Polarized vs Non-Polarized Mains input - Page 1
Forum section: electronics / beginners

author: staze
author_rank: Frequent Contributor
timestamp: October 06, 2013, 07:07:21 am
content: So, question. And maybe it's just late, and I can't grok this at the moment... but I can't seem to figure out a logical reason why some devices (Flat panel tv's, stereo receivers, etc), have polarized IEC C7 mains inputs, where other things (other flat panel TV's, laptops, etc), have non-polarized IEC C7 mains inputs.Is this just that the designers are grounding the device to the "known" neutral side? Or is there something else going on?

author: Bored@Work
author_rank: Super Contributor
timestamp: October 06, 2013, 07:20:13 am
content: Polarized is overrated. There are large parts of the world where they use non-polarized main sockets. As a consequence, any manufacturer who plans to sell on a global scale has to design their stuff in a way that polarity of the mains input doesn't matter. If it does matter than it is for a limited market.Polarized C7 on one side makes only sense when the mains plug on the other side is also polarized. Otherwise it is just a joke one can sometimes see. It is in fact a warning sign that the manufacturer doesn't know what he is doing.

author: Psi
author_rank: Super Contributor
timestamp: October 06, 2013, 07:37:29 am
content: It's probably more to do with connector manufactures.If a connector company is designing a new 2pin plug/socket it's better for them to make it polarized.That way it's usable for a wider range of applications and customers.If a device manufacture needs a connector for their product, but doesn't care about polarized vs non-polarized, they may still pick a polarized connector if it's cheaper or suits their needs in other ways. But if the device manufacture needs a polarized connector then they can't use non-polarized.This favourability of polarized connectors leads to a wider range being available and makes it common for them to end up in places where their not strictly needed

author: AndyC_772
author_rank: Super Contributor
timestamp: October 06, 2013, 07:42:12 am
content: It's probably more to do with whether or not a device requires an earth connection. If it's earthed, use a 3 pin connector which is inherently polarised. If no earth is required, save space and use a 2 pin.

author: AndrejaKo
author_rank: Frequent Contributor
timestamp: October 06, 2013, 07:44:47 am
content: Quote from: AndyC_772 on October 06, 2013, 07:42:12 amWhy would a 3 pin connector be inherently polarized? For example there's the Italian mains connector that's 3 pin and not polarized. Something like that can easily be made on the device side as well, if non-polarization is wanted.

author: Stonent
author_rank: Super Contributor
timestamp: October 06, 2013, 07:46:11 am
content: Quote from: Bored@Work on October 06, 2013, 07:20:13 amBefore I started hanging out here I never really understood the point of polarizing an AC plug because I figured, well the electrical polarity flips so it doesn't matter. But now understand that AC isn't just simply a battery being flipped back to front constantly but one side going positive relative to a fixed point and then negative relative to a fixed point rather than AC being used as peak to peak voltage.And also because of that, you have a zero point to work off of that never has electricity going at you. So you can safely have one hand on your electric oven and grab a piece of toast from your toaster with no possibility for electrical potential between them.

author: Stonent
author_rank: Super Contributor
timestamp: October 06, 2013, 07:48:26 am
content: Quote from: AndrejaKo on October 06, 2013, 07:44:47 amOn the inline 3 pin connector, the chassis would be grounded to the center pin which would always be in the center position and the reversing of the hot and neutral wouldn't matter.

author: Stonent
author_rank: Super Contributor
timestamp: October 06, 2013, 07:55:27 am
content: Quote from: Bored@Work on October 06, 2013, 07:20:13 amNow I realize that as a kid what a bad thing it was for me to force a non polarized plug into the polarized receptacle on the appliance when I lost the original cord, even one time hacking away at a shaver cord to make it work in a C7 connection.

author: Bored@Work
author_rank: Super Contributor
timestamp: October 06, 2013, 08:01:05 am
content: Quote from: Stonent on October 06, 2013, 07:46:11 amThat is a dangerous assumption, because things get wrongly wired. If you live in polarized land and blindly trust that everything is always wired correctly you can have a rude awakening. Bzzzzzzzt.

