Power switch - Double or single pole? - Page 1
Forum section: electronics / beginners

author: RoycePC
author_rank: Newbie
timestamp: June 18, 2023, 12:24:53 am
content: I watched Dave's video of the strip down of a Rigol Osc and he said he was very pleased to see a double pole switch on the mains (240V in Oz).I have always just switched the active and then into a fuse.Should I be switching the active and the neutral?

author: Benta
author_rank: Super Contributor
timestamp: June 18, 2023, 12:53:44 am
content: Quote from: RoycePC on June 18, 2023, 12:24:53 amYes, always.You may think you know what's what on a three-prong plug, but that only applies until someone uses a travel adapter on it to make it fit a two-prong outlet.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: June 18, 2023, 02:44:32 am
content: My power tools that switch both wires don't need to be grounded or polarized. Also, you want to protect from a wall socket being wired backward.

author: RoycePC
author_rank: Newbie
timestamp: June 18, 2023, 10:31:03 pm
content: So I guess it is just economics that causes so many devices to have single pole switches.Thanks for the help.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 19, 2023, 04:29:30 am
content: Quote from: RoycePC on June 18, 2023, 12:24:53 amHere in Northern Europe, mains sockets are nonpolarized –– see schuko sockets; AKA CEE 7/3 ––, so it is an absolute must.I very recently bought some socket adapters with a switch, because it is easier to turn the switch than disconnect devices like chargers, and my tea maker that I removed the two-hour keep-warm limit accidentally; otherwise its plate would be always hot. I have to check the switch in such things so they really do have a dual-pole switch, because many cheap Chinese devices have only a single-pole one.I refuse to be a slave to my cellphone, so I often leave it in its charger. To prolong the battery life, I can now just switch off the charger from mains, without having to remove any cables or connectors, and only turn it on at night for charging every couple of days. I wanted to do the same to this laptop charger, but the mains socket is in an awkward place, so will have to get an extension cable with a built-in switch.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 19, 2023, 08:24:33 am
content: For "normal" electric appliances, a single pole switch is sufficient. It opens the circuit, so no current can flow though your appliance when it is "off".But there are a few occasions where a double pole switch has an advantage.When you are working with electronics, a double pole switch adds extra safety. Here in Europe for example mains sockets are non polarized (as Nominal Animal already mentioned)I also really like the "Cliff Quicktest" as used by BigClive:It gives you a really clear indication whether your device under test is connected to mains voltage or not. It also makes it very unlikely that the switch is activated accidentally (for example by dropping something on it). The big mechanical separation also increases the safety margin. There is for example no chance that the internal contacts can get welded together without you noticing it.You can also make a (DIY) extension cord with two neon lights. a green one between "live" and "earth", and a red light between "Neutral" and "Earth". This gives you an unambiguous indication whether the output wire which should be the neutral wire really is the neutral wire.When working with mains voltage on your desk such things add up and reduce the chance for accidents.

author: DavidKo
author_rank: Frequent Contributor
timestamp: June 19, 2023, 08:27:53 am
content: Quote from: RoycePC on June 18, 2023, 10:31:03 pmProbably double insulated device.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 19, 2023, 08:28:16 am
content: Quote from: Nominal Animal on June 19, 2023, 04:29:30 amI have had some bad experiences with that.What happened with me is that the phone discharged it's battery through the unpowered but connected charger. USB "on-the-go" is designed with delivering current from your phone to an external device, so I guess this is normal, and the amount of current depends on how your phone charger is built.

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 19, 2023, 10:10:17 am
content: Quote from: Doctorandus_P on June 19, 2023, 08:28:16 amI haven't noticed any change in the discharge rate, but I do need to check this! Thanks!(Also, the chargers I use are non-cheap ones from reputable stores intended for phones and tablets; having been zapped with 230 VAC a few times, I'm averse to even 'tingly' wall wart outputs. I've even thought about making my own T12 soldering iron controller, using Mean Well medical-rated Class II isolated power supplies...)Time to wire up some kind of low-voltage low-current measurement circuit I can put in between my charger and my phone. I think anything above 1 mA or so is not acceptable. Or perhaps construct a charging cable with a built-in switch?