Why are some things not earthed?

[outmyway]

Just a ponder whilst fitting my kitchen ...

Why are some items not earthed ?

ie. My hotpoint cooker hood is just 2 core ...
My under unit worktop lights are 2 core ..

Both have metal/stainless casings ....

Having had an electrician move my consumer unit it seems NICEIC are obsessed with earth continuity throughout the house it seems strange that some appliances are 2 core?

 

[big-all]

they are double insulated in other words the electrics are within an insulated non conductive housing
look for a square within a square symbol

 

[holmslaw]

..

 

[ban-all-sheds]

Having had an electrician move my consumer unit it seems NICEIC are obsessed with earth continuity throughout the house

1) It's not an "obsession", it's a valid and genuine desire for an electrical installation which won't kill you.

2) The interest in having an electrical installation which won't kill you is not a NICEIC-specific one.

 

[ericmark]

Trying to put into basics either you make very sure electricity can't get out. Double insulated and no earth.

Or you make sure if it does get out it will automatically switch off. Items with earth wire.

For the latter there are two ways to make it auto disconnect. The old method was for enough current to leak to blow a fuse or open a trip. For this to happen within a very short time so you are not injured it may need 5 times the normal current to flow. This is why it seems we have very heavy earth wires.

The second method is to use a device called a RCD and this needs a lot less current to flow for it to work. However with some items it can disconnect when we don't want it to. So often we need some form of compromise and have to use a mixture of methods.

I could talk about loop impedance but I am sure you don't want the technical bit.

 

[outmyway]

OK .. thanks for the replies ...

Yeah they are Class II or have that square symbol double insulated ...

I feel enlightened!


As an aside ... My electrician told me when I changed my light switches from plastic to metal plate ones I had to earth them the back box ... why arent these switches double insulated?
(It took me ages to do it ...)

 

[Adam_151]

Because it would add to the manufacturing costs... the back of the switch where it goes onto the backbox would have to be plastic coated, there would have to be sufficent layers of plastic around where the actual switch part is, and around the screw lugs where it goes onto the class 1 backbox...

Its far easier to manufacture them as class 1 fittings

 

[Spark123]

I'd put it down to cost.
I take it you mean you put a piece of wire between the earth terminal on the face plate and the earth terminal in the back box (along with the circuit protective conductors)?

 

[Steve]

As an aside ... My electrician told me when I changed my light switches from plastic to metal plate ones I had to earth them the back box ... why arent these switches double insulated?
(It took me ages to do it ...)

Carry on - Why isnt everything double insulated?

Often it is not practical, and very expensive to DI everything. How would you DI a toaster, for example, which by its very nature has exposed live parts! You dont DI it, but make it very easy for a large fault current to flow should someone poke something metal in there, by earthing everything around the live parts - the toast grips and the slot surround at the top.

 

[outmyway]

.... fair comments ... I see the issue now ...

Maybe we should all just wear plastic gloves and shoes when handling anything electrical in the house