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Post by MartinT on Jul 13, 2014 10:07:15 GMT
The "poor" figures are for the AG500 UPS. This figure is not poor for a commercial UPS which typically feeds a computer SMPS, so distortion is not an issue. I don't know how you arrive at that conclusion, but the figure is poor for a hi-fi application, especially when it's in danger of being worse than the incoming mains. |
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Post by MartinT on Jul 13, 2014 10:13:37 GMT
An rcb on the supply side of an isolating transformer will not be tripped by a short on the output side This is wrong. A correctly rated RCB will trip at the kind of instantaneous load that a shorted transformer will present.
As already said, a transformer transforms, including a shorted load. It's exactly the same as if a shorted secondary winding in equipment will blow either the fuse or the RCB, or often both. Whether we're talking about a 1:1 ratio BPS, or an equipment 1:10 ratio step-down transformer, the principle is the same.
However, all equipment must be fuse protected - that is a must. |
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Post by Dr Bunsen Honeydew on Jul 13, 2014 10:22:23 GMT
Very good post Martin but still some misunderstanding. A fuse is necessary with Class I appliance regs but with Class II it actually breaks the regs. Also Class II constructions takes away any potential risks (no matter how extreme) with the BMU (balanced mains unit) itself. en.wikipedia.org/wiki/Appliance_classesEverything NVA is built to Class II regs. |
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Post by Deleted on Jul 13, 2014 10:43:02 GMT
Not just for Pinkie but as a general query about equipment. I am quite sure that most of us ex-pats use stuff designed for the UK but now of course, run under a different system here in France. No fused plugs. Can we assume that there will always be internal fuses and that using the equipment is not in any way dangerous? Certainly, I have never given it a thought before. On the main system, I have kept the fused mains plugs and use an extension block but every other system has been changed to French plugs. Sorry if this is not directly related to the thread  |
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Post by Dr Bunsen Honeydew on Jul 13, 2014 11:12:56 GMT
France uses a sensible radial system, we use a stupid ring system. So due to over current possibilities with a ring (which some people consider to be inherently dangerous in itself) we should have fuse in the plug. But that was decided in wire fuse days, with current fast trip RCBs it really is not necessary. en.wikipedia.org/wiki/Ring_circuitRead history and use and safety to see what a bad decision we made and why. To answer your question - no there is no danger or compatibility problem, just think yourself lucky you have a sensible system with a good plug (Schuko) compared with our crap system and plug. AND yours will make you system sound better which is why people put in dedicated radial circuits for their hi-fi. Pre war with the 2 - 5 and 15amp separate radials using BS546 we had a good system with the best plug ever made, and we threw it away because we were broke as a country and wanted to save money. |
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Post by Deleted on Jul 13, 2014 11:24:32 GMT
France uses a sensible radial system, we use a stupid ring system. So due to over current possibilities with a ring (which some people consider to be inherently dangerous in itself) we should have fuse in the plug. But that was decided in wire fuse days, with current fast trip RCBs it really is not necessary. en.wikipedia.org/wiki/Ring_circuitRead history and use and safety to see what a bad decision we made and why. To answer your question - no there is no danger or compatibility problem, just think yourself lucky you have a sensible system with a good plug (Schuko) compared with our crap system and plug. AND yours will make you system sound better which is why people put in dedicated radial circuits for their hi-fi. Pre war with the 2 - 5 and 15amp separate radials using BS546 we had a good system with the best plug ever made, and we threw it away because we were broke as a country and wanted to save money. Thank you. I had intended to do the sensible thing and change all the plugs so now I will have to lay out some dosh  |
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Post by pinkie on Jul 13, 2014 12:29:13 GMT
An rcb on the supply side of an isolating transformer will not be tripped by a short on the output side This is wrong. A correctly rated RCB will trip at the kind of instantaneous load that a shorted transformer will present.
As already said, a transformer transforms, including a shorted load. It's exactly the same as if a shorted secondary winding in equipment will blow either the fuse or the RCB, or often both. Whether we're talking about a 1:1 ratio BPS, or an equipment 1:10 ratio step-down transformer, the principle is the same.
