I agree with the importance of good training however I am not sure I see the level of danger that you are suggesting.

Most countries other than the UK allow power sockets in bathrooms. There doesn't appear to be a higher accident level in these lands.

Many countries have far lower electrical installation standards. On one Chinese building site I complained about a twisted and taped joint in a 400V 3phase cable being out in the rain. They considered this to be resolved by putting an upturned plastic bucket over it.

Solar panels on roofs have two intrinsic risks, working at height, and they can't be switched off, you just have to wait for it to get dark. I would suggest that injurys due to falls from height are much more common than electrical accidents.

What are you considering to be dangerous and are there any accident statistics?

Indeed working on a pitched roof is a self evident hazard.  Joe public doesnt always appreciate the nature of continuous high current from a panel - its not obvious, furthermore you cant test for a "live" circuit"  like using a neon screwdriver, you must have a special dc clamp meter and these have only been commonly available in the last few years (ca£60 for reliable meter - how do you test it is working? , a neon you stick it in the nearest mains socket).

Then you come downstream to the installation wiring and switchgear/fuse protection - this is where it all become a can of worms.  Joe Public will generally not have an appreciation of the risks involved there after - I wont labour that point here - it should be understood by IET Members  although without a particular study of this area, the risks may not be truly appreciated.  Im a highly trained EE rtd  and have studied this for over a year as I was chastened to discover how little I appreciated the problems of ELV high current dc.  I was never involved in Power Systems Engineering, nor did I practice at electrician level - 3 phase scared me - and still does.

A glaring example of regs patchy treatment is that a Firemans Switch is not mandatory. for solar systems.

Note that whatever system is cobbled together by amateur treatment has to run 24/7 unattended and have emergency shutdown or routine operation by untrained persons.

We take for granted the purpose and operation of our domestic consumer board and its MCBs.  A solar system distribution up to the inverter and its  input to household supply and maybe a grid export metering and/or batteries.

Most amateurs Ive seen on YT  Vids just string it all together somehow  - never a hint on an SLD.  or system safety analysis

This is made all the worse by the tidal wave of Cheap Charlie switches, fuses, breakers, inverters etc comprising the installation

No consideration of smoke detectors AFFD's, heat detection , temperature logging

And you ask why I think the risks are not being taken seriously in UK?  We dont have trained inspectors (LGA employed not subcontracted out)  who issue a PTO - permit to operate.  When the amateur gets it wrong it can burn his house down.  There are countless examples on YT.

A couple of quick points:

What are you expecting the firemans switch to do? What can it isolate, what will it leave live?

Are there countless examples on YT of what you consider incorect or countless examples of houses burning down?

furthermore you cant test for a "live" circuit"  like using a neon screwdriver, you must have a special dc clamp meter and these have only been commonly available in the last few years

You've lost me there I'm afraid. Surely DC volt meter (or other DC voltage indicator) can be used on exposed DC terminals (or connectors) just like you would use a neon screwdriver on AC terminals? And doesn't a DC clamp meter only show current, not voltage? (via the clamp at least) - which would mean a downstream break would result in a zero reading even though the conductors were still live?

Not that anyone here would use a neon screwdriver for proving dead anyway - they fell out of favour many many years ago (too many accidents where either the internal resistor failed to provide a high enough resistance (internal fault or exposure to moisture) or the user's finger didn't provide a sufficiently low earth path. Non-contact indicators are preferred (e.g. volt-sticks) and usually for formal proving dead they've have to be backed up by a proper 2-pole voltage indicator direct on the conductors anyway.

   - Andy.

AJJewsbury said:

Not that anyone here would use a neon screwdriver for proving dead anyway - they fell out of favour many many years ago (too many accidents where either the internal resistor failed to provide a high enough resistance (internal fault or exposure to moisture) or the user's finger didn't provide a sufficiently low earth path

AFAIK that is an urban myth, neon screw drivers are still commonly in use.  Leccies of course are well versed in fake kit and would habitually check anyway.  BTW its not a finger poke, that maybe wet, its the bare knuckle test which apprentices (if we still had any) would be well tutored (goes with the neon test).  Have done it myself when a neon wasnt to hand.

