General > General Technical Chat
MOV fire risk
iJoseph2:
In the UK fitting MOV's to the mains incoming supply will become more and more common since the regulations have been updated. For example ..
https://hager.com/uk/support/regulations-18th-edition/surge-protection
--- Quote from: hager.com ---18th Edition Requirements
The 18th edition BS 7671 now stipulates
Protection against transient overvoltages shall be provided where the consequences caused by an overvoltage could
(i) result in serious injury to, or loss of, human life
(ii) failure of a safety service, as defined in Part 2
(iii) significant financial or data loss
For all other cases, protection against transient overvoltages shall be provided unless the owner of the
installation declares it is not required due to any loss or damage being tolerable and they accept the risk of
damage to equipment and any consequential loss.
--- End quote ---
CosteC:
--- Quote from: T3sl4co1l on December 19, 2023, 02:50:12 pm ---
--- Quote from: CosteC on December 19, 2023, 02:28:23 pm ---Nobody mentioned that while in EU nominal voltage is 230 VAC, the realistic voltages in in many places of network reach 250 V due to photovoltaic and other prosumers trying to sell energy. If MOV is rated for 250 VAC it will leak a lot and age quickly. I am not sure how this phenomenon widespread in USA with its 120 VAC system.
--- End quote ---
Very rarely, it can be much worse: since the supply is a 240VCT transformer, if the neutral comes loose for some reason (say, improper, faulty, or damaged wiring), more load on one side than the other will shift the neutral voltage, browning out one side and overvolting the other. UL 1449 for example covers this.
--- End quote ---
240 VAC is UK peculiarity :) Still, the lost neutral is surely fault condition, unfortunately it may last hours. Good fuse shall disconnect equipment, MOV usually does not survives it, and this is expected behaviour for commercial equipment.
Again, fuse selection is critical, thermally protected MOV will help, but not be enough in case of so long overvoltage - other components will not survive.
AVGresponding:
--- Quote from: CosteC on December 19, 2023, 05:34:21 pm ---
--- Quote from: T3sl4co1l on December 19, 2023, 02:50:12 pm ---
--- Quote from: CosteC on December 19, 2023, 02:28:23 pm ---Nobody mentioned that while in EU nominal voltage is 230 VAC, the realistic voltages in in many places of network reach 250 V due to photovoltaic and other prosumers trying to sell energy. If MOV is rated for 250 VAC it will leak a lot and age quickly. I am not sure how this phenomenon widespread in USA with its 120 VAC system.
--- End quote ---
Very rarely, it can be much worse: since the supply is a 240VCT transformer, if the neutral comes loose for some reason (say, improper, faulty, or damaged wiring), more load on one side than the other will shift the neutral voltage, browning out one side and overvolting the other. UL 1449 for example covers this.
--- End quote ---
240 VAC is UK peculiarity :) Still, the lost neutral is surely fault condition, unfortunately it may last hours. Good fuse shall disconnect equipment, MOV usually does not survives it, and this is expected behaviour for commercial equipment.
Again, fuse selection is critical, thermally protected MOV will help, but not be enough in case of so long overvoltage - other components will not survive.
--- End quote ---
In this case, the 240V is not a UK peculiarity; the quoted poster is in the US and was referring to the 240V centre-tapped neutral found in domestic supplies there. AKA split phase, they use both phases where they need more power, ie a tumble dryer, for example.
CosteC:
--- Quote from: AVGresponding on December 19, 2023, 06:22:28 pm ---In this case, the 240V is not a UK peculiarity; the quoted poster is in the US and was referring to the 240V centre-tapped neutral found in domestic supplies there. AKA split phase, they use both phases where they need more power, ie a tumble dryer, for example.
--- End quote ---
True, yet USA split phase or two phase system is even more peculiar. Still lost neutral at source may generate even more exothermic effects...
You are right. I am forgetting about USA "solutions" mea culpa.
coppercone2:
well it seems that I read about more MOV and RIFA explosions from europe. I don't think the US power grid is that bad of an idea. Split phase reserved for crazy devices that belong in the garage.
You pay a bit extra in copper weight but in general the failures are less spectacular.
and I noticed way more brown outs / surges in europe then in the USA. They have less local transformer in europe and there is more line effects that damage devices.
and its nice to be able to service most domestic things with a much less hazardous voltage.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version