automatic splices

[stevenal]

Following a recent failure (that preceded last week's ice storm), I've been looking into these things. [ol 1]
[li]They reduce the allowable tension to 60% of that of an un-spliced conductor.[/li]
[li]They need at least 15% of the conductor breaking strength to function.[/li]
[/ol]

Does this 15 to 60% window seem rather limiting to you? Where would one want to install these things? What's your experience? Thanks.

Clarification: This was a copper wire and automatic splice. Aluminum automatics are available for "full tension" (95%), but the copper automatics apparently are only available in "normal tension" (60%).

 

[bacon4life]

In my area it is rare to install distribution conductors near the breaking strength of new wire, so the 60% criteria is is not particularly limiting.

The criteria of 15% prohibits the use of automatics in slack spans and jumpers.

There are differing opinions about where automatics should be allowed. Automatics are notably easier to install