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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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16th Oct 2018, 12:22 pm | #1 |
Heptode
Join Date: Jul 2012
Location: Daylesford, Victoria, Australia
Posts: 674
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Separate current transformer?
A repair café is being set up in my home town, and the organisers have sent me a guide to safety written by the original promoters. It states in slightly odd English that for safety, electrical appliances must not be plugged directly into the mains, but through a "separate current transformer" that has no earth connection, which prevents "unilateral body connection to live parts". Any idea what they mean? Are they talking about an isolation transformer?
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The Waves That Rule Britannia |
16th Oct 2018, 12:36 pm | #2 |
Dekatron
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Re: Separate current transformer?
sounds like an automatically translated text.
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Kevin |
16th Oct 2018, 12:37 pm | #3 |
Dekatron
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Re: Separate current transformer?
I'd guess so. A current transformer wouldn't fit the rest of the wording - but an isolation transformer would.
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16th Oct 2018, 1:42 pm | #4 |
Heptode
Join Date: Dec 2014
Location: Lincoln, Lincolnshire, UK.
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Re: Separate current transformer?
In my opinion - yes!
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16th Oct 2018, 2:21 pm | #5 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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Re: Separate current transformer?
It sounds as though they mean an isolation transformer, with the output "floating" so that you can't receive a shock from touching one side of the "mains".
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16th Oct 2018, 4:14 pm | #6 |
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Re: Separate current transformer?
I hope they don't think that using an isolation transformer makes everything magically safe. It improves safety for live chassis designs; it does nothing at all for everything else, but may give the false impression of safety to those who do not understand.
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16th Oct 2018, 4:32 pm | #7 |
Dekatron
Join Date: Nov 2011
Location: Surrey, UK.
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Re: Separate current transformer?
Agreed- "separate current" as idiom-free "isolated supply"- in other words, someone's cut-and-pasted standard recommendations that were written in another language as a minimum-effort tick-box exercise! Curious- I think of Aussies as practical and down-to-earth, surely there are pertinent national guidelines that don't require the post-Babelfish technical re-interpretation.
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16th Oct 2018, 4:56 pm | #8 |
Dekatron
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Location: Newcastle upon Tyne, Tyne & Wear, UK.
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Re: Separate current transformer?
Hi Sue, I'm sure we would be interested in hearing more about this repair café when it is set up.
The current transformer could be an oblique reference to using a "clamp meter" to give an isolated feed to a DVM when measuring mains currents. Ed |
16th Oct 2018, 9:18 pm | #9 |
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Re: Separate current transformer?
I expect that the phrase 'current transformer' means a transformer of a recent design - i.e. one that is of 'current' manufacture, as opposed to something old and of possibly dubious quality. In the context of its proposed use, safety is obviously paramount - so a new / recently manufactured transformer has been stipulated.
Just an unfortunate mis-application of the word 'current' in the context of something electrical. The transformer will almost certainly be an isolating transformer. Al. |
16th Oct 2018, 9:24 pm | #10 | |
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Re: Separate current transformer?
Quote:
Al. |
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16th Oct 2018, 9:29 pm | #11 |
Dekatron
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Location: Croydon, Surrey, UK.
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Re: Separate current transformer?
I wonder if it has been translated from Chinese? You can get some very odd phrasing!
Most likely an isolating transformer. However it might be an idea to find out exactly who is going to install this equipment and as stated in post #6 an isolating transformer does NOT make everything safe. 230V coming out of an isolation transformer is still 230V and still hurts (or worse)!
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17th Oct 2018, 12:34 am | #12 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
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Re: Separate current transformer?
It (the conditions re the 'current transformer') will have been translated from Dutch as the "Repair Cafe" foundation is headquartered in Amsterdam (and that is assuming this set up is based on the foundation of that name - there are others).
