neutral to earth fault blow rewireable fuse/mcb??

[Kev2632]

can a neutral to earth fault blow the rewireable fuses/ MCB?? when the load is applied to the neutral? is that at all possible??

 

[malcolmsanford]

I would say unlikely ............................. especially on a fuse, is this happening to you?

 

[Kev2632]

yea its happening just now at the moment? is it possible for a neutral to earth fault to blow a rewireable fuse or a MCB?? I Always thought that the MCB/ rewireable fuses could only detect short circuit or L to N isnt that correct????

 

[malcolmsanford]

Yes it should...................... in older installations, or even in special conditions you will find neutrals fused, and they can often blow, but that is normal a dead L_N short that would do that, not a N-E one though

I have yet to see an MCB on a neutral conductor so would have thought that was impossible for any neutral fault to trip it.

Have you the right polarity? What type of circuit is it?

 

[Kev2632]

Yea why would the neutral be fused though? And why would it only cause it to happen on a dead circuit? Why does a L to
N trip the mcb or fuse??!" is it because of the potential difference??? It's a lighting circuit

 

[MarkieSparkie]

... Why does a L to N trip the mcb or fuse??!" is it because of the potential difference??? ... /QUOTE]
I think the fact you ask this question, that you must have little electrical knowledge and therefore recommend that you employ the services of a qualified electrician. If you post your location I'm sure one of the local members on here will be able to help you.

 

[BlueToBits]

Kev

In very early days, there was no standard for electricty supply. Some were DC, Some were AC, all were without an earth and therefore there was no neutral, just 2 lives (or a +ve and -ve), so they used to fuse both of them. When the supply was standardised, fuses only ever protected the live but some of the old fuse boards still exist. One of my would-be customers still has one. She says she is too old to think about upgrading and rewiring, and is happy to take the chance that her electric installation may shorten her remaining time in this world, against my advice.

If your fuse board has a wooden frame with shiny white porcelain fuse carriers behind a hinged wooden door/cover - often with a hook and eye catch, then you may indeed have fused neutrals and should get it professionally checked out. It could be quite expensive to sort this so be prepared for a large bill.

What exactly do you mean by "...And why would it only cause it to happen on a dead circuit? " I am thinking maybe you do have one of these old boards.

The fuse (MCB) can blow due to a L-N or a L-E fault.
2 possibilities come to mind:
1) You have a L-E fault somewhere else, with a poor (absent) or broken earth upstream. The neutral-earth fault passes the current of that L-E fault as the neutral becomes the earth, and it would appear that the N-E fault causes the fuse to blow. This would, however mean that some or all earths are live, but on a circuit of just plastic (dare I say porcelain) pendants and switches, this may not be immediately apparent. If you have a fused neutral, a L-E fault on any other circuit may cause the neutral fuse to blow even with the lighting live fuse removed. If you do have fused neutrals it's likely you have no incoming earth system but could well have lead sheathed waxed paper cables that would provide the earth continuity that would allow your symptoms to exist.

OR
2) A black or blue switch wire may be confused as being a neutral.

 

[Kev2632]

Kev

In very early days, there was no standard for electricty supply. Some were DC, Some were AC, all were without an earth and therefore there was no neutral, just 2 lives (or a +ve and -ve), so they used to fuse both of them. When the supply was standardised, fuses only ever protected the live but some of the old fuse boards still exist. One of my would-be customers still has one. She says she is too old to think about upgrading and rewiring, and is happy to take the chance that her electric installation may shorten her remaining time in this world, against my advice.

If your fuse board has a wooden frame with shiny white porcelain fuse carriers behind a hinged wooden door/cover - often with a hook and eye catch, then you may indeed have fused neutrals and should get it professionally checked out. It could be quite expensive to sort this so be prepared for a large bill.

What exactly do you mean by "...And why would it only cause it to happen on a dead circuit? " I am thinking maybe you do have one of these old boards.

The fuse (MCB) can blow due to a L-N or a L-E fault.
2 possibilities come to mind:
1) You have a L-E fault somewhere else, with a poor (absent) or broken earth upstream. The neutral-earth fault passes the current of that L-E fault as the neutral becomes the earth, and it would appear that the N-E fault causes the fuse to blow. This would, however mean that some or all earths are live, but on a circuit of just plastic (dare I say porcelain) pendants and switches, this may not be immediately apparent. If you have a fused neutral, a L-E fault on any other circuit may cause the neutral fuse to blow even with the lighting live fuse removed. If you do have fused neutrals it's likely you have no incoming earth system but could well have lead sheathed waxed paper cables that would provide the earth continuity that would allow your symptoms to exist.

OR
2) A black or blue switch wire may be confused as being a neutral.

Yea i understand what your saying, im just through my time and ive put to the job today.

Why does a MCB(fuse) trip when L to N happens? is it because of the overload yea?

 

[ezzzekiel]

hardly an overload is it? l-n would create a dead short between the two with very little resistance and massive current. (you do know this)

what makes you suspect a n/e fault? have you done ir and whats results

 

[Darkwood]

Not been disrespectful but you say your through your time and by the sounds of it on your first fault.... what qualifications and how long was your training??? the confusion and questions you ask are basic for even a first yr apprentice... your asking why a L/N trips a mcb 'is it because of overload' ---- seriously this a question you should already know and question your abilities to be doing your job.... sorry harsh but true.

 

[needasparks]

Its not because the switched lives not sleeved is it ? Thinking black is neutral.