MOV Surge Protector Questions ?

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  #1  
Old 08-10-05, 05:10 AM
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MOV Surge Protector Questions ?

Hello:

Am thinking of installing a point of use type of secondary surge protector to protect the circuit board in a new furnace.

Was wondering if anyone has ever used the Intermatic AG2401 model ?
If so, opinions on ?

It supposedly clamps at 490 V.

This seems to me awfully high, and possibly above what many solid state components and microprocessors would be destroyed. Do you think it (still) would provide adequate protection and be worth installing ?

Any thoughts on this, or recommendations, perhaps, on similar units that clamp lower ?

BTW: - when MOV's fail due to excessive Joules or current flow when they do their job, do they "usually" fail as an open or as a short ?

- when having worked within their limits, are they usually good for many such clampings, or do they degrade quickly, even if the clampings were "nominal" ?

Much thanks,
Bob
 
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  #2  
Old 08-11-05, 10:31 AM
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Not specifically answering your question, but a friend of mine had to replace several MOV's from his electrical appliances (TV, VCR, stereo) when a contractor accidentally connected 240 to the 120 line in his house , the words "Turn it off! Turn it off!" were shouted imediately after the main was turned on.
 
  #3  
Old 08-11-05, 02:41 PM
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Location: Central Florida
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Do you whole house surge protection? I would put that in first.

I can't comment on the particular product you mention - but most mainstream surge protectors are suitable.

As to your question regarding the clamp voltage - the thing is that a surge protector needs to flash over at about 200% - 250% of the line voltage to avoid wearing itself out when normal household electrical loads turn off and on which results in considerable spikes very often during a day. So the 490V sounds reasonable for a 240V circuit.

The transformer powering the circuit board will also absorb a lot of the surge energy due to its own inductance, and there is likely some sort of protection on the board itself.

MOV's generally fail open - problem is you can't test them without specialized equipment so you can't tell if they've failed unless they've exploded. If a MOV fails closed - it will (hopefully) trip the breaker or certainly fry itself open.

MOV's aren't perfect - but they're better than nothing at all!!!
 
  #4  
Old 08-11-05, 09:41 PM
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Surge protectors are rated at instantaneous voltage, so for a 240 volt AC main you have peak voltage of 339. If the clamp voltage is too low, leakage will occur. Remember that MOV are used to protect against very short duration ( ms or us ) very high voltage transients. They do not protect against a power surge from the power company.
 
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