with a groundless supply, all 3 neons will light
Appliances dont care a whatsit about polarity, earth, fusing or RCD. Its people getting electrocuted or burnt by faulty appliances that care.
NT
I don't think you will find a single system that will be "safe" or give correct indications under all circumstances. You just have to be pragmatic, like use a plugin tester and rotate the plug if the tester indicates a reversal. Not forgetting to check again after the plug rotation and being aware of the limitations of the plugin tester.
One should never stop learning, I'm reading "In Search of Schrodinger's Cat" by John Gribbin. Now I don't stand a cat in hells chance, let alone in a box, of really understanding quantum theory but it doesn't stop me getting some knowledge of the very basics. It's an old book now, 1985, I wonder what developments there have been in the last 20 year? And is there similar book about covering them?
The earth on some laptop and similar PSU's is for interference reduction. Switched mode power supplies can generate a lot of radio frequency noise and some filter designs to prevent interference require an earth. It has no safety function.
Thank-you. I didn't know that.
I'm not try CAUTION: FOR USE WITH INFORMATION TECHNOLOGY EQUIPMENT ONLY. UTILISER AVEC DU MATERIEL INFORMATIQUE SEULEMENT DAS NETZEIL DARF NUR IN VERBINDUNG MIT GERATEN NACH EN 60950 VERWENDET WERDEN Apparatet skal tilkoples jordet stikkontakt Apparaten skal an slutas till jorolat uttag.
I'm not sure of the German, but EN 60950 is a standard maintained by CEN (European Committee for Standardization) and CENELEC (European Committee for Electrotechnical Standardization), entitled "Safety of information technology equipment". I can't find a copy on the web, but this gives some idea as to the contents:
If the earth provides no safety function (just RF screening), then shouldn't it be double insulated, and say so? I have an example of a three-pin wall-wart which has a metal earth pin, and also the double insulated symbol (It's a standard transformer, non switched mode (by the weight) used for powering a four port LAN switch).
Cheers,
Sid
Thank-you. I didn't know that.
I'm not try CAUTION: FOR USE WITH INFORMATION TECHNOLOGY EQUIPMENT ONLY. UTILISER AVEC DU MATERIEL INFORMATIQUE SEULEMENT DAS NETZEIL DARF NUR IN VERBINDUNG MIT GERATEN NACH EN 60950 VERWENDET WERDEN Apparatet skal tilkoples jordet stikkontakt Apparaten skal an slutas till jorolat uttag.
I'm not sure of the German, but EN 60950 is a standard maintained by CEN (European Committee for Standardization) and CENELEC (European Committee for Electrotechnical Standardization), entitled "Safety of information technology equipment". I can't find a copy on the web, but this gives some idea as to the contents:
If the earth provides no safety function (just RF screening), then shouldn't it be double insulated, and say so? I have an example of a three-pin wall-wart which has a metal earth pin, and also the double insulated symbol (It's a standard transformer, non switched mode (by the weight) used for powering a four port LAN switch).
Cheers,
Sid
And some earthed switching supplies have an earth pin only to protect the mains supply in to the box, but stop at connecting to any metal shielding that prevents RF interference. In cases where the nylon case is penetrated by a metal chair leg Etc. while you use the IT equipment attached to it, it pops the fuse in the plug. But that's mostly on PSU's that have a trailing mains lead..
There won't be as it isn't double insulated.
The metal earth pin in your conventional PSU won't have any connection and the device will be double insulated. In a PSU using a filter which requires an earth it isn't usually screened but has two capacitors going to earth one from each line so it isn't double insulated. The output is still isolated from the input though so there is no risk to the user. With the earth disconnected the earth connection on a filtered supply will rise to half the mains voltage but with negligible current capacity - the most you will get is a slight tingle as you touch it.
On 12 Nov, 16:44, Peter Parry wrote: .
Thank-you for the follow-up and clarification. Much appreciated.
Regards,
Sid.
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