Unsheathed Basic Insulation Outside Of Enclosure

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Unsheathed Basic Insulation Outside Of Enclosure

If you’ve recently had a landlord/homebuyer report completed on a property and received a fault for “Unsheathed Basic Insulation“, you may be a little confused as to what this all means.

Sadly the terminology used within electrical reports may as well be in a foreign language (unless of course you are an electrician!). Many electricians also do not take the time to explain or provide pictures of the fault in order that you may understand further.

So lets take a look at what “Unsheathed Basic Insulation” is and why this is a problem:

Cable & Insulation

Without boring you to death with science, we need to quickly look at what makes up a cable so you can understand this type of fault.

A domestic power cable is mainly of a type called “Twin & Earth”. This is a “slang” term for BS6004 cable and comes from the fact that the cable has two equal sized conductors (Live & Neutral) and a separate “earth” conductor also.

The 2 main conductors are copper wire covered in “basic insulation” which is the first layer of insulation. In the case of domestic cables, this used to be coloured Red & Black (Live & Neutral respectively), however since 2004 are now coloured Brown & Blue (again, Live & Neutral respectively).

The “basic insulation” is then covered over with another layer of insulation. This layer is known as the sheath and on the cable in question is normally grey.

  • So What Is The Problem Exactly?

In order that a cable may be connected, for example into a socket, the insulation needs removing. First the sheath is stripped back to reveal the separate conductors within (and the basic insulation protecting them).

These are then spread to the correct terminals in the accessory. Once this is done a small amount of the basic insulation is removed to expose the inner copper core. This is then connected to the terminals.

All sounds OK so far right?

Well the wiring regulations require that no outer sheath of the cable is stripped back outside of the enclosure to which it is connected. This means that no basic insulation should ever be visible outside of the enclosure.

Unsheathed Basic Insulation - Electrical Report Explained

If the inner “basic insulation” is unsheathed outside of an enclosure, this greatly increases the risk of damage occurring to this. This is the only defence against dangerous live cores within the cable.

Knocks, bangs, movement, rubbing of the cable or excessive bending (which can cause splitting) are all possible ways in which the basic insulation can be damaged.

Expect this to be classed as C2 – POTENTIALLY DANGEROUS if the basic insulation is unsheathed anywhere where it may be accessible to touch. A prime example of this would be in the meter cupboard, an area easily accessible by the end user.

Unsheathed Basic Insulation - Homebuyer/Landlord Report

This fault may attract a C3 – IMPROVEMENT RECOMMENDED code if the cable is in an area not accessible to touch.

Regardless of whether accessible to touch or not, unsheathed basic insulation should not be in contact with metallic enclosure/sharp edges, this would be a C2 – POTENTIALLY DANGEROUS issue

  • What Causes This Problem?

Whilst physical damage occuring to cables can cause this problem, most instances of this fault are due to poor workmanship by the installing electrician.

The cable may have been stripped back outside of the enclosure as it wasn’t long enough, however this is not an excuse!

This issue is often seen on meter tails (the cables between the meter and your fuseboard) and also often on cables leaving the fuseboard.

  • How Best To Fix This?

The fix for “Unsheathed Basic Insulation” is to simply re-terminate the cable and properly take the sheathing into the enclosure.

This can cause problems on cables if there is not enough spare to enable it to be cut back and sorted. In this instance, it may be necessary to extend the cable to facilitate the repair properly.

Unfortunately this is often done incorrectly (often by junction boxes hidden under floorboards) also causing further issues/non-compliances, and big problems if wires come loose.

If you are interested, the regulation pertaining to this particular issue would be REG 526.8 which requires that: “the cores of sheathed cables from which the sheath has been removed must be enclosed”.

