Non-tech manufacturer folks on the list [RE-wrenches]

[Michael Welch, Home Power]

Hey gang, I am posting this on behalf of Kent, who is undergoing an email glitch.

wrenches, here is my lay understanding of surge arrestors and lightning: 

surge arrestors are not going to protect against a direct hit no matter what
you do. all bets are off regardless of the arrestor. at best they will come
apart and not take out too much of the stuff they are supposed to protect.

MOV's don't work, they only take a limited amount of energy before they fail
and short. when they fail, they light on fire real nice and take out
everything around. they will generally continue to short the array to ground
until something stops the fire. to protect against this, a fuse must be
installed in series with the mov, so when the mov shorts the fuse blows.
typically, there is no indication they have failed, so the next time the
system is hit there is no surge protection.

SOV's seem to work better. they are designed to take repeated hits without
failing (or so the mfg says). we have had much better luck with these. at
one time sandia only recommended sov's. i've heard they have changed their
tune, but unsure why.

lighning and lightning induced surges are seeking earth ground. as this is
their electrical return path to complete the circuit (the reason there is
lightning).

in the event of a near hit, the SA may redirect a large induced dv/dt away
from the electronics if properly installed. for this to work the SA must be
grounded, else you will redirect the energy to the other pole. the SA's i've
seen are just electrodes in sand, spaced an amount to arc when the voltage
exceeds a threshold. some games may be played by grounding different poles,
but this will just change the clamping point of the sa. regardless, one of
the poles must be grounded. if you don't ground the sa i don't see how it
will work. but, given the nec requirement of pv conductor grounding, you
will always have a ground referrence through the pv ground. the only way i
can see connecting these things is either pole-to-pole or
plus-pole-to-ground with neg-pole-to-groung. either way, the sa is grounded
if an array conductor is grounded. in terms of a bi-polar array, if you are
just pole-to-pole connected, the surge will be exaggerated by the negative
potential of the array, causing even more damage as the surge will more
readily jump to the electronics as it seeks ground. 

in terms of proper grounding, there should be one point of system ground for
the pv ground fault detection to work properly. multiple pv grounds cause
circulating ground currents. this is what is referred to in our literature.
safety grounds (and sa grounds) may be dropped all over the field, but they
must be bonded together to the single point of system ground. you don't want
potential differences in your safety grounds.

for what it is worth, 

Kent Sheldon 
PV Product Manager 
Distributed Industrial & Utilities Markets 
Xantrex Technology Inc. 
Direct 925 245 5463 - Fax 925 245 1022 
kent.sheldon at xantrex.com  www.xantrex.com

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

==^================================================================
EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9
Or send an email To: re-wrenches-unsubscribe at topica.com
This email was sent to: michael.welch at homepower.com

T O P I C A -- Register now to manage your mail!
http://www.topica.com/partner/tag02/register
==^================================================================