"Uncle Peter" wrote in message
news
On Mon, 24 Feb 2014 14:15:06 -0000, Graham. wrote:

On Mon, 24 Feb 2014 13:48:25 -0000, "Uncle Peter" wrote:

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?

Yes.

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.

This: http://petersphotos.com/temp/surge.jpg

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 **** 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?


RMS=Root of the Mean Squared.
It gives the equivalent of the DC for the purpose of calculating power usage
etc.

It is the peak voltage x 0.707 = RMS voltage (but only for sine waves).

So if you have 650Vpeak, the RMS value will be 460V

Mains power 230 volts (RMS) peak value is 325 volts.

So the cable insulation has to stand 325 volts.

For square waves the factor is 0.5