However, all equipment must be fuse protected - that is a must. Thank you Martin. Are you absolutely sure? Can you explain to me how this device works? www.ebay.co.uk/itm/ISOLATION-TRANSFORMER-for-RCD-Testing-Test-and-Tag-/110832140253 |
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Post by pinkie on Jul 13, 2014 12:34:28 GMT
Very good post Martin but still some misunderstanding. A fuse is necessary with Class I appliance regs but with Class II it actually breaks the regs. Also Class II constructions takes away any potential risks (no matter how extreme) with the BMU (balanced mains unit) itself. en.wikipedia.org/wiki/Appliance_classesEverything NVA is built to Class II regs. I don't think the issue is the fusing in the transformer. Your NVA transformer may be different, but currently available devices have several 3 pin sockets. Into this a user would plug their conventional mains lead. Lets assume its one of the common class 1 devices. It will be protected by a suitable fuse to prevent a fire in the cable. Say a 3 amp fuse, which if there is a fault blows and stops any current flowing down the wire on the right hand pin. If the lead is plugged into the mains, there is 240vAC on the right pin and 0v (ignoring DC offset) on the left pin. If the fuse on the right pin blows there is no longer any current flowing through the wire. If the same plug is plugged into a balanced transformer there is 120v on both the right pin and the left pin. When the fuse blows on the right pin, there remains 120v on the wire to the left pin. The device fuse, not the transformer fuse, has failed to provide protection. |
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Post by MartinT on Jul 13, 2014 12:47:04 GMT
A fuse is necessary with Class I appliance regs but with Class II it actually breaks the regs. Ah yes, quite so. However I believe UK law still requires a fused plug, even on Class II equipment? |
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Post by Dr Bunsen Honeydew on Jul 13, 2014 13:23:25 GMT
Yes, in theory to protect the cable. But speak to anyone in the mains wiring know and they will tell you that as long as you have a new RCB(D) consumer unit then the fuse wont even blow as the RCB(D) has protected it. So there is little point. The safety regs were written when houses had wire fuses like in the plugs, or even with earth trips the fuse may go, but very unlikely with a RCB(D). So in reality now-a-days having a fuse following another fuse following a RCB(D) is music damaging overkill, so surely a RCB(D) following a RCB(D) is the same.
EDIT - the law only applies to ring circuits. Build a house a la Francais with radials and Schuko and it is quite legal not to have plug fuses.
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Post by Dr Bunsen Honeydew on Jul 13, 2014 13:28:06 GMT
Very good post Martin but still some misunderstanding. A fuse is necessary with Class I appliance regs but with Class II it actually breaks the regs. Also Class II constructions takes away any potential risks (no matter how extreme) with the BMU (balanced mains unit) itself. en.wikipedia.org/wiki/Appliance_classesEverything NVA is built to Class II regs. I don't think the issue is the fusing in the transformer. Your NVA transformer may be different, but currently available devices have several 3 pin sockets. Into this a user would plug their conventional mains lead. Lets assume its one of the common class 1 devices. It will be protected by a suitable fuse to prevent a fire in the cable. Say a 3 amp fuse, which if there is a fault blows and stops any current flowing down the wire on the right hand pin. If the lead is plugged into the mains, there is 240vAC on the right pin and 0v (ignoring DC offset) on the left pin. If the fuse on the right pin blows there is no longer any current flowing through the wire. If the same plug is plugged into a balanced transformer there is 120v on both the right pin and the left pin. When the fuse blows on the right pin, there remains 120v on the wire to the left pin. The device fuse, not the transformer fuse, has failed to provide protection. Partial knowledge and wrong interpretation nonsense! |
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Post by Barry on Jul 13, 2014 15:40:34 GMT
Very good post Martin but still some misunderstanding. A fuse is necessary with Class I appliance regs but with Class II it actually breaks the regs. Also Class II constructions takes away any potential risks (no matter how extreme) with the BMU (balanced mains unit) itself. en.wikipedia.org/wiki/Appliance_classesEverything NVA is built to Class II regs. I don't think the issue is the fusing in the transformer. Your NVA transformer may be different, but currently available devices have several 3 pin sockets. Into this a user would plug their conventional mains lead. Lets assume its one of the common class 1 devices. It will be protected by a suitable fuse to prevent a fire in the cable. Say a 3 amp fuse, which if there is a fault blows and stops any current flowing down the wire on the right hand pin. If the lead is plugged into the mains, there is 240vAC on the right pin and 0v (ignoring DC offset) on the left pin. If the fuse on the right pin blows there is no longer any current flowing through the wire. If the same plug is plugged into a balanced transformer there is 120v on both the right pin and the left pin. When the fuse blows on the right pin, there remains 120v on the wire to the left pin. The device fuse, not the transformer fuse, has failed to provide protection. If you use a centre-tapped balanced transformer, both the secondary terminals are regarded as "phase" terminals (since they are both at 120V with respect to earth). It follows therefore that both terminals should be fused. This is the recommendation of the IEE in the UK. I'm not sure what regulations apply in France or elsewhere. |
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Post by Dr Bunsen Honeydew on Jul 13, 2014 15:48:15 GMT
There are so many people here with a *little* knowledge that it really is becoming a dangerous place, if you follow the saying.