author: AndyC_772
author_rank: Super Contributor
timestamp: October 06, 2013, 08:04:04 am
content: Quote from: AndrejaKo on October 06, 2013, 07:44:47 amThe world uses 3 pin IEC mains connectors. They just do, it's a standard and it works. Everywhere I've ever worked has a pile of cables with a (local) mains plug on one end and an IEC socket on the other, and I can just grab one whenever I need to plug in any appliance.If I were designing a product, why would I even consider using a different connector unless there wasn't physically enough room for it?

author: IanB
author_rank: Super Contributor
timestamp: October 06, 2013, 08:12:11 am
content: Quote from: AndyC_772 on October 06, 2013, 08:04:04 amRight, but in much of Europe the local mains plug can be inserted either way round and this negates the inherent polarization of the IEC connector.

author: G7PSK
author_rank: Super Contributor
timestamp: October 06, 2013, 08:47:19 am
content: I have some equipment that uses a IEC socket on it that does not have the earth pin fitted. I suppose that is due to the IEC socket is pretty well ubiquitous these days all around the world and as the equipment is multi voltage SMP and double insulated it does not require the earth pin but wherever I go in the world I will be able to locally source a lead for it. The manufacture of IEC plugs with the earth pin left out must save how much per unit? not a lot any way, there is a problem with them though the plug retention is not all that good.

author: Stonent
author_rank: Super Contributor
timestamp: October 06, 2013, 09:51:22 am
content: Quote from: Bored@Work on October 06, 2013, 08:01:05 amTrue.*As long as all the wiring is correct.

author: Zero999
author_rank: Super Contributor
timestamp: October 06, 2013, 11:26:25 am
content: I love the comments about the wiring being incorrect. The truth is, any wiring fault can be dangerous, especially reversal of the earth and phase connections. Reversal of the live and neutral connections is only a problem if the device is earthed and there's a protective element such as a fuse, switch or breaker which only interrupts the phase side. If it's wired correctly, the protection in the fixed wiring (RCD/GFCI, circuit breaker etc.) will normally provide adequate protection.

author: staze
author_rank: Frequent Contributor
timestamp: October 07, 2013, 04:03:42 am
content: So the issue really is just laziness on the designers part? I realize standard 3 prong IEC connectors are the norm, but C7 is pretty common here in the states, both polarized and not (Playstation 1 and 2, Sharp TV's, Vizio TVs, stereo amps, all commonly have polarized C7 power connectors).But from what I understand, there wouldn't be any real HARM in plugging something in with the wrong polarity, it could just be a safety hazard since the neutral would likely be fused (or switched) at that point, yes?

author: Unknown
author_rank: Unknown
timestamp: October 07, 2013, 04:18:37 am
content: Quote from: Hero999 on October 06, 2013, 11:26:25 amReversing earth and phase will prevent equipment from working, something that usually prompts people to ask a tech to investigate. Reversing earth and neutral will trip the RCD/GFCI (if fitted) as soon as the power is switched on, something that will also attract attention. Reversing phase and neutral can go unnoticed until someone plugs in something that assumes correct polarity.

author: staze
author_rank: Frequent Contributor
timestamp: October 07, 2013, 05:20:24 am
content: Quote from: alm on October 07, 2013, 04:18:37 amYes... which C7 connectors non-polarized, are just neutral and phase. Polarized just force which is on which "side". So it's just... bad design/laziness?

author: ciccio
author_rank: Frequent Contributor
timestamp: October 07, 2013, 01:30:01 pm
content: I must admit I've never seen a polarized C7 connector, but most devices that have double insulation and a switching power supply have internal mains filters that connects secondary to primary (usually a RC series network).Noise cannot be sent to ground (no ground connector) but is sento to neutral (usually) because neutral has a lower impedance to ground than phase.So the equipment needs a polarized plug, or it will not meet it's EMC specifications (neutral must go to neutral)The other side of the mains cable (the wall socket) may be polarized (as in US sockets) or not (as in most european sockets when plugged with a 2 pin plug)In the last case maybe the EMC specs are not respected, but this is not a concern of the equipment manufacturer...