I'm upstairs, and have carpeting on the floor - while my shoes have rubber soles, they certainly aren't 'good rubber shoes', and I've never worn a pair of rubber gloves either.
I'm a service engineer, I repair TV's, amplifiers, Satellite Receivers etc. - although there are very few repairs these days.
Most items are double insulated, although some are earthed - it makes no difference in either case though.
There seems a unfounded belief that earthing things makes them safer - this is only true under certain specific circumstances.
For example, you have an item with a metal cabinet (washing machine, valve amplifier - it doesn't matter what) - if the live lead inside comes off and touches the cabinet it would make the entire cabinet live, if the case is earthed then it will blow the mains fuse. This is a GOOD example of earthing making things safer for consumers.
But whatever the case you get a shock by applying a high enough voltage across your body - worse case hand to hand (across the heart!). 'Mostly' a shock of this kind would be from live to earth (live to neutral would be less common, and more clumsy). A classic example of this kind of shock would be from a live chassis (many TV's, old radios etc., or any switch-mode supplies) to an earthed scope - simple answer, don't earth the scope 😀
This isn't just about scopes though, it's about anything earthed that might be in range - and you certainly don't want large earthed metal objects of any kind lying within touching distance.
As you've got a poured concrete floor, presumably you have more of a risk to earth than otherwise - and isolation transformers (as I mentioned above) for the 'device under test' would be a good idea.
Another thing to consider is to protect the circuit from you. If you work with semiconductors, the tabletop should be electrostatically dissipative and grounded through a resistor. There should also be a ground snap for an ESD wristband. Setting these up safely is not something I'm an expert on, but I suspect you can get help from those who sell the products needed (dissipative mats, etc.).
Tom
Tom
That's a different thread all together 😀
But my benches are wooden, with a 1/8 inch MDF covering, so inherently 'static free' - but for any static sensitive operation I utilise a commercial anti-static mat and wristband (obviously not an earth 'hazard' as they are high impedance).
Any insulator presents a static risk. That's why materials used in ESD certified labs are either conductive and grounded or electrostatically dissipative (very slightly conductive).
You're right, though. It's a topic for a separate thread.
My workbench is the desk I received for my 14th birthday. It's pretty solid particle board with an oak veneer. I have a shelf mounted above the table with test equipment on it. Works pretty well.
Tom
The professional advice is to use the proper probes - isolated differential probes with the adequate voltage rating.
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I use a Tek P5205. Useful for off line SMPS and other line connected equipment. These are getting reasonable on ebay of late. Need a probe power unit unless you have a tek probeII interface scope.My test/work bench is as cheap as you can get, 2x4spruce,lag bolts,5/8"OSB, lots of coats of varathane.
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Agreed. Right tool for the job when there is a question about isolation or safety. Too many jump to isolation transformers.
too many for who?
there is nothing wrong with using an isolation transformer, if you know what yer doing. period full stop.
it's stupid these people that tell you 'the tool' you must use even before they have an idea what THE JOB is. they give out no information as to model numbers test setups nor techniques, like there just reading off some generic rule book. generic advice on safety is well an good hence the "look both ways before stepping off the curb".
BTW almost all folks answered the OPs question wrong, so advice from most here is to be treated like another internets many grains of sand.
there is nothing wrong with using an isolation transformer, if you know what yer doing. period full stop.
it's stupid these people that tell you 'the tool' you must use even before they have an idea what THE JOB is. they give out no information as to model numbers test setups nor techniques, like there just reading off some generic rule book. generic advice on safety is well an good hence the "look both ways before stepping off the curb".
BTW almost all folks answered the OPs question wrong, so advice from most here is to be treated like another internets many grains of sand.
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And the right tool for the job would be an isolation transformer, or no earth on the scope - some sort of silly probe isn't a very safe option at all 😱
Live chassis - big piece of earthed metal nearby - silly probe connecting the two
Accident waiting to happen - or probably already happened 😀
Hello,
I design often off-line smps with high voltage inside, and i use both of them (isolation transformer AND diff probes).
Using isolation transformer allow more safe bench, because accidental touch of any live part (from earth) is not dangerous.
Using differential probe allow to measure different signals with no common ground (this can be a major issue !).
The main concern with differential probe used to measure at line level is that their
attenuation is very high and bandwidth much limited, and so it's difficult to measure low level and/or fast signals.
There is a compromise you need to do with price,bandwidth, attenuation and common mode rejection (CMRR).
Because we are here on DIY forum, i'll suggest first to USE an isolation transformer first.
It's a cheap lab tool, and you live worth it.
Then, you can build you own differential probe.
It's very interesting tool to build, and you will save lot of money and you will learn much at same time ! 🙂
Regards.
FRex
I design often off-line smps with high voltage inside, and i use both of them (isolation transformer AND diff probes).
Using isolation transformer allow more safe bench, because accidental touch of any live part (from earth) is not dangerous.
Using differential probe allow to measure different signals with no common ground (this can be a major issue !).
The main concern with differential probe used to measure at line level is that their
attenuation is very high and bandwidth much limited, and so it's difficult to measure low level and/or fast signals.
There is a compromise you need to do with price,bandwidth, attenuation and common mode rejection (CMRR).
Because we are here on DIY forum, i'll suggest first to USE an isolation transformer first.
It's a cheap lab tool, and you live worth it.
Then, you can build you own differential probe.
It's very interesting tool to build, and you will save lot of money and you will learn much at same time ! 🙂
Regards.
FRex
Live chassis - big piece of earthed metal nearby - silly probe connecting the two
Well I've never heard of dead DIY'ers posting...
These are a really important points - isolation transformers form one border and perform one function, the diff probe forms another border for another function. In practice the diff probe isn't going to save you from things that the isolation transformer will and vice versa.
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