Need any further information? Speak to ElectricBlu Contractors, experts at Inspection & Testing

James – ElectricBlu Contractors

(01924) 654034

We base our guide (and our inspection coding in general) on the ethos of that found in Electrical Safety First Best Practice Guide 4:EICR – Please note this is a simple attempt to outline what particular faults are and why they may (or may not) pose a risk.  It in no way represents professional advice.  Each installation is unique and only a qualified, experienced electrical tester who has the appropriate registrations (and insurances) can make judgements on the condition of wiring and electrical installations.  



6 Responses

  1. Thanks for the super informative post! We had a landlord report completed and it listed this but there wasn’t any further explanation of what it was.
    Now I’ve read this I know exactly what the issue is! Now to just get it repaired

    • Hello Ms Davies, thank you for your kind words about our post! The object of our blog posts is that we may build up a bank of pictures and issues so that people can search and find what everything means. There is nothing worse than staring at a page full of electrical jargon explaining all the faults found when testing if you don’t understand it.
      If you ever need any assistance with the repairs or indeed with a Landlord Electrical Report in Wakefield, then give James a call today on (01924) 654034

      James – ElectricBlu Contractors, Your Local Electrician Wakefield

    • Hi Bev Shields, thanks for the comment.

      It is something that often gets debated with other electricians about meter tails being classed as double insulated. My personal opinion is the following:

      Double Insulated‘ with regards meter tails is a common misnomer for the outer ‘cover’ of the cable (just to identify it before I explain further!). Obviously it does effectively describe having one layer of insulation and then another, but it more accurately describes Class 2 appliances/fixtures. These are having no external conductive parts which are not separated by supplementary insulation. This could be a handheld drill, or a light fitting, but I personally would not use it with regards any cable. Anything which has ‘double insulated’ parts, for me, carries the double square symbol. Every other appliance, fitting or item which is ‘doubly insulated’ has the double square symbol. Cable does not carry this symbol.

      6181Y (Meter tails) cables have inner basic PVC insulation and then have a further PVC oversheath for mechanical protection. This is no different to the 6242Y (Twin & Earth) cable.

      Would you consider 6242Y twin &; earth cable to be ‘double insulated’? The inner coloured basic insulation is covered over by a PVC outer sheath which is stripped back to enable termination. Obviously as meter tails are only single conductor the sheath and insulation can be cut the same length, however I don’t consider the construction of these cables to be significantly different, other than the number & size of conductors. They are both considered as BS6004 cable, describing the manufacturing process.

      Whilst I accept the term is widely used amongst distributors online, the ‘double insulation’ term with regards cable has just become regularly accepted slang for 6181Y cable. This post was hoping to demystify landlord/homebuyer electrical reports, which are often written in technical language. We ourselves, even whilst trying to be as transparent with customers as possible, would still use this ‘code’ on an EICR to denote basic insulation being visible on meter tails outside of an enclosure.

      Draka Cables (UK) also term it as insulated/sheathed on their page regarding 6181Y cable.
      Eland Cables, despite calling it doubly insulated quite a lot on their page, do admit the following:
      “….can see from the cable construction table, these double insulated cables are more accurately insulated and sheathed cables.”
      Cleveland Cables on their website, discuss again the construction as conductor/insulator/sheath and make reference to the sheath colour.
      Prysmian Cables, again refer to it as double insulated meter tails, however the construction of the 6181y cable is again, conductor/insulator/sheath
      Doncaster Cables 6181y cable is classed as PVC insulated/PVC sheathed.

  2. OK, perhaps “double Insulated” is the wrong definition but it is insulated and sheathed so are you saying it needs a further sheath? I have never seen meter tails (with two layers of insulation ) further protected.

    • Hi no that is not what we are suggesting.
      This blog article is relating to instances where the inner (basic) insulation is exposed because the sheath has been cut back too far. Of course they need cutting back to enable termination, however BS7671 requires that the inner, basic insulation is not visible “outside an enclosure”.
      The enclosure could be a switch, a socket backbox or the fuse board/consumer unit. What matters is that the basic insulation cannot be accessed outside of that “enclosure”.

      Where the cable is and how accessible it is to be touched determines how serious the issue is considered when any electrical report is completed.

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