Electronics > Beginners

Measuring Mains with Rigol DS1052E

<< < (8/8)

djacobow:
I just wanted to chime in to say that knowing what you are doing is NOT sufficient for safety with live mains equipment. You also have to not make mistakes.

That is harder than it sounds, since we all make mistakes all the time. Discipline and the use of checklists can be assets. Sure, you can look over the isolation xformer and rats nest of power cords on your bench, but did you actually make sure that the DUT you are working on right now is the one plugged into the xformer? Or you could have a policy of always powering the "DUT side" of your bench from isolation, but then you have to remember that when you're working in the field, etc.

Mistakes happen all the time. We've all let the smoke out many times. And yet, with mains AC, the cost of a mistake can be much more exciting.

Just sayin'.

Personally, I prefer to use a HV differential probe. They're not that much more money than an isolation transformer, particularly if your application requires a large one, like 2kVA, and obviously much more convenient if you have to work in the field.

newbrain:
Just to add one data point:
There are places in Italy where two phases (out of three) are distributed, with no meaningful distinction between Neutral and Phase.

Protective Earth is, electrically, 127V from each phase, and the difference between phases is 220V.

127 x sin(60) x 2 = 220.

I have personally verified this in all the apartments I've been living in (Rome area);
I just checked here in Sweden and I have real Phase and Neutral.

Is this type of distribution common elsewhere? I think it has something to do with the conversion from 110 to 220 that happened some 40 years ago, but I'm not sure.

Nivr:

--- Quote from: mikeselectricstuff on August 02, 2011, 04:41:10 pm ---
--- Quote from: logicnibble on August 02, 2011, 04:17:36 pm ---
--- Quote from: ejeffrey on August 02, 2011, 03:33:03 pm ---What are you trying to measure?

--- End quote ---
I'm trying to measure a uC circuit which is powered by a capacitive (transformerless) power supply.
This means all circuit is LIVE.
I also would like to measure a dimming circuit, which is LIVE too.

--- End quote ---
In which case use a mains isolating transformer, and connect the circuit's 0v rail to mains earth so you can ground the scope to it.

--- End quote ---

Isn't this creating a very dangerous situation, something powered by an isolation transformer, but then earthed nonetheless?
If you touch anything connected to the non-earthed secondary side of the transformer, nothing (no rcd/gfci) would be able to interrupt the current and save your life.

Zero999:

--- Quote from: Nivr on October 30, 2019, 08:54:50 am ---
--- Quote from: mikeselectricstuff on August 02, 2011, 04:41:10 pm ---
--- Quote from: logicnibble on August 02, 2011, 04:17:36 pm ---
--- Quote from: ejeffrey on August 02, 2011, 03:33:03 pm ---What are you trying to measure?

--- End quote ---
I'm trying to measure a uC circuit which is powered by a capacitive (transformerless) power supply.
This means all circuit is LIVE.
I also would like to measure a dimming circuit, which is LIVE too.

--- End quote ---
In which case use a mains isolating transformer, and connect the circuit's 0v rail to mains earth so you can ground the scope to it.

--- End quote ---

Isn't this creating a very dangerous situation, something powered by an isolation transformer, but then earthed nonetheless?
--- End quote ---
Yes, it does increase the risk of getting shocked somewhat, but I wouldn't describe it as a very dangerous situation.


--- Quote ---If you touch anything connected to the non-earthed secondary side of the transformer, nothing (no rcd/gfci) would be able to interrupt the current and save your life.
--- End quote ---
Well no, the secondary of the transformer would be be earthed.

Expanding on my previous comment. It's true that using an isolating transformer, then earthing the secondary, would defeat and RCD/GFCI, thus increase the risk of shock, but that isn't necessarily a very dangerous situation. It's only dangerous if you touch a live part of the circuit, which can be avoided by adhering to safe working practices. People worked on live circuit fine before RCD/GFCIs were invented and didn't get electrocuted.

Navigation

[0] Message Index

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod