BMU Safety issues

[Ninanina]

As these remarks have no relevance to the topic I take it you would rather they be moved to a more suitable place Bev?

Grant the question is 'loosely' to do with this thread.. I can't say anymore as I don't think I'm allowed to... if you know what I mean

[struth]

Best not to then

[anthonyTD]

http://www.airlinktransformers.com/b..._power_supply/
Anyone interested in a decent BMU at a realy good price, go for the largest VA rated version you can afford to minimise the affect of increasing the mains impedance, their larger versions also have RCD's built into the secondaries, so no issue with safety.
A...

[r100]

http://www.airlinktransformers.com/b..._power_supply/
Anyone interested in a decent BMU at a realy good price, go for the largest VA rated version you can afford to minimise the affect of increasing the mains impedance, their larger versions also have RCD's built into the secondaries, so no issue with safety.
A...

They are not expensive either ..
and we may finally be getting to a conclusion ?

[anthonyTD]

Indeed,
However, from experience i have found in many cases the most affective way of lowering the potential of mains born noise getting into your system is to keep the mains impedance as low as posible rather than increasing it, unless of course its a passive mains filter, which by its very nature will increase the mains impedance due to the inline chokes, but as its a filter, and as long as its designed right, the positives should way out way the negatives. Balanced mains supplies do have their positives when used in the type of enviroments they were designed for, and in regular audio equipment and systems they will have an affect, whether that affect is a positive one ??? IMHO that would be mainly down to the end users opinion more than fact...
A...

They are not expensive either ..
and we may finally be getting to a conclusion ?

[Joe]

Balanced mains supplies do have their positives when used in the type of enviroments they were designed for, and in regular audio equipment and systems they will have an affect, whether that affect is a positive one ??? IMHO that would be mainly down to the end users opinion more than fact...
A...

But isn't that true of almost everything in audio? You'll either hear a difference or you won't when switching/adding components. If you hear a difference, it's either going to be to your taste or not. There are no absolutes here.

[anthonyTD]

But isn't that true of almost everything in audio? You'll either hear a difference or you won't when switching/adding components. If you hear a difference, it's either going to be to your taste or not. There are no absolutes here.

[Oldpinkman]

Oh dear. I'd been trying to avoid thread drift into what they do and how they do it because I just find it funny when people talk nonsense about how things work, rather than saying they like what they hear. I have been happy to let "secret recipes" and "sprinkled with fairy dust" go since nobody got killed by believing that nonsense. The function of an RCD and its role in saving lives and fires is a different matter.

The appalling attitude taken by some people regarding safety legislation, recognised best practice, and industry experts like BEAMA makes me inclined to a little thread-drift. On the subject of Isolation transformers. Not least, because its only slight thread drift - the term is used loosely and in different contexts. Some shadowy figure suggested isolation transformers were used in bathrooms for safety so a BPS must be safe

Not true. The isolation transformers,whether balanced or not, have a floating ground on the secondary. As such you cannot get electrocuted by making a path to true earth by coming into contact with the live wires on the secondary - there is no circuit. However, by virtue of grounding the secondary centre tap to true earth, to enable a path to earth for class I devices plugged into it - the ground no longer floats and is bonded to true earth. So the transformer is not isolating in that sense any more, and it isn't safe to use in the bathroom in the way that one with a floating earth would be.

The other nonsense was the article about common mode rejection, and "isolating transformers" being any and every transformer. Actually - the article very clearly says quite the opposite. "Contrary to popular opinion, isolation transformers cannot effectively isolate a circuit from noise caused by grounds without the intelligent use of proper shielding and ground design.". It goes on to discuss why capacitive coupling in the transformer limits its high frequency band pass - its effectiveness as a low pass filter. Keeping it short it says "isolation transformers" are the answer. But contrary to the beliefs of some, it is not true to say "ALL transformers are isolation transformers" . In this context they mean "isolation transformers with electrostatic shields". I'm so sorry guys, but this brings us back to Faraday shields and their grounding. Suffice to say for now that the erudite article had in mind devices more akin to these than an off the shelf toroidal http://www.shepherdindia.in/ultra-transformer.html

Sometimes it helps to read an article rather than just link to it. But "isolation transformer" can have at least 3 different contexts or meanings. To the extent it isolates a current flowing to earth on the secondary, from the RCD detection devices on the primary - a BPS is "isolating". A transfomer designed for safety testing is "isolating" by virtue of a floating ground not bonded to true earth. And for common mode noise rejection without high frequency leakage, we are talking about a specialist built device with additional internal shielding (more faraday cages) and a construction which usually has the windings physically separated more than in a normal off the shelf toroidal.

But nobody ever got killed mis-understanding common mode noise rejection, so I wasn't so fussed about it. They might well get killed thinking a BPS with its secondary ground bonded to earth was an "isolating transformer" and using it in a bathroom as "safe" (unless of course it is fitted with RCD's on the output )

[Joe]

Wow. A simple smiley gets a 600-word response. What was that saying about brevity being the soul of wit?

[Marco]

I made it 602.

Marco.