Electronics > Beginners

Lab with NO grd, what about gear?

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FriedMule:
I know that it was a a bit fare out but what I ment was: Security level should be, if I am idiot, its my own fault, if the gear fails, it shall not influence me. :-)

The system in Denmark do the following: It compare the in and out power and if there are the slightest irrigularity it triggers a breaker and the whole house goes dark!
So if a case is live and i touch it, the breaker will trigger in ms.

What I am concerned about is some says that no ground is the best when measuring electronic i.e. Dave's "how not to blow up your scope". On the other hand, there are also a lot about preventing noise, static electricity and so on.

So the "simple" question: "what would you do if you was in the same situation, lots of power but no earth.

CatalinaWOW:
What I would do is go ahead and use it without grounds.  But that isn't really useful to guide you.  I have both experience and knowledge that you are apparently lacking, and a hard won understanding of the cosequences of error.

Dave is correct, you can blow up your scope.  If you don't understand the mechanism and avoid it you can do this in many ways, and no single rule will avoid it.

This also plays into noise.  Much noise results from unplanned and/or uncontrolled signal paths.  Which includes multiple returns to ground.  While a brute force, ground everything approach it is quite possible to reduce noise without minimizing.  And making it really difficult to figure out what to do to further reduce it.  "Which path did that ground current take, anyway."

I'm sorry I can't give you a quick and pat answer, but there really isn't any substitute for thinking through all of the consequences of different choices.  A couple of examples.  How much total power will your lab consume.  All instruments, lights, fans solder stations and the like.  The how much does an isolation transformer to support that load cost.  Or, how diligent would you be in periodically checks of case isolation if you choose that method for protecting yourself?  How diligent would you need to be to satisfy your safety requirements.  How do the answers to those questions relate to your standard of "If I make a stupid mistake that's my tough luck, but I don't want to be hurt by someone else's error.

FriedMule:
Wow what a lot of great questions!!

As you rightly says, I am to new to this, my first lab, therefor all my "problems" :-)

About noise and signal path, I am thinking of using one power outlet and then one power strip, all without grd connection.

I do not understand the following: "brute force ground" and "Which path did that ground current take, anyway."

About the consequences, that's it, I do not know the consequences or my options at all.

About testing case isolation, all I know is that if I touch a case with voltage in it, the breaker will shut off in milli seconds.

EDIT: would a cheap max 500W isolation transformer be ok? (https://www.amazon.de/gp/product/B0067K0ESA/ref=ox_sc_act_title_1?smid=A3JWKAKR8XB7XF&psc=1)

CatalinaWOW:
Your ground fault breakers cannot detect all faults in equipment on the output side of an isolation transformer.  Whether that matters depends on details of your lab set up.  Again thinking is the only solution.  What would the current path be if case isolation failed and you touched the case.  Think of all the other things you might be touching at the same time.

A 500W isolation transformer may or may not be fine.  I have no idea how many devices you have in your lab, or what their power requirements are.  If you are testing high power stereos or amateur radio transmitters that unit you are testing could consume all of that with nothing left for test instruments or anything else.

Ice-Tea:

--- Quote from: FriedMule on October 14, 2018, 07:17:13 am ---About safety: In Denmark the circuit breaker trips if there are any different in the power between phase and neutral so if you touch a metal case, it will trip in a tiny fraction of a second.

--- End quote ---

Funny thing though: the RCDs are ussually for 300mA. Too bad that a rule of thumb says things get hairy from, say, 100mA or so.

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