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[TowerTalk] Whole house surge suppressor's.

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Subject: [TowerTalk] Whole house surge suppressor's.
From: "Jim Thomson" <>
Date: Mon, 3 Jan 2011 04:11:31 -0800
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Hi Dale.

I've been in the fire service for 27 years now and I can't tell you the 
number of surge suppressors of the type that are typically installed on 
a 1/2" or 3/4' knockout hole* *that created 
the structure fire that we were responding to.  On a couple of 
occasions, I've seen them violently shoot green flames out of them in 
every direction as they burned themselves to a cinder.

My power company installs the meter base style suppressor which places 
it outside of the structure the majority of the time.  I'm sure that's 
probably what you're also looking at.


Jon Pearl - W4ABC

##  The Joslyn brand surge protector's are used by the 10's of thousands  by 
telco's  across NA. 
They are mounted below, or close by a main panel.   Conduit  between main panel 
+  protector. 
The protector's we used at work, were all in steel  enclosures, and those 
things  were latched
shut tighter than a drum.   Each of the two  [ 3  movs used for  3 phase]  huge 
movs  are wired
between hot and neutral [ ditto with 3 -phase].   Each mov had a 20A slow blow 
fuse in front of it. 
[600V rated... big cartridge fuses.. like the .375" to .5"   x 2" long variety] 
Output of each fuse feeds a  neon.  Output of neon wired to same neutral.   A 
4pdt relay..with a 120 vac coil
is also used... one per mov.   120 vac coil wired between output of fuse and 

##  OK, with everything normal, all the neons are lit green.    If one or more 
MOV's  shorts out, the mating fuse
that feeds it blows open asap, and MOV is  now out of the circuit.   Associated 
neon also goes dark.   Mating
120 vac  dpdt relay  also drops out..... bringing in an alarm to the alarm 
center/NOC etc.  All the relay's of course,
in normal operation, are always operated 24/7..... except when a mov fuse blows 

##  I never saw one of those joslyn protector's  ever catch fire in 34 yrs I 
was there. [ no equipment failures  from
lightning, transients/spikes/surges either].   As long as they are fused 
I don't see how the mov could burst into flames.   Even if it did, none of it 
would get past the steel box.  Those box's
were sealed very good, with a pair of real heavy duty latchs.  They were not 
like a regular steel electrical box either. 
These things were water proof, fire rated  nema box's.   The seal design was 
the best yet.   If they were the slightest fire hazard,
the insurance co  would have been reading us the riot act.  [ factory mutual in 
the US  is the main insurance co for most of the telco's 
in the usa + canada.]   In some parts of Florida, etc, home insurance co's will 
insist that whole house protector's are employed. 
Insurance co's  were getting tired of paying out claims in lightning prone 

##  I have seen some of the whole house protector's..sold at home depot etc.. 
that use way smaller mov's.... and contain 
no internal fuses... but use a spare 40-60A  breaker position on the main 
panel.  The box's  they use  look flaky to me.  They also 
use plane romex, etc,  from main panel to plastic box... and no conduit.  

Later... Jim  VE7RF


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