[RE-wrenches] Ferrules for large fine-stranded wire.

Tom McCalmont tom.mccalmont at pairedpower.com
Wed Sep 3 17:02:06 PDT 2025 

I’ve been monitoring this thread with interest and wanted to add some perspective since we have experience with this.

Listed lugs in combination with DLO cable are a good solution for connecting batteries to inverters.  The DLO cables are much more flexible at large wire sizes typical of battery cables, and listed lugs provide a safe method to connect the cables to the inverter that assures you will not lose strands in the connection.  Because DLO cable contains many strands and there is some amount of open space between those strands, the overall diameter of the DLO for a given gauge is higher than it will be for equivalent sized stranded THWN.  Therefore, you need to locate lugs that are appropriately sized specifically for DLO cable.

In addition, many of the crimping devices that I’ve seen pass through the group for attaching the lugs will not result in a listed connection, and they could create fire risk.  Screw lugs may not tighten appropriately on the fine strands of DLO as one commenter mentioned.  Hammer-type crimping tools may work to result in what feels like a firm connection, but there is no way to judge that you have hammered with the exact appropriate force to result in a listed connection.  The only sure-fire way to do so is with an over-center crimping tool that is listed for the purpose of attaching the specific lug you have selected to the cable type of a matching size.

These tools are very expensive, and I understand the pain of having to purchase the correct one.  We are all tempted by cheaper options.  But the pain of that one-time expense is likely to be much less than the pain of compensating a very unhappy customer following a fire started by a substandard connection.

As we all know, battery cables carry a lot of current, and substandard connections are much more likely to create fire risk than would be the case for high voltage, low current connections.  I hope this voice of experience is helpful!

Tom McCalmont, P.E.
CEO, Paired Power
pairedpower.com <http://pairedpower.com/> | LinkedIn <https://www.linkedin.com/company/paired-power/>
Direct: (669) 877-2931

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> On Sep 3, 2025, at 4:33 PM, James Jarvis via RE-wrenches <re-wrenches at lists.re-wrenches.org> wrote:
> 
> William,
> 
> None of the crimpers you sent photos of are for ferrules. Those are all lug crimpers. Some are barely that. Nobody should be seriously considering anything you hit with a hammer to be a proper tool for installing any type of connector.
> 
> Ferrule crimpers produce a square crimp and do what they are supposed to.
> 
> Last Wednesday I sent you a note with this link:
> https://www.ferrulesdirect.com/collections/hand-crimping-tools/products/vag240
> 
> It makes a square shape and won't have weird edges and the artifacts you mention you get when you smoosh a ferrule with a non-ferrule crimper.
> 
> Ferrules are highly useful and reliable when installed correctly. You just need the right tool.
> 
> The other thing I mentioned last week were pin adapters. They are crimp on fittings that are rated for fine stranded wire and they convert it to course stranded or solid shape. Here was the example I sent:
> https://www.ilsco.com/Ilsco/ccrz__ProductDetails?sku=F2C-1%2F0-1%2F0-ILSM-ILS&cclcl=en_US
> 
> 
> 
> 
> Best regards,
> 
> 
> 
> -James Jefferson Jarvis
> APRS World, LLC
> +1-507-454-2727
> http://www.aprsworld.com/
> 
> 
> On Wed, Sep 3, 2025 at 6:10 PM William Miller via RE-wrenches <re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org>> wrote:
>> Friends:
>> 
>>  
>> My understanding is if the lug has a set-screw that contacts the strands, fine strands can wind around the set screw, get into the threads and not tighten adequately.  If you are crimping fine strands inside of some type of barrel your connection should be OK. 
>> 
>>  
>> I had been using Outback until they imploded and all of the battery connections were via studs or bolts that required crimped-on rings.  Now I am back to set screw lugs and fine stranding became an issue again.
>> 
>>  
>> I did try another experiment: I took a 4/0 ferrule that would not fit into the Envy lugs and snipped a section out of it.  I curled it into a slightly smaller diameter and it fit into the lug.  I suppose one could cut the ferrule in half longitudinally and insert a portion of the ferrule between the set screw and the strands.
>> 
>>  
>> I am pleased with the copper sheeting wrapped around the fine strands.  That will be my SOP.
>> 
>>  
>> William
>> 
>>  
>> Miller Solar
>> 
>> 17395 Oak Road, Atascadero, CA 93422
>> 
>> 805-438-5600
>> 
>> www.millersolar.com <http://www.millersolar.com/>
>> CA Lic. 773985
>> 
>>  
>>  
>> From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org <mailto:re-wrenches-bounces at lists.re-wrenches.org>] On Behalf Of Ray Walters via RE-wrenches
>> Sent: Wednesday, September 3, 2025 1:40 PM
>> To: re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org>
>> Cc: Ray Walters
>> Subject: Re: [RE-wrenches] Ferrules for large fine-stranded wire.
>> 
>>  
>> I've got to ask: Are none of the lugs on these Chinese inverters approved for fine strand cable?  I just have not had a problem with that, but I've mostly used Magnum, Midnite, and Outback equipment over the years.   What were the lugs on the old Trace DC 250 boxes?  Were they fine strand rated?  They sure were tough to get 4/0 into, as William mentioned. 
>> 
>> Ray 
>> Remote Solar
>> 
>> On 9/3/2025 12:57 PM, Kent via RE-wrenches wrote:
>> 
>> William,
>> 
>> If the only reason the ferrule wouldn't fit after using the hex crimper was the ridge left where the dies meet, you could rotate the cable 120 degrees and crimp the ferrule again.
>> 
>> I doubt that the indenter crimper will do a decent job with large ferrules.
>> 
>> I do like your thin piece of copper solution. Not UL approved but I dare say wrench approved.
>> 
>> Kent Osterberg
>> Blue Mountain Solar
>> 
>>  
>> On 9/2/2025 8:55 PM, William Miller via RE-wrenches wrote:
>> 
>> Friends:
>> 
>>  
>> Thank you for all of your input on this question.  I feel it only right I report back how this turned out
>> 
>>  
>> I tried a crimper like this:
>> 
>>  
>>  
>>  
>> It left a jagged ridge on both sides of the ferrule where the dies met.
>> 
>>  
>> The crimper below was suggested but I have not tried it:
>> 
>>  
>> This was suggested but I have not tried it either:
>> 
>>  
>>  
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