One of the 'requirements' here in Australia is/was for the primary and
secondaries to be on separated parts of the bobbin. I haven't looked for the
'rule', I just remember that when it was introduced the blurb with various
electronic kits [and advertisements] highlighted the fact that the mains
transformer met xxxx. I prefer the split bobbin windings because they 'should'
be safer if the transformer gets very overheated. I do not know what
transformers are required to have the inbuilt thermal fuse. I also do not know
if separating the windings on the bobbin [as is done on the small transformers]
is efficient enough to be used on larger transformers.
There was a debate in a local electronics magazine about safety and
transformers. It was pointed out there that toroidal transformers had a history
of failing when hot due to mechanical pressures between the layers. I don't
know how well-built the offending transformers were. Might have been 'cheapies'
for an amplifier kit.
Lots of "I don't know" from me there - but it might contribute to talking
points :-)
AND, the topic of RCDs. There are RCDs built in to mains plugs available. They
might be good for extra safety.
One aspect of RCD useage which is often overlooked: they can shut off the power
if there is a fire. It can be worthwhile taking an earth/ground into "2-wire"
equipment or installations to assist with protection against water ingress and
fire. It is a long story, but I was in a position to analyse faults of PIR
[passive infra red] detector installations and it is amazing what actually goes
wrong. Plan for the worst thing to happen - it will somewhere !
John K
Australia
----- Original Message -----
From: Dekatron42
To: neonixie-l
Sent: Friday, October 02, 2015 4:37 PM
Subject: [neonixie-l] Re: Linear power supplies for nixies
Can anyone direct me to a document that says that it is allowed to sell an
electronic apparatus that uses a primary winding as a secondary winding - I
spent a lot of time Googling this and I can't find anything. I am also
concerned about safety and what an insurance company would have to say if a
fire breaks out and the culprit is the home built equipment which uses a
primary winding as a secondary winding.
/Martin
On Thursday, 1 October 2015 06:14:11 UTC+2, gregebert wrote:
I did some research on UL/CSA approved transformers, and there is a
requirement that all windings withstand a minimum breakdown voltage, even if
they are intended to be connected together, such as dual-primaries. Depending
upon the VA rating and the voltage, the breakdown must be between 1050 and 4000
V RMS according to how I read the spec (UL5058-2 / CSA C22.2 #66). The test is
conducted between 1 winding, and all other windings and the core combined and
at elevated temperature. There are copies of the spec online.
I knew there had to be some amount of isolation, but I did not realize it
was that high. While I would never expose or touch anything that is supposedly
"isolated", it does reassure me there is decent insulation.
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