I damaged my meter tails

[JohnW2]

My point was that this thread seems to be a search for a definition of 'double insulated'. The only place you are going to find a definition is in a Technical Standard that uses the phrase.

That might be your view of the thread, but it's a little different from mine. I'm not 'searching for a technical description' but, rather, are suggesting that, whatever the industry may have decided, I don't personally think it particularly reasonable (or helpful/useful) that people get criticised for saying that something is "double-insulated" when, in terms of everyday English, that is precisely what it is!

I know that technical definitions can sometimes cause difficulty and confusion for 'lay people', but I do think it would be a pretty stupid industry which defined a phrase in a manner which made the usual English use of the phrase 'incorrect'!

Kind Regards, John

 

[JohnD]

If a wire has insulation over it, it is insulated. Regardless of the thickness, colour or composition of the coating

In the same way that if a naked person is wearing clothes they are clad.

I would argue that a person wearing pants, a vest, trousers, a shirt and an overcoat is not "triple clad"

 

[SUNRAY]

To throw a spanner in the works...
Back in the day no one ever referred to meter tails as 'insulated and sheathed', it was always 'double insulated'. If I had to give a date I ever it referred to as insulated and sheathed I reckon it had to be within this forum so since 2009.

 

[JohnW2]

If a wire has insulation over it, it is insulated. Regardless of the thickness, colour or composition of the coating .... In the same way that if a naked person is wearing clothes they are clad.

True, although that doesn't stop the concept of "double insulation" being fully accepted in the context of Class II items.

However, what you say rather begs the question as to why 'double thickness insulation' is (for cables) not acceptable as an alternative to 'double insulation' or 'insulated and sheathed' - in much the same way as 'reinforced insulation" is an acceptable alternative to "double insulation" for Class II items.

I would argue that a person wearing pants, a vest, trousers, a shirt and an overcoat is not "triple clad"

I agree that would not be usual use of English in the case of the word "clad", although the concept hat multiple layers of clothing (as an alternative to one layer of 'extra-thick clothing') gives additional protection (against cold) is obviously fully accepted.

However ,in more restricted contexts, "double-gloved" and "triple-gloved" are widely used in medical, laboratory and some industrial contexts, in which cases the 'protection' concerned is against the transfer of pathogens or hazardous substances.

Kind Regards, John

 

[JohnW2]

To throw a spanner in the works... Back in the day no one ever referred to meter tails as 'insulated and sheathed', it was always 'double insulated'. If I had to give a date I ever it referred to as insulated and sheathed I reckon it had to be within this forum so since 2009.

I can offer the same spanner. Before I joined this forum (2011 in my case), I had never heard or seen anyone being told that it was 'incorrect' to describe the likes of meter tails as "double insulated".

Kind Regards, John

 

[RandomGrinch]

...and If anyone is still interested, I have just randomly found this article from the IET

Mythbusters #4 Double insulated cables

Following on from the last Mythbuster article on appliance testing in the workplace in Issue 74 (March 2019), a reader suggested looking at the confusion between protective measures for electric shock and the construction of flexible cables.

electrical.theiet.org

 

[Harry Bloomfield]

I can offer the same spanner. Before I joined this forum (2011 in my case), I had never heard or seen anyone being told that it was 'incorrect' to describe the likes of meter tails as "double insulated".

Kind Regards, John

In my opinion, the outer layer/sheath cannot be regarded as insulation at all. I was always taught to strip the outer back, so it was clear of any terminals, simply because the sheath was never designed to insulate, rather to provide mechanical protection. After all, why bother making cables with two layers, of the very same quality of plastic, when a single layer is adequate?

 

[Notch7]

If that was me, Id stuff some insulation tape on it and forget it

oh and think my self lucky I didnt up half away across the room clutching a melted cordless drill.

 

[JohnW2]

In my opinion, the outer layer/sheath cannot be regarded as insulation at all. I was always taught to strip the outer back, so it was clear of any terminals, simply because the sheath was never designed to insulate, rather to provide mechanical protection.

That's what most people seem to believe.

After all, why bother making cables with two layers, of the very same quality of plastic, when a single layer is adequate?

Very good question. However, the outer sheath is generally at least as thick as the insulation of the cores, and is usually described simply as "PVC" (just as is the insulation of the cores) - so, if there is a difference (in terms of performance as an insulator) what is this variant of PVC that has inferior electrical insulating properties to those of the PVC used for insulating the cores?

In terms of safety, the outer sheath is only relevant if/when the inner insulation is seriously damaged and, rules/regulations/definitions apart, I am personally more than happy for the 'second layer of protection' to be provided by any sort of "non-conductor" (including any sort of PVC I've ever heard of {other than ones deliberately made to be conductive!!}).

Also, as I wrote above, this seems to be a fairly new 'issue'. As I said, until a decade or so ago, I'd never heard it being suggested that it was 'incorrect' to describe the cables we are talking about as "double insulated".

Kind Regards, John

 

[EFLImpudence]

How is it decided how thick to make a layer of insulation?

So if one layer were twice as thick as 'normal', would that be described or considered as double-insulated?

 

[JohnW2]

How is it decided how thick to make a layer of insulation? So if one layer were twice as thick as 'normal', would that be described or considered as double-insulated?

Quite so.

However, as I said, I think that the sheath is usually at least as thick as the insulation of the cores - so, if it is made out of the same/similar material, one would expect it to be at least as good as 'insulation'.

Returning to your question, although in the context of Class II items, BS7671 (I presume reflecting other Standards) accepts the concept of "reinforced" insulation as an alternative to "double insulation", there is nothing similar in relation to cables - although, as you imply, one might expect that "very thick insulation" would, logically, be an acceptable alternative to "(thin) insulated and (thin) sheathed".

However, as always, it's probably not meant to be logical ...

,,, and, even as things are, I really can't get excited by these arguments about some alleged difference between a (PVC) "sheath" and (PVC) "insulation"

Kind Regards, John

 

[SUNRAY]

The silly thing about all of this is the tails could be run in conduit, metal or plastic, as the required sheath with insulated wire and comply.

 

[JohnW2]

The silly thing about all of this is the tails could be run in conduit, metal or plastic, as the required sheath with insulated wire and comply.

I would say that the whole thing is very 'silly'.

As I've said, I'm perfectly comfortable to have by life protected by a second layer of PVC, no matter what it's called, to cater for the (itself very improbable) event of the insulation of the core becoming seriously damaged!

Kind Regards, John