My second electrical question this week

[The Bear]

Sorting out all things electrical is my aim this week.

I want to make my own plug in extention lead as I want to make it a specific length, and just fancy doing it.

I have the plug and the socket for the other end, my Q is about the cable.

I assume I need twin core and earth, but what size?
Does 2.5mm sound right?

Mark

 

[bubbabear]

I think twin core and earth is the type that you would wire a house or shed with, 3 core flex is what you need for an extension. 2.5 is a little on the heavy side 25 - 30 amps iirc , the more usual size for a good heavy duty lead would be 1.5 which will take about 16 amps which is enough if you are using a 13 amp plug and socket. Unless it is really long and then voltage drop may require a thicker conducter, but that would need to be a very long cable.

 

[Esox Lucius]

Depends on what you are going to be using it for on the cable to work the sizings. 2.5mm T&E would not be the cable to choose or any in the T&E bracket (flat grey wire). You need to be picking something like flex or butyl flex so it "flexes" with little or no memory.

2.5mm T&E is what feeds most properties socket ring main so unless you are aiming for higher load than 13 amp you will be fine.

Over 13 amp and your into a whole new ball game as the normal socket circuit will not manage it.

Hope that helps

 

[The Bear]

Both answers help a lot. Moral - don't always trust google

The extension is 95% of the time going to run a 2000w router in the table, so would 1.5mm flex be OK for that?

I have now had another thought, would I be able to put a double socket on the end and use the router and a vacuum off it at the same time? (after all I've seen extensions with an 8 way socket on the end) - 1.5mm still OK or would I need bigger if I went for this set up?

Mark

 

[Esox Lucius]

Whilst 1.5mm will manage to do that job a 2.5mm cable will ALWAYS do the job.

For the sake of a few extra quid i would go for 2.5mm.

Other thing to think about is future proofing it...you may increase your power usage and overload the cables.

The power ratings of cables are not easy to determine accuratly due to ambient temps that they are in.

But i usually err on the side of slightly over sized than "just about do it" sizes.

The other thing you need to think about with using extension leads is the fact that the socket you plug it into is still only rated to 13amps with equates to 3000 watts.

for example:- 2000 watt router and a 1500 watt vacuum may be abit much for it.

Regards

Mark

 

[The Bear]

Blimey, didn't realise it could be this complicated.

Might give the double socket a rethink and plug the vacuum in elsewhere.

Just out of interest, how do those 6 and 8 way extension sockets work then, or don't they if anything power hungry is plugged in?

Mark

 

[RogerP]

...
Just out of interest, how do those 6 and 8 way extension sockets work then, or don't they if anything power hungry is plugged in?

Mark

The same applies, and most multi-sockets will have a sticker warning not to exceed the 13amp plug/main socket rating - which of course is all too easily done with multiple appliances plugged into a 4/6 way extensions.

Roger

 

[Pond]

2.5mm T&E is what feeds most properties socket ring main so unless you are aiming for higher load than 13 amp you will be fine.

A 32 amp ring main has TWO 2.5mm2 cables, hence the 'ring'. Please don't think that 2.5mm2 cable is rated at 32 amps at 240v, IT ISN'T!

A few very useful things to remember with electrics:
1. The fuse is there to protect the cable! NEVER EVER use cable rated at less than the fuse protecting it, this is how electrical fires start!
2. Cable ratings differ depending on the use, i.e underground, sealed in trunking, exposed etc. Look on-line, or ring a local electrical wholesaler, they have rating books.
2. 'Plug top' fuses are slow blow. A 13 amp plug top will often require considerably more continuous current before it blows.
3. Always fully uncoil any extension lead. A partly coiled cable will pull a LOT less current before it overheats!
4. If you are at all unsure, don't do it!

I don't want to seem like a 'jobsworth' but I wouldn't want to hear of someone's workshop burning down because of guesswork!

 

[The Bear]

Pond

I have described the use of the extension, so what do you recommend? I am quite capable of wiring it if some one tells me what to use (which i thought they already had?)

Mark

 

[Ateallthepies]

I would be happy using an extension lead with two 2 KW appliances plugged in and in fact use a twin socketed lead I made up from some 1.5mm flex for that very purpose and often have a 2 KW hot air gun and maybe a 2 KW steamer going for hours on end.

The 1.5mm cable will take 4 KW no problem if not reeled up ( coiled up you will have a glowing ball of copper and plastic :shock: ) and while most twin sockets are rated at 13A max (that's 13A spread across both outlets on a Twin!) they will happily take more current for a considerable time and most are tested well beyond 13 A. So running 16-17 Amps from a twin socket is no problem for me as long as I am present whilst in use.

The plug-top fuse as already stated will not blow at 13 Amps anyway and will take several Amps above it's rated current for an unknown time. 16 Amps may never blow a 13 Amp fuse or it may blow quickly or take several minutes.

Mark, do what ever you feel safe with. I have been a Sparks over 20 years so would feel more than safe using a lead made of 1.5mm flex with a twin socket on the end for your application.

Steve.

 

[Pond]

Mr Bear,

As Mr Pies said above, do whatever you are happy with.

I wrote the above more as a general overview than your specific request for advice, sorry.

It concerns me when 'educated guesses' are posted on the subject of electrics, however well meaning.

 

[bubbabear]

1.5 mm is a very common size for 13 amp extensions, 2.5 mm is the size you would find in a 16 amp extension, the type with the smaller round blue plug and sockets on the ends ( the bigger diameter blue plugs are 32 amp). The point made earlier about making sure the cable is unwound is a very good safety tip, if the cable is wound up the heat cannot disipate quickly enough which will lead to a vicious circle effect as the hotter the conducter gets the greater the resistance becomes and higher resistance = more heat. So the bottom line is a 1.5 cable fully unwound will be ok but there is definately no drawbacks to using 2.5.

 

[Ateallthepies]

That's right, if you can terminate a 2.5mm cable into a plug-top then no draw-backs, some you can't!

1.5mm is all that is needed unless you have a 100 metre run or more :shock: !!!

Steve.