Archive for January, 2009

Hello, and a happy new year to you all!  I hope the present economic “difficulties” are not affecting you too much.  Rest assured that if your business does go “belly up” you will be able to stroll down Whitehall with the captains of industry/banking and get a tasty bale-out from ministers, not….

Anyhow, now for something on a different subject.  When I teach 2391 (inspection and testing) I do get rather bored looking at the same old questions. One that comes up all the time is regarding circuit polarity.  This basically means keeping the wiring “correct” and to convention. Now the question goes along the lines of “Where must correct polarity be observed”

Guidance note 3 states that it is necessary to check that all fuses and single pole switches are in the line conductor, so far so good. It also states that sockets must be wired correctly and finally that screw type lamp-holders have line connected to the centre contact, with neutral being assigned to the screw thread.

Now this pretty sensible because you don’t want the thread as a live conductor as it is exposed, big and easily touchable!  An exception is given to E14 and E27 holders to BS EN 60238. When I teach this part there are a lot of blank expressions around the room.  The regulations people are talking about this…

So there ends the confusion! Yes it is an edison screw lamp-holder but the line and neutral contacts are buried deep inside so it does not matter which way you connect it up.  If you stick your pinky in here you cannot be saved and probably asked for it anyhow….

Now for completeness I will talk about the numbers and letters.  The “E” means edison, named after the great American inventor and one of the fathers of electricity.  the number is the size of the thread in mm.

The three sizes available here in this part of the world are E14, E27 and E40.  The big ones are used on street lights and such…You may also hear some sparkies refer to these by their old names.  The small one is sometimes called a  ”lilliput” type ( you know as in Gulliver’s travels) and the big one, wait for it, “goliath” (as in David and Goliath from the old testament) The middle one has no name, as it is all complicated enough as it is!