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Old 2nd December 2010, 03:44 PM   #401
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by CopperTop View Post
What are your views on RCDs? What if they were built into the cable?
Hi,
every power distribution ring in this and my last home had it's individual RCCB at the distribution board. Yes, 5 RCCB on 6 power rings.
Except the audio circuit in the lounge. It is breaker protected and uses fused plug tops.
Does that confirm my viewpoint?
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Old 2nd December 2010, 04:11 PM   #402
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Are you saying that you didn't protect your audio circuit with an RCCB, but instead only installed MCBs..?
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Old 2nd December 2010, 04:30 PM   #403
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The purpose of a fuse is to protect the wires.

NEC page 70-83, Article 240.

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Old 2nd December 2010, 04:45 PM   #404
AndrewT is offline AndrewT  Scotland
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Originally Posted by CopperTop View Post
Are you saying that you didn't protect your audio circuit with an RCCB, but instead only installed MCBs..?
yes.
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Old 2nd December 2010, 05:07 PM   #405
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"yes. "

Sometimes I worry that I seem to need really clear explanations of things that others just pick up straight away. Consequently I probably make my posts too long, needlessly attempting to anticipate the reader's questions...

Just to indulge me, what is wrong with using RCDs with audio equipment if you are worried about death by electricity? Isn't an RCD a good last resort, even if you wouldn't want to rely on it?

Admittedly, a plastic RCD costing £10 might tarnish the sound from your solid gold mains plug - but we don't really believe in that stuff do we..?
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Old 2nd December 2010, 05:12 PM   #406
AndrewT is offline AndrewT  Scotland
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My din rail mounted RCCBs cost about £40 each.

I don't want nuisance shutdown of my Audio Power due to detection of excess Earth Leakage.

It's bad enough in rural Borders with mains brown outs and total loss on an almost weekly basis.

Fortunately , this heavy snow fall has not been accompanied by strong winds. No power outs at all this week !
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Old 2nd December 2010, 05:52 PM   #407
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Ah, I get you. But what is causing your excess earth leakage? I haven't encountered a problem like that for years.
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Old 2nd December 2010, 06:28 PM   #408
AndrewT is offline AndrewT  Scotland
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Default earth leakage current

any parasitic capacitance from Line to Earth + RF filter capacitors from Line to Earth.
Then include any SMPS in TV/Monitor/Tuner/DVDplayer/Freeview box etc.
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Old 2nd December 2010, 06:42 PM   #409
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But our whole house is covered by an RCD (30mA I think) and in 5 years it has never tripped. Perhaps I should test it..!
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Old 2nd December 2010, 07:30 PM   #410
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Quote:
Originally Posted by CopperTop View Post
If so, then all that is needed to banish ground loops forever, is to use fully-shrouded connectors with no exposed metal parts. Then the audio circuits can remain fully isolated from the mains. Could it really be so simple?
It could be, if you don't need to use standardized components that don't fulfull that requirement.

Quote:
Originally Posted by CopperTop View Post
cable screens and bonds to phono sockets etc. are of arbitrarily skinny cable with soldered joints of doubtful mechanical strength. I don't think current rating is usually one of the headline specs people look for in a screened cable. Maybe they should.
These components must have their own fuse which has to blow fast enough to avoid damage. Decent designs will comply with that demand.

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Originally Posted by CopperTop View Post
It seems to me that as long as you earth the box, physically keep the mains section away from the transformer-isolated electronics and, possibly most important of all, ensure that cables are physically restrained from touching anything they shouldn't even if the electrical joint breaks, you will be fine. (We do place a lot of trust in isolating transformers don't we..?)
That is called class II.

Quote:
Originally Posted by CopperTop View Post
What are your views on RCDs? What if they were built into the cable?
Power strips with built-in RCDs are available.

Quote:
Originally Posted by CopperTop View Post
If you think about it, every large metal object has the potential to make a very small area of contact with "live" (caused by a damaged cable, or a pool of water around a trailing mains block etc.) and to then to present a very large, low impedance connection to the next human who touches it. Kitchen sinks and bathroom taps are already protected against unpleasant potentials, but maybe large unearthed metal objects in general should be banned from the home!
Correct. The regulations that force us to connect conductive cases of electrical devices to earth usually refer to external, but neighboring conductive bodies as well.

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Originally Posted by jneutron View Post
The purpose of a fuse is to protect the wires.
That is one of its purposes. Regulations require us to tune fuse and wire sizes to each other so that fires are avoided.
They also require us to ensure protection against indirectly touching dangerous voltage which class I devices do by making the fuse blow. In that case the fuse is also there to protect lives.
Another purpose of a fuse is to protect components other than wires according to the designer's choice.

Quote:
Originally Posted by CopperTop View Post
But our whole house is covered by an RCD (30mA I think) and in 5 years it has never tripped. Perhaps I should test it..!
Yes, you should test it on a regular basis. Here in Germany regulations dictate to do that once a month. Not many people know that they have to test it regularly. Those who know, don't do that, because it means to shut off the power resulting in all the inconvenient resetting of clocks, reprogramming of video recorders and such.
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