inspect. And yes noting the parallel thread on this topic I would expect similar in someone's loft.

Hence the use of connectors, and connections generally, made to a standard.

Rob Tes said:

Have you amortised the total cost of installation inc wiring switchgear inverter (fails in 5 years maybe) panels need replacing etc?  Batteries?

Panels should have a warranty of 20 - 25 years.  Inverters these days tend to come with a 10 warranty, or more.  I assumed no battery.

Surely this doesnt apply to ELV <50V systems?  You refer to heatshrink protection.  Some of the quality products seem to be very well suited to outdoors UV resistant, adhesive forms a sealed clamp on a round sheath.  I would put additional coat of Si grease on the metal parts of the barrel and around wire strands after crimping and use a 50mm length sleeve - seems belt and braces to me.  But then electrolytic corrosion can only occur with a positive and negative splice being close together in the event of a moisture path - seems remote risk.  You dont see auto wiring harnesses suffer unless in extreme circumstances.

(mustnt violate copyright)

I think we're OK with small extracts for the purpose of academic discussions

  - Andy.

can you quote the relevant excerpt 526.5 that outlaws crimped joints?

It wasn't the crimp I was alluding to, but the method of enclosure...

526.5 Every termination and joint of a live conductor or a PEN conductor shall be made within one of the following or a combination thereof:

(i) A suitable accessory complying with the appropriate product standard

(ii)An equipment enclosure complying with the appropriate product standard

(iii) An enclosure partially formed or completed with building material which is non-combustible when tested to BS 476-4.

which a bit of heatshrink doesn't obviously meet, if used on its own to extend tails to reach your marshalling boxes.

   - Andy.