final connections

[Harry Lee]

hello,

i have this question in assignment. I've been surfing the net for hours and i cant seem to find an answear maybe someone here could please help.

Q) Before the final connections are to be make to the distribution board, the electrical supply must be isolated, Describe this procedure and why it is so important.

i just dont understand what it means.

 

[breezer]

if we told you the answer that would be cheating, but a little pointing in the right direction will not do any harm.


Before the final connections are to be make to the distribution board, the electrical supply must be isolated, Describe this procedure and why it is so important.

before the final connections are made. what do you suppose they are

the electrical supply must be isolated. you must know what that means, if not you are in the wrong aprenticeship

Describe this procedure. how would you do it

why is it so important . why do you think. Clue: you want to be alive to do it again don't you

 

[Stod]

Most jointing on LV cables and lines of Distribution Network Operators is done live. 11KV lines are worked on live too.

So why not the same for electricians? That would sort out the cowboys from the pros!

 

[Harry Lee]

Thanks for the guideance do you think my answear is ok?
before the final connections are made. what do you suppose they are

the electrical supply must be isolated. you must know what that means, if not you are in the wrong aprenticeship

Describe this procedure. how would you do it

why is it so important . why do you think. Clue: you want to be alive to do it again don't you[/quote]

Before the final connections are made to the distribution board they must be tested using an insulation resistance tester and all faults must be noted and corrected before you carry on. The electricity supply must then be isolated either by the double pole switch or individual cb’s. Once it has been isolated it can then be tested using a voltage indicator. Before testing the distribution board you must test the instrument to make sure it is not damaged. Once all the testing is done you can proceed to wire it up. It is important to follow this procedure to prevent injury or even death.

 

[Harry Lee]

Most jointing on LV cables and lines of Distribution Network Operators is done live. 11KV lines are worked on live too.

So why not the same for electricians? That would sort out the cowboys from the pros!

No person may work on or near live conductors unless:
• it is unreasonable in all circumstances for it to be dead;
• it is reasonable in all circumstances for that person to be at work and/or near it while it is live;
• suitable precautions are taken to prevent injury

 

[Inspector]

Check meter with known supply
Check circuit to be isolated with meter between live & neutral, live & earth and neutral & earth
Isolate the circuit, fit lock to isolation point (and retain key)
Hand a 'Work in Progress' sign at the isolation point
Check circuit has been isolated with meter between live & neutral, live & earth and neutral & earth
Get permit to work

... or something to that effect

 

[Big_Spark]

Most jointing on LV cables and lines of Distribution Network Operators is done live. 11KV lines are worked on live too.

So why not the same for electricians? That would sort out the cowboys from the pros!

Stod, you can only work on 11KV live if it is an overlead line and you have all the correct fibreglass equipment.

It is ILLEGAL to work on 11KV kit without the correct license and also ILLEGAL to work on 11KV live if it is not an overhead line, ie, in a Trench or in a substation etc. The lines must be isolated.

 

[plugwash]

it depends a lot on the conditions without knowing more info about the kind of assignment this is it's hard to to answer

in the case of most domestic and sommerial boards if you are hired in you test your tester turn of the isolator supplying the board (which should be in or near it) test it's dead and get on with it unless you have been explicitly told of a special procedure to follow

locking off of isolators and cuircuit breakers is generally for when you have to make a connection away from the board to stop anyone turing it back on and giving you a shock

 

[securespark]

And for working live on 240 you should have (amongst other things)

training, insulated tools, rubber mat, rubber soled shoes, insulating gauntlets etc....

 

[Stod]

240?? That voltage became obsolete over nine years ago.

The standard low voltage in the UK is now 400/230 and has been since 1/1/1995.

 

[Big_Spark]

240?? That voltage became obsolete over nine years ago.

The standard low voltage in the UK is now 400/230 and has been since 1/1/1995.

Stod, now your being pedantic, and if that is the case, 240V went out the window on January 1st 1983, that was when CENELEC harmonisation meant we starting using 230V for all calculations.

 

[Stod]

FWL - Look in BS 7671 : 2001 Amendment No 2 : 2004, page 13 and you will see that 230V was introduced on 1/1/1995.

Or do you know better than BS 7671?

 

[Big_Spark]

FWL - Look in BS 7671 : 2001 Amendment No 2 : 2004, page 13 and you will see that 230V was introduced on 1/1/1995.

Or do you know better than BS 7671?

Yes I do

CENELEC Harmonisation Document HD193 was published in 1982, with effect from 1st January 1983. This required all signatory states to harmonise their respective power generation networks to 230 V ac rms +10% -6%. The UK was a signatory state.

With effect from 1/1/83, all power calculations in the UK had to be done using 230V ac rms. The actual supply votage did not change as it fell withing the error bars of the statute documents.

The IEE adopted this new voltage in 15th Edition Amendment 4 as published in January 1983.

The confusion occurs because the BSi did not officially adopt the voltages as prescribed by CENELEC until 1994, which was then official from 1/1/95, that is why this date appears in the Regs book.

However the UK government, CEGB (as it was then) and the IEE, NICEIC and the Industry, accepted the 400/230V ratings as of January 1983.

It is fresh in my mind as I was an apprentice then and remember all the debates at college about the difference etc.

 

[Harry Lee]

It's for a new installation in a building/office block..

there is an existing, single phase, 10way metel clad distribution board by the entrance of the office suite. The 230vV, 50Hz, single phase supply and the installation together forms a TN-S System.

tell me more about distribution boards,, they same as 100A CCU?

10way metel clad? call me stupid dont i dont have much practical experiance.

TN-S is the earthing system i take it..

cheers for replys; it's expanding my knowledge.

 

[securespark]

My college lecturers must have been dinoaurs, cos from 1987-1991 they used 240 in calcs. Wonder why?