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Products: Metal electrical sockets - Dangerous ?

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  1.  
    • CommentAuthorstorm
    • CommentTimeJul 30th 2008
     
    Large corrugated metal garage referb standing in the middle of a very exposed field. I have already raised the subject of lightening conductors before now This time, perhaps, a less obvious concern ? Electrical sockets. I was thinking of having the MK metal clad range installed as advertised in Screw-fix. Three switched double sockets plus a 3 gang 2 way switch, to control the lighting inside as well as externally. My qustion is. Would metal sockets be more prone to cause electrical shocks ? In particular, perhaps, during a thunder storm ? I realise there are plastic sockets available, but so boring in comparison to the metal clad range, I feel. Any views, for or against ?
    •  
      CommentAuthornigel
    • CommentTimeJul 30th 2008
     
    Metal sockets have an earth connection so I cannot see why they would be less safe.
    • CommentAuthorSimonH
    • CommentTimeJul 30th 2008
     
    How about if the earth connection became detached? Or the earth wire somewhere along it's length had become criped and split, or had been snagged/drilled through at some point.

    That said - these risks must have been considered before allowing metal sockets to gain approval for sale.
    • CommentAuthorstorm
    • CommentTimeJul 31st 2008 edited
     
    Thank you, Nigel and Simon for your input on the subject. Shame there isn't more of it though. I would have thought this topic would get several electricians champing at the bit to offer their opinions, but, apparently not !
    Has the topic of sockets lost its charge ? I might ask :smile: are there no lightening intellects out there suffused with enough electrical brain power to have a good rip roaring debate, I wonder :cool:
    or am I the only bright spark in town :bigsmile:
  5.  
    Metal cover plates are pretty standard over here in 120V Canada. The electrical boxes themselves are most often (at least, where I live) metal and are grounded (of course). If you're really worried you could as AFCI or GFCI breakers which should trip if the earth is compromised. Surely, though, the electrical codes are designed such that the installation should be done in such a manner that the wires cannot be subject to physical damage. That's what the codes here require - any wire that is in a vulnerable location must be either in an approved conduit or the requisite armoured cable. We also have code requirements now for AFCI (arc fault circuit interrupters ) be used as the circuit breakers on all bedroom outlet circuits - this was prompted by fires caused by damage to cables on table lamps behind furniture such that sparks were being produced of sufficient intensity to cause a fire but not of sufficient current to trip the breaker.

    Paul in Montreal with several degrees in Electronics
    • CommentAuthorCWatters
    • CommentTimeAug 1st 2008
     
    Why not use plastic conduit with your metal MK sockets? It's easier to install than metal. Personally I wouldn't worry too much.
    • CommentAuthorstorm
    • CommentTimeAug 1st 2008 edited
     
    Thank you , Paul, for your advice, I don't have any degrees in electronics,I must confess. Arc fault circuit interrupters ! :confused:
    but I did win a Rupert bear scarf once ! truly,Yellow Plaid ! :bigsmile:
    I was wondering why metal sockets are usually sited for industrial use. This has made me tend to think that the quality external and internal must be more robust than others designed for ordinary domestic use. I like Cwatters idea of plastic conduits coupled with the Mk sockets, sounds like a good, safe balance of materials. Much to ponder .....
    • CommentAuthorchuckey
    • CommentTimeAug 1st 2008
     
    The main claim to fame for metal boxes and fronts kit is that they are physicaly more robust. So its down to you and your garage users. On the purely electrical side, plastic boxes must be safer because they can't ever be "live", even if it takes two faults to get to that situation (no earth on metal box, live wire drops off and touches box) with the metal kit.
    Frank
    • CommentAuthorjamesingram
    • CommentTimeAug 3rd 2008 edited
     
    as chuckey said metal boxes are physicaly robust

    All socket outlets that may be used externally must be protected by an additional RCCD , or trip switch which recognises a small
    30mA leakage to earth in addition to the over current protection device , circuit breaker ,MCB
    the new 17th edition regs. goes further than this , with increased RCCD protection on most circuits depending on the method of installation
    Your electrian will advise as its illegal to do such work yourself unless you have some part P inspection from the council
    or use a part P registered electrian
  10.  
    This one is a conundrum as old as electrical installation, to earth or not to earth! In a garage situation I would say that the metal sockets are the safest way to go. They are less likely to get damaged, exposing live wires, they are also well earthed (or should be) so if they get wet they are much more likely to blow the RCD before you touch them. With a plastic socket covered in moisture, the first time you know anything is wrong may be when you touch it and it earths through you! The earth wires run to all the sockets anyway, and the earth contacts in most plastic sockets are actually visible from the front of the socket, so in case of a lightening strike, I don't think it will make much odds.The garage is metal anyway! Most industrial installaions and schools use metal clad for increased safety. Simon sugested that the earth may come detached ( a very real risk hence the to earth or not to earth comment) you can earth each socket to the building using an earth bond if this helps put your mind at rest.

    Perhaps a lightening conductor expert needs to be consulted!
    • CommentAuthorCWatters
    • CommentTimeAug 3rd 2008
     
    Metal faceplates are invariably plastic coated or painted so I don't think it make any real difference that they are metal.
    •  
      CommentAuthorAEC
    • CommentTimeJan 27th 2009
     
    Metal faceplates are plastic coated !!!!!!!!!!!!

    Sorry but time you gave up talking about electrical work.

    Dont take it personally, there are a few about the pages.:cry:
    • CommentAuthorCWatters
    • CommentTimeJan 27th 2009
     
    That was meant to be tounge in cheek.

    What difference would using plastic vs metal faceplates really make to lightening? It's already arced through hundreds of meters of air.
    • CommentAuthorchuckey
    • CommentTimeJan 27th 2009
     
    Ah, CWatters you have got it round the wrong way. Its called "step potential". Take this case of a metal framed building, if it gets hit by lightning, a large current (1000 - 20,000+Amps) flows through it to earth,the effect is that the whole ground around the building gets raised to some potential, could be as high as 10,000V. The real problem to the occupiers of the building is that anything connected to a different earth, like the mains,telephone, water mains etc. now appears to have this 10,000V on them compared to ground the person is standing on. So the first thing to go is normally the telephone (kits only rated at 50V) then things connected to the incoming mains and the local earth. So the buildings frame should be bonded to the incoming mains earth, to try and keep the step voltage, within the mains cables (even though it might see them off).
    It is called the step voltage because as you step across the ground, you end up with a voltage difference between your feet that could kill you. So in a lightning storm keep your feet together:bigsmile:.
    Frank
  15.  
    I have the MK metal sockets and light switches from Screwfix, and no problems so far (6 years) including thunderstorms with several power outages. The only thing that has ever blown is the modem - possibly from a direct lightning strike to the phoneline.
    Also think they look really good.
    •  
      CommentAuthorAEC
    • CommentTimeJan 27th 2009
     
    Chuckey ur 2 intelegent 4ur own good.

    Trying to explain how the voltage gradiant would apply is wasted on this disscussion. Anyway the closest tree would have a better earth.
    To earth or not, as mentioned earlier is just plain stupid. You must earth as per BS7671 2008.

    If you stay rural a would always recommend devices to protect against lightning and other power problems.
    • CommentAuthorJackyR
    • CommentTimeJan 28th 2009 edited
     
    Posted By: AECTrying to explain how the voltage gradiant would apply is wasted on this disscussion.

    Er, hello?

    Thank you Chuckey, I found that both interesting and enlightening (no pun intended). Like many here, my physics is quite up to the discussion. It's also up to realising the answer in engineering is often precisely the opposite to a physicist's "ideal world" answer (you know, that world without brakes cos there's no friction...).

    So just because an evolved solution isn't obvious doesn't mean we can't understand it.
    • CommentAuthorTheDoctor
    • CommentTimeJan 28th 2009
     
    apart from a lot of Screwfix products being ropey at best, they are a nice fitting.
    We have installed similar ones.

    bear in mind that it could not be sold in the UK if it didn't meet strict regulations / BS requirements etc.


    It does rely more on a quality installation, though, with earthing and sheathing to be installed

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