My understanding is that he is saying that there is 'fusing down' (whether in an FCU or wherever) for the 1mm² cable, but that the fuse is in the neutral, not line, conductor.
Kind Regards, John
Fuseing neutral
- Thread starter AndyPRK
- Start date
Kind Regards, John
Sponsored Links
- Joined
- 26 Aug 2016
- Messages
- 6,833
- Reaction score
- 1,010
- Country
Fair enough my opinion is based on a fault can occur at any time and cause a fire whereas the neutral conductor would be insulated and it's more likely someone is testing for dead after isolating before working on the appliance or circuit.
Regarding the rcbo i was on a more general case where the rcbo polarity was reversed. Agree if the rcbo is correct.
Regarding the rcbo i was on a more general case where the rcbo polarity was reversed. Agree if the rcbo is correct.
We (I presume including Andy) know that - but Andy asked, "out of interest", what were "ALL the reasons" (his capitalisation) why we shouldn't put fuses in the neutral conductor.
Kind Regards, John
Sponsored Links
Isn't that just wrongly connected (reversed polarity) rather than fusing the neutral per se?
- Joined
- 27 Apr 2008
- Messages
- 9,438
- Reaction score
- 894
- Country
Fair enough, I guess he may have to be explaining to someone why it's a stupid idea, been there - got the T-shirt 
I try to tell the senior (aged) electrician at work to stop considering the neutral as being safe, as if it's at ground potential (coz "it's connected at the transformer anyway" he says) because there is never a guarantee
that the L & N are not swapped round in the socket. (we build appliances that often plug into a 13A socket).
But he's in his dotage and won't listen.
I try to tell the senior (aged) electrician at work to stop considering the neutral as being safe, as if it's at ground potential (coz "it's connected at the transformer anyway" he says) because there is never a guarantee
that the L & N are not swapped round in the socket. (we build appliances that often plug into a 13A socket).
But he's in his dotage and won't listen.
Fair enough, but we are then in the business of debating which of two (both very rare) events is the more likley - which is why I would prefer to just say that both reasons were very important (with the attempt that 'ordering' I previously made).
Let's face it, we all agree that it should not be done - we're just having an 'academic' discussion about the reasons.
I'm not quite sure how that could be achieved with 'standard' RCBOs, given that the supply-side L usually connects to the L busbar. One could, of course, wire the circuit (from the load side of the RCBO) with reversed polarity - but it would then still be the L that would get disconnected in the case of a residual current, even if the circuit 'thought' that it was the neutral, wouldn't it?
Kind Regards, John
Are you just distinguishing between intentional/deliberate and unintentional/accidental fusing of the neutral?
I would imagine that if/when it happens, it will virtually always be unintentional, since I can't think of any reason why someone would deliberately fuse (only) the neutral.
Kind Regards, John
Although, as I've just written, I cannot think of any reason why anyone would deliberately fuse (only) the neutral, historically speaking, double-pole fusing (L and N) seemed common. I may be wrong, but I have the feeling that this was once even true of at least some cutout fuses.
Back in the 60's, and perhaps a little beyond, I built umpteen mains-powered PSUs. In those days, it seemed totally 'standard' (probably for no reason other than "that's what we've always done"), at least amongst amateurs, to put fuses in both L and N of the incoming supply (as well, often, as some fuses on the outputs) - and we routinely used Bulgin panel-mounting dual fuse holders, which seemed to exist primarily for that use, for that purpose (the left hand one in the below dusty/rusty photo - the RH one is for outputs {and the actual fuse carriers are currently 'somewhere else!}) ....
However, I guess that we had thought about the potential problem of doing this since (as can be seen in the photo), we usually put panel-mounted neons between L and N on both sides of the fuses (the two green neons) - so that one could see that the equipment was still 'live' if only one of the fuses (particularly the L one) had blown.
However, why we did it, other than because of 'habit', I have no idea.
Kind Regards, John
Back in the 60's, and perhaps a little beyond, I built umpteen mains-powered PSUs. In those days, it seemed totally 'standard' (probably for no reason other than "that's what we've always done"), at least amongst amateurs, to put fuses in both L and N of the incoming supply (as well, often, as some fuses on the outputs) - and we routinely used Bulgin panel-mounting dual fuse holders, which seemed to exist primarily for that use, for that purpose (the left hand one in the below dusty/rusty photo - the RH one is for outputs {and the actual fuse carriers are currently 'somewhere else!}) ....
However, I guess that we had thought about the potential problem of doing this since (as can be seen in the photo), we usually put panel-mounted neons between L and N on both sides of the fuses (the two green neons) - so that one could see that the equipment was still 'live' if only one of the fuses (particularly the L one) had blown.
However, why we did it, other than because of 'habit', I have no idea.
Kind Regards, John
- Joined
- 17 Aug 2010
- Messages
- 2,741
- Reaction score
- 453
- Country
Um... I may be misunderstanding your point, as I so often seem to. But any item which is considered to require internal fusing designed to operate if a live accidentally connects to the externally touchable earthed metal of the item, must be two pole fused, because there is no guarantee which country it will be used in and which way round the mains plug will be inserted. Such items are also required to carry a warning internally that double pole fusing is in use, to protect service engineers.
Wasn't it the case that a suitably rated fuse would be put in the live side and a solid 'fuse' or link put in the neutral side so giving the provision of total isolation whilst ensuring it was the live side that disconnected in the event of a fuse rupture.
When I worked on floating 125VDC systems it was essential that both sides were fused and capable of disconnection as a single ground fault would still leave in excess of 60 volts on the other line. No prizes for guessing how I found that out !
When I worked on floating 125VDC systems it was essential that both sides were fused and capable of disconnection as a single ground fault would still leave in excess of 60 volts on the other line. No prizes for guessing how I found that out !
I must admit that I hadn't thought of that 'international' issue - but I cannot say that I can
If there are two fuses, then I reckon that (in addition to the Warning notice you mention) there is probably quite a lot to be said (as an additional 'safety factor') for my decades-ago practice of having an indicator light between L and N on the supply side (if not also on load side) of the fuses!
Kind Regards, John
Edit: crucial typo corrected
Last edited:
Maybe, but I had a feeling that, at least in some cases, that 'solid neutral link' came later, replacing what had originally been a fuse in the neutral. However, I may well have been wrong about that.
In situations more complicated than a simple 2-wire L+N supply, there is presumably a need for a fuse in every feed that is at a potential significantly different from earth (the most common being a 3P+N supply).
Kind Regards, John
- Joined
- 27 Apr 2008
- Messages
- 9,438
- Reaction score
- 894
- Country
Can you identify what legislation forms the "must" for this please?
Is it part of a European standard or something?
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
