Reference methods - ceilings

Discussion in 'Electricians' Talk' started by *rab*, Sep 7, 2022.

  1. *rab*

    *rab* New Member

    You've got t&e fished over an insulated ceiling, unclipped. >100mm insulation. What's the reference method?

    You'd say 101, right? But is it guaranteed to be "touching the plasterboard ceiling surface" (Table 4A2)? what does it become if it's not? 100, 101 and 102 all have to be touching the ceiling surface. But you can't guarantee that right? If a cable exists above a ceiling, but never touches the surface of that ceiling, what would its reference method even be?? (Woa man, that's out there).

    103 is the only 10x method which doesn't mention touching the surface, but it doesn't mention anything about ceilings either. Can you use 103 on ceilings? Did IET just write Table 4A2 in a hurry and forgot to mention ceilings for 103?
     
  2. Coloumb

    Coloumb Screwfix Select

    What is it you are wanting to achieve/do/observe/recommend? Is this for a EICR?
     
  3. *rab*

    *rab* New Member

    I got asked a question about cable ratings and didn't know the answer. I don't like saying "because it is right". Read the specific table and came back more confused because it looks really poorly thought out and wrong. Thought I'd ask. Doesn't affect safety/MCB/cable/EICR etc. Consider it a musing.
     
  4. Coloumb

    Coloumb Screwfix Select

    New builds these days it seems the cable is just chucked in over the insulation in the loft space. It shouldn't be like that in the first place so I guess that's why there isn't a method.
     
  5. The Happy Builder

    The Happy Builder Screwfix Select

    It’s an issue, because?
     
  6. Coloumb

    Coloumb Screwfix Select

    Is that question meant for me or the o.p?
     
  7. sparko69

    sparko69 Screwfix Select

    Is the cable under the insulation or is it on top of the insulation?
    There are 2 different ratings so you check the cable and choose which installation method has been used
     
  8. *rab*

    *rab* New Member

    Method 104# cable chucked across insulation. :)

    This is one of the possibilities that I thought it could be. I didn't know if it was that the cables just weren't meant to "officially" be like that or just a case that the regulations just didn't reflect real life.

    I guess if you're doing an inspection and you never saw the cables you could put n/v or lim - but in actuality if a place was rewired and the cables pulled tort they just don't seem to match any reference at all because they don't touch the skin of the plasterboard.

    Anyway it's more a musing... But there's a faint nag that it could affect cable ratings given the right situation and present a risk of overload (i.e. 34A vs 23.5A for 6mm) if you compare 100 to 103.
     
  9. *rab*

    *rab* New Member

    Aye totally I'm with you - but what I was saying is that if it goes through the insulation there's no reference at all. Not in a ceiling anyway. Unless I've got it a over t.
     
  10. The Happy Builder

    The Happy Builder Screwfix Select

    Reference method 103 = worst case scenario for twin and earth cable.

    1.0mm = 8 amps
    1.5mm = 10 amps

    so there’s no issues with using Method 103 for 6 or 10 amp lighting circuits in a domestic property.

    Lighting circuits generally have to run in or under insulation above ceilings somewhere in a house or flat, so it is pretty hard to avoid contact with insulation completely.

    Other circuits such as sockets and shower can be more of a problem, but the issues are generally resolved using a box of cable clips or a larger cable.

    Covering cheap down lights with insulation is actually an issue, not the cables to them.
     
  11. *rab*

    *rab* New Member

    They're totally cool with it touching the insulation, it's just that it needs to be touching he plasterboard as well. Absolutely, in reality clip back or uprate the cable.
    But if the issue's not spotted and something worse happens, especially on something like an EV charger where max current can be drawn for 8-12h.
    Then the cable can become an issue and the MCB wouldn't protect it.

    For the IET to say cable has to be touching the outer skin of the plasterboard in a ceiling throughout its entire run - that's great for lab tests - but not the real world.
    I mean according to the IET you can't take a T&E through the centre of a joist??
    Point is really that you can't apply 103 if you know the cable's exclusively in a ceiling.
    So you're left with a cable that has no reference method...
     

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