I've got a few cheap micromark surge protectors, and noticed they have a clamping voltage of 650V. Anyone know where I can get a much lower one? I've heard of protectors as low as 270V, but I can't find any to buy.
For 230V RMS?
650 is the peal to peak equivalent, but I think it's just the peak voltage that's relevant here, so anything less than 325v is no good, and you are going to need some margin above that.Don't know what micromark offer, but if it's just a few twopenny MOVs I shouldn't bother.
Yes.
This:
It's to protect computers. Looking at other surge protectors up to 100 quid (this one was 4 quid), nothing is lower than 650V. And some of the 100 quid ones are 750V!
Am I right in thinking 650V is rubbish? I mean the surge could double the peak supply voltage without the protector doing anything, and if the surge was more, it would clamp it down to double, which is enough to f*ck up a computer. Mind you if it's just the power supply caps that go bang, I suppose it doesn't matter. Does a PC power supply stop surges getting past it?
Or.... does 650V mean peak to peak as opposed to zero to peak?
Absolutely not! I've just done a partial rebuild of a gaming machine for someone that has cost United Utilities (their electricity supplier) over £1,500 after it was hit by a voltage surge - same house also had two TVs and a microwave oven blow up too. And about twelve other houses were affected so not a happy time for UU.
This sounds like a loss of neutral fault, and a MOV is useless for protecting against such a sustained fault - it will just burst into flames if the fault goes over the clamping voltage (and they have been known to start fires).
Consequently, the MOV must have a clamping voltage above the 3-phase peak of 570V. Secondly, each time it takes a significant spike, its clamping voltage drops a bit, and it must still remain over 570V after this.
The device is used up a bit by each spike (unless the spike is tiny).
Finally, a MOV (or any surge supression) just across live and neutral is remarkably ineffective for protecting against lightning, where the spike tends to be between different services, such as the phone line and mains, or mains and ground, etc. and not between live and neutral. It won't generally protect against broken neutral (which sees the mains voltage rise to up to 400V). Just what is it you are trying to protect against?
Computers are designed to withstand about 2.5KV spikes and survive minor lightning strikes. A 650V surge protector is quite adeaquate, but might not last long as my local supply frquently gets 1500V fast transients (microseconds), zero to peak. The surge protector is bidirectional, ie it doesn't care which way round the volts are. The current flowing is purely determined by the source impedance, which for lightning strikes is close to zero if local. For interference spikes, surge protectors work OK, but if your supply is cables in the air, then they may well fail quite soon. My worst experiences have been "brown outs", where the supply suddenly reverses phase or skips cycles, which causes transformer saturation and doubles the peak supply volts(up to
700V zero to peak) for a cycle, which then takes a few cycles to settle down. This also buggers up switched mode PSUs, which don't like having their dc supply briefly doubled. If this happens, no surge protector will operate correctly and survive. IME, unless you have a transformer fed supply with a good UPS you are going to lose a few PSUs with the current state of our electricity supply. I lost a couple last year. Just be thankful you are not in the US, where lightning strikes are common and the supply is frequently crap as well.
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I've seen that. At my 2nd last place of work, an electrician mixed up t= he wiring as they had some old colours and some new, causing L1 and L2 t= o be connected to a ring of 13A sockets instead of L1 and neutral. A su= rge protected plug on a digital projector melted, and the bulk capacitor= s in all 20 computers in the room burst (they had no surge protectors), = giving off some stinky smoke. All this tripped the circuit breaker for = the room, which presumably stopped any further damage or a fire. After = I replaced all the capacitors, the computers were fine.
Why? If I get a momentary spike or surge between single phase peak and = three phase peak, I want it removed. Also one above the 3-phase peak I = want clamped down to the 1-phase peak, not the 3-phase peak!
This one claims to be across any pair of pins. I thought they all were.=
Why does it rise? If there was no neutral, and the load on all three ph= ases was equal, nobody would notice. You'd get a rise (or fall) if your= phase was not the same as the other two.
A spike or surge. I don't want it just trimmed to 650V! The spike is s= till there!!
-- =
I'm not so think as you drunk I am...
e:
Maybe it depends how long the surge was. See my other post (reply to a = reply to yours) where a room full of computers was fine when connected t= o two phases by mistake. Just the bulk capacitors in the PSUs blew. I'= ve also accidentally connected a printer and a computer to 240V instead = of 110V when the switch was incorrectly set at the back. Also I've seen= about 10 computers with the switch set wrongly on purpose by kids. Jus= t a bang and a new capacitor required. I would have expected the fuse o= r breaker to blow before the voltage got through to the equipment in you= r case though - the bulk capacitors go short circuit?
-- =
The world's largest fruit are giant pumpkins. The world record is 1061l= bs (481.3 kg).
Aye mains voltage spec is 230 V -6% +10% or 216 to 253 V. The peak for 253 is 358 V.
Dave Liquorice was thinking very hard :
All they are intended to do is temporarily short out a brief surge, maybe even long enough to pop the fuse, after which they (the MOV) need to be replaced. In many cases, without having the means to none destructively test them, you will not even know the MOV has failed.
I feel you are on a loser here. Most power supplies can withstand modest surges in their own right.
Surge protectors offer minimal protection, though I guess any is better than none.
The voltages you quote are way of the mark. 650V is chosen for perfectly good reasons.
If you want true protections then you should be looking at an Online UPS.
At least if that goes down, your equipment will still be working, and furthermore will offer protection against power outages.
What are the reasons? I can't find any details about clamping voltage online, just a brief description of what it is.
Because under fault conditions the mains peak can reach 700V. This is very rare, so 650V is a reasonable compromise. I suggest you look up varistor characteristics for more information.
Then you need an online UPS. Not cheap, but this isn't a level of protection most things need.
I would have thought doubling the voltage was bad for a lot of things.
Exactly, "fault conditions". Surely the point of a surge protector is to remove faults? Maybe it won't last long, but even if it sacrifices itself, and trips the breaker, you've save the more expensive equipment. What I seem to have here should be called a spike protector.
Mains impedance is very low with a short circuit current measured in kA, so a MOV has to dissipate a lot of energy if it should start to conduct.
How big an MOV do you want to use, or how many?
Unless you have a crowbar type of protection no breaker is ever going to open under a fault condition before it's all too late.
A surge protector does not remove faults. It merely reduces the symptoms of a fault. A bit like closing a stable door whilst the horse is escaping.
Oh, I assumed that the surge protector could handle a huge current for long enough for the breaker to open.
Can you get a crowbar surge protector that would blow the 13A plug fuse or the 30A breaker?
That is a much better description of what they can effectively deal short spikes with very little current behind the spikes.
But the short spikes will only be reduced to 650V will they not? I'd much rather they were reduced to 340V and lose a surge protector now and again.
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