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Wal
18-05-2017, 12:15 PM
Hi all,

I recently refurbished an anglepoise lamp for a friend of mine - it needed a new push switch at the back of its head along with a new bayonet lamp-holder - what was in there was a bit of a horror story:

21731 21732

The replacement switch I bought was one of these: http://www.diy.com/departments/bq-black-press-switch/178021_BQ.prd

...and on the packaging it stated that the switch was rated for 2 amps. Currently I have a 3A fuse fitted in the plug - but I'm going to order a 2A, possibly even a 1A. My question is this, though: why would they sell a 2A lamp switch when it's all but impossible to buy 1A* and 2A fuses on the high street..? Am I being overly cautious, or is a 1A/2A fuse a sensible proposition..?

Ta!

Wal.

*EDIT 1A found on the High Street (http://www.diy.com/departments/bq-1a-fuse-pack-of-2/177930_BQ.prd)...

Clive S
18-05-2017, 01:05 PM
Wal
I don't think you can buy any smaller than 3A fuse for standard plug.

It will be fine a 100W lamp will only take about 0.5A so no prob with the switch.

edit make sure there is an earth wire to the lamp

Wal
18-05-2017, 01:19 PM
Cheers Clive,

Yeah - the bulb won't be drawing any more than 0.5A - but if it malfunctions and ends up drawing a bigger current I'd rather have the fuse blow than the switch melt, if you get me. I saw some 1A fuses in a small electrical shop in Didsbury yesterday - he reckoned he could get 2A, was just out of stock at the time. As far as the earth cable goes - the lamp has a two-core L/N 3A flex - am I best off replacing this with a 3-core and securing the earth cable to the metal chassis of the lamp? ie. perhaps the bracket that holds the bayonet fitting..?

Wal.

Clive S
18-05-2017, 02:41 PM
Cheers Clive,

Yeah - the bulb won't be drawing any more than 0.5A - but if it malfunctions and ends up drawing a bigger current I'd rather have the fuse blow than the switch melt, if you get me. I saw some 1A fuses in a small electrical shop in Didsbury yesterday - he reckoned he could get 2A, was just out of stock at the time. As far as the earth cable goes - the lamp has a two-core L/N 3A flex - am I best off replacing this with a 3-core and securing the earth cable to the metal chassis of the lamp? ie. perhaps the bracket that holds the bayonet fitting..?

Wal.

Yes you need an earth cable to the lamp Just keep the 3A fuse they are different than the glass fuses I have never seen a smaller one fitted to a British 13A plug

Wal
18-05-2017, 02:52 PM
>Yes you need an earth cable to the lamp Just keep the 3A fuse they are different than the glass fuses I have never seen a smaller one fitted to a British 13A plug

Okay - but it wasn't a glass fuse - it was a fuse for a household plug - like this: http://www.diy.com/departments/bq-1a-fuse-pack-of-2/177930_BQ.prd

I've seen 2A online (https://www.rapidonline.com/TruPower-TDC180-2-2A-1-Plug-Top-Mains-Fuse-26-0400?IncVat=1&pdg=kwd-305641629245:cmp-757438067:adg-42338105440:crv-178952908744:pid-26-0400&gclid=CjwKEAjwjPXIBRDhwICRg-DbgHISJADP6QXpUW2xNUIV7tgif6Wxzpf6wyNYHSUv8Mhm9Lpy HePfARoCHDHw_wcB), but not on the high street...

Wal.

Clive S
18-05-2017, 03:02 PM
>Yes you need an earth cable to the lamp Just keep the 3A fuse they are different than the glass fuses I have never seen a smaller one fitted to a British 13A plug

Okay - but it wasn't a glass fuse - it was a fuse for a household plug - like this: http://www.diy.com/departments/bq-1a-fuse-pack-of-2/177930_BQ.prd

I've seen 2A online (https://www.rapidonline.com/TruPower-TDC180-2-2A-1-Plug-Top-Mains-Fuse-26-0400?IncVat=1&pdg=kwd-305641629245:cmp-757438067:adg-42338105440:crv-178952908744:pid-26-0400&gclid=CjwKEAjwjPXIBRDhwICRg-DbgHISJADP6QXpUW2xNUIV7tgif6Wxzpf6wyNYHSUv8Mhm9Lpy HePfARoCHDHw_wcB), but not on the high street...

