Fuse on neutral?

[jamminuk]

Apologies for asking more questions but having trouble finding the answers. On this past test paper one question asks for two reasons why you shouldn't place fuses on neutral conductors only. The only one i can think of is that if the fuse went the whole of the system would still be live, what could the other be?

Thanks in advance.

Ben

 

[telectrix]

2nd answer is in the q. fuse in the neutral only. there would therefore be no fuse in the line.

edit. that could give rise to a massive fault current with no protection

 

[mogga]

it would also give NO MEANS OF ISOLATION

 

[tony mc]

Have a look at these and replace putting your fuse in the neutral and work out what happens !!

Hope it helps

Fault Loop Diagrams.

 

[jamminuk]

Thanks all, much appreciated. B-)

 

[oxocube]

The other reason is that a losing a neutral causes all 230v single phase circuits to become 400v circuits.

 

[20al]

The other reason is that a losing a neutral causes all 230v single phase circuits to become 400v circuits.

can you elaborate on that oxo ?

 

[UKMeterman]

Depending on the loading, if this neutral is common to two or more phases then the loss of the neutral path for star connected loads can result in them effectivly connected in delta...

 

[oxocube]

can you elaborate on that oxo ?

Sorry, I should have said a main neutral an a 3 phase system feeding 1 phase supplies. For example, if it becomes disconnected at the TX star point the disconnected neutral cables then form a link between the phases. If you draw it out you will understand.

 

[stevegs]

Found in the packaging of a 300W 118mm linear lamp that was made in China:

USING INSTRUCTION Installing or changing the lamp-stand, please severing the electrical. The temperature of kindling the lamp-stand is rather high, it must be installed on the suitable lamp. Don't close to the combustibles.please notice the good ventilative on and radiation when installing. Don't touch the lampstand or wich when then lampsatand working,so as not to scald. In the return circuit of the working lamp, it must be installed fuse, fuse specification with that of lamp identify power correspondence.

I would hope, despite the appallingly bad translation into English, nobody would be stupid enough to take a pair of wire cutters to the supply cable before changing the lamp! However, the last sentence is a greater cause for concern: one would be forgiven for construing 'return' to mean 'neutral' in this context. I have come across many instances in Chinese consumer equipment of the internal fuse (where fitted) being in series with the neutral connection. It seems this is common practice in China - why?

 

[Top Cat]

2nd answer is in the q. fuse in the neutral only. there would therefore be no fuse in the line.

edit. that could give rise to a massive fault current with no protection

I missed that Tel, just shows you have to read and re-read the question. Probably why i was no good at exams!