Sometimes when I plug in devices with the socket on, I see a spark in the socket. I wonder if it’s safe to do this? Will the spark jump out one time? Every time I see it, I think, “I’m glad there’s no gas leak.”
Some places I’ve been to have no switches on the sockets, e.g. Europe and China. Is this common? How do people living there plug in devices?
the arc will only “jump” as far as the voltage/potential allows it to; 120 VAC can’t really sustain a “long” arc in most cases. The main concern (aside from proximity to a gas leak, as you mention) is that repeated arcing can erode the contacts on the plug and in the receptacle. It also will spew out a bunch of EM noise (which you can hear on an AM radio) but that won’t really harm anything per se.
Outlets in the US do not have built-in switches, but rather are normally wired directly to a circuit breaker. The exception is for some bedroom outlets which may have lamps plugged into them and are controlled from a light switch near the door. I can’t think of any devices offhand that don’t have an on-board switch of their own (probably part of the UL code), thus negating the need for an outlet switch like the UK has.
You can have the spark at the outlet or hidden in a switch. One of the reasons plugs, outlets, switches, etc. have electrical ratings is not how much current they can carry, but how big of a current it is safe to interrupt.
When I was younger, I worked in the paint industry. All the electrical equipment was carefully regulated. Unless you go to oil filled switches, there will always be sparks when things are connected and disconnected. They must be controlled to avoid igniting fumes. Even the telephones.
The contacts in wall receptacles are not designed to quench arcs. By contrast, AC power switches are able to safely handle arcs by using contacts made of an alloy that is minimally affected by arcs. In addition, an RC snubber circuit may be placed across the switch contacts to further reduce arcing across the switch contacts.
In other words, you should try not to plug/unplug devices when the device is on.
if a device is switched on or always on then it might draw a spark just before making contact. having the device switched off will prevent that.
the oxidation (blackening) that might occur is not of serious consequence (much of the time), the design of a receptacle (in good condition) is to scrape itself and the plug clean enough to make good contact. when you stop seeing this happen then replace the receptacle.
in a situation where there might be combustible gases the sparks would be bad.
As noted above, 120 volts (or 240 volts outside North America) shouldn’t produce a very big spark when you plug things in. When you unplug certain devices, though, their inductance can cause a pretty high voltage spike to be produced, which is why you sometimes see a spark when you unplug a heater or motor that’s running at the time.
Socket switches are pretty uncommon everywhere I’ve been in the U.S. and Canada, too — or at least, the majority of the outlets in a house are not controlled by any switches. (Occasionally you’ll get an outlet that’s controlled by a wall switch, like a light switch, but that’s for convenience rather than safety.) Out of curiosity, what part of the world do you live in?
My assumption was UK, where those switches are the norm, as are fuses inside the outlets.
Lots of devices with standby modes don’t have switches, like microwaves, fridges and adapters, but I haven’t observed sparks from them. Maybe their load isn’t high enough.
That’s true, I sometimes see sparks from the switch as well. I thought they’re designed that way, so that’s safer.
How about countries with no wall switches and appliances with no switches?
I’ve heard about sparks from vacuum cleaners being unplugged. Wanted to see them, but YouTube doesn’t have any videos and I don’t dare to try. I’m currently in Singapore, where every socket has a switch. The same is true in Australia.
In the plugs, actually. Not sure about Australia, haven’t figured out where the fuses are. Their plugs are one-piece moulded and can’t be opened up.
Load capacitance (due to a switched-mode power supply, for example) will cause a spark when you plug it in.
Load inductance (due to a vacuum cleaner motor, for example) will cause a spark when you unplug it.
Even a purely resistive load will usually give a spark when you plug/unplug it, since there will be a finite time interval where the distance between the contacts is small enough that voltage breakdown of the air occurs.
The magnitude of the spark will depend on a lot of variables, including the time it occurs relative to the zero-crossing time.
Thanks for all your replies. Oh I didn’t know the US doesn’t have individual switches either. Maybe I’m not used to it, but I get nervous when plugging devices in when the switch is on.
Generally speaking, plugging in / unplugging a “live” appliance likely won’t damage the plug or receptacle unless it is done on a routine basis.
The usual advice here in Germany is to buy an power strip with a switch and 5 or 10 holes, and plug devices without off-switches into that. Instead of unplugging all those tangled wires (esp. if you have to crawl under something or behind sth.), you just click the switch on the power strip.
Oops, bad on me for a faulty memory. I haven’t worked in the UK since about 1990.
