I am putting in a new 32A ring main that will just be for garage internal sockets and external outside sockets. This is on a RCBO.
Reason for this if anything happens outside, it does not affect anything else internally in the house.
I am using IP67 rated kit for all the sockets that are outside.
The garage is integral to the house, has no windows, has a upvc door and an up and over garage door.
I am using 20mm conduit to mechanically protect the cables from accidental damage throughout
Now do the socket face plates and pattresses that are INSIDE the garage have to be IP rated as well or is white domestic faceplates and pattresses inside a garage acceptable for meeting 17th Ed wiring regs?
The standard faceplates are fine for a garage; but I'd be using my own judgement as to whether they were appropriate; eg if the roof leaked or rain blows in through cracks etc.
Personally I use the metal clad type in the workshop / garage as they're a bit more robust bearing in mind what goes on out there.
The only requirement in the circumstance is that they are appropriate for the situation. So assuming it does not routinly get rain blowing in there then normal domestic ones will be fine.
Depending on what you plan to do in there you might want to consider metal clad (and the surface pattresses will have knockout holes ready to take a conduit terminator) since they are physically more robust.
(flush mounted plastic sockets are also quite damage resistant!)
I have tried to take a common sense approach. So far:
I have mounted the sockets at least 0.5m away from a door/opening as a mitigation against blown in rain when opening/closing doors.
I have used 20mm round conduit to protect the cable drops from the ceiling to the wall mounted sockets as I believe the wall cable drops are more likely to sustain damage than the ceiling level ring main.
The ring main has been clipped to the wall at approx 2.8 metres above ground level so above clumsy tall people.
As mentioned earlier, the garage sockets and outside sockets are on their own ring main with its own 32A RCBO.
In addition, the garage lighting and outside lighting is on its own 6A RCBO.
The pattresses are PVC which are not as brittle as moulded ones so I believe that will be better when impact occurs.
Getting the 20mm knockouts out of the PVC pattresses seems to be an art.... I broke two today trying to get the knockouts out. You can't realy use a hole saw as there is pilot hole in the plastic disc to align the drill bit with
Since i was dry lining my workshop I simply mounted all the sockets flush - makes them much harder to hit in the first place, and since I wanted lots of them, much cheaper!
On 15/02/2013 16:46, John Rumm wrote:> On 15/02/2013 16:31, Stephen H wrote: >> On 15/02/2013 16:14, John Rumm wrote: >>> On 15/02/2013 15:16, Stephen H wrote: >>>> Hi, >>>> >>>> I am putting in a new 32A ring main that will just be for garage >>>> internal sockets and external outside sockets. This is on a RCBO. >>>> >>>> Reason for this if anything happens outside, it does not affect >>>> anything >>>> else internally in the house. >>>> >>>> I am using IP67 rated kit for all the sockets that are outside. >>>> >>>> The garage is integral to the house, has no windows, has a upvc door >>>> and >>>> an up and over garage door. >>>> >>>> I am using 20mm conduit to mechanically protect the cables from >>>> accidental damage throughout >>>> >>>> Now do the socket face plates and pattresses that are INSIDE the garage >>>> have to be IP rated as well or is white domestic faceplates and >>>> pattresses inside a garage acceptable for meeting 17th Ed wiring regs? >>> >>> >>> The only requirement in the circumstance is that they are appropriate >>> for the situation. So assuming it does not routinly get rain blowing in >>> there then normal domestic ones will be fine. >> >> I have tried to take a common sense approach. So far: >> >> I have mounted the sockets at least 0.5m away from a door/opening as a >> mitigation against blown in rain when opening/closing doors. >> >> I have used 20mm round conduit to protect the cable drops from the >> ceiling to the wall mounted sockets as I believe the wall cable drops >> are more likely to sustain damage than the ceiling level ring main. >> >> The ring main has been clipped to the wall at approx 2.8 metres above >> ground level so above clumsy tall people. >> >> As mentioned earlier, the garage sockets and outside sockets are on >> their own ring main with its own 32A RCBO. >> >> In addition, the garage lighting and outside lighting is on its own 6A >> RCBO. > > Yup all sounds eminently sensible.
That reminds me my existing two way light switches are almost at the edge of the doors frames. As is pre-existing installation, can I leave them as they are or should I uprate them to IP67?
How do you line up the drill's holesaw blade with the groove around the
20mm knockout as there is no pilot hole in knockout for drill bit?
To an extent, only you can answer that. How likely are they to get rained on? Is it significantly more than say a lightswitch next to a back door?
Just by eye - in the grand scheme of things it does not matter if they do not line up perfectly (unless the knockout section is likely to fall out once drilled close to).
(some "knockouts" are not really knockable anyway!)
Going off slightly at a tangent, I recently wanted some MK sockets for a mate's business (normal domestic stuff keeps getting knackered), and this guy
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has new but "shop soiled" sockets and surface mount metal boxes at a very decent price. As far as I can see, these are genuine un-used components. I have a few spares waiting to go into my own workshop.
Cor, I've just been doing a bit of that today and what a bloody horrible job it was - courtesy of the fact that the temp was about 1 deg, and the cable was therefore almost rock solid. Very hard to bend it where I wanted it to go, wouldn't cut or tear easily, hard to stuff down the conduit etc...
Note to self: in future, exterior wiring is a job for the summer!
Incidentally, I was working on this new ring main today.
I have used 2.5mm2 T&E for the ring main and to the garage sockets.
Some of the external sockets are in publically accessible or child accessible areas, so I have run the 2.5mm2 ring main to 45amp double pole isolator switches inside the garage. 4mm2 T&E ran from the 45amp isolators to to each individual outside double gang socket.
