Plug fuse for 50W LED floodlight

[Graeme]

Hi,

I am installing a 240V, 50W LED motion sensor floodlight outside. The power cable is to come through the brickwork and plugged into a RCD adapter, which goes into a wall plug socket.

My only concern is what size of fuse to put into the plug once it is installed?

Thanks

 

[Taylortwocities]

3AMP is the usual.

Why do you need an RCD adaptor?

 

[Graeme]

OK 3-AMP thank you.

I just thought as it was coming from the outside I should use a RCD adapter in case rain water gets inside it.

 

[JohnW2]

I just thought as it was coming from the outside I should use a RCD adapter in case rain water gets inside it.

Does the circuit to which it is connected already have RCD protection in your Consumer Unit. If it does, then little/nothing (other than 'redundancy') is gained by having a second RCD - in the event of a fault (whether due to rain water or anything else), it's just as likely that the house RCD would trip as that the adapter one.

If the circuit is not already RCD-protected, then an RCD adapter makes sense.

Kind Regards, John

 

[ericmark]

The smallest fuse you can get for a plug is 1A which is 4 times bigger than required, in the main the fuse in the plug is to protect the cable and so 3A is ample in most cases. In real terms normally either 3A or 13A is fitted even though we have 1,2,3,5,7,10 and 13 in most cases it's either 3 or 13 the others are rarely used.

As to RCD each RCD should be 1/3 of the size of the one before. So having a 100 mA feeding a number of 30 mA or a 30 mA feeding a number of 10 mA units can result in a fault taking out less power when it trips. However in practice a 2A 1 minute delay fed a 1A at 30 seconds delay which fed a 100 mA S type which in turn fed a 30 mA with 40 mS or less delay and when the worker put a nail through the cable to hang his coat on it took out the lot. So in real terms not worth feeding one RCD from another. The only exception is boats and caravans why we have a 30 mA RCD feeding a 30 mA RCD I don't know but the regulations require it with boats and caravans.

My outside light is plugged in so if it does get wet it is easy to disconnect it.

 

[Iggifer]

In real terms normally either 3A or 13A is fitted even though we have 1,2,3,5,7,10 and 13 in most cases it's either 3 or 13 the others are rarely used

I would say 5a fuses are becoming almost as common as 3a. Pretty much every piece of modern technology (that doesn't use a wallwart) has a 5a fuse, computers, printers, tv's, monitors, games consoles, some routers, dvrs. Just by the sheer number of these devices we all own now, I would suspect the number of 5a fuses in circulation is approaching that of 3a. (Obviously not every single one of these devices will have a 5a fuse, but every one I own and have encountered does - one modern tv I know of had a 10a fuse in it).

1,2 & 7 I don't think I've ever seen in real life.

 

[JohnW2]

1,2 & 7 I don't think I've ever seen in real life.

Ah - you should come here, then - not to see 2A or 7A ones, but I may be the main market for 1A fuses I just don't see the point of using anything bigger for the (many) things that don't take more than a few dozen mA at most!

Kind Regards, John

 

[kai]

My PC has a 5 amp fuse in it - there is even one on a little pull out drawer in the cable inlet on some appliances, reachable by withdrawing the mains lead to get at the fuse. (Probably to that the fact they are made in countries that use unfused plugs, so the fuse has to be situated in the appliance itself!)

 

[ericmark]

Cable or flexible cords comes in 0.5 mm², 0.75 mm², 1 mm², 1.25 mm² etc which means 3, 6, 10 or 13 amp rating and the fuse in the plug is to protect the cable I have not ever seen a BS1362 6A fuse or for that matter a 4, 8, 9, 11 or 12 amp version. So 3A for items with 0.5 mm², 5 amp (6 amp is not made) for 0.75 mm² cable, 10 amp for mm² and 13 amp for 1.25 mm² and above when fitted in the BS1363 plug.

The 2 amp fuse is required for C7 IEC 60320-1 Appliance Couplers as it is only rated at 2.5 amp and 200 mA is maximum load for a shaver socket so even a 1A fuse is a bit OTT.

Why a 7 amp is made I don't know? I will guess for used with a FCU on fixed appliances as although with a portable appliance the fuse only protects the cable that is not the case with a fixed appliance where the manufacturer is free to stipulate protection required.

 

[Astra99]

I tend to look at the IEC connector on the other end of the cable to decide the preferred fuse rating. C7 and C5 are rated at 2.5A, so I install a 3A fuse. With C13 depending on whether it is 0.75mm² or 1mm² I install 5A and 10A respectively unless it is clear from the rating of the appliance (PC, printer etc) that a lower-rated fuse is indicated. Reference 7A fuses, I have a few of these to use with servers which have multiple cooling fans which all come on at start-up and then switch off until needed. It avoids potential nuisance failure of a 5A fuse (where 0.75mm² flex is used) especially with Y splitters in the power lead.