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Hero999 said:I'm only 25 and I've heard about it and to me it's common sense why the earthed, mainly because if it isn't earthed it can float at whatever voltage it wants to.
However, on a controlled environment like a test bench, it's normally only single phase and you know what you're connecting to it so the above problems don't occur.
Not if you're using an isolation transformer as there's no return path to earth.
No, it isn't safe if you don't have an isolation transformer. The -Ve pulses up an down at mains potential with respect to earth so as soon as you touch that scope you're a goner. You're better off blowing a fuse or rectifier then learning from it and buying an isolation transformer.
When was this?
In the 1960s may be, but not in 2008 and just because you've seen it done before it doesn't mean it's safe.
crusty said:since you have 2 of them, you could short the leads on one PSU and see what blows up, then follow down what blew up, and it should be the same problem on your other. Of course if 2 failed, they were probably el cheapos with every party not being worth a crap, so in that case, throw it in the recycle bin and send it back to china!
Without a circuit to look at, I can only guess.dbtoutfit said:Len,
Yea I have removed each component as I have tested. Good
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Shorting out the unit is not going to give me the same results as a component that shorts out internally, as far as what does and doesn’t become damaged. Agreed. You don't know which component failed first, and even if you did, the result may be different if you tried to simulate.
Eric
That's very unlikely if it conforms to the safety regulations, I can't remember the exact British standard but it states that the secondary shall have double insulation from the primary and that it shall be able to withstand spikes of 2kV.Nigel Goodwin said:Only from any source connected via an isolating transformer, and assuming it's insulation doesn't break down.
No, it won't be a completely earth free environment because the earth is bonded to the neutral unless you use an isolation transformer.Why would you be a 'goner' - to get a shock you need to complete a circuit, operating in an earth free environment ensures that isn't possible - apart from directly between neutral and live (which would be the same with an isolation transformer as well).
I disagree, if I went for a job anywhere and discovered they used the cowboy practises you promote then I'd walk out on the first day, after taking photographs and reporting them of course.1970's - and because modern practices have changed, doesn't mean it's any less safe than it was back then. There are significant advantages in an earth free service environment - which are obvious if you consider the mechanisms by which you can get a shock.
Hero999 said:No, it won't be a completely earth free environment because the earth is bonded to the neutral unless you use an isolation transformer.
Hero999 said:Ideally yes but how is an earth free environment practically possible?
I don't see how it is.
Your soldering iron's tip is earthed.
Even the concrete floor will conduct electricity to some degree (it absorbs water).
The metal bench you're working on is earthed.
Your chair is earthed.
Even the screws on the plug socket are earthed!
What happens if a conductor shorts to the scope's cause?
The case will either become neural or live with respect to the other circuit.
The isolation transformer isn't dangerous, you obide by normal safety practice and don't touch the circuit being tested.
Your floating scope's at mains potential is a death wish, as soon as touch it the current will find a path to earth where you leaset expect it and kill you.
The only way you can safely not connect your scope's case to ground it if you run both it and what you're testing from an isolation transformer but in practice, it's only really important you run the device under test from an isolation tranformer.
ESD earthing is done via a 1M resistor for safety reasons.Hero999 said:What about ESD?
Adequate ESD measures require the bench and you to be earthed which is totally incompatible with what you're suggesting.
ljcox said:ESD earthing is done via a 1M resistor for safety reasons.
There is no need for a direct earth since any charge will leak away quickly via a 1M resistor.