Why no earth in "double insulated" appliances

[Ross Trician]

A few of us had a ciscussion tonight as to why there isnt an earth in the cable of say a hair dryer, obviously it is double insulated but would the earth core in the cable not be able to be conected at the plug and therefore earth the cable if it got damaged?

oposite thoughts of it, it you run a supply to an unatatched shed or garage, am I right in saying you would use 3 cores but only earth it at the supply end and then create a TT instalation scenario at the shed end. you would therefore have the cable earthed??

any thoughts or views????

Ross

 

[LukeScotty]

Maybe I'm been totally stupid here, But i thought that theres only 2 cores in those type of cables. Line and Neutral, no exsistance of an earth core?

 

[mdavismccoy]

Hi, your first question, double installation simply indicates that the live parts are so well insulated that faults from live to conductive parts cannot occur, even if there are exposed conductive parts. Earth the cable if it got damaged this is not required, economically a waste of money hence not required.

Second question, supply to a detached garage or shed. I take it there are extraneous-conductive parts, make the garage or shed part of a TT system, otherwise it is not required. Back to the TT. A two core armoured cable would suffice, the armour would only be earthed at the supply end, and not be simultaneously accessible with any exposed conductive parts in the garage or shed, an earth rod in to the ground, an MET, associated cables and sizes and don't forget a label.

I hope it answers your question.

 

[Ross Trician]

Lscotty, yes I realise there are only 2 cores in the cable, ( I know I may not be the sharpest tool in the box but even I can count to 10,,,lol) but the discussion some of us had was why only 2 cores and not an earth core as well to give the supply cable and earth core if the cable were to get damaged.