This has several benefits:
no one can steal electricity from the front sockets can be turned off in garden if children are playing if a fault develops in an outside socket, it makes fault locating down to socket level easy if I need garage power and a outside socket is playing up and tripping the RCBO, I can throw the switch for that socket to Off and work in the garage.
My outdoor socket circuit is a TT 20A radial (with a 10mA RCBO), but I did almost the same. I used a cooker switch with integral socket, positioned just inside the garage door. This gives me a socket just inside the garage which is handy when using something just outside the garage with the door open, and separately switched (by the cooker switch, relabeled), are all the other outdoor sockets, which I normally keep switched off except when I'm expecting to use them (and when I forget to turn them back off afterwards).
I did actually sit down and think this through from a good design point of view...
As stated, there is a 2.5mm2 ring main with a 32A RCBO.
I was not worried about L-E or N-E shorts as there is the 30mA RCD part in the RCBO that takes care of that.
However, I had two scenarios to think about regarding my outside sockets.
I wanted to put a single external socket in the front porch.
So that meant a single 2.5mm2 spur T&E cable from the 32A ring main in the garage to a single socket in the front porch via a bedroom.
Given that the max current available on the ring main would be 32A before the consumer unit's 32A RCBO opens and that the maximum in-service non-fault conditions continuous current would be 13A at the porch socket, (limited by the 13A or less fuse in the plug of whatever appliance plugged in)
I had thought about what could happen if there was a dead L-N short on the single 2.5mm T&E cable running between the ring main and the single gang socket.
Obviously this single 2.5mm cable is capable of taking a 13A current continuously between the ring main and the single socket via the spur cable, I felt uncomfortable with it potentially carrying up to 32A before RCBO opens in case of a L-N short on the spur cable.
Thus, I put a 13A fused switched neon faceplate at the point where the spur is connected to the ring main in the garage to protect the spur.
The other scenario was the double gang socket on the front driveway.
Now I could plug in two appliances. Lets say both draw up to 13A before their individual plug fuses pops. Thats a total load of 26A which is on a 32A rated 2.5mm ring main.
Now doing 26A continuously on a single 2.5mm2 spur cable between the ring main and double socket I was not comfortable with, let alone a potential up to 32A flowing in the case of a dead L-N short.
Switch isolators come rated as 20A or 45A. So 20A is less than 26A that the double gang socket could be going up to. So I went to 45A rating for the switch neon isolator.
So I put a 45A rated neon switch on the 2.5mm2 ring main and reasoned that as current flows both ways round the ring, that 5.0mm2 is the same as 2 x 2.5mm2. So I opted to run the spur cable as 4.0mm2 from the 45 amp isolator to the double gang socket. Now I am then comfortable with up to 26A flowing continuously on this 4.0mm cable from isolator to double gang socket.
I fully appreciate the above scenario is highly improbable and that I have probably over-engineered my circuit but hopefully at least a sparky can't find fault with my reasoning!
Ah, right I see the line of thought you are following. In fact you are over worrying since this exact scenario has already been thought about in the design of unfused spurs...
As you are probably aware there are two overcurrent categories that need to be considered with these things - that of overload, and that of a fault. Each have their own characteristics, and each need (possibly) separate handling.
The fault current situation is the most important - i.e. stopping the cable vaporising or bursting into flames on a hard short. The circuit protective device at the origin of the circuit *must* protect against fault currents. It has been shown that a single 2.5mm^2 cable (as used in a typical spur arrangement from a standard ring circuit) will be adequately protected from the effects of fault current by the B32 MCB at the origin of the circuit.
For more on this see:
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The second issue is that of overload. i.e. what happens if a load in excess of the design current is placed on it for an extended period. (short term overloads are permissible, and it is even desirable that a circuit will not trip in response to them). You are correct in assuming that you can't rely on the B32 MCB/RCBO to offer overload protection for a single 2.5mm^2 cable. However this class of over current does not have to be covered by the device at the origin of the circuit. In the case of fused spurs, its enforced by the downstream fuse. In the case of unfused spurs, then it is imposed either by the number of available connections (e.g. a single socket can't take a load large enough) or by the characteristics of the load itself (e.g. a fixed appliance that has no mechanism for drawing a sustained overload)
A cable that if surface wired on in masonry actually has a 27A capacity... however that's not the point. For the purposes of design, a double socket is rated at 20A total load. In reality some will do better than that, but many will not like it if you actually stick two 13A long term loads on. Chances are the socket will suffer long before the cable.
Some will argue that you can get even more load on it since a 13A BS1361 fuse will carry 20A before blowing... armed with some multi way extension leads you could have the socket in a molten mess in very short order ;-) In reality it never happens since actually getting long term loads (i.e. those that are not intermittent due to usage patterns, or due to the actions of thermostats etc) is actually quite difficult (a couple of 3kW fan heaters to warm the garden perhaps?).
Along the same line of thought it is also worth remembering that a 32A circuit breaker does not trip at 33A. In fact you need 1.45 x nominal current to ensure they trip, and 5x normal current to insure they trip "instantly" (i.e. when clearing fault currents)
Have a look at the response curve of a 32A type B MCB:
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No harm in doing that, except that you pay more for the switch, and the socket etc is not really up to the job of matching the performance of the switch.
Indeed. although normally if one were proposing to have very heavy loads on sockets in this way, they would ideally be better in the ring and not on a spur.
For your actual application, I would be entirely comfortable with a single 2.5mm^2 cable and a double (IP 56) socket on the end.
There is nothing dangerous about what you propose, although its over egging things a tad. Lots of design effort over the years has gone into make sure that these things work well in reality, and while there are theoretical weaknesses in the designs of unfused spurs, they prove time and again in practice to be very robust and reliable.
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