# extension leads guide + help

#### winston1

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 item clearly shows you how many amps it draws, and that's what you need to know, as it is current which matters to the cable, not wattage.

You only use wattage to calculate amps if you have to - no point in trying to calculate wattage when you already know the load in amps.

That label shows the maximum current it draws. As it is a switch mode power supply that will only happen when used on the minimum design voltage, 100v. When used on 240v it will draw considerably less current.

You cannot simply add the current rating of all your attached appliances anyway. If the phase angles are different the total will be less than the sum of the individual loads. In extreme cases with an inductive and a capacitive load the total current will be less than either individual load on its own.

#### JohnW2

That label shows the maximum current it draws. As it is a switch mode power supply that will only happen when used on the minimum design voltage, 100v. When used on 240v it will draw considerably less current.
... and even less still if the load is drawing less than the maximum output of 2A (at 12V). That was pointed out a couple of pages ago.
You cannot simply add the current rating of all your attached appliances anyway. If the phase angles are different the total will be less than the sum of the individual loads. In extreme cases with an inductive and a capacitive load the total current will be less than either individual load on its own.
As I've said, such issues will merely confuse the OP of this thread even further. He really doesn't need to know about things like this, even if they are theoretically true. If this were a 'spin-off' discussion, long after the OP of the thread had been answered and gone away, things would be different. However, he's still with us, and is undoubtedly reading, trying to understand and worrying about everything he reads.

Kind Regards, John

#### ban-all-sheds

You are welcome to disagree with me.

Being rude and insulting is another matter altogether.
Your use of the term "Eurocrat" really is idiotic - it shows so little grasp of how international standards are developed, and such a dismissive attitude to the people who work on standards bodies that your position really is one of ignorance.

That you feel insulted by your idiocy and ignorance being pointed out is of no concern to me.

B

#### busterboy

OK now I'm a little confused........

B

#### busterboy

Im confused as a few people helped me here to use wattage as a guildline to get a rough estimate of a total load in a 13A extension lead.

Example

-lcd Tv 130w
-dvr 50w
-nightlight 40w
-pc + monitor 600w
---------------------------

so 3000 - 820 = 2180

since theres 2180 watts left the extension is no near being overloaded and is in a SAFE ZONE.

Ok now thats what i had tought as a basic guide to use but now People here are confusing me by talking about using amps instead?
so is the above guide wrong or what way do i use amps to get an idea of total load?

also anotyher thing is some of my electrical devices shows out put in wattage (ie LCD TV 130W) which is easy to note down as its stated on back of device but some dont give wattage and thats what I wanted help to find out how to work out the output of these devices so i cud use the above method as a basic guide with extension leads.

#### EFLImpudence

Im confused as a few people helped me here to use wattage as a guildline to get a rough estimate of a total load in a 13A extension lead.
It's just that amps is what we use because that is the determining factor when loading a cable.

At 240V, 13A is 3,120 Watts but at 12V, 13A is only 156 Watts yet the same size cable would be required.
For cable sizing, an amp is an amp is an amp but wattage depends on the voltage.

-lcd Tv 130w
-dvr 50w
-nightlight 40w
-pc + monitor 600w
---------------------------

so 3000 - 820 = 2180

since theres 2180 watts left the extension is no near being overloaded and is in a SAFE ZONE.
That is so.

Ok now thats what i had tought as a basic guide to use but now People here are confusing me by talking about using amps instead?
so is the above guide wrong or what way do i use amps to get an idea of total load?
No, it is not wrong - but it is the 13A which is the limit so we use amps.

also anotyher thing is some of my electrical devices shows out put in wattage (ie LCD TV 130W) which is easy to note down as its stated on back of device but some dont give wattage and thats what I wanted help to find out how to work out the output of these devices so i cud use the above method as a basic guide with extension leads.
They always state the wattage at a certain voltage because the wattage changes with voltage.

A light bulb in the home may be 60W, at 240V that is 0.25A.
You car headlamps also state a wattage (60W) but at 12V that is 5A

As amperage is required to determine the cable size that is what we use.

You may, when always talking about 240V, add up the wattage if you wish.

B

#### busterboy

So can the amps be added up instead of wattage like the following

Example

Light 60w ÷ 240=0.25 amps
TV 130w ÷ 240 = 0.54 amps
DVR 50w ÷ 240 = 0.20 Amps
Hairdryer 1500w ÷240 = 6.2 amps
-----------------------------------------------
Total 7.1 amps

So 13amps - 7.1amps = 5.9

So on a 13amp extension there Wud be 5.9 amps left to keep it in the safe zone and not overloaded.

Is this way of or am I learning anything?? Lol!

#### ban-all-sheds

Light 60w ÷ 240=0.25 amps
TV 130w ÷ 240 = 0.54 amps
DVR 50w ÷ 240 = 0.20 Amps
Hairdryer 1500w ÷240 = 6.2 amps
-----------------------------------------------
Total 7.1 amps
Only if you know that those are the wattage values at 240V.

B

#### busterboy

Yes if the device states 240v then I will divide it by this unless it states 230v then I will use

#### ban-all-sheds

Or if it doesn't state a voltage.

B

#### busterboy

All my devices I use state voltage at 230v

B

#### busterboy

Searching internet and found my answers in a few paragraphs. The following is explained very basically for people like myself who just need basic information to calcylaste load using wattage. Here is a basic guide taken from the net.

How to Calculate Load on a Single Circuit

"If you want to evaluate the load on a single circuit in your home, you can do it rather easily. To do this, you'll simply need to add up the wattage consumption numbers for all of the devices that are plugged into outlets on a single circuit. Look for a label on the device that tells you how many watts the device consumes. If this information is not available, then look for a label that shows you how many amps the device uses. If you know how many amps the device uses, you can easily calculate the wattage. To do this, just multiply the number of amps that the device uses times the number of volts. For instance, if you have a computer that uses 10 Amps and is plugged into a 110 V outlet, then you could correctly estimate that the computer uses about 1100 Watts.
After you know the total wattage for all the devices on a single circuit, you can tell if the circuit is overloaded or not. Just go to the breaker box and look at the amp rating for the breaker switch. For example, a 20 Amp circuit would have a maximum wattage capacity of approximately 2200 to 2400 Watts. Therefore, if you have more than this installed on a single 20 and circuit, the circuit may be overloaded"

So if I'm applying this to 13amp extension lead. I first find out the wattage of all devices plunged into it then add them all up at deduct that total from 3000w.

Is this a correct method obvisiouly changing the 110v to uk 240/230?

#### JohnW2

Is this a correct method obvisiouly changing the 110v to uk 240/230?
Not necessarily, if it's a precise answer you want. As people keep telling you, the "label on the device that tells you how many watts the device consumes" may not be telling you how many watts it consumes at the voltage you want (e.g. 230V).

However, as I keep telling you, for your purposes any of these methods are plenty accurate enough. Indeed, as I've told you, provided you keep away from heat-producing appliances (apart from electric blankets or short-term use of hair dryerts/straighteners etc.), you don't really need to do calculations, because you're not going to get a total load anywhere near 13A.

Kind Regards, John

B

#### busterboy

OK John thanks again

Regarding my making of extension lead what is the best cable to use for the 13amp plug? I take it 3 core flex with a minimum of 1mm wire or any 3 core flex above this size wud do?

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