Appliance power switch in neutral line - legal in aus? - Page 1
Forum section: electronics / general

author: Circlotron
author_rank: Super Contributor
timestamp: February 16, 2021, 12:34:08 pm
content: The other day I bought this small 10 watt Peavey guitar amplifier. Naturally I opened it up, as you do. First thing i noticed was the AC power switch is in the neutral line, and the active goes to a fuse then straight to the power transformer. i understand the safety aspects of this, but is this even legal in Australia?

author: RoadRunner
author_rank: Frequent Contributor
timestamp: February 16, 2021, 12:50:03 pm
content: Australia is upside down. So

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 16, 2021, 01:27:49 pm
content: What's with the "trans tube" when I don't see any tubes? Is that marketing for a FET based amplifier since FETs are basically the solid state equivalent of triodes?

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: February 16, 2021, 02:33:44 pm
content: Quote from: NiHaoMike on February 16, 2021, 01:27:49 pmhttps://peavey.com/TransTube-Series(Don't Google "trans tube" unless you want to end up in a very different place)

author: bjbb
author_rank: Contributor
timestamp: February 16, 2021, 06:36:00 pm
content: AUZ/NZS 3000 -> see 3.8.3: phase (line) is brown and neutral is blue, so your analysis is correct. Current interrupt for appliances in the neutral input can be allowed for some standards and some construction; e.g., for Class II equipment where exposed metal is not referenced to a protective earthing and the equipment does not rely on a ground bond. Otherwise, current interrupt device on neutral wire is typically disallowed unless the interrupt device is dual-pole; ie, both line and neutral are being opened.But the puzzle is the c-tick mark. These are deprecated per the RCM marking requirements. But the ACMA has allowed manufacturers of some stuff to continue using c-tick labels until stock has been exhausted. This should not apply for your equipment because it is printed on-demand. So something does not smell good.Once again, I implore our glorious Dave to find a local accredited regulatory engineer and do a series on corporate compliance and product conformity.

author: ozcar
author_rank: Frequent Contributor
timestamp: February 16, 2021, 09:09:58 pm
content: For a start, I would check that the brown wire really is the active. I suspect it is, but anything is possible.I have absolutely no idea what the regulations might say- in fact I'm not even sure that regulations would be the same in all states in Australia. For example, a few years ago plug-in timers suddenly became unavailable in NSW, but were still available in other states (so, yes, residents in Tweed Heads (NSW) could step over the road into Coolangatta (QLD), and stock up on such banned devices). One supplier said that this was because some regulation had changed and that double-pole switching was now mandated. This was the subject of a very long thread on another forum (Whirlpool), but nobody could point to some specific regulation that had changed, nor figure out why NSW would be different to other states.My observations:Some "appliances" have no switch at all. There happens to be such a device sitting on the shelf in the background in the third photo posted above (the radio).That very same device in the photo is an example of a device where the active and neutral can be interchanged depending on the way it is plugged in (Aussie mains plugs only fit one way around, but the plug on the other end of the detachable cord can be rotated through 180 degrees).Some devices have switches in both active and neutral, but for different purposes. For example I have a garden tool with a trigger switch in the active, and another switch in the neutral that acts as a safety device to prevent the unwise from making certain mechanical adjustments when the thing is running.Are fuses any different? In another thread here, somebody asked why fuses seemed to be always in the neutralhttps://www.eevblog.com/forum/chat/two-mysteries-of-chinese-ebay-products/. If the wire colour coding is correct, then the guitar amplifier may be a counter example (there is a fuse on the PCB adjacent to the terminal that the brown wire goes to).As for C-tick or RCM marking, is there some way for consumers to check these?

author: amyk
author_rank: Super Contributor
timestamp: February 17, 2021, 12:38:26 am
content: Different places have different wiring regulations, and it might even be impossible to satisfy them all simultaneously because they conflict, but ultimately everyone has to follow the same laws of physics...

author: AntiProtonBoy
author_rank: Frequent Contributor
timestamp: February 17, 2021, 02:37:25 am
content: Quote from: bjbb on February 16, 2021, 06:36:00 pmLooks like the amp does not meet the Class II equipment exemption, as defined above, which means the wiring should be considered dodgy. That pretty much settles it, I reckon.

