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<p class="MsoNormal"><span style="font-family:"Aptos",sans-serif">For what its worth, I am aware of an APsmart rooftop fire in 2021 that was almost certainly the result of crosstalk. Multiple other failed APsmarts were found outside of the fire area, all exhibiting
some degree of melted plastic and, in some instances, having melted nearby PVwire (I think the Brooks analysis suggested this as the likely failure method – arcing between adjacent strings due to melted wire from bundled homeruns under APsmart). It is very
important that anyone using RSDs understand and eliminate crosstalk. I am amazed how little this issue is discussed and how few installers seem aware. Just Wednesday we inspected a newly installed rooftop with rampant crosstalk and APsmarts.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Aptos",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Aptos",sans-serif">I would generally avoid RSDs altogether if possible.
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<p class="MsoNormal"><span style="font-family:"Aptos",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Aptos",sans-serif">Matt<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> RE-wrenches <re-wrenches-bounces@lists.re-wrenches.org>
<b>On Behalf Of </b>William Miller via RE-wrenches<br>
<b>Sent:</b> Friday, April 3, 2026 3:54 PM<br>
<b>To:</b> Tyrone Houck <tyronehouck@gmail.com><br>
<b>Cc:</b> William Miller <william@millersolar.com>; RE-wrenches <re-wrenches@lists.re-wrenches.org><br>
<b>Subject:</b> Re: [RE-wrenches] Insurance and rapid shutdown<o:p></o:p></span></p>
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<b><span style="font-family:"Aptos",sans-serif;color:#222222">Caution:</span></b><span style="font-family:"Aptos",sans-serif;color:#222222"> This email originated from outside SES. Do not click links or open attachments unless you recognize the sender and know
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Below is a message I received off-line a while ago re: AP Smart, along with photos.
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<p class="MsoNormal">I thought I’d contact you off list. You have been asking about RSD units, I wanted to pass along my experience with the AP Smart RSD unit. I’ll let the pictures do most of the talking - see below. Bottom line, APSmart is a nice little
easy piece of plastic junk to install and commission. However, when something goes wrong it can be a real pain to ID the fault. They have a little gadget that you have to wave over the conductors to listen for a pulse (not always easy on a roof! I went
thru 2 inverters about 6 hrs on the phone with SMA (I got ALL sorts of weird errors, but only 1 arc fault), 2 weeks of back and forth with AP Systems/Smart. After I finally got the arc fault, in an act of desperation, I started tearing the array apart at
significant expense and much frustration by my client (he totally lost faith in solar and had been wanting it for years) I finally found the problem. Luckily this one was on a new install on a metal roof and not on a system that had been through a few seasons
with build up of leaf detritus under the array on an asphalt shingle roof. I’ve been at this for 17yrs now and have never had a piece of equipment fail this catastrophically - especially a piece of unnecessary safety equipment. Their tech support engineer,
while well meaning, is extremely difficult to understand due to language barrier and completely failed to take any responsibility for this failure which could have resulted in a house fire and who knows what else…. My strong recommendation is to limit the
use of any RSD unless pressed to do so by an AHJ. It’s my opinion that these units should be at least in metallic enclosures. I worked at Tigo back before RSD was a “thing” and do see the advantages, but I just think (like BB) that there are more downsides
than up at this point in time given the available tech. I keep this unit in my van and show every AHJ then ask them to tell me what they want me to do in writing. I am not going to be on the hook the consequences of such a catastrophic failure.<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">William Miller</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:#1F497D">Miller Solar</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:#1F497D"><a href="http://www.millersolar.com/">www.millersolar.com</a></span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:#1F497D">CA License C-10 77398</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif;color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma",sans-serif">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma",sans-serif"> Tyrone Houck [mailto:<a href="mailto:tyronehouck@gmail.com">tyronehouck@gmail.com</a>]
<br>
<b>Sent:</b> Friday, April 3, 2026 10:17 AM<br>
<b>To:</b> <a href="mailto:william@millersolar.com">william@millersolar.com</a><br>
<b>Subject:</b> Re: [RE-wrenches] Insurance and rapid shutdown</span><o:p></o:p></p>
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<p class="MsoNormal">Thanks for sharing. I've asked this group multiple times for any anecdotes or pictures of APSmarts failing and never recieved any response. Tigo failures are mentioned often. Personally, I've installed upwards of 1000 APs with no issue(I
don't make a habit of stress testing them by repeatedly hitting the switch during peak production though). All that said, I wouldn’t bother installing them in a situation that didn't warrant RSS.<o:p></o:p></p>
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<p class="MsoNormal">On Fri, Apr 3, 2026, 10:06 AM William Miller <<a href="mailto:william@millersolar.com">william@millersolar.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">I have seen photos of one AP Smart RSD that had melted and burst into flames. <o:p></o:p></p>
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<p class="MsoNormal">The job they are required to do : open a high voltage, arc sustaining circuit under load is a difficult task to accomplish, especially in a small package in an extreme environment. <br clear="all">
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William Miller<br>
Miller Solar.com<br>
805-438-5600<br>
<a href="http://www.millersolar.com/" target="_blank">www.millersolar.com</a><o:p></o:p></p>
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<p class="MsoNormal">On Fri, Apr 3, 2026 at 10:00 AM Tyrone Houck <<a href="mailto:tyronehouck@gmail.com" target="_blank">tyronehouck@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">If considering retrofitting rapid shutdown I would recommend APSmart. I have never had any failures or heard of anyone else who has. <o:p></o:p></p>
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<p class="MsoNormal">On Fri, Apr 3, 2026, 8:05 AM William Miller via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">re-wrenches@lists.re-wrenches.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">If he wants to be more assured of filing an insurance claim he should install RSS. <o:p></o:p></p>
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<p class="MsoNormal">Seriously, the equipment has a bad safety record. I would recommend a safety inspection and a modern charge controller with arc flash and ground fault detection over RSS. <br clear="all">
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<p class="MsoNormal">William Miller<br>
Miller Solar.com<br>
805-438-5600<br>
<a href="http://www.millersolar.com/" target="_blank">www.millersolar.com</a><o:p></o:p></p>
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<p class="MsoNormal">On Fri, Apr 3, 2026 at 7:46 AM Drake Chamberlin via RE-wrenches <<a href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">re-wrenches@lists.re-wrenches.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">Hello All, </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">A client, for an off grid system, is in an area with no code requirements nor inspections. He is concerned that if he does not get rapid shutdown, it could affect his ability to get an insurance claim
paid, if ever needed.</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">The array is on a separate utility building that houses a water pump and tank as well as the inverter and batteries. Since there is more in the building than just solar related equipment, RS is technically
required. </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">Has anyone ever had to deal with this issue?</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">Thank you,</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New""> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">Drake</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New"">-- </span>
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<p><em><span style="font-size:10.0pt;font-family:"Courier New"">Drake Chamberlin</span></em><o:p></o:p></p>
<p><em><span style="font-size:10.0pt;font-family:"Courier New"">Athens Electric LLC</span></em><o:p></o:p></p>
<p><em><span style="font-size:10.0pt;font-family:"Courier New"">Ohio Electrical Contractor’s License 44810</span></em><o:p></o:p></p>
<p><em><span style="font-size:10.0pt;font-family:"Courier New"">NABCEP Certified PV Installation Professional</span></em><o:p></o:p></p>
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