extension leads guide + help

[busterboy]

Just was looking at a few extensions leads in the house and noticed that its rated do not exceed 13amp fuse 250 volts .

I have been reading about over loading extension leads and I have been trying to add up wattage of devices used on the one lead

Example
4 way extension lead with 13amp fuse at 250v so do we multiply 13x250 and that givesbus the total load the extension lead can take in terms of safety but in watts.
So its 3250 watts

LCD TV 150w
DVD player 12w
Nightlight lamp 40w (goes by size of bulb I think?)

Total load = 202w

Then do we do 3250 - 202 =3048watts
So the extension lead has still got 3048 of watts available for over devices and is safe as long as this number is not reached or passed (overloaded).

Is this the right way to calculate the load we have on our lead s? I think if someone could show us the right way to calculate watts load of our devices it might help myself and others (mother in law lol!) to watch that we are not overloading leads.

One other thing some devices tell you the watts that they use and some don't so how can we calculate the devices that don't so we can add these to our calculations.
Thanks

 

[Robin0577]

You've got the right idea, but we use the nominal supply voltage of 230v for calculation purposes.

So it would be 13 x 230 but other than that, you're doing fine.

Someone might come along and mention power factor but that really only becomes significant on an industrial level, on a domestic level it's usually worth considering.

 

[busterboy]

So how do I work out the watts of other devices like my DVR.
Here is a Pic of the power label

View media item 66021
Thanks

 

[davelx]

So how do I work out the watts of other devices like my DVR.
Here is a Pic of the power label

View media item 66021
Thanks

That's an external switching power supply, so you have to use the output figures plus an allowance for efficiency - which is typically 80% or better, unless it's a very cheap and nasty design.

So the maximum power that that PSU should draw is
12 X 2 /0.8 = 24/0.8 = 30W.

Note that the ACTUAL power consumption will depend on the equipment that the PSU is supplying - which must be less than or equal to the max that the PSU can provide.

 

[JohnW2]

So how do I work out the watts of other devices like my DVR. Here is a Pic of the power label

If you're only talking about 'electronic' devices (TVs, DVRs, computers etc. etc.) there really is no chance of your overloading a 13A extension lead. It's only if you started bringing things which deliberately produce heat (heaters, kettles, toasters, washing machine etc.) into the equation that you'd get anywhere near 13A. What sort of additional loads did you have in mind?

Working out the actual load represented by a device like your DVD is not easy, although one knows that the answer will be very low. The maximum output of that power supply is stated as 2A at 12V, which is just 24W (i.e. less than 0.1A at 230V). However, there will be some 'losses' in the power supply, so the actual maximum current drawn from the mains would be at least a bit more than that. However, it also says 100-240V 0.6A. If it really did take 0.6A at 240V (or 230V), that would be nearly 140W, which I very much doubt would ever be true of a power supply delivering only 24W maximum. Whatever, even if you wanted to consider$ that very worst possible case, that 0.6A at 230v/240V would not go very far towards using up your 13A total.

Kind Regards, John

 

[busterboy]

So we multiply the output 12v times 2 ( is this 2 from the 2.0amps?) And the 0.8 is the 80% you talk of.

So for example if an appliance was the same but rated output 12v 5.0amp and I wanted to calculate 80% it wud be
12v x 5.0/0.8 =75watts

How I'm I doing?

 

[JohnW2]

So we multiply the output 12v times 2 ( is this 2 from the 2.0amps?) And the 0.8 is the 80% you talk of. So for example if an appliance was the same but rated output 12v 5.0amp and I wanted to calculate 80% it wud be
12v x 5.0/0.8 =75watts
How I'm I doing?

Yep, that's the idea, if it's the sort of power supply for which an 80% efficiency is a reasonable guess. However, as has been said, that is the maximum that the power supply could supply. In practice, the actual current is likely to be less than that maximum.

Kind Regards, John

 

[busterboy]

OK I'm think im getting it. In our bedroom we have one double socket with 2 main extension leads in each side.

In my side I have a

Main Extension Lead coming from socket (6 ports Surge protected)
Port 1 -extension cable1(6way ):
- Computer + LCD monitor
- Internet hub
- Wireless headphones
-external hard drive

Port 2 -extension cable (4 way)
-LCD TV
-DVR
-DVD player

Port 3. -Lamp 40w

Port 4 - heated under blanket

Port 5 - phone charger


On my wife's side she has

Main extension lead from mains plug (4 way)
Port 1 - 40w lamp
Port 2 - baby monitor
Port 3 - phone or tablet charger
Port 4 - used time to time for hair dyer or hair straighteners


I'm just wondering as its the only socket in the bedroom are we OK with the extension lead loads ( been like it for 6 years now lol!) And just trying to add up The watts to keep things safe and for general knowledge as well. All leads r 13 amps if this helps you to understand the setup

Thanks

 

[JohnW2]

I suspect that someone may well tell you that this extensive use of extension leads (including one plugged into another) is not 'ideal', but that lot on your side is not going to add up to anything like 13A. On you're wife's side (I presume that comes from a different socket), the only significant loads are the (occasional) hair dryer/straigheners, the rest being trivial.

Kind Regards, John

 

[busterboy]

Yeah both mains extension leads mine and my wife's come from the same double socket in the wall as its the only socket in the room. I know about the extension leads in one another but as there is no additional sockets its all we can really do.

 

[JohnW2]

Yeah both mains extension leads mine and my wife's come from the same double socket in the wall as its the only socket in the room. I know about the extension leads in one another but as there is no additional sockets its all we can really do.

Fair enough. Although it's a topic of (sometimes heated) debate around here, you can't assume that you can safely draw 2 x 13A (i.e. 26A total) from one double socket. Most people feel that the maximum (total for both outlets) is around 20A, although some think that the total should be restricted to 13A total for both. However, with the sort of loads you're talking about, I don't think there is any issue, no matter what interpretation of 'ratings' one adopts.

Kind Regards, John

 

[busterboy]

Thanks for the reply.that's why I'm trying to get a feel to calculating the watts of devices around the house especially my mother in laws lol!. I feel if I know the total watts of devices on any extension lead and know the leads limit (13amp 230v total 2990w) then I am more reassured That its within a safe zone. Its more a be safe to keep count than risking an overload lol!
Thanks again

 

[JohnW2]

Thanks for the reply.that's why I'm trying to get a feel to calculating the watts of devices around the house especially my mother in laws lol!. I feel if I know the total watts of devices on any extension lead and know the leads limit (13amp 230v total 2990w) then I am more reassured That its within a safe zone. Its more a be safe to keep count than risking an overload lol! Thanks again

Fair enough. Of course, the fuse in the extension lead's plug is there to (amongst other things) protect its cable from overload. Although a 13A fuse in the plug will allow a fair bit more than 13A to flow for an appreciable time, provided that the cable is correctly rated, the fuse should blow before the cable comes to any harm, even if you plugged well over 13A's worth of loads into the extension. As I said before, provided you keep away from loads/devices designed to produce heat, you're pretty unlikley to get anywhere near overloading a 13A extension lead.

Kind Regards, John

 

[busterboy]

Thanks John I feel a lot better about it now. And have learned a few things.

 

[Astra99]

If it should become necessary to daisy-chain trailing sockets, then a method of control would be to down-fuse the second socket strip to 10A or 7A, and, (assuming there is a third!) the third to 5A or 3A. This would help act as a control on loading. Please also bear in mind that the socket to be used for daisy chaining is that closest to the cable inlet. This helps avoid high(er) loads having to travel all along the copper inside the trailing sockets.

Any comments?????