author: Someone
author_rank: Super Contributor
timestamp: February 17, 2021, 03:08:02 am
content: Quote from: AntiProtonBoy on February 17, 2021, 02:37:25 amhttps://reddwarf.fandom.com/wiki/Space_Corps_DirectivesAppliances are AS3100, not AS3000, and then may have a bunch of other more specific standards applicable. Australia has some oddball requirements from an international perspective, but the example "problems" above are actually a-ok for Australian compliance.p.s. I could quote the nonsense 3.8.3 clause here, but its not quite as funny as the above. Asking random people on the internet for serious advice, get random nonsense replies.

author: Berni
author_rank: Super Contributor
timestamp: February 17, 2021, 06:57:46 am
content: This sort of thing is even legal in the EU where every silly little thing is illegal for some stupid reason.We have plugs that are symmetrical so you can rotate it 180 degrees and it still fits. So you have a 50/50 chance of your switch being on the live or the neutral side. Since IEC C13 power connectors are also commonly used this also means the live and neutral might swap on those too. Yeah i blame the Germans for these damn schuko plugs. But in general you see a lot of double pole power switches that solve this problem.But yeah putting the switch on the neutral wire on purpose is a ridiculous move, especially with a non detachable power cord in a country where the live and neutral can't swap places due to plug design.

author: dave_k
author_rank: Frequent Contributor
timestamp: February 17, 2021, 10:48:03 am
content: 240V - C0HZ .. yeh nah not dodgy at all.

author: GlennSprigg
author_rank: Super Contributor
timestamp: February 17, 2021, 11:59:31 am
content: Well it certainly isn't the 'norm' here in Australia. Just assembly slackness I think.Often, as mentioned, we often see double-pole switches, for various reasons. As someone stated, I wouldcheck that the 'blue' is 'actually' Active or not, from the wall-plug? (Blue is normally Neutral). We don't havethe problem of 50/50 with our plugs, as the pins on our plugs are always angled/orientated for one directiononly insertion, with or without an Earth pin.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 17, 2021, 01:41:18 pm
content: The normal reaction from Technicians would be to reconfigure the connections so the switch & fuse are both in the Active line.(Techs don't go "Aieee! the high voltage, fear, terror!")Certainly, for many years, switching the Neutral was pretty much forbidden, as points that you might expect to be at a zero, or very low potential, will be at Mains potential via the power transformer primary.A lot of stuff like this slips past, & has for years.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 01, 2021, 02:59:23 pm
content: I googled zebrastrip once while my female assistant was sat next to me- embarrassing... Particularly as she thought we should check it out.

author: Medved
author_rank: Contributor
timestamp: March 10, 2021, 12:10:16 am
content: There was one reason, coming from the real high impedance tube era:The switch has to be located on the front panel, along all the volume control and other controls handling small signals at high impedance.There is a parasitic capacitance between wires or components in the proximity to each other.When wiring the switch to the Phase side, there is the full AC mains voltage between the wires to the switch vs all the rest, include the signal wires, so you get mainly the mains hum into your signals.Now if only the Neutral is switched, there is very low potential on the lines towards the switch, so way less hum and noise coupling into the sensitive signal lines.Yes, the correct way is the use of shielding, but that cost money. Just wiring the switch to the Neutral is for free.Safety wise such device should be then treated as "always ON, no disconnect switch", so has to feature means to prevent the mains wire to remain connected while the covers are taken off (e.g. only "just big enough" hole in the back cover to pass the IEC connector, so the connector connected does not allow the cover to come off) and similar. But not sure if such approach would ever fly anymore, given the small size the modern components are...In modern designs the problem is solved by placing the mains power switch onto the back side (just along the IEC connector, so out of reach from the sensitive part; and being there just to satisfy the wording of the Code) and put onto the front panel just some "GoToSleep" pushbutton controls.And it looks strange to me SPST would be allowed with class-II devices.Here it was the exact opposite: Class-II (double insulated or equivalent) must have DP switches, while class-I devices had no limitation, so may use even SP switches even in the Neutral (as the electrical safety was covered by the PE wire, which obviously should have no interruption at all).In fact many appliances (mainly the heating ones, like hot plates, ovens,...) were wired with the control thermostat in the Neutral and the (usually overtemperature) protection cutout element in the phase. The reasoning is, the thermostat is way more likely to fail, because being "clicked" all the time. So may a short circuit happen between the N side and PE (when plugged to non-GFCI circuit), in both ways it will heat up without any control, overheat, so likely trip the protection element in the phase. This phase protection element then cuts the phase input. Of course, if a short to PE happens on the L side, the MCB/fuse trips and shuts the power off.In this way at least some temperature limiting device is in either input wire, so even when L and N get swapped, the thing remains safe even when short to PE, not causing MCB to trip, happens.So I thing yes, it could be OK to connect the SP switching element only into N wire, but you should have good proof it is for your case the safest option. So won't fly for a combo anymore, I guess...

