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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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#1
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Electrical regs question - key operated FCU
I'm involved in specifying the supply for an application that needs a fused connection unit with a key-operated switch. This will be supplying a device embedded in a wall, with cabling channelled from the FCU to the device. Current draw would be 3A, probably a 5A fuse in the FCU. I was looking at 'making' one using parts from MK's GridPlus range - a 2-unit faceplate K3632 (RS 341-4042), with a 'secret key' 20A DP switch K4917 (RS 341-3982) http://docs-europe.electrocomponents...6b8002c8a0.pdf and a fuseholder K4890 (RS 341-4008) http://docs-europe.electrocomponents...6b8002c890.pdf However the electrical contractor on-site claims they can't do this as it will be connecting to a 30A ringmain and the switch is only rated at 20A. The fuse would located right next to the switch on the faceplate, and be connected directly to the output of the switch, and the switch will only be switching 5A (13A if the wrong fuse gets fitted). The switch has a cable capacity of 2x2.5mmsq or 2x4mmsq. Is their guy right? If not, can anyone suggest how to correct him without causing offence ( e.g. quoting a reg...). This will be installed in a school if that makes a difference ( hence the need for the key operation). or does anyone know of a key-operated FCU that will fit a single socket back-box? |
#2
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Electrical regs question - key operated FCU
On Tue, 29 May 2007 16:32:05 GMT someone who may be Mike Harrison
wrote this:- I'm involved in specifying the supply for an application that needs a fused connection unit with a key-operated switch. [snip] However the electrical contractor on-site claims they can't do this as it will be connecting to a 30A ringmain and the switch is only rated at 20A. The fuse would located right next to the switch on the faceplate, and be connected directly to the output of the switch, and the switch will only be switching 5A (13A if the wrong fuse gets fitted). The switch has a cable capacity of 2x2.5mmsq or 2x4mmsq. The contractor is not particularly au-fait with electrical design then. It is no different to fitting a spur in a kitchen which has a 20A switch at high level and a socket outlet at low level. The fuse limits the current flowing through the switch to below that which the switch is rated at. What it means is that overload and short circuit protection are undertaken by different protective devices. Neither is it different to fitting a switched socket outlet. Does your contractor think that the switches of these are rated at 30/32A? Why not connect the ring main to the fuse unit (which might be an interesting task). Then the switch is on a fused spur and your contractor should be happy. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
#3
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Electrical regs question - key operated FCU
On 29/05/2007 17:32, Mike Harrison wrote:
However the electrical contractor on-site claims they can't do this as it will be connecting to a 30A ringmain and the switch is only rated at 20A. Isn't that like saying e.g. on a cooker radial in 10mm^2 cable, you can't continue the 10mm^2 from the oven connection unit to an FCU for the hob, beacuse the FCU is switched at 13A while the circuit might be fused at 40A? |
#4
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Electrical regs question - key operated FCU
On Tue, 29 May 2007 16:32:05 GMT, Mike Harrison
mused: I'm involved in specifying the supply for an application that needs a fused connection unit with a key-operated switch. This will be supplying a device embedded in a wall, with cabling channelled from the FCU to the device. Current draw would be 3A, probably a 5A fuse in the FCU. I was looking at 'making' one using parts from MK's GridPlus range - a 2-unit faceplate K3632 (RS 341-4042), with a 'secret key' 20A DP switch K4917 (RS 341-3982) http://docs-europe.electrocomponents...6b8002c8a0.pdf and a fuseholder K4890 (RS 341-4008) http://docs-europe.electrocomponents...6b8002c890.pdf However the electrical contractor on-site claims they can't do this as it will be connecting to a 30A ringmain and the switch is only rated at 20A. The fuse would located right next to the switch on the faceplate, and be connected directly to the output of the switch, and the switch will only be switching 5A (13A if the wrong fuse gets fitted). The switch has a cable capacity of 2x2.5mmsq or 2x4mmsq. Is their guy right? If not, can anyone suggest how to correct him without causing offence ( e.g. quoting a reg...). This will be installed in a school if that makes a difference ( hence the need for the key operation). or does anyone know of a key-operated FCU that will fit a single socket back-box? Contactum 3467 or 3469. Can't remember exactly what they are but they are switched fused spurs with key operated switches. -- Regards, Stuart. |
#5
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Electrical regs question - key operated FCU
In article ,
Owain writes: One aspect is that if it needs a keyswitch then there's an argument that the fuse carrier shouldn't be within reach of pupils either. So you could use a FCU at high level with a keyswitch lower down, which might keep everyone happy. The gridswitch fuse carrier is retained by a screw, so you need a screwdriver to take the fuse out. -- Andrew Gabriel [email address is not usable -- followup in the newsgroup] |
#7
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Electrical regs question - key operated FCU
On 29 May 2007 22:09:09 GMT, "Bob Eager" mused:
On Tue, 29 May 2007 20:30:23 UTC, (Andrew Gabriel) wrote: In article , Owain writes: One aspect is that if it needs a keyswitch then there's an argument that the fuse carrier shouldn't be within reach of pupils either. So you could use a FCU at high level with a keyswitch lower down, which might keep everyone happy. The gridswitch fuse carrier is retained by a screw, so you need a screwdriver to take the fuse out. When I was at school, I always carried a small toolkit... I think the term for that nowadays is 'tooled up' or 'loitering with intent', or something. I had most of my tools confiscated at one point or another. -- Regards, Stuart. |
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