AJJewsbury said:

Surely DC volt meter (or other DC voltage indicator) can be used on exposed DC terminals (or connectors) just like you would use a neon screwdriver on AC terminals

What you do yourself is your choice and there are many who show that they wont be told.  However, put yourself in the position of instructing an installer - is this what you would tell him?

Where are these convenient bare terminals to Volt test when you are on the roof?  The Volt meter will not tell you if significant current is flowing?  Can I safely uncouple an MC4?  If there's only a few amps flowing say <5A then no damage will occur.  If its 50A, you will damage the MC4 and it has to be replaced (leaving a damaged one in service is asking for incipient arcing to start at some future time and start a fire.  This should be a mandatory procedure. 

Remember these MC4 are usually tucked behind panels so scaffolding and dismantling panels needed

More homework needed rather than armchair speculation.

Here is the conventional Firemans switch often seen on shop fronts

https://www.youtube.com/watch?v=GZD7hdXP0oI

Unfortunately its a 3ph blade switch for ac only.  But you can see the purpose

I havent seen an equivalent suitable for dc use yet  - try browsing and let us know.

Here is an example of a huge scandal in OZ when a mandatory mcb was installed on Solar systems.  In OZ they have a national sponsored push to get every roof retro-fitted with panels

https://www.youtube.com/watch?v=EJC6wKir_Lo&t=9s

A test to show what happened - there were numerous fires before their Regs were hastily changed and this particular device was outlawed.  There are numerous Cheap Charlie MCBs offering dc disconnection as well as 1/4 turn rotaries

I spent over a year researching these horror stories, there are hundreds of YT examples and some from Companies who should have known better.

Some enlightening reading

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/630641/fire-solar-pv-systems-frs-recommendations.pdf

Conclusions

Recommendations to improve the safety of firefighters responding to fire incidents on buildings where PV
is present are summarised:
 Information on appropriate emergency response methods of making PV systems safe – requires
further research.
 Ability to identify the presence of a PV system early on in firefighting operations – this could be
improved through training and through PV installers use of the ‘Solar PV on roof’ label as
required by MCS [9].
 Revision of NOG information – in discussion between CFOA and BRE Fire & Safety Team.
 Consistency of SOPs for PV across all UK FRSs – preferably using new NOG information.
 Provision of training to fire crews in the following:
o Basic understanding and recognition of the PV system components and labels - in order
to quickly identify the presence of a PV system, assist with risk assessments and to
provide more detailed information to fire investigators and during debriefs.
o Details of the hazards that a PV system may introduce to a fire incident – including
associated hazards such as potential to electrify other conductive objects.
o Safe isolation procedures – including an understanding of what parts of the system
should still be considered live.Other approaches that can be taken to deenergise systems
and the risks that these could pose to fire crews.

And here is a source that will show where the USA and its revered UL  are going with the technology

iaeimagazine.org/.../

I will repeat my question, what does the Fireman's switch isolate and what does it leave live? They were originally used for high voltage neon signs on shop fronts and then I believe for electric petrol pumps (may be wrong). If you break the circuit from the solar panels to the inverter the panels and the wiring down to the switch are alive. You also need a switch capable of breaking a few hundred volts DC. A shorting switch might be better?

Similar problems exist with EVs. The HV cables are required to be in defined places that are in the emergency services documentation. They must also be orange and have a grounded screen. These carry similar voltages and higher currents than PV systems.

More house fires are caused by other things than solar panels, probably smoking and cooking are the main causes. Do some Pareto deal with the 20% of the causes that result in 80% of the problems.

BTW its not a finger poke,

I meant the finger that has to make contact with the top of a neon screwdriver for it to illuminate - making the user part of the circuit (if, hopefully, at an extremely low current). Unusually dry skin, or contamination (or gloves) can mean the screwdriver doesn't illuminate even when the tip is live.

knuckle test which apprentices (if we still had any) would be well tutored

You are joking? Not this century (or even the latter part of the previous one) - reg 14 of Electricity at Work regs put paid to people being taught to do such things long ago. Use the proper safety equipment or go home is the mantra these days.

Can I safely uncouple an MC4? 

Ah, OK I see where you're coming from now. Probably more conventionally described as being 'on load' rather than 'live'. There are similar considerations with high current connectors on AC system. Generally operating procedures are used to reduce the risk (typically shut down the inverter and then open the (downstream) DC isolator, at that point there should be no current flowing ... unless there's a short in the DC wiring somewhere. I agree a clamp meter would be useful in mitigating the remaining risk.

