[Amps] MOVs

[Roger]

On 11/25/2010 12:53 PM, Ken Brown wrote:
The original post for this thread has not shown up here yet.
>>    A similar thing happened with garden variety  130 v rated MOV's....
>> too many house fires.  Modern MOV's  for 120/240 v use, will  have a 3rd lead sticking out [offset to one side]
>> and an internal fuse built into em.
>>
>>
A 130V MOV on the 120V AC line would get hot in a hurry 1,414 * 120 = 
169.7V so the thing would be conducting a high percentage of the time.  
You'd want at least a 180V MOV.
>   I don't understand how this can be a useful device. I thought that MOVs
> were supposed to draw lots of current, instead of letting it got
> elsewhere causing damage to more expensive and sensitive electronics.
That is correct, but an under sized, under rated MOV could cause a fire 
by itself.
>   I
> had always thought of MOVs as sort of "sacrificial" devices, intended to
> blow up under the worst power surges,
They are.
>   and mounted  inside a metal
> cabinet so that when they do blow up nothing else is damaged.
Unfortunately many omitted this part.
> I would
> never mount an MOV where it could set fire to something else.
>
Many did. <:-))  MOV's are, or used to be, rated by their breakdown 
voltage.  So people were purchasing 130V MOVs for 120 V AC lines 
forgetting, or not knowing, the peak voltage is 1.414 times the RMS.
> DE N6KB
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73

Roger (K8RI)