On Sat, 20 Sep 2008 21:12:19 GMT firstname.lastname@example.org wrote:
| I cannot see any valid reason for doubling the live to ground clamping
| voltage, it the same as saying why bother to fit surge suppression in the
| first place. The lower the clamping voltage the less likely it is to damage
| the connected equipment.
I do agree with this concept. But my point is something else.
go ahead and change the surge protector designs so that the clamping
voltage is doubled for the 120V protectors, then maybe that creates a device
that could be used on twice the voltage.
If the clamping voltage in the USA is doubled, but this does not happen in
Europe, then the devices in both would end up being about the same, right?
I'm looking for devices to protect against surges at point of use for 240V
as wired in the USA. I could use a protective device from Europe, but it
would not be optimal. But my big point is, if they double the clamping
voltage of protective devices from USA, they would basically be the same
and this gives me another choice to find a device that should work be will
be less than optimal.
The optimal design would be one that considers the voltage to be 240V L1-L2,
120V L1-G, and 120V L2-G. The less that optimal designs have one advantage
over the optimal designs: they are available.
So the remaining question is, if they do double the clamping voltage on the
the models for the 120V market, are they usable on 240V? Would there be any
difference between these "doubled for 120V" compared to the "normal for 240V"
models in UK (not considering the NEMA vs. BS outlets and plugs, fusing
| One perceived advantage of using higher voltage MOVs is the transient energy
| rating, for example a 20mm 150 VAC MOV typically has a rating of 120J, while
| a 20mm, 300V MOV has a rating of 250J. Therefore the higher voltage device
| can withstand a larger surge energy level before failure, but against this
| you will have the higher clamping voltage that is more likely to damage the
| connected equipment. Energy ratings are used as a marketing tool by some
| manufactures. Finally it is the connected equipment that we are trying to
| protect not the MOVs from failure. The simple answer is use a large diameter
| MOV, which gives the best of the both, a similar clamping voltage and a
| higher energy rating. Some manufactures attempt to increase this by the use
| of MOVs in parallel, unfortunately this does not normally work. For it to
| work it requires matched MOVs, without this the lowest rated MOV takes all
| the surge energy, while the other does very little.
Apparently some "experts" think that today's home appliances can withstand
some higher surge levels, and that the MOVs are being destroyed more often
than desireable in the protectors.
When I look at my computer SMPSUs and see "100-240V 50/60Hz" on them, should
I assume these units can withstand the surge levels that would not be clamped
by a 240V protector device in UK, when used in the USA whether on 120V or 240V?
Surges that originate upstream on the power utility distribution lines might
well have twice the voltage on a 240V connection compared to a 120V connection.
But surges that originate after the utility transformer steps the voltage down
to the utilization voltage, are going to be the same.
The only reason I see to have any more protection in the USA compared to the UK
is that we have areas of the country with more frequent lightning.
| The basic circuits we have been discussing, do provide reasonable levels of
| protection, but do have limitation, in relation to the energy they can
1. So maybe we don't need a lower clamping voltage in the USA, given that
more and more appliances (especially computers) handle all of 100-240V.
2. So maybe there is an advantage in the ability to handle more energy with
the clamping voltage doubled. That and being destroyed less often.
1+2 = maybe the "experts" are right.
3. I want to use 240V, even though that means a different system configuration
in the USA (compared to UK).
1+2+3 = more devices available (but I have to be very careful to choose units
that have this doubled clamping voltage else the MOVs will give up their magic
smoke as soon as I plug them in).
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