Hot, Neutral and Earth Questions - Page 1
Forum section: electronics / beginners

author: lu1sl234
author_rank: Newbie
timestamp: June 22, 2015, 03:34:06 pm
content: Hi Dave, I have some questions about Hot, Neutral and Earth connections on AC single-phase outlets. Lets assume that any particular electronic you imagine has proper earth grounding.1) Hot - Neutral Inverted:- I know that this affects only safety of the user.- I know this not affect any full AC designs.- It would affect in a particular way any kind of AC-DC converter (considering Neutral to Earth voltage is around zero) or electronics after it?2) Neutral to Earth Voltage:- Is there any particular maximun Neutral to Earth voltage allowed?- It would affect any particular electronic design or it is just for user safety?3) If any of the previous questions result in electronic damage, is there any electronic design to avoid it?Thank you very much!

author: Simon
author_rank: Unknown
timestamp: June 22, 2015, 03:40:49 pm
content: As far as i know swapping neutral and live won't make much different to electronics. The main problem is safety, if you know which is live you can use it as UK plugs are, if you swap live and neutral you loose the use on live and it means where wiring a house if you don't keep sockets consistent you will never know what is what.why are you asking ?

author: lu1sl234
author_rank: Newbie
timestamp: June 22, 2015, 04:18:18 pm
content: Hello! I ask for these reasons:1) I work with medical equipment that ask for this configuration.2) In case of malfunction of the equipment I want to be sure if these rules are just for safety or it can cause real problems.3) I think is good to know if someone says that that was the reason the equipment failed.Thanks

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 22, 2015, 04:29:19 pm
content: First, some of the questions you ask depend on WHERE you are. For example the standards for "hot" and "neutral" are quite different between North America and Europe. If you want sensible and applicable answers, we need to know what country you are in. Complete your user profile at least to identify your country.Your questions seem rather odd. Equipment, especially equipment that is certified for medical use, is designed, constructed, and tested to show that it is wired properly. The only way for someone to claim that swapping hot/neutral was an issue is where there was some "after market" fooling around with the mains wiring. Which seems quite seriously dodgy to begin with.As Simon said, the main reason for keeping hot and neutral in their proper places is safety. Especially medical equipment should be insensitive to full mains voltage on either primary input node. But there should be proper standards and prescribed test methods for ensuring mains wiring safety. You shouldn't have to come to a public forum like this and seek answers to your questions from strangers.

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: June 22, 2015, 04:57:06 pm
content: Quote from: lu1sl234 on June 22, 2015, 04:18:18 pmSome might say that the point of safety is topreventreal problems.Others might say that lack of safety is, in itself, a real problem.Those two groups probably overlap quite a bit.

author: TimFox
author_rank: Super Contributor
timestamp: June 22, 2015, 05:38:24 pm
content: One important reason to keep track of which is actually live (line or neutral) is for circuits with a single-pole switch and/or a single fuse. These should be in the hot side, so that a short to case (very dangerous) will blow the fuse. Otherwise, the fuse only blows on a line-neutral short or excess load current, but the line-case short may not cause high current.

author: Halvmand
author_rank: Regular Contributor
timestamp: June 22, 2015, 11:02:47 pm
content: Quote from: TimFox on June 22, 2015, 05:38:24 pmYep. If inverted the chassis could be live for the amount of time your house's circuit breaker or fuses takes to blow. If a 10 amp fuse is installed, this could take some time. this is determined by the impedance in your circuit. could be minutes.regarding your second question.If you mean earth potential rise in case of fault. Yes there are some rules. these vary from country to country.

author: Shock
author_rank: Super Contributor
timestamp: June 23, 2015, 06:49:56 am
content: It all depends on where you are, here in Australia we use a MEN system, multiple earthed neutral. There are very specific standards to ensure proper wiring.So all your assumptions here would be wrong. While neutral to earth voltage should be zero, you don't go messing about with your mains wiring or testing it without training (especially ground or earth rods) as in certain circumstances you can be electrocuted.

author: houkensjtu
author_rank: Contributor
timestamp: June 23, 2015, 01:04:48 pm
content: For a newbie like me, there are several subtle concepts which REALLY should be clarified clear enough, but it seems it takes centuries to have that done...(1) Those terms "Earth" and "Ground" could have totally different meanings depends on whether one is referring to a "electrical ground" or "electronic ground". By "electrical ground" or earth, I mean those electrical wires PHYSICALLY connected to earth, usually a conductor rod or plate buried in ground. While by "electronic ground", it refers to those reference points during circuit design, they may or may not be PHYSICALLY connected to ground.(2) In case of medical equipment, you may want extra safety, which means normal electrical earthing may be not sufficient. In order to reduce the risk of electric shock, usingisolation transformeris better than connecting directly to earth.BTW I really think the topic related to earth and ground worth some discussion on "Fundamental Friday", hoping Dave could do that!

author: TimFox
author_rank: Super Contributor
timestamp: June 23, 2015, 02:00:53 pm
content: For safety, it might be wise to restrict the wording to:PE = protective earth = green/yellow wire, connected to equipment case, should not carry substantial current.Neutral = AC connection to building ground somewhere, carries current.

author: jeroen79
author_rank: Frequent Contributor
timestamp: June 23, 2015, 05:07:23 pm
content: The only way having live and neutral reversed could be a problem is when a device would use neutral as a 0V reference (instead of positive earth) and either share this with others (through the chassis or a 'ground' connection) or be inconsistent internally with this 0V reference.That could result in a live-neutral short or offering mains voltage to something that is not expecting this. (another device or the user)I can't think of a good reason for this and such a device would be a bad design IMO.Also:Here in the Netherlands mains outlets will accept plugs both ways so there would be a 50% chance of a live/neutral reversal.If this were dangerous even with normal devices then surely our outlets would have been changed long ago.

author: TimFox
author_rank: Super Contributor
timestamp: June 23, 2015, 06:10:35 pm
content: I disagree. With live and neutral connected properly and PE connected to the chassis, with the fuse or breaker in the "live" line, then a dangerous short from line to the chassis should blow the fuse/breaker. With the fuse or breaker in the neutral wire by mistake, a short from line to chassis (not to the neutral) will not blow the fuse.

author: IanB
author_rank: Super Contributor
timestamp: June 23, 2015, 06:52:47 pm
content: In places with symmetrical plugs the mains wiring regulations are going to be arranged so that the orientation of the mains plug in the socket does not affect the safety of the connected device or the wiring.

author: TimFox
author_rank: Super Contributor
timestamp: June 23, 2015, 06:57:05 pm
content: With double pole switches and companion-trip breakers?My worry is for any piece of equipment (electrical or electronic) with a metal case accessible to the user.Double-insulated power tools, for example, should be OK regardless of the plug orientation, but that's a specific type of equipment.

author: IanB
author_rank: Super Contributor
timestamp: June 23, 2015, 07:13:56 pm
content: If the metal chassis or case of a device is grounded then it should not become a shock hazard to anyone touching it. Furthermore, if a live conductor touches the chassis it should cause a fault current large enough to trip the breaker in the distribution panel. Therefore people are protected from shock and wiring is protected from overheating. Is that not so?

author: Monkeh
author_rank: Super Contributor
timestamp: June 23, 2015, 07:21:08 pm
content: Quote from: IanB on June 23, 2015, 07:13:56 pmNo, because you're assuming both the conductor size and the contact between it and the chassis will result in a sufficiently low impedance for the breaker in the panel to trip.