Wal.

Ok Wal you win:crushed: But I still would not use one as when a lamp is first lit it will draw a lot more current for a few m/seconds and might just blow a 1A fuse. But hey it is your decision

Wal
18-05-2017, 03:34 PM
Heh - Clive - you know me, I know NUFFINK..!

I was just a bit confused as I'd have thought you'd want the fuse to blow before an unsuitably high current went further up the pipe... Dunno, maybe I'm just over-thinking it..!

Wal.

m_c
18-05-2017, 05:26 PM
You are over thinking it.

While you are technically correct, even a 2A rated switch will more than likely survive switching a load that will blow a 3A fuse.
You've got to consider what kind of load that's likely to blow a 1A fuse, but not a 3A, and not be noticed in a basic lamp?
L&N would need to be shorted together in such a way that they only drew 2.5A, and what is the real possibility of that happening?

The far more likely fault, is L and/or N wires rub through on something earthed, in which case it should trip the RCD. Even if you don't have an RCD upstream of your sockets, you should notice a fault before it even gets to the point of blowing a 1A fuse.

Web Goblin
19-05-2017, 07:32 AM
For a standard uk BS1363 square 3 pin plug the fuse sizes are 3amp and 13amp. There used to be 5 amp but this was done away with a few years ago.
So for your lamp fit a 3 amp fuse that complies with BS1362.

john swift
19-05-2017, 09:20 AM
one inch 1A , 2A, 3A 5A , 7A ,10 and 13A HRC (High Rupture Capacity) Fuses for the UK 13A plugs are available
but the range in the typical high street shop is very often limited to 3A, 5A & 13A

John

PS

https://www.tlc-direct.co.uk/Main_Index/Necessities_Index/Plug_Top_Fuses/index.html?ad_id=15790937587&source=msn&kw=plug%20fuses&matchtype=p&qry=assorted%2013a%20plug%20fuses

pinballdave
19-05-2017, 12:27 PM
The 2A rating on the switch is the breaking capacity of the switch. That is that it will reliably switch off a current of 2A without the inevitable arcing across the switch contacts welding the contacts closed. The switch itself will be safe to carry higher currents without damage if it remains in the on position, far higher than is necessary to blow a 3A plug top fuse.

As m_c said the only over-current situation you are protecting against by choosing a lower value fuse, is an overload between 2A and 3A occurring while the switch is being turned off. As the lamp holder is designed for lower wattage bulbs (max 100-150W) and I don't believe there are bayonet fitting 500-750W bulbs easily available that could be used, you can state that the design load is inherently low enough to ignore this.

If the lamp holder is fully insulated (has the box inside a box 'double insulated' symbol on it, then you don't need an earth cable. The flex must also be double insulated (ie brown/black insulated wires inside an insulated sheath). If the flex is only single insulated it _must_ be replaced, also if it's black/red then it would be wise to replace it with something a bit newer.

Dave.
(16th edition qualified electrician)

Wal
19-05-2017, 02:29 PM
Thanks guys,

Some really helpful information here. Flex is blue/brown double insulated and so is the lamp-holder - to fit the lamp-holder to the existing bracket (which is part of the lamp-head tensioning mechanism) I've had to thread its neck (where the wires go in) and use the original threaded brass tube which holds it all together - the wires at this point have extra sheathing around them and the tube ends are chamfered and smooth - even though the risk here is minimal that bit of brass warrants having it earthed. Good to know.

Thanks again.

Wal.

Neale
19-05-2017, 06:24 PM
The other thing about fuses is that people talk about them protecting equipment, which isn't usually correct. In fact, the chances are that if the fuse blows, it's because something has already gone wrong! Mainly, the fuse is there to prevent a fire if there is excessive current because of a fault. The nominal fuse rating isn't something to rely on too closely either - a normal fuse will probably carry its rated current for at least tens of seconds before blowing, and probably needs at least twice that to blow quickly. That's fine in practice as it gives just a little bit of headroom for switch-on peak currents but will still blow before the wiring bursts into flame!

routercnc
20-05-2017, 07:41 AM
For info I just bought a 10A fuse for the plug on an extension cable reel. This was on the high street (Wilko)