A common question asked by PC users is how much is safe to plug into one 13A socket. If your setup is anything like most of ours at Tech Advisor, you’ll have a multiway power strip connected to a mains socket in the wall and into that your PC, monitor, speakers, printer and possibly other devices.
Fortunately, it’s easy to work out whether overloading it or not, and we’ll explain how.
First, note that UK sockets aren’t actually rated as 13A (13 amps). They’re typically on a ‘ring main’ which is fed from a 32A breaker or fuse.
It’s usually the plug which is limited to 13A, but most electrical devices – certainly anything PC related – is much more likely to have a 3A or possibly 5A fuse.
How much can I plug into one mains socket?
There’s a simple formula to work it out: Amps * Volts = Watts.
We know the volts – the UK uses 230V (+/- 10 percent) – and let’s limit Amps to 13 as that’s the highest-rated fuse you’ll find in a plug, including in multiway adapters.
13 * 230 = 2990W
So, you can connect devices which use up to 2990W to a single UK mains socket without overloading it.
You could check exactly how much power each device consumes by plugging it into a power meter such as the £12.99 Energenie or you could check the manufacturer’s specifications in the manual or online.
With PCs, you’ll easily find out the rating of its power supply by looking on a sticker on the side, such as 550W. However, this isn’t the amount of power the PC will use: it’s the maximum wattage the power supply is capable of delivering to the PC components.
In general use, a PC will consume much less than its PSU’s maximum rating. In our experience PC’s typically use between 80 and 300W.
LCD monitors and inkjet printers are roughly 20-50W, and speakers generally less than this. Laser printers only use hundreds of watts when they’re printing, and when idle hardly any.
So, it’s obvious you can run at least two complete PCs safely from a single mains socket.
If you want to do your own calculations, simply add up the maximum power consumption (in watts) of each device and make sure the total doesn’t exceed 3000W.
Is it safe to use an extension lead for a PC?
Yes. However, you should make sure that the cable isn’t coiled or covered.
Current flowing in a cable generates heat, and this heat needs to be dissipated. When a cable is coiled and the current is near the maximum the cable can handle, the heat generated can melt the insulation and cause a fire when the copper cables touch each other.
This is also why you shouldn’t cover cables under carpets, rugs or anything else. Here's what can happen when a coiled extension lead is used to power appliances that use a lot of it:
PCs and peripherals use a relatively small amount of power and therefore a coiled or covered power cable shouldn’t pose a major risk, but it’s still best to avoid that risk.
You’ll find more electrical safety advice on the Electrical Safety First website.