Electronics > Beginners
My first scope is arriving but my home (old) doesn't have mains grounding
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Fergo:

--- Quote from: Kalin on August 13, 2019, 04:15:48 pm ---I am not an engineer but I am an electrician. Some people have weird ideas in this thread. An RCD or GFCI is a very good idea since if current that flows out through L1 and doesn't return on L2 wil cause it to trip. This is the danger with having no group d at the out let since you can become a path to ground just by touching the metal enclosure of the device. The danger in not having a grounding means at your outlet is that you could have damage or a fault in your device or dut and energize something that shouldn't be, if supplied from a grounded outlet this would cause your breaker or fuse to trip and deenergize the circuit. Since you don't have that the next best thing is to detect when current is flowing outside of the intended circuit and deenergize at that point. This is what an RCD/GFCI will do.

Sent from my SM-G965W using Tapatalk

--- End quote ---

Thanks!
But from what I've read in other replies, you do need a ground wire at least in the distribution box for the RCD do work. I don't have that :(

One way or another. I couldn't be happier. The scope arrived and I've been playing and getting used to it almost non stop on my free time:



It's so cool (and yes, the Arduino is connected to my laptop running on batteries). Definitely worth it's price, considering I managed to get it new with almost 50% off.

KR,
Fergo
Electro Detective:

--- Quote from: Kalin on August 13, 2019, 04:15:48 pm ---I am not an engineer but I am an electrician. Some people have weird ideas in this thread. An RCD or GFCI is a very good idea since if current that flows out through L1 and doesn't return on L2 wil cause it to trip. This is the danger with having no group d at the out let since you can become a path to ground just by touching the metal enclosure of the device. The danger in not having a grounding means at your outlet is that you could have damage or a fault in your device or dut and energize something that shouldn't be, if supplied from a grounded outlet this would cause your breaker or fuse to trip and deenergize the circuit. Since you don't have that the next best thing is to detect when current is flowing outside of the intended circuit and deenergize at that point. This is what an RCD/GFCI will do.

Sent from my SM-G965W using Tapatalk

--- End quote ---

OP Fergo states in the post that there is no Earthing,

better to not blow money on a RCD that won't work (although the TEST button might  :horse:)

and buy up on PPE instead,
and a fast fuse and MCB combo.

Personally, in that situation, I would prefer two unearthed lines coming from a properly fused isolation transformer humming nearby,
rather than two unearthed lines coming directly from the street transformer via power station,
and relying on an aged sticky mechanism 16 to 30 amp breaker to trip at the mains board = good luck and happy barbeque!   :scared:

 
Ian.M:
No ground at outlets does *NOT* mean the building is free of grounds.  Its likely that any metal conduit and pipes go to ground, however their ground resistance is almost certainly too high to safely trip a breaker, and the integrity of any ground they might appear to provide is suspect. 

A RCB (GFCI) requires a ground referenced supply to operate, but it is extremely unlikely that the supply isn't ground referenced.  In fact its virtually certain the neutral is grounded at the supply company's neighbourhood distribution transformer.  The only non-ground referenced (floating) supplies you are ever likely to encounter are from isolation transformers or portable generators etc. operated without a ground rod.  RCDs don't do anything useful if fed from a floating supply.

Using a RCD (GFCI) does therefore increase safety in the O.P's situation as it will trip on any hazardous leakage to ground, even if the ground path is too high resistance to trip the existing circuit breaker or fuse.
kamtar:

--- Quote from: Fergo on August 08, 2019, 08:50:35 pm ---which can provide some risks as the USB negative is theoretically tied to earth (theoretically because my computer is not grounded either, as the sockets don't have the ground pin).

--- End quote ---

just a little bit of off-topic: most notebooks aren't grounded unless you connect an external monitor or something like that. There is only some minor leakage current as with every switching power supply.
Ian.M:
That depends on the notebook or rather its PSU 'brick'.  If its got a two pin mains connector you can be certain its *NOT* grounded.  However most OEM notebook PSUs with a three pin connector have the output 0V grounded.

I say OEM, because there is a flourishing trade in fake replacement PSUs assembled in the far east from a clone of the OEM case moulding and whatever PSU board salvaged from eWaste, of near enough the same output voltage they  can find to cram in there and those often omit any connection from the mains connector ground pin.  Also beware of fake power leads with three pin connectors on both ends but only wired with two wire cable.

Anyway, its easy enough to check - with the PSU unplugged, check continuity from the ground pin to the contacts of the DC output connector.  If they aren't easy to probe, plug the DC connector in and check continuity from the ground pin of the mains connector (still unplugged) to the shell of a USB socket or similar on the notebook.
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