Sockets in Garage....

Discussion in 'Electricians' Talk' started by MrE, Aug 9, 2019.

  1. Bazza

    Bazza Well-Known Member

    The photo of the CU confirms the RCD protecting the garage circuit is rated at 30mA.
    AS (I hope) you know, the current rating on an RCD (63A in this case) does not indicate any sort of current limiting characteristic.
  2. Tony Goddard

    Tony Goddard Active Member

    Exactly, the current stated on an RCD only indicates the maximum capacity of the contacts, it would not trip because of overcurrent, there is no mechanism inside to do that, it would just get hot and fail - the 63A RCD is absolutely fine, no issues there.
  3. MrE

    MrE New Member

    Im back with an update, (and some help, I know, im sooo needy haha)

    Cant see any join in either of the round metal access covers, so i think the cable is actually all grey.

    Ive drawn out a diagram of how the garage is wired, feel free to laugh at it, i did lol.
    It shows part of the cabling goes to an attached brick shed (through a hole in the wall)
    Im sure this was all done properly about 4 years ago (was renovated)

    Couple of questions
    1. This might sound mad but i can't get my head around how the strip light switch turns the light on. I would have thought a switch would be between the power source and the light, ie breaking the current. But this switch seems to be at the end of a cable run. (I've tried looking it up on google but without luck)

    2. Im not really bothered about the electrics in the shed, don't need any of that, but happy to keep it if it's easier.

    3. How would be best to wire in a couple of new double sockets?

    4. Double poll or single poll, what do you go for? and is SP easier to wire up?

    5. Is the shed wiring a 'ring circuit' and the strip light a radial circuit?

    Im going to use metal sockets, cos they look sooo much more man cave like.

    Any help and tips much appreciate.

    Garage circuit.JPG
  4. Bazza

    Bazza Well-Known Member

    1. The light is wired in the same way as most of the lights in houses are wired. Live and neutral go to the light. But the live goes to the switch and back again to operate the light. Google lighting wiring. It’s simple.
    2. Keep it
    3. Wire your two new sockets up to the existing one in the garage.
    PS. I thought you had 2 sockets in the garage? Your diagram only shows one. And the fused switch above the first socket, what does that switch off?
    4. Is pole not poll. It refers to the switch. They are the same to wire up. Use DP.
    5. All the circuits in your garage and shed are radial circuits.

    Don’t look for complications. There are none. Just connect your two new sockets to the existing one.
    That’s it
  5. MrE

    MrE New Member

    Thanks Bazza, im just trying to learn some of this (as its interesting), so bound to be some pointless questions.

    sooo, I think you are saying spur off the existing double socket? aren't you only allowed one spur? and is there a length limit for spurs?

    thanks again
  6. MrE

    MrE New Member

  7. Bazza

    Bazza Well-Known Member

    You are only allowed one spur from a socket on a RING FINAL circuit. Your garage is one 16A radial. You could have a thousand sockets attached to that (subject to a current limitation of 16A at any one time!)

    Connections to radial circuits are not spurs. They are the circuit. Additions to an existing radial are often called branches.
  8. Tony Goddard

    Tony Goddard Active Member

    Mr E on your light switch question.

    The cable going into the strip light has three cores Live (feed) Neutral (return) and Earth (safety), to keep it simple we will ignore the earth. The Live goes into the body of the strip light, but it does not connect to the light, it joins to one of the cores of the cable running to the switch, the other core brings that live back after the switch, what we call the switched live, it is that which connects to the light, and then the light to the Neutral of the supply cable.

    This method is used to reduce the number of cables as there is no need to take a neutral to the switch where it would do nothing except go back again. Lighting circuits look complicated to the untrained eye, but they are just the same circuit you would have done with a battery, bulb and switch in science at school, we just configure the wiring to make the most efficient use of cable, which if you use lots of it is expensive and unsightly.

    If you have a Newey & Eyre / Rexel branch near you their Newlec brand metal sockets are good quality and very fairly priced even for non-account holders.

    Hope that helps!
  9. MrE

    MrE New Member

    Thanks Bazza and TonyG (and everyone else), for so much help.
    Ive watched a couple of videos explaining Ring and radial circuits, which explained that soo clearly to me (save me asking you again)


    I'm happy I can now do the work safely, and it all makes sense.
    Bazza, I cant find those gaskets (and the 4mm screw) for the round metal inspection covers, have you got a link or anything?

    One thing, is it right that i could, if needed in the future, change the 16A MCB for a 20A MCB and still be fine with the 2.5mm cable?
  10. Bazza

    Bazza Well-Known Member

    20A is OK for 2.5mm cable BUT a measurement called Earth Fault Loop Impedance needs to be checked before making the upgrade to ensure that the MCB will trip in the evnt of an earth fault. Theoretically the RCD should do this, but it needs verification - you' need an elecrtician to do this.

    Gaskets and screws available at any decent electrical wholesaler. You wont find them in the 'sheds'.

    Easiest way is buy a box from SFX
  11. MrE

    MrE New Member

    perfect thanks again.
  12. Tony Goddard

    Tony Goddard Active Member

    You can buy one of these "plug top" loop testers for around £50

    I carry one in my toolbox for verification, handy tool, not as accurate as a full size tester or a substitute for one, but for your purposes MrE it will verify the earth connection within a range as shown by the LEDs, might be chaper than hiring in an electrician to test it.
  13. MrE

    MrE New Member

  14. Bazza

    Bazza Well-Known Member

    Just plug a lamp in. It'll tell you almost as much as that.
    I have something similar, the feature I use is that it gives a sound when the power is applied. Useful for identifying mystery MCBs. But I don't trust it to tell me anything more than that.
  15. MrE

    MrE New Member

    well, for £2 i wasn't expecting much, and you confirmed it.
  16. Tony Goddard

    Tony Goddard Active Member

    Yep, the £50 martindale one will tell you the Zs (loop impedance value) to within a fair accuracy, so is a practical tool, your £2 one will confirm an earth and polarity, but won't tell you how good it is. As bazza says the beeping version is very handy for finding circuits, sadly the Zs testing version doesn't beep, so I carry two, a beeping one and the Zs one!!!
  17. MrE

    MrE New Member

    Thanks for all you help, which allowed me to do this myself, its worked out fine. Here are my new sockets
  18. dobbie

    dobbie Well-Known Member

    Why no female or male adapters to the boxes?
    Why use a 25mm inspection bend on 20mm conduit?.
    Why no metal saddles, they all look plastic.
    If you are going to do a job, do it properly.
  19. MrE

    MrE New Member

    er yea i bought the wrong bends, ill change those. and why do you need metal saddles?
  20. Tony Goddard

    Tony Goddard Active Member

    The adapters (female are best) are to grip the conduit to the boxes, the 20mm bend will be better, put the inspection side outwards. Metal saddles where it runs overhead to comply with the regs (so in case of a fire the conduit cannot collapse and cause an obstruction for a fire fighter)
    All bare copper earths should be covered with sleeving and a link of earth wire (sleeved) between the terminal on the back box and the socket plate is a requirement.
    dobbie likes this.

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