Why do some electronics not use grounding?

[Anza Power]

Dunno if this is the right forum as all PSU's I've ever seen had grounding, but when I bought a new Samsung 27" Monitor I was surprised it's wall plug had only 2 pins, why doesn't this device need grounding? and which devices usually do?

[UnknownEngineer]

Usually all devices with a metal construction will have grounding, that means if the outside of the monitor is metal. I am pretty sure your monitor has no exposed metal on the outside.

Some devices have fully plastic construction, these devices will only have 2 connectors.

EDIT: Other things could have an affect as well, such as if the device has a high power draw, i could be wrong though.

[Anza Power]

^ Thanks for the answer, can you elaborate more? why does exposed metal require grounding? also my netbook charger has 3 pins even though I don't see any exposed metal on it or the netbook...

[schwat]

^ Thanks for the answer, can you elaborate more? why does exposed metal require grounding? also my netbook charger has 3 pins even though I don't see any exposed metal on it or the netbook...

 

Because if you don't have the chassis tied to earth ground it could be floating at voltage above earth ground. This could cause potentially dangerous voltages to be exposed on the metal chassis.

 

By having the chassis physically connected to earth ground via a cable if anything inside shorts out & touches the metal cage it will have a return path for the current which means that it should either blow a fuse or at least keep the chassis from killing you if you touch it. 

[othertomperson]

Things entirely encased in plastic are doubly insulated so there's no conducting part for you to touch so there's no need for them to be earthed.

[UnknownEngineer]

^ Thanks for the answer, can you elaborate more? why does exposed metal require grounding? also my netbook charger has 3 pins even though I don't see any exposed metal on it or the netbook...

I cannot guarantee that i am 100% correct when i say this, i am struggling to recall what i learned in class.

But the principle is that if a wire come loose inside the device and touches the case, it will allow current to flow trough the bare metal, and when touched, this current will go through the person into the ground. The human becomes the grounding wire.

This cannot happen in plastic appliances, as the case is non conductive.

Also, some high current drawing alliances may have a ground, this is where i am uncertain as to why exactly they have one.

 

EDIT: The 2 post above said it way better then i did.

[s3ns3]

The human becomes the grounding wire.

you become the consumer

[Anza Power]

So it's only for safety? there's no other functional need?

[ShadowCaptain]

How come the UK has an earth point on our plugs but US dont and we have shuttered slots so you cant stick your fingers in. also they are normally all fused too

[schwat]

How come the UK has an earth point on our plugs but US dont and we have shuttered slots so you cant stick your fingers in. also they are normally all fused too

 

US has grounded outlets too but devices can have either 3 prong (grounded) or 2 prong (ungrounded) plugs. Not sure why we haven't adopted fused outlets though, that does seem like a decent idea. 

 

Although we do typically use GFCI outlets in places where there is additional risk of shock hazard, like a bathroom. These outlets are designed to mitigate shock risk by cutting power when it detects an imbalance between the current flowing through the hot conductor & the netural conductor indicating current being diverted through another path to ground (ie: a person being shocked). They're supposed to open quick enough to prevent electrocution. 

 

I'm not an electrician though, just an electronics tech so I'm not up to speed on US electrical codes. 

[schwat]

So it's only for safety? there's no other functional need?

 

Mostly only for safety. That is the biggest reason to have a connection to earth ground when you have a metal chassis. Most consumer electronics are going to have a transformer in between the plug & the actual electronics because most things actually run off DC voltage. This transformer steps down the 120VAC to something smaller which is then rectified into a DC voltage. This transformer breaks the physical connection to 120VAC coming from the wall and provides additional protection through isolation. 

 

Big appliances that have motors will typically actually run off AC & have no isolation transformer meaning you have 120 to 240 VAC inside a device with a big metal chassis & for these you definitely need a chassis ground tied to earth ground for safety purposes.