Outdoor Socket Advice

[JohnW2]

...He can likely use any black cable, black as it resists UV better ...

We all say that, so I presume it must be true, but I've never fully understood ...

... a black object will totally absorb all wavelengths of visible light that hits it, so I imagine also UV and IR. One might therefore be forgiven for assuming that any damage the UV causes to the material would tend to be at its worst in the case of a black object. I wonder where my thinking is going wrong?

Kind Regards, John

 

[plugwash]

Yes but black plastics/rubbers aren't black because the plastic/rubber itself is black, they are black because a pigment has been added that absorbs light. So the light is not absorbed in the plastic itself but in the pigment.

Carbon black is cheap and very effective at absorbing both visible and UV light, so the cheapest/easiest way to make a plastic/rubber UV resistant is to make it black.

 

[JohnW2]

Yes but black plastics/rubbers aren't black because the plastic/rubber itself is black, they are black because a pigment has been added that absorbs light. So the light is not absorbed in the plastic itself but in the pigment.

Yes, I understand that much, but I had assumed (presumably incorrectly) that the pigment was sufficiently closely 'associated' with the plastic that a problem might theoretically still exist. I suppose the real issue is that I don't understand the mechanism whereby UV affects the plastic.

Carbon black is cheap and very effective at absorbing both visible and UV light, so the cheapest/easiest way to make a plastic/rubber UV resistant is to make it black.

Indeed. As I said, since that's what we all say, I assume it has to be correct

Kind Regards, John

 

[flameport]

Hopefully flameport can clarify but, as you say, on the face of it, it looks as if what was being tested with was an L-N imbalanced DC current ,

That test rig was made to demonstrate a particular DC detection device made by Blakley (the large white item in the centre), and uses a 4 pole type AC RCD with 3 poles used, L, N and the third one with a variable DC current through it.

How type AC RCDs react when exposed to DC is undefined, they are not designed or tested for that, and the standard for them doesn't have anything on DC either. That particular one in that rig will not work at all with 250mA of DC, but that's only one example of one specific RCD from one manufacturer.

To detect smooth DC, a type B RCD or equivalent is required, which is what the white Blackley device is. Smooth DC on an AC circuit is only likely if there is a fault with some DC item such as an electric vehicle or solar installation, or in the case of that demonstration rig, a railway with DC traction current returning through the AC installation. That's why EV charge points contain DC current detection or a type B RCD.

Type A RCDs will detect pulsed DC, which is far more likely in normal use from items which contain rectifiers / diodes. How type AC RCDs react to that is also undefined.
The 6mA referred to is just the maximum amount of smooth DC that a type A is stated to work as intended, above that it's behaviour is undefined. Generally unrelated to normal use on an installation with pulsed DC loads, as the smooth DC would as above typically only be from a fault or some other source external to the installation and a type B would be used instead if that was a possibility.

For normal installations, pulsed DC in normal operation is common, and type A is intended to be the minimum requirement.
Some installations will require a different type, such as type B in situations where faults or external influences could result in smooth DC or type F for certain types of equipment.

Exactly, and it's the grave difficulty I have had in trying to ascertain "the extent of the problem" that I have been moaning about for a long time.

No information is available, because no one bothered to even consider it until fairly recently.

However type AC RCDs are not fit for purpose, and haven't been for a very long time. They were designed for AC loads, something which is rare in a modern installation.

Germany banned the use of type AC RCDs almost 40 years ago. Many other countries have done the same.
Meanwhile in the UK, BS7671 has been more concerned with not having socket outlets in bathrooms, perpetuating the use of 70+ year old circuit designs and other minutiae.

 

[JohnW2]

That test rig was made to demonstrate a particular DC detection device made by Blakley (the large white item in the centre), and uses a 4 pole type AC RCD with 3 poles used, L, N and the third one with a variable DC current through it.

That's what bernard and I thought, but the rest of what you go on to say (about various types of DC current etc.) seems to be missing (or, at least, not addressing) the point that bernard and I were making.

By having the DC current flow through only one of the poles of the RCD, it seems that you were simulating a situation in which not only was a DC current flowing through the L conductor but also that the DC current was (presumably because of a simultaneous 'earth fault') not returning through the corresponding N conductor.

To simulate the situation in which there was a DC current (maybe 'during normal operation') but no simultaneous 'earth fault', you presumably should have routed that return current through the 4th pole of the RCD, shouldn't you? As bernard said, had you done that, one might expect that the DC fields of the two conductors would have largely cancelled, thereby greatly reducing the tendency, if any, for it to saturate (or whatever) the core? ... or are we missing something?

No information is available, because no one bothered to even consider it until fairly recently. ..... However type AC RCDs are not fit for purpose, and haven't been for a very long time.

I have to say that, having been working in highly evidence-based disciplines for most of my life, I find those two statements to be essentially incompatible .... my 'work mind' finds it rather difficult to understand how one can declare that something is not 'fit for purpose' on the basis of 'no information'

Germany banned the use of type AC RCDs almost 40 years ago.

Hmmmm. If one looks at some of the seemingly extraordinary decisions that Germany has made in relation to the AZ Covid-19 vaccine in the past 3-4 weeks (particularly the last 24 hours) (first 'banning' its use in one half of the population, and then swapping that 'ban' to the other half!) I'm not convinced that I can have much confidence at all in the rationality of German 'banning' of anything

As I have said repeatedly during these discussions, I am not saying that there is not a problem (indeed, at least qualitatively, there clearly is) - but I am saying that I would love to see some information about (particularly quantification of) the nature and extent of the problem.

Kind Regards, John

 

[Bubbauk]

Hi All

Thank you for all the replies, I didn't intend to start such a lengthy discussion but it has been interesting to read through.

I have read on some forums that the charger should have all of the required protection built in and the charger is actually in the car, the box plugging into the wall is a Electric Vehicle Supply Equipment (EVSE).

The Type A RCD is cheap so I will go ahead and change this. I plan to fit the additional MCB to the left RCD as I no longer have an electric shower and this cable is now wired to a socket in my attic, this RCD has the lowest load out of the 2 and should have no problem with adding this 13a socket onto it.

I do have someone coming on Friday to quote for a proper electric charger but rough quote was about £800 but dont think I need to go to this extent