Yes it will, because there's no other earth source available - so you can't get a shock between live and 'earth', only between live and neutral - EXACTLY as you could with a transformer.

Your isolation transformer scheme is far more dangerous - you isolate the incoming mains, so you have two 'lives' with no earth reference. You than clip your scope to one of them, earthing it - making that neutral again, and leaving the other a full 240V live - where you can get a shock to earth exactly as if the transformer didn't exist.

Where as my earth free environment makes this impossible under all circumstances.

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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.

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Only if you earth it!.

That's assuming a concrete floor?, which it isn't, and being at ground level?, which it isn't. The floor is a Pitchmastic type of substance (not exactly sure what?), but it's non-conductive, and has rubber matting over it as well.

I can stand on the floor and hold a 240V live wire perfectly safely - and usually do a couple of times a year.

Who uses metal work benches? - I certainly wouldn't entertain them!.

Why would a chair be earthed?, why would you assume it's even made of metal?.

Possibly! - obviously depending entirely on the wiring, and for an earth free environment they wouldn't be.

What happens if it shorts to some where else? - you can't just randomly assume something is going to happen like that, and there are plenty of random conductors shorting to things that are more dangerous in an earthed environment.

But if it does short to the scopes casing nothing happens, because it's not earthed.

But is completely of no consequence, as there's no earth reference to get a shock from.

Normal safety practice doesn't allow you not to touch the circuit in a service environment - although you obviously take great care in everything you do. Keeping one hand in a pocket is always a good idea, but earthed or not makes little difference to that (apart from you're more likely to get a shock if you touch a live conductor in an earthed environment).

There is no earth, so that isn't possible - why do you find that so hard to understand?.

You appear to have been 'brainwashed', you've been told there's only one possible way to do something, and can't think 'outside the box' for alternatives.

There are normally multiple ways to do most things, with varying advantages with each - you are stuck in a single minded approach and can't conceive that there may be alternative methods just as good, and possibly better.

In an attempt to prove your single minded point of view you have made loads of completely incorrect assumptions in your last post - just think of what earthing is for, and what it's supposed to do, and why it's done like it is. It's not perfect, it has major flaws, but for a domestic environment it's probably the best choice - I wouldn't deny that!.

My only reason for repeatedly posting in these threads is to try and make people understand that blindly following a single idea isn't always the best way - use your brain, consider the alternatives, don't be a sheep!.

Like I've said everytime this has come up though, if you don't understand it, then DON'T DO IT!.

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I can see your point, I just think that relying on something like an earth free environment isn't good enough to protect you from electrical shock. All that needs to happen is that you come in to contact with something that's earthed.

What happens if someone plugs your unearthed scope in to a non-earthed environment and there just happens to be an earth fault?

Even in a non-earthed environment, the scope's case will become earthed if the neutral acidentally touches the case.

I understand that if there are no electrical paths to earth and you touch a live conductor you won't get shocked. I'm just not stupid enough to trust that there are no paths to earth.

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But there are less chances of a shock than with an earthed scope and an isolation transformer - particularly bearing in mind as soon as you connect the earthed scope to the primary side of the power supply, you're earthing the secondary of your isolation transformer - making it completely useless, and it may as well not be there!.

Like I've said all along, we run all benches via their own isolation transformers, but we still maintain an earth free environment and don't earth the scopes - this provides the maximum possible amount of safety.

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What about ESD?

Adequate ESD measures require the bench and you to be earthed which is totally incompatible with what you're suggesting.

I don't know why the scope manufactures don't just make double insulated scopes.

Nearly all power tools are double insulated these days.

They could still ensure the unit has adequate EMC screening by wire mesh on the inside of the case, there's not excuse.

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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.

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Yes, we use ESD mats and wristbands where applicable - as you say, no direct earth requirement, so still no shock hazard.

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What if someone borrows your un-earthed scope with an internal fault and plugs it in someone else whilst touching the metal chassis and not stood on a rubber mat? They could potentially receive a fatal shock.

Removing the earth from a scope could potentially cause a fire risk if an internal fault develops, you may as well short out the fuse whilst you are at it, that’s just as dangerous.

Don’t Techtronic make battery driven scopes?

 

I agree, just use an isolation transformer when testing mains circuit on an oscilloscope, it's the only really safe way of doing so.

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Here's a good article about power supply troubleshooting. It doesn't cover the latest models but should be good up to ATX. http://www.repairfaq.org/sam/smpsfaq.htm

 

Hero999: Not to start an arguement, but I think all Nigel was trying to say is that there is more than one way to create a safe enviroment which depends on the situation. All methods have their advantages and disadvantages.

Anyhow, isn't the point of isolating the PSU to allow you to connect the scope probe's ground to a live portion of the PSU ? Shouldn't this ideally be done with a differential probe ?

Just a though, I'll admit that I have no experiance in this area.