[Amps] MOVs

[Roger]

On 1/26/2014 1:05 AM, John Lyles wrote:
> I have had a pair of large Harris MOVs across my main panel to neutral
> and line to line, for 21 years now. They are fed through a
> double pole breaker and there is a relay that fires a sonarlert if the
> breaker trips. We get some great lightning locally during
> summer monsoon season, and I haven't had any equipment failures that I
> know about. Only once has the breaker tripped. I knew it when I came
> home from work, the sonalert was sounding.
>
> If they do fail open, then I would stand to be unprotected.

It happens, but usually when they take a hit that exceeds their capacity 
by a substantial amount. IE: enough to blow them apart
It's far from the normal mode of failure which would be a short.

73

Roger (K8RI)


>
> Professionally, I use more Transorbs (from companies like OnSemi and
> Microsemi). They are superior to back to back zeners for transient spike
> clamping.
>
> 73
> John
> K5PRO
>
>
>
>> Message: 5
>> Date: Sat, 25 Jan 2014 04:43:23 -0800
>> From: "Jim Thomson" <jim.thom at telus.net>
>> To: <amps at contesting.com>
>> Subject: [Amps] MOVs
>> Message-ID: <5ADE14C0E8F14EA392909F4C98133279 at JimPC>
>> Content-Type: text/plain;    charset="utf-8"
>>
>> Date: Thu, 23 Jan 2014 22:31:53 -0800
>> From: Jim Brown <jim at audiosystemsgroup.com>
>> To: amps at contesting.com
>> Subject: Re: [Amps] MOVs
>>
>> On 1/23/2014 7:18 AM, Paul Baldock wrote:
>>> If the amp is running off 240V where in the USA this is symmetrical
>>> about ground and then the MOV is placed between the two phases, it
>>> seems to me that there would not be a surge current to ground.
>>
>> Right.  The problem comes when you take the MOV to the ground.
>>
>> 73, Jim K9YC
>>
>>
>> ##  On whole house protectors, they use a pair of huge, FUSED
>> 130 V rated movs.... wired from each hot side to the neutral...which of
>> course is also grounded.   So you end up with 2 x movs, nose to tail,
>> in series
>> across the 240 V line..with the junction point bonded to neutral +
>> ground.
>
>> ##  On paper, it should work.  Ideally the best way would be to use
>> the whole house protector scheme
>> right at the main 200A  panel.  Then the entire 200A panel is
>> protected from transients  coming down the
>> drop wire into the home.  It should also kill transients + spikes
>> from any equipment  on any branch lines...
>> like electric motors etc.   But then again, the electric motor, etc
>> could be a loooong way from the main panel
>> movs.
>>
>> ##  On paper, using  MOVS  at the 200A main panel  AND the equipment,
>> line to neutral  and not line to ground  at the
>> equipment end...  should work.   IF  movs are not fused..you are
>> asking for trouble.   Real simple to fuse em..plus add
>> a neon or led on the output side of the fuse to serve as a visual
>> indicator that the fuse is functional..... which of course
>> also means the mov is functional.
>>
>> ##  I will defer to Jim Brown as to his thoughts  of using movs wired
>> from hot to neutral at the equipment end of things.
>> Another thought is to wire all ham gear for 240 vac use if
>> possible..including xcvrs etc..but that is not always possible.
>>
>> Jim   VE7RF
>>
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