Is this kind of connection to a power connector safe? - Page 1
Forum section: electronics / beginners

author: canol
author_rank: Contributor
timestamp: April 09, 2014, 08:31:53 am
content: Hello,Below is a picture of a power connector connection taken from one of the EEVblog videos. We are using the exact same power connector in our device. But we are having difficulty trying to do a safe connection from this connector to our power supply.You can see the power connector from different angles here, it is a commonly used connector I think since I see it everywhere with different brand names:http://www.arcadebits.com.au/power/53-power-socket-with-switch-and-fuse.htmlI wanted to take this device's connection as an example for our own connection but there is a pretty big exposed metal there which I pointed out on the image above. It carries the "line voltage", not the neutral or ground voltage. Isn't this unsafe?

author: Psi
author_rank: Super Contributor
timestamp: April 09, 2014, 08:56:06 am
content: Yeah, it's unsafe.But my guess is that it falls between cracks in the regulations.i.e, they might say something like 'all mains connections must be protected from physical contact'So all the spade terminals get protection but that bit of metal is part of the connector itself, so not actually a "connection".

author: david77
author_rank: Frequent Contributor
timestamp: April 09, 2014, 09:04:06 am
content: It's not unsafe as such. Wires have to be isolated as they could come loose and touch other things, thereby putting mains voltage on things that could be touched by the user from the outside like a connector or something. This metal strip is highly unlikely to do that, even if it came loose on one side it couldn't touch anything.But if somebody was poking around inside the case they could touch it and get a shock, that is true.As most things seem to be designed to avoid that risk these days, it would appear to be a bit of an oversight not to insulate it.Then again you shouldn't be poking around inside a live device willy-nilly anyway, and if you do you should know the risks, so from my point of view it's not ideal but also not a big deal.

author: David_AVD
author_rank: Super Contributor
timestamp: April 09, 2014, 09:18:05 am
content: I don't believe the exposed metal is against any Australian standard as it's internal and not exactly flapping in the breeze.

author: Monkeh
author_rank: Super Contributor
timestamp: April 09, 2014, 09:20:31 am
content: It's inside the device, where's the concern?

author: canol
author_rank: Contributor
timestamp: April 09, 2014, 10:22:39 am
content: From what I understand from your posts it is pretty safe for user's point of view. Maybe some ground cable might come loose and touch the exposed metal but in that case it would blow the fuse, I guess...But it is still a concern for us engineers. Currently we are in prototyping stage and we do a lot of arrangements inside the device and we sometimes forget unplugging it before doing stuff. So our hand might accidentally touch that exposed metal.Maybe we can cover it via tapes during our prototype development and not think about it during shipments since it is safe for users.This is our first product and we are all new graduates (there is one electrical engineer in the team) so we don't know if we are doing precautions too much or too littleActually I am considering opening a topic about the basic precautions engineers need to take when designing electronics devices (especially the interior of the device, cables/connector connections, grounding the body etc). Maybe it might even be a new video idea for Dave

author: Monkeh
author_rank: Super Contributor
timestamp: April 09, 2014, 11:01:22 am
content: Quote from: canol on April 09, 2014, 10:22:39 amUse hot glue. Fairly common practice even in production, won't slide off.

author: nihilism
author_rank: Regular Contributor
timestamp: April 09, 2014, 11:17:18 am
content: Quote from: canol on April 09, 2014, 10:22:39 amSounds like your oh&s procedures aren't up to scratch there.

author: amyk
author_rank: Super Contributor
timestamp: April 09, 2014, 01:06:28 pm
content: Quote from: david77 on April 09, 2014, 09:04:06 amAgreed. Things like the PSU boards on monitors will also have exposed metal on the back of the IEC connector; it's no problem since it's inside a case and if you have to work on it live then you train yourself not to go near that area.

author: electronics man
author_rank: Frequent Contributor
timestamp: April 09, 2014, 01:12:36 pm
content: Quote from: amyk on April 09, 2014, 01:06:28 pmor you use an isolation transformer

author: wraper
author_rank: Unknown
timestamp: April 09, 2014, 01:44:16 pm
content: Just regular IEC connector with built in fuse holder.

author: chipwitch
author_rank: Frequent Contributor
timestamp: April 09, 2014, 02:21:11 pm
content: It's perfectly safe. Ever see the inside of an electrical panel? It's not"exposed"if it's inside an enclosure. You'd be hard-pressed to find no exposed line voltages in most modern appliances and devices. It isn't practical to insulate against every conceivable danger, electrical or otherwise.

