[RE-wrenches] Surge arrestors on strings

Tue Oct 9 18:10:25 EDT 2018

We have been using Midnite SPD's since they came out. The one suggestion
I have is the light is too intense. I have clients who have covered the
SPD's in tape to keep the light from attracting small flying insects to the
electronics area. Some places just have too many bugs :( The blue seems to
bring them. I saw an inverter fan filter that was an 1/8 of an inch thick
with gnats. 

Fly paper will help but the battery circuit and AC panel
SPD's need some help here. 
Dave Angelini Offgrid Solar
"we go where
powerlines don't"
http://members.sti.net/offgridsolar/ [1]
e-mail
offgridsolar at sti.net [2]
text 209 813 0060

On Tue, 09 Oct 2018 17:02:32
-0400, Drake  wrote: Hi boB,

 I will keep putting an SPD on each string
and on the AC line. Sometimes my systems end up with a lot of blue lights
hanging from a wiring gutter!

 Have you ever heard of any problems using
the Midnite SPDs with Sunny Boy TL series inverters? So far, I don't think
I've had a problem, although one TL-22, on a large metal roof, had arc
fault protector trips. 

 Thanks,

 Drake

 Drake Chamberlin
 Athens
Electric LLC
 OH License 44810
 CO License 3773
 NABCEP Certified Solar PV

 740-448-7328
 http://athens-electric.com/ [3] 

 At 01:39 PM 10/9/2018,
you wrote:
 Content-Type: multipart/alternative;

boundary="------------98C0DCEF93B9ECF248E0580B"
 Content-Language: en-US

For an inverter with two MPPT inputs, you will need to treat the negatives
and positive lines separate unless
 the manufacturer says something else.
That means one SPD per array unfortunately. Negative and positive connect

to separate leads of the SPD and then ground in the middle. As both
positive and negative PV lines rise together
 relative to ground, the SPD
is supposed to clamp that rise to below the equipment's hi-pot voltage that
they test
 to at the factory. (i.e. common mode voltage rise) All wires
except for ground (chassis) of the equipment are tied 
 together and the
hi-pot machine (sort of like a Megger ?) applies the high voltage between
all those wires on one 
 side and ground on the other to make sure the
insulation doesn't break down inside the equipment. 
 This hi-pot test goes
for AC utility input/output connections and DC from the PV input side. 

The SPD has to clamp plus and minus and AC inputs to a lower voltage than
this hipot rating but higher voltage
 than lines will see differentially in
voltage. Remember that in a 3-wire SPD, there is two sets of MOVs in series
and
 the center is tied to ground. If one MOV starts conducting at say, 500
volts DC then you can apply up to 1000
 volts between the hot leads. Each
plus and negative line can rise up to 500 volts from the lightning before
they
 start to clamp. The bigger the lightning strikes effect, the more
current will be applied to the MOVs though and
 the clamp voltage will rise
somewhat. That's why the SPD arrestor voltage should be well below the
hi-pot voltage,
 whatever that is... Hi-pot voltages are quite a bit higher
than the operating voltage. For example, All Classic CC's
 are tested to
2270 volts DC from hot lines to ground. It's something like double the
operating voltage plus 1000V
 and multiply by 1.414 for DC rating..... I'm
going off memory so don't quote me on that but something like that.

 I
think that Ray has the right idea about short connections like from the
local generator. Battery also.
 Just apply SPDs to anything that goes
outside like an antenna.

 boB

 On 10/9/2018 8:26 AM, cwarfel wrote:

 I
think something on the order of 90+% lightning strikes come from the
utility feed, not the dc side. That has to be ignored if in a high strike
area or grid isolated. 

 On 10/8/2018 10:37 PM, Ray wrote:

 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.

 Maybe someone from Midnite
can clarify this.

 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.

Ray Walters
Remote Solar
303 505-8760
 On 10/8/18 4:03
PM, Drake wrote:
 Hello Wrenches,

 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? 

 I believe the Midnite units are the best. Are they worth
the expense?

 Thank you,

 Drake

 Drake Chamberlin
 Athens Electric LLC

OH License 44810
 CO License 3773
 NABCEP Certified Solar PV 

740-448-7328
 http://athens-electric.com/ [4]

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