author: TimFox
author_rank: Super Contributor
timestamp: March 10, 2021, 12:14:16 am
content: On vacuum tube radios, the power switch was usually mounted on the back of the volume control, so that one turned the unit on by twisting the single knob clockwise off the detent (in the switch), then turning it back down after the tubes warm up.

author: Medved
author_rank: Contributor
timestamp: March 10, 2021, 12:31:08 am
content: Quote from: TimFox on March 10, 2021, 12:14:16 amThere it was a must to have it on the "cold" side, as it was really barely 1cm from the signal with no shielding within the pot whatsoever. Plus these had to be really dirt cheap (talk about "planned obsolescence" being a new thing, when these radios connected the scale illumination bulb in a way once it burned, it took the rectifier tube with it in a short time; circuit originated from ca 1936).But even on the combos it played a role, because those usually required way better S/N then the radios, so even if it was 5cm away, it still caused hum. Plus often the wires were in various bundles, so not that far apart.

author: TimFox
author_rank: Super Contributor
timestamp: March 10, 2021, 01:50:33 am
content: The 35 V 150 mA heater rectifiers used in US 110 V series-string radios had a tap for the panel bulb to allow operation with a burned-out bulb. Radio repairmen were urged to replace the bulb to impress the client with an obvious improvement.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 10, 2021, 01:54:52 am
content: Quote from: Medved on March 10, 2021, 12:31:08 amI can only speak from the Australian viewpoint, where the standard in those years was to use a transformer power supply.Oz tube radios switched the active ("hot") side of the Mains, removing power from the transformer primary.The switch was normally in a separate part of the pot body, with just the mechanical part that operated the switch protruding between them.In the usual 4/5 "valve" superhet, the audio out of the detector is at a relatively high level, thanks to the substantial IF gain, so any hum induced was a long way down, in comparison.In any case, the "cold" side of the Mains in a transformer power supply did not return to chassis earth (ground), the common connection between those being at the Mains entry to the house, allowing hum or other noise pickup on the house wiring, if that was really a concern.The only time I have seen the dial illumination lamps connected directly to the rectifier are with those rectifiers which were directly heated with 5v.Probably to use up old stock, some older radios using these had 5v dial lamps directly connected to the rectifier filaments-------andthe HT line!!A "trap for young players", indeed!When a dial lamp burnt out, it normally went open circuit, so I fail to see how that could affect the life of the rectifier tube in such a design.If the insulation failed, maybe that would do it.

author: james_s
author_rank: Super Contributor
timestamp: March 10, 2021, 02:09:55 am
content: Quote from: vk6zgo on March 10, 2021, 01:54:52 amIIRC the bulb was wired in parallel with a tapped segment of the tube heater, so if the bulb burns out the voltage across that segment rises due to the higher resistance. This causes that part of the heater to run hotter and burn out.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 10, 2021, 06:44:46 am
content: Quote from: james_s on March 10, 2021, 02:09:55 amOK, it seems that in Oz, we did a lot of things differently.Radios were quite a lot more expensive, so less drive to go cheap.The tube factories ramped up during WW2, concentrating upon 6v heater tubes, so were reluctant to start making series string types in the postwar period.On top of that, we had the problems of a higher supply voltage compared to the USA, so would have needed to produce tubes for some exotic heater voltages & use barreters, or big series resistors, like the UK & Europe.It was just easier to go with power transformers, allowing fullwave rectification, easier HT filtering, higher HT for greater output stage efficiency, & a "cold chassis", removing the necessity of a lot of the extra insulation necessary on "hot chassis" designs.