It’s not ideal to plug a washing machine permanently into an extension cable because it introduces an extra risk of electrical overheating. Miele for example say in their washing machine instruction book, "do not connect via an extension lead. Extension leads do not guarantee the required safety of the appliance (e.g. danger of overheating)"
In reality many washing machines, dishwashers & and tumble dryers are plugged into extension cables, and anyone deciding to do so should at least use the right type of extension cable. You cannot use a 2 core extension cable which has no earth. If you do, although your machine will work, it is in a potentially lethal condition because it isn’t earthed – see getting electric shocks from an appliance
Only 13 Amp extension leads can be used
You must also ensure the cable is rated for 13 Amps. Some extension leads may have thinner cable than that of the washing machine. This is an indication that the cable may be meant for lawn mowers, lamps etc. and not white goods appliances. If the cable is just as thick or thicker than that of your appliance then it should be 13 Amp and 3 core (with an earth lead) but don’t assume anything. Using a 5 or 10 Amp rated cable can cause overheating and is potentially dangerous. Using cable that has no earth can kill if your appliance develops an insulation fault.
How many appliances can you plug in?
Mutiple socket extensions are very common these days. I remember when no one thought of inventing them and extension sockets just had one socket at the end. In those days people used to plug socket adapters in the end to be able to plug more than one appliance in. These days you can get extensions with 4 or 6 sockets. You can have something plugged into each one, but attention needs to be given to what is being plugged in and how much current it draws. As a rule of thumb, no two things that have heating elements inside them should be plugged into the same wall socket.
Useful Tool for checking safe amount of appliances to plug into an extension socket
Retractable extension reels
Extension cables that wind up must be fully unwound when in use. This type of extension cable will have two ratings written on it in amps. One advises the maximum amps it can take when fully unwound, and the other (lower figure) is the maximum it can cope with when not fully unwound. Washing machines, dishwashers and tumble dryers can easily draw 10 amps alone so they need to be fully unwound or they can overheat and potentially cause a fire. Any extension cable should be rated for 13 amps.
What about wall socket adapters
These old fashioned adapters are less needed these days but still in use, and still more appropriate for certain circumstances. They are always 13 amp so fine for appliances but as the white goods appliance we are talking about draw around 10 amps you can’t use another white goods appliance at the same time or it will overheat. A washing machine and a dishwasher or tumble dryer being used in the same adapter can be dangerous.
I’ve been told by a fireman that the fire brigade recommend you do not plug large appliances into double adapters because they often often don’t have good connections inside and can over heat. I’m sure they are likely to recommend not using extension leads too. Ideally, white goods appliances should be plugged directly into a wall socket.
Fishy smell from socket?
On two separate occasions I’ve noticed a strong fishy smell which I fortunately tracked down to faults on electrical sockets. It seems that by either accident or design, when modern wall plugs, adapters, sockets and light fittings overheat they can give of a very strange and pungent smell, which is “fishy” in nature. If you ever smell a strange fishy smell don’t ignore it, try to track its source because dangerous overheating could be taking place inside an electrical fitting. In my two cases, one was a faulty plug overheating in the wall socket in a kitchen cupboard and the other was an overheating light fitting.