Circuit braker for workbench - Page 1
Forum section: electronics / beginners

author: grevan
author_rank: Contributor
timestamp: December 05, 2016, 06:12:30 pm
content: Hi guys,i´m a newby designing my workbench and would like some advices.I thought of having a circuit braker on the bench so i could shutdown the outlets when i leave the room.During my researches about circuit breakers i´ve read about RCD (Residual Current Device), a device meant to protect you against electrical shocks. Do you think this is a good solution?I was wondering, will the RCD "turn on" when using the variable power supply looking for notebook shorts, for example?Sorry for my not so good english.Thank you.

author: Kremmen
author_rank: Super Contributor
timestamp: December 05, 2016, 07:51:25 pm
content: In many parts of the world RCDs are required by law (or electrical code, actually) in all new installations. Generally, it is an excellent idea but please understand that it will not make your wall outlet foolproof. If you grab the live and neutral wires, you _will_ be electrocuted and the RCD will not do anything.Only when current leaks to ground (through you!) the RCD will detect the imbalance and break the circuit saving your life.So by all means install a RCD but also put a breaker in series if you want to disconnect power. (It is a circuit breaker - brake is something that stops a car) . But no worries, everyone understands what you were askkng.

author: rstofer
author_rank: Super Contributor
timestamp: December 05, 2016, 07:53:33 pm
content: Some form of 'shock' prevention is a good idea. In some countries it is called RCD, in the US it is call GFCI. Same thing, really except I believe the GFCI trips at a lower current. Ask Google...Often these devices are incorporated into a receptacle form factor. This may be quite convenient, or not... Just replace the wall outlet. Which might not be so convenient if it trips...I wouldn't expect PC power supplies to trip the device. If they did, it would be a flame war on Google. Everybody would be blaming Microsoft Windows!

author: AG6QR
author_rank: Frequent Contributor
timestamp: December 05, 2016, 07:58:36 pm
content: The English term is "circuit breaker".A normal circuit breaker only protects against excess current. Its main purpose is to limit the risk of fire or melted wires. It's possible to be killed from a small current, so a circuit breaker is not sufficient to protect against that.A RCD (we call them ground fault interrupters in the USA, but in many other countries they're called RCDs) is a good idea, because it protects against very small currents that leak to ground. It shuts off current when there is an imbalance in current between the hot and neutral wires. That's good, but even that is not always enough to prevent fatal shocks. An RCD does not protect against shocks from touching the hot and neutral lines of a circuit simultaneously, nor does it protect against shocks that happen on the secondary side of a transformer. And of course it can't protect against shocks that come from charged capacitors.It's probably a good idea for every electronics workbench to have a very visible, clearly labeled, main power shutoff, at a location slightly away from the bench. You should instruct every member of your household or anyone who might be near the workbench that, if you seem to be incapacitated near the workbench, they should first turn off that main switch before approaching you. Of course, the need for that kind of precaution depends on what kind of work you are doing, but if you regularly work with high voltages, it may be wise.

author: Zero999
author_rank: Super Contributor
timestamp: December 06, 2016, 12:11:52 am
content: Quote from: rstofer on December 05, 2016, 07:53:33 pmRCDs come in a variety of tripping currents, ranging from 5mA to 500mA, with 100mA and above being for protection against fire only. I believe the typical tripping current for a GFCI in the US is 5mA, whilst in the UK it's 30mA for most RCDs. In the US GFCIs are normally integrated into the wall sockets, which means a lower tripping current can be used, without nuisance tripping but it won't protect someone who drills a hole in the wall and hits a cable. In the UK, RCDs are normally on the main consumer unit (breaker box) which means a higher tripping current is required (5mA would cause nuisance tripping) but it also provides protection against someone drilling into a cable.

author: flynwill
author_rank: Regular Contributor
timestamp: December 06, 2016, 04:37:23 am
content: When I was in engineering school the work benches were equipped in exactly that manner, there was a circuit breaker on the back panel and habit was in fact to switch it off when we left for the day and back on when resumed work.The wags among the students devised a way to make this feature a bit of a trap for the unwary, by inserting a small low-voltage electrolytic capacitor into one of the free sockets in the bench. Come in the next day, flip on the switch and BANG (plus a small cloud of very bad smelling smoke).

author: grevan
author_rank: Contributor
timestamp: December 06, 2016, 12:36:51 pm
content: Thanks for everybody that helped me.Now i know, in the US it´s called GFCI.

author: 3db
author_rank: Frequent Contributor
timestamp: December 07, 2016, 10:52:21 am
content: I strongly support @AG6QR suggestion regarding the power off.We used to use those red emergency buttons that remain depressed once activated.We actually had them distributed around the walls on the labs and when pressed they de-energised the supply contactors.3DB