Fused or Unfused 2-way plug adaptors?

[bernardgreen]

However, I don't see what that has got to do with the Variac "introducing an inductive component"

The oscillatory circuit will affect to some extent the operation of the variac

 

[JohnW2]

The oscillatory circuit will affect to some extent the operation of the variac

I understand what you are suggesting, but what I am struggling to to get my head around is the question of why the Variac (which, after all, is just a type of {auto} transformer) should differ in this respect from the DNO's transformer.

What if the the variac was very close to the substation transformer - would you still be saying the same?

Kind Regards, John

 

[JohnW2]

I understand what you are suggesting, but what I am struggling to to get my head around is the question of why the Variac (which, after all, is just a type of {auto} transformer) should differ in this respect from the DNO's transformer.

... or, to put it another way, what would be different if you replaced the Variac in your diagram with the secondary of the DNO's tranny?

Kind Regards, John

 

[JohnW2]

The volt drop has also impacted on the loop impedance, we have to now allow an extra 5% to allow for volt drop.

Eh?

@ericmark ... I realise that my post was extraordinarily brief by my (or your!) standards (maybe so brief that you missed it!), but I was hoping that you would be able to help me understand your statement which I quote above.

Kind Regards, John

 

[JohnW2]

I have questioned PAT testing limits where a house is all RCD protected, an extension lead is safe even when rather long with RCD protection but the permitted 2.42 Ω for 13 amp and 16.4 Ω for 3 amp (BS 7671:2008) for a BS 1362 fuse still is required where not RCD on the sockets.

Just noticed this one!

Your 2.42 Ω and 16.4 Ω figures have actually become 2.30 Ω and 15.6 Ω respectively since the introduction of "Cmin" in Amd 3 of BS7671:2008.

However, even with the now-correct figure of 2.30 Ω for a 13A BS1362 fuse, even if the extension only has 1.25 mm² cable (the smallest that can {just} take 13A), that would allow for a length of 62 metres, and one doesn't commonly come across extension leads longer than 50 metres.

Kind Regards, John

 

[JohnW2]

Yet again ...

 

[ericmark]

My point was simply that any PAT test includes the environment the item is tested for use in, so we could pass an item for office use, but it would fail for use on the factory floor, as there could be loads of water on factory floor. Be it the RCD or water, or even chance of impact, once you move items around the PAT testing pass sticker becomes meaningless. I had this problem with fig of 8 class II lead sets, I had no problem with their use in the office, but banned by me on the factory floor as the floor often covered with water, so radios in the office could use the leads, but on factory floor the lead needed to be fixed into the radio.

And this is the problem talking about some ones home on the forum. I tend to relate to my own home, and forget other peoples homes may not have the same safety equipment. Also one forgets people can do what seems daft. We had a course on fire fighting, and we were told should not use water on an electrical fire, however in real terms in this house using water would have a duel affect, one it would put out fire, and two it would trip the RCD automatically removing the source of fire. So is not using water still good advice, I would say yes as can't rely on the RCD working, however now not so cut and dried.

 

[JohnW2]

My point was simply that any PAT test includes the environment the item is tested for use in, so we could pass an item for office use, but it would fail for use on the factory floor, as there could be loads of water on factory floor. Be it the RCD or water, or even chance of impact, once you move items around the PAT testing pass sticker becomes meaningless.

Whilst what you say makes sense, it also means that, as you say, passing a 'PATest' can be pretty meaningless - particularly give that the "P" of "PAT" means "Portable".

I suppose that doesn't mean that PATests are completely useless, since many (probably most) of the things that would cause something to fail such a test would probably apply in any environment. It's passing a PATest that is the potential problem.

However, this doesn't really address the question I was asking, about your statement that "voltage drop has impacted on loop resistance", and I woukld be interested to hear what you had in mind when you wrote that.

.... We had a course on fire fighting, and we were told should not use water on an electrical fire, however in real terms in this house using water would have a duel affect, one it would put out fire, and two it would trip the RCD automatically removing the source of fire. So is not using water still good advice, I would say yes as can't rely on the RCD working, however now not so cut and dried.

Totally off-topic, but I suspect the truth is (and probably always has been) that, if the situation arose in anger, then if no alternative were available, then most of us probably would use water (cautiously/judiciously), rather than 'do nothing'. As you say, if RCDs were present, then the water would probably make them operate - but I suspect that the official line might be that even if some/all RCDs operated, there would still be some 'live electricity' upstream, of those RCDs which could pose a threat to those fighting the fire if there was water all over the place. As for ...

... it would trip the RCD automatically removing the source of fire.

You seem to be suggesting that 'removing the source of the fire' would achieve something. However, as I've often said, even if a fire was 'cause by' something electrical, by the time there is a fire sufficiently established that it needs to be 'fought', I don't think that de-energising the electrical system would make any difference to the fire, although it would reduce risks to those fighting the fire.

Kind Regards, John