ooops! I had assumed MOV's were a given for any semi on an AC line.
I must have forgotten the old adage "when you ass u me.... '
c
ps: I second the MOV's. I live & work in the thunderstorm  capital of N.A.
and the combination of MOC3052's and 300V MOV's used w/ boards on 240V lines
have never failed through many intense storms and strikes here....while
often consumer appliances have been destroyed.

cl

> MOC305X series fry at >600V, which can happen several times a
> day during
> thunderstorms. You have to use something like a MOV to clamp
> just above the
> operating voltage to protect any semiconductor device that is directly
> attached to the mains. The MOV has a slow turn-on time
> whereas lightning
> produces the fastest spikes known. The inductance of the
> wiring reduces the
> rise time of a spike, so fast-acting suppressors are
> necessary only if you
> are near the source of the spikes. I have found that a 130V
> MOV across the
> terminals of the 400V rated power triac is adequate at home.
>
> /\/\/\/*=Martin
>
> ----- Original Message -----
> From: "Chris Loiacono" <chris@mail2asi.com>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Tuesday, November 27, 2001 9:55 PM
> Subject: Re: [EE]: favorite opto isolators?
>
>
> > I have had all MOC3XXX optos get destroyed by noisy AC
> lines, with the
> > exception of the 3051 & 3052's. Although the rated Viso is
> the same as the
> > MOC 3031 at 7500V, the actual detector voltage rating is
> about 200V higher
> > on these. I have it on advisement from the Fairchild App
> eng dept to only
> > use MOC305X chips in commercial environments, and the
> results have proved
> > true.
> > Chris
> >
> > > -----Original Message-----
> > > From: pic microcontroller discussion list
> > > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Vern Jones
> > > Sent: Tuesday, November 27, 2001 7:38 PM
> > > To: PICLIST@MITVMA.MIT.EDU
> > > Subject: Re: [EE]: favorite opto isolators?
> > >
> > >
> > > Spike through relays - Maybe yes, maybe no
> > >
> > > If relay spikes are with AC relays, use an MOC3031 with a
> good triac.
> > > The MOC3031 is a '0' point opto isolator trigger for Triacs.
> > >
> > > When using Relays and Solenoids, overkill is in order, if
> > > your load is 3
> > > to 5 amps, use a 20 - 30 Amp device, and place the flyback
> > > protection at
> > > the driver device, not at the load end. If a fast
> recovery diode is at
> > > the load, and there is any wire length at all, then the
> > > induced spike in
> > > the wiring can kill your driver as well. Make sure that
> your flyback
> > > diode is fast enough, and its current rating is
> sufficient to damp the
> > > flyback waveform, and place it at the driver.
> > >
> > > Vern
> > >
> > > "Peter L. Peres" wrote:
> > > >
> > > > > spike through relays
> > > >
> > > > You can buy relays with groundable armature. This acts as a
> > > shield between
> > > > the contacts and the coil. I don't have a type number for you...
> > > >
> > > > Anyway if the grounds are no laid properly then there is no
> > > need for the
> > > > strike to jump the coils, it can be induced or direct
> > > ground current that
> > > > does your circuit in.
> > > >
> > > > Peter
> > >
> > > --
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> > >
> > >
> > >
> >
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