   - Andy.

AJJewsbury said:

Generally operating procedures are used to reduce the risk (typically shut down the inverter and then open the (downstream) DC isolator, at that point there should be no current flowing ... unless there's a short in the DC wiring somewhere.

Really?  is this what you would stand up and say in court after the owners house burnt down?

Try sketching out and studying an SLD of a Solar energy system, 10kW panels, installation kit, inverters, batteries, Victron stuff, standby genny, metering to grid etc and start with Andy's https://www.youtube.com/@OffGridGarageAustralia/videos - over 500 Vids packed with solid personal experience.

AJJewsbury said:

Generally operating procedures are used to reduce the risk (typically shut down the inverter and then open the (downstream) DC isolator, at that point there should be no current flowing ... unless there's a short in the DC wiring somewhere.

Really?  is this what you would stand up and say in court after the owners house burnt down?

Try sketching out and studying an SLD of a Solar energy system, 10kW panels, installation kit, inverters, batteries, Victron stuff, standby genny, metering to grid etc and start with Andy's https://www.youtube.com/@OffGridGarageAustralia/videos - over 500 Vids packed with solid personal experience.

Really?

Of course - the electrical industry uses similar procedures all the time - prove instruments, switch off, lock off, prove dead, re-probe instruments, before exposing live parts. The ones above are actually on a sign supplied with my own PV system and match the instructions from the inverter manufacturer for safe isolation.  Why would I even end up in court if some DIYer caused themselves damage by not following sensible precautions? Would the original installation electrician be called to account if a DIYer decided to unscrew a socket from the wall without turning off the supply first or tried to wire a 10kW shower in 1.0mm²?

   - Andy.

The problem of course that while we can detect alternating current and voltages with clamp meters and capacitive probes  respectively that are non contact, and large DC currents by their magnetic fields using a hall effect probe (in a DC clamp meter) with reasonable confidence, there is no equivalent  reliable non-contact method of detecting the presence or absence of a  DC voltage before some metal is exposed..

Breaking of high current DC is going to have to be taught with extra emphasis and maybe a  few old techniques  re-learnt - things that get overlooked include the fact that magnetic arc traps used for DC breaking are polarity sensitive - the arc being pushed one way or the other, and there are certain kinds of fault (parallel sources such as strings of panels)  where quite conceivably a fault current could be flowing either way.

I don't see it as a big deal but we do need to make sure the information is available and well disseminated so folk know what to look for.

Mike

Great stuff - it supports my OP - we are not teaching this emerging speciality anywhere AFAIK.  Practising Leccies dont have time to self study this area, and there are no accredited text books you can pick up on. Worse still is the amateur with a superficial grasp of electrics who thinks he knows dc systems from meddling with cars/trucks. When you get into Lithium storage there is a great deal to learn and your path is twisted and confused by YT and Ggle rubbish highly influenced by suppliers of kit or bogus courses.  Its a nightmare fighting through it all - then you have to deal with Cheap Charlie.

FWIW I recently discovered fake solar cable floating around on the market. - 6mm2 turned out to be neared 4mm2 - so be careful to check a sample before laying out for a drum.  Fake MC4 connectors are everywhere and a major cause of roof fires. Panel installers may well have no credentials as Installation is ca 50% of total cost.  Solar energy is wild west country.

What actually is your point here? There is not enough training? People buy cheap substandard components?

I can accept that substandard connectors could start fires especially if non flame retardant plastics are used. The question is what can the fire spread to. The cables again should be flame retardant. I agree if PVC cables had been used rather than the correct solar cables there could be a problem.

The current rating of solar cables is a different problem.  The current rating of a cable is based on a temperature rise in the conductor to give a temperature in the insulation that will give a defined service life. This may be 40 years for building and railway cables or 3000 hours for automotive cables. The ambient temperature obviously plays an important part. If I use a 4mm2 cable in place of a 6mm2 cable what will happen? At full load the temperature rise may be doubled (roughly). How long will it be at full load? For a typically solar installation probably at most 25% of the time. Will this reduce the service life? Probably not. The cable temperature will be higher with the addition of a higher ambient temperature due to the sunshine. This will not be a problem if the correct crosslinked polymers are used for the insulation, it will not melt. Will the temperature be enough to ignite anything nearby?