Whoever is setting this up would be advised to get a ruling from the state electricity authority about some of the conditions regarding the electrical set-up in the"cafe". They might not be entirely in-line with Australian regulations and practice. |
17th Oct 2018, 12:57 am | #13 |
Heptode
Join Date: Jul 2012
Location: Daylesford, Victoria, Australia
Posts: 674
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Re: Separate current transformer?
Confusing automatic translation from Dutch, eh? I'll convey Terry's advice to the local organisers. I can understand the need for an isolation transformer when dealing with live chassis, but live chassis appliances are hardly ever seen in Australia, and they're possibly illegal now. I've never used isolation, I just test as much as I can with the power off, run the thing up through a limiter, and take care when it's on. If there's HT, I add plastic gloves and plimsolls.
Is there a previous thread about the pros and cons of an isolation transformer? It'd have to be quite large to run something like fan heater or a toaster through, wouldn't it? And if there's no earth, there's no residual current protection. The café guide to safety admits this. I'd find that worrying. The Repair Café safety guide in question is attached below:
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17th Oct 2018, 2:39 am | #14 |
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Re: Separate current transformer?
There is a major paradox with hot chassis sets and isolation transformers, now the primary safety from electrocution comes from the dwelling's RCD. The isolation transformer defeats the RCD.
Also, the utility value of isolating the hot chassis set with a mains isolating transformer is so that the set's chassis can be deliberately earthed. This is so earthed test instruments can be attached. Any high voltage points in the set then sit above ground and a shock to one hand through the body to earth can be lethal if the current is over 30mA, and now, with the isolating transformer present, there is no operational RCD protecting that event. So as noted, adding an isolating transformer is not the ultimate solution to safety and in reality, if no earthed test instruments are to be attached to the hot chassis set (only isolated meters etc) it may well be safer to rely on the dwelling's RCD for safety and not use the isolating transformer, provided the RCD is tested and in known working order. Even with an isolating transformer or an RCD, electrocution risk remains from connection to two parts of a circuit with a high enough voltage that can supply enough current to stop the heart or trip it into an abnormal rhythm. Last edited by Argus25; 17th Oct 2018 at 2:44 am. |
17th Oct 2018, 7:51 am | #15 |
Nonode
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Location: Bognor Regis, West Sussex, UK.
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Re: Separate current transformer?
I would agree that the text is referring to an isolation transformer, a further hint is given by the phrase "Never plug a device that you want to test directly into a power socket, when the device is (partly) directly connected to the mains supply."
The reference to "directly connected" implies hot chassis equipment. Peter |
17th Oct 2018, 12:08 pm | #16 | ||
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Re: Separate current transformer?
Quote:
I am prepared to discuss this further in a P.M. with anyone. Quote:
Also, to me, the phrase "directly connected" implies not using an isolation transformer and also does not necessarily imply the connection of 'hot chassis' equipment. Al. |
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17th Oct 2018, 1:26 pm | #17 |
Dekatron
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Re: Separate current transformer?
I regard an isolating transformer as having two purposes.
Most commonly to create a "regional" earth on the chassis of an AC/DC radio or TV or to create the same at half mains voltage on a half mains voltage chassis such as a computer power supply. The other is to make a Variac isolated. |
17th Oct 2018, 1:50 pm | #18 | |
Dekatron
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Re: Separate current transformer?
Quote:
Almost certainly. It won't be a current transformer, that's for sure.
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17th Oct 2018, 6:36 pm | #19 |
Heptode
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Re: Separate current transformer?
Agree with the isolation aspect. I think that is what they are trying to describe where the current is separate from the local mains. They specify no earth so that in order to get a shock you would need to contact two conductors in the device under test not just one.
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17th Oct 2018, 7:06 pm | #20 |
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Re: Separate current transformer?
Although the translation 'separate current' is garbled, the description 'electrically separate' would be correct in the terminology of UK electrical installation practice. The transformer provides 'electrical separation' from the supply and from earth, subject to certain requirements being met in accordance with the definition of 'electrically separate.'
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