author: rdl
author_rank: Super Contributor
timestamp: April 09, 2014, 02:23:18 pm
content: I don't know how common this is among other manufacturers, but Schurter make these molded covers for some of their AC inlet modules. I use one of their IEC input modules with a built-in fuse holder and one of this type of insulating covers. I use a little silicone or hot glue to hold it in place.http://www.mouser.com/Schurter/_/N-1z0zpei?Keyword=insulation

author: electronics man
author_rank: Frequent Contributor
timestamp: April 09, 2014, 02:25:46 pm
content: Quote from: chipwitch on April 09, 2014, 02:21:11 pmjust think about every single psu cuircuit board, the traces and the solder joints are not insulated, its exactly the same

author: ResR
author_rank: Regular Contributor
timestamp: April 09, 2014, 02:33:29 pm
content: Quote from: chipwitch on April 09, 2014, 02:21:11 pmAnd there's even DC involved that is ten times as dangerous as AC.

author: AlfBaz
author_rank: Super Contributor
timestamp: April 09, 2014, 06:59:41 pm
content: Here in Australia the requirement for electrical enclosures, which I believe now also includes the insides of devices, any part of the circuit containing voltages above Extra low voltage (50VAC 120V ripple free DC) have to be at least IP20 rated, which basically means inaccessible to fingers.As lot of our Oz standards have (IEC or ISO or both?) equivalents you'll see this as mandatory in a large part of the world.Lots of contactors, relays, Circuit breakers and other electrical devices now come with measures to make them IP20. If it's impractical to protect portions of built circuits then it's usual to place see-through perspex covers over those circuits.What's not clear to me is the difference with one of the above perspex shields which have to be "unscrewed" to gain access and the cover on an electrical device that has to be "unscrewed"In electrical cabinets, I have seen micro switches that knock power off to the circuit in question if a cover is removed. As this is impractical to implement in a device it may well be the reason why IP20 protection is employed in them

author: LukeW
author_rank: Frequent Contributor
timestamp: April 10, 2014, 12:40:54 am
content: QuoteMaybe you could get this:http://www.amazon.com/The-Origin-Of-Species-Anniversary/dp/0451529065/Anyway, if you do have to do "live work" on the inside of the device with the cover off, and you do have to probe the live device with instruments etc while it is running and it is not practical to avoid this:- Be careful!- Don't stick your fingers anywhere near the IEC connector or mains SMPS components.- Try and have somebody else around when working, if practical.- Learn first aid, for you and those you work around.- Make sure you have a RCD at the local distribution board closest to you, and make sure it works. If you're in Australia this should be required by law anyway, but it may be missing if you are in an old building.

author: ludzinc
author_rank: Unknown
timestamp: April 10, 2014, 01:23:16 am
content: Not sure about the rest of the world, but here in Oz, grab yourself a copy of AS/NZS 60950 Information technology equipment - Safety - General requirements (IEC 60950-1, Ed. 2.0 (2005), MOD) - the guidelines in there will set you straight.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 10, 2014, 02:59:39 am
content: Quote from: chipwitch on April 09, 2014, 02:21:11 pmAnd then,there are the "cordless" electric kettles,which have a base with bare conductors recessed into them.If you are very lucky,they will actually have some kind of switch operated by the kettles presence or otherwise,& it you are very,very,lucky,it will be in the Active line.If you are right up there with Lotto winners,it will be a DPST switch,but don't hold your breath.

author: pickle9000
author_rank: Super Contributor
timestamp: April 10, 2014, 04:02:56 am
content: In an industrial situationIn Canada you'd probably want to see a Nomex insulator, easy to install and long lasting. A separation is desirable (a plate running down the middle of your box) if you are switching mains voltages and ideally you would like to keep your low voltage pcb's away from that. Even so a simple Nomex card (basically like fireproof cardboard) would suffice if fastened correctly.In reality, provided the case/box is screwed together and rated correctly you can get away with some undesirable setups. If the case is not screwed (has a door) then it needs to be isolated.

author: LukeW
author_rank: Frequent Contributor
timestamp: April 10, 2014, 06:16:16 am
content: Quote from: ludzinc on April 10, 2014, 01:23:16 amAnd how much does that cost, just to read the standard?