Go back and read my text and do some homework

a) There most certainly is not enough quality training in Electrical Eng of the type that existed with the tech College HNC courses.  The lecturers were great, knowledgeable guys.  The pseudo Uni factories dont offer the same level as the day release system.  Certainly you wont get instruction on the special conditions for dc ELV systems. Given the parlous state of employment conditions for lecturers, I doubt whether any quality staff can be retained (get more as a warehouse shelf filler). I have great sympathy for all those students who were cheated out of "face time" lecturing hours substituting on line instruction and tutoring which is of inferior quality yet still have to pay for huge tuition fees.

b) Try buying the Lucas pattern push fit spade connectors common in older cars.  On EB you are totally flooded with Cheap Charlie copies with substandard materials and much thinner brass sheet ( bad news, cant carry current or maintain spring contact pressure).  You unlikely to find the original item but are presented with hundreds of identical listing utterly wasting your time.  Even drilling into GGL wholesalers often offer them same gear. Eventually you find a real EU manufacturer, but the MOQ is 1000's

c) My point about Solar cables (which have EU TUV markings on the sheath - you specify 6mm2 but are supplied with nearer 4mm2 is that acceptable.  Your other questions relating to 4mm" instead of 6mm2  are for the professional designer to decide and justify

You need to look at your view of the professional responsibilities here  as what you do in your own shed is your business.  A designer must weigh up the info and credentials from the supplier and prepare a PO with tech spec and this is used the an inspector to approve delivery of a shipment before payment is approved.  Look at the utter fiasco of the recent COVID PPE masks that were found to be CHEAP CHARLIE fakes of the genuine International Std product and totally in effective as a filter for micron virus particles. 

The designer makes drawings and docs which  specify the wiring installation and components which must all be compatible and fit together. This is given to unknown buyers and electrician installers somewhere to implement.  No place for the trivial minded lazy "catalog engineer".

Many a leccie wannabee designer (who has extensive - and valuable field experience) fail utterly in the design office when it comes to putting it all down on paper as a set of instructions for another unknown installer or a buying spec.

I'm still confused as to why you think this is any different to any other electrical installation work.  For any genuine component, there is likely to be a cheap Chinese copy available from the more dubious outlets.

You describe yourself as a certified and authentic EE (not Power btw). What do you mean by certified?

a) What are the special conditions for DC ELV systems? Current ratings are the same as AC and only as you get above 24V you need to think about arcing when switching. When you get above ELV arcing is more of a problem. The largest DC power supply I work with is 15kV 15A which does require thought and care when testing as well as in design.

b) What is the relevance to Solar PV?

c) Yes, my employer manufactures Crosslinked Solar cable to meet the various national specifications so I am quite aware of the requirements and I am quite conversant with electrical design and current ratings. I have been previously involved in various aspects of cable testing, short circuit performance where the conductor can reach 250°C is quite spectacular, not something I would do in my shed.

Roger B said:

You describe yourself as a certified and authentic EE (not Power btw). What do you mean by certified?

a) What are the special conditions for DC ELV systems? Current ratings are the same as AC and only as you get above 24V you need to think about arcing when switching. When you get above ELV arcing is more of a problem. The largest DC power supply I work with is 15kV 15A which does require thought and care when testing as well as in design.

b) What is the relevance to Solar PV?

Apologies about the language in the commentary of this short video but it does illustrate some of the points that have been discussed here: www.facebook.com/.../3507234699527923

I think the fact this kind of thing goes on is an issue.

And if you have a fault L+-L- before a combiner box or inverter, say because of vandalism or (possibly unforeseen) mechanical damage, it's the only way of stopping current flow with the way PV is designed ... and yes, there's perhaps a discussion on whether that is in line with "general parts" Part 4 and 5 of BS 7671 ...

Hello Graham,

I think that the replies have got a little confused. I was referring to Rob Tes’s post where he was talking about the quality of Lucar connectors. Thank you for the video, it would be useful to know what voltage and current they were interrupting. I have previously wondered that as we are dealing with an almost constant current supply whether shorting switches would be a better option that isolators as  the first action on small systems.

Roger B said:

a) What are the special conditions for DC ELV systems? Current ratings are the same as AC and only as you get above 24V you need to think about arcing when switching.

www.youtube.com/watch