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For an inverter with two MPPT inputs, you will need to treat the
negatives and positive lines separate unless<br>
the manufacturer says something else. That means one SPD per array
unfortunately. Negative and positive connect<br>
to separate leads of the SPD and then ground in the middle. As both
positive and negative PV lines rise together<br>
relative to ground, the SPD is supposed to clamp that rise to below
the equipment's hi-pot voltage that they test<br>
to at the factory. (i.e. common mode voltage rise) All wires except
for ground (chassis) of the equipment are tied <br>
together and the hi-pot machine (sort of like a Megger ?) applies
the high voltage between all those wires on one <br>
side and ground on the other to make sure the insulation doesn't
break down inside the equipment. <br>
This hi-pot test goes for AC utility input/output connections and
DC from the PV input side. <br>
<br>
The SPD has to clamp plus and minus and AC inputs to a lower
voltage than this hipot rating but higher voltage<br>
than lines will see differentially in voltage. Remember that in a
3-wire SPD, there is two sets of MOVs in series and<br>
the center is tied to ground. If one MOV starts conducting at say,
500 volts DC then you can apply up to 1000<br>
volts between the hot leads. Each plus and negative line can rise
up to 500 volts from the lightning before they<br>
start to clamp. The bigger the lightning strikes effect, the more
current will be applied to the MOVs though and<br>
the clamp voltage will rise somewhat. That's why the SPD arrestor
voltage should be well below the hi-pot voltage,<br>
whatever that is... Hi-pot voltages are quite a bit higher than the
operating voltage. For example, All Classic CC's<br>
are tested to 2270 volts DC from hot lines to ground. It's
something like double the operating voltage plus 1000V<br>
and multiply by 1.414 for DC rating..... I'm going off memory so
don't quote me on that but something like that.<br>
<br>
I think that Ray has the right idea about short connections like
from the local generator. Battery also.<br>
Just apply SPDs to anything that goes outside like an antenna.<br>
<br>
boB<br>
<br>
<br>
<div class="moz-cite-prefix">On 10/9/2018 8:26 AM, cwarfel wrote:<br>
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cite="mid:d9456b9d-7f42-89d7-1ffb-53810345cd2f@entech-engineering.com">
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<p><font face="Verdana">I think something on the order <font
face="Verdana">of 90+% lig<font face="Verdana">htnin<font
face="Verdana">g strikes come from the utili<font
face="Verdana">ty feed, not the dc side. That has to
be ignored if in a high str<font face="Verdana">ike
area or<font face="Verdana"> grid is<font
face="Verdana">olated. </font></font></font></font></font></font></font></font><br>
</p>
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<div class="moz-cite-prefix">On 10/8/2018 10:37 PM, Ray wrote:<br>
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cite="mid:50c7a8a6-0a86-90cf-0075-c5d755da1069@solarray.com">
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<p>I believe you can use the SPD 300 AC on 2 strings, if PV neg
is grounded. You would connect the green to ground (or PV
neg) and then connect the red to one string pos, and connect
the black to the other string pos. This would be limited to
300 v also. I haven't tried that exact configuration, but I
have used the 300 AC to protect both the AC in and AC out on
120 vac inverters. I also believe you can use a 600 DC
version, and wire as I mentioned, but the LEDs won't light. If
you are using ungrounded inverters, then I think you would
need an SPD for each string in order to protect both the pos
and neg of each string, like you've been doing.</p>
<p>Maybe someone from Midnite can clarify this.</p>
<p>As far as it being worth it, I haven't had lightning related
damage since I started using the Midnite SPDs, and I used to
have system damage every year. If you are not in lightning
country, or the install is in a low spot with less likelihood
of taking a hit, you might be able to skimp. But for some of
these off grid ridge top installs, I consider it a must. Some
times I don't install one on the gen circuit, if its really
close.<br>
</p>
<p> <br>
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<pre class="moz-signature" cols="72">Ray Walters
Remote Solar
303 505-8760</pre>
<div class="moz-cite-prefix">On 10/8/18 4:03 PM, Drake wrote:<br>
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cite="mid:20181008220322.B75F41071B1@pdx1-mailman03.dreamhost.com">
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Hello Wrenches,<br>
<br>
Do you use surge arrestors with multi MPPT input string
inverters? Do you put a separate arrestor on each MPPT input?
I find it sort of pricey using a Midnite Solar arrestor on
each string, but have been doing that. Is there a less
expensive approach that is effective? <br>
<br>
I believe the Midnite units are the best. Are they worth the
expense?<br>
<br>
Thank you,<br>
<br>
Drake<br>
<br>
<br>
<a name="_MailAutoSig" moz-do-not-send="true"></a>Drake
Chamberlin<br>
<i>Athens Electric LLC<br>
OH License 44810<br>
CO License 3773<br>
NABCEP Certified Solar PV <br>
740-448-7328<br>
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<font size="-1"> Christopher Warfel, PE<br>
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