In theory maybe, however if a lamp pops then it would be fun to watch all the others on the same phase getting brighter, popping, brighter, popping, bang!
Not sure how discharge lighting would react with this sort of setup too
Single phase breakers on 3-phase circuit
- Thread starter mfarrow
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Not sure how discharge lighting would react with this sort of setup too
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Thanks. Does this not mean that it would be sensible to have an over-voltage-triggered breaker of some sort?
Kind Regards, John.
H
holmslaw
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And you, holmslaw, are demonstrating what you are: a wannabe BAS. It is not a compliment, BTW.
There is no need for insults.
Oh and by the way, you spelt "you're" wrong.
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Getting back to the side discussion regarding lost neutrals. I was called to a large cheese factory some years ago after their lab was gutted by fire. The initial cause was deemed to be electrical so they were trying to blame us for excessive volts. Now the site is supplied at 11kV so had that been the case we'd have pretty much have caused problems in a small town.
The cause of the fault was a loose neutral connection on the switch fuse feeding the lab!
The cause of the fault was a loose neutral connection on the switch fuse feeding the lab!
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holmslaw
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Thanks for the replies.
Just to clarify a few things:
- The shared neutral starts at the distribution board
- The 3-pole MCBs cannot be used for isolation as it is a TT system - they are just their for protection
- When I say 'balanced' sorry, I mean across the whole system, i.e. on each circuit their aren't necessarily liminaires in multiplies of 3. Therefore if you lost the neutral, wouldn't you have the same voltage problem?
- As far as I'm aware, there's no prohibition to having more than one protective device per circuit, and fuses are a prime example of this.
Just to clarify a few things:
- The shared neutral starts at the distribution board
- The 3-pole MCBs cannot be used for isolation as it is a TT system - they are just their for protection
- When I say 'balanced' sorry, I mean across the whole system, i.e. on each circuit their aren't necessarily liminaires in multiplies of 3. Therefore if you lost the neutral, wouldn't you have the same voltage problem?
- As far as I'm aware, there's no prohibition to having more than one protective device per circuit, and fuses are a prime example of this.
In theory maybe, however if a lamp pops then it would be fun to watch all the others on the same phase getting brighter, popping, brighter, popping, bang!
Not sure how discharge lighting would react with this sort of setup too
In the factory I used to work in one of the overhead busbars lost it's neutral. All of the fluorescent lights glowed purple with the varying increased voltages across their control gear.
P
Paul_C
I think that John's posts show that he is thinking about the situation and considering all the possibilities at any given time. He shows a far better understanding of basic principles and the ability to think through various scenarios than some "qualified" electricians who seem unable to figure out anything beyond the BS7671 mantra of "If it complies with BS7671 then it's perfect, if it doesn't comply then it's dangerous and needs changing."
It would certainly provide some protection against this sort of problem. With a TN-C-S arrangement, having a local earth electrode at the house connected to the supply neutral would also be a way to help keep down the voltage, although its effectiveness would depend upon the resistance, connected loads at the time of the fault, position of neutral fault etc. Of course, in many cases a TN-C-S house will already have such an earth connection anyway by way of bonded pipework.
True, but the average earth electrode would not have a low enough resistance to make a lot of difference if there were appreciable' loads - since, even if full supply voltage were applied to such an electrode, you'd be hard pressed to get more than a small handful of amps down it. PME earths might have somewhat lower resistances (and therefore might help a bit more)(if they were downstream of the neutral break), and bonded pipework might, provide a much lower resistance path to earth, and therfore might help quite a lot. However, the sort of (hypothetical) protection I suggested would presumably more direct and sure. Do you know if such a protection system is ever actually implemented?
Kind Regards, John.
The reality is that the only earths that are tested are those installed at new substations. Any installed at the remote points of the system are not required to be tested and only consist of a single rod, it is not unknown to find these disturbed when others have been excavating after they were installed.
That doesn't surprise me - which is why there was a "might" in the sentence of mine you quoted!
Out of interest, do any parts of the distribution network have any over-voltage protection devices such as I was hypothesising about - since I presume that the end-user chaos of a lost neutral we've been discussing could be an even greater nightmare further upstream?
Kind Regards, John.
Never seen any except on private systems.
Most of the protection below 132kV is overcurrent and earth fault in various forms. Local transformers may be by relay but more often HV fuses (these have actuator pins to trip switches to disconnect all phases, most overhead systems just have fuses that just disconnect one phase) and fuses on the LV network
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