Grounded versus ungrounded laptop power supply

"Ross Vumbaca"

** Err - so two parallel, flat pins for old and new style US outlets ? ** The ground pin is likely not used.

Lots of Aussie plug pack adaptors and double insulated appliances have 3 pin plugs with NO connection to the earth pin.

** Standard Aussie plugs are 3 pin. ** Not strange at all.

....... Phil

Yes. The mains cable can be unplugged from the plug pack, it uses a "figure 8" on the plug pack end.

I see. So even though the Australian plug pack has a "mickey mouse" socket on it for the mains plug, you reckon that it probably does not make use of the earth plug.

Except that I cannot find the "double insulated" logo on my Australian Thinkpad power supply which uses three prongs.

But if I take a look at a 2 prong, US version

it does have the double insulated logo on it.

Also, if I take a look at a 3 pong US version (very uncommon) it also lacks the double insulated logo, like my Australian one

Lasly, I can measure 1M Ohm between the earth pin of my Thinkpad power pack and both of the outpin pins on the DC end.

So I think that the earth prong is being used, but I have little knowledge with this stuff (in case I'm talking crap).

Hence I wondered why the Australian spec one is (possibly) not double insulated, and being a bit over cautious, whether it would hurt to use the US supply here for the long term.. probably not though..

But the US also has 3 prong outlets (at least I thought so).. But if 3 prong outlets are uncommon in the US/Canada, perhaps that is why IBM/Lenovo does not use 3 prong power packs in the US (or Canada), but uses them in many other places, including Australia.

Thanks,

Regards,

Ross..

** That is NOT what I what I said !

The mere presence of a 3 pin plug does not prove an item is grounded - as many counter examples exist. However, the use of 3 pin plug with 3 core cable and the absence of a double square symbol is good proof that it IS grounded.

** Dunno where YOU got the MAD idea that double insulated items are less safe than earthed - the opposite is true actually. ** The troublesome issue with such SMPSs is NOT safety but EMI suppression.

By using a 3 core lead, the ground conductor can be used to provide earthing for the low value capacitors that form part of the RF interference filter on the input ( high voltage) side of the SMPS. As you found, the DC output side can then have no connection or earth or a high resistance path (like

1Mohm) to eliminate stray AC voltages.

With the double insulated version, there is no ground conductor available so the same RF suppression caps are typically connected to the DC output cable common. This is sufficiently effective for RFI, but will cause an annoying buzzing noise if the laptop's audio output is ever connected to an external audio system.

Also, the use of the old US 2 pin plug allows maximum convenience to those users, since quite a number of premises in the USs and Canada still have 2 pin outlets that do not permit a 3 pin plug to be used.

....... Phil

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Thanks heaps for the information, all makes sense now..

Regards,

Ross..

"Ross Vumbaca"

" Phil Allison "

** My Gawd - we have a satisfied customer .....

..... ought to have him stuffed .....

( Apologies to John Clease et alia .... )

...... Phil