[RE-wrenches] Surge arrestors on strings

Tue Oct 9 17:02:32 EDT 2018

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/>http://athens-electric.com/

At 01:39 PM 10/9/2018, you wrote:
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>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
>>>303 505-8760On 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/>http://athens-electric.com/
>>>>
>>>>
>>>>
>>>>
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>>--
>>
>>          Christopher Warfel, PE
>>        ENTECH Engineering, Inc.
>>PO Box 871, Block Island, RI 02807
>>                (401)466-8978
>>
>><http://entech-engineering.com>
>>EEI logo
>>
>>
>>
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