If a fuse blows in the plug on a balanced circuit then I can guarantee the RCB(D) on the supply side will have tripped before it, or as a result of it.
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Post by pinkie on Jul 13, 2014 17:14:51 GMT
With all changes to the electric supply and electrical safety TAS recommends that people consult with a qualified electrician It's a good post, but I fear it will be lost and un-noticed by too many. I would take further steps to protect members. And yourselves. |
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Post by pinkie on Jul 13, 2014 17:24:27 GMT
Richard, you are being challenged because you are being rude. Don't call someone a prick and maybe your advice will be appreciated. No more, please. I didn't call anyone a prick, please re-read the post. It was a generic term as to how I would react. I seriously couldn't give a toss how (a lot of) people take my advice as you see it. In reality I don't presume to advise anyone and I defy you to find any post from me containing advice, my posts contain information. What people do with that information is up to them. I react when that information is challenged for erroneous or fatuous reasons. In response to a criticism of how you did, in fact react. So not unreasonable to link the two |
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Post by pinkie on Jul 13, 2014 17:25:25 GMT
I'm afraid I've had enough of the muppet scientists rudeness and snide comments instead of explanations of the type provided by gentlemen like Barry (and my patient expert friends outside the forum). I suspect the Muppet does it to throw up a smokescreen and deflect attention away from fundamental errors like stating that 12v from a car battery is enough to kill you. Likewise the attention seeking posts which breach forum rules and result in moderator edits.
The amount of voltage which will kill you depends on where the voltage (ok - current, I know) flows. If it flows across the heart 60v will usually cause cardiac arrest, although in some exceptional circumstances 30V could. 12v is never going to be lethal in a healthy human. If the current flows through the body without crossing the heart then significantly higher voltages above 300v are survivable. That was why Nikola Tesla recommended keeping one hand in a pocket when working on high voltages, since the path to earth would not be across the heart as a result of the "other" hand touching earth
The fact that isolating transformers are used in PAC testing to protect the main system RCD's whilst testing portable ones demonstrates in a practical way the point. Using a transformer plugged into the mains allows a short to earth on the secondary side of the transformer which has no effect on the RCD's on the primary side. another link for you link
I'll leave you all to it now - be safe!
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Post by Dr Bunsen Honeydew on Jul 13, 2014 17:34:28 GMT
Nonsense, rapid fire RCB(D)s have changed the game for everyone, regs are still written from the days people had to replace bits of wire in the fuse box.
I was stupid the other day and forgot to switch off an amp with case off before picking it up. My thumb went on live I dropped the amp, as it made me jump but the belt was of milli seconds duration as the RCB had tripped. 5amp fuse in the plug was intact, didn't get a chance to blow.
I felt more awake and buzzy for the rest of the day, I should do it more often.
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Post by Dr Bunsen Honeydew on Jul 13, 2014 17:48:06 GMT
In building testing and repairing amps I often short or cross the secondaries (well not that often maybe a couple of times a year). I use a split raii (balanced) step down transformer, and if I do it how ever I do it it trips out my RCB, and this is on the secondary side of the transformer. ANYTHING that happen to create high current flow causes it to trip and OBVIOUSLY that current flow will translate from secondary to primary side of the transformer. So once again you are talking nonsense.
Last week an old tungsten bulb we were still using blew and out went the RCB
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Post by Dr Bunsen Honeydew on Jul 13, 2014 18:24:16 GMT
Well you know what they say about the proof of the pudding, so I decided to make a pudding. 13amp plug with a short wired between neg and earth, so in theory no fuse protection when used on balanced mains. On insertion into the BMU (balanced mains unit) I have here the house RCB(D) immediately tripped. I knew it would happen but when dealing with a pedant you have to cross the "t"s and dot the "i"s.
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Post by MartinT on Jul 13, 2014 20:30:01 GMT
Good practical experiment that, Richard.
However, PLEASE NO-ONE ELSE TRY THIS!
Pinkie - we take your point and will post a warning about tampering with mains power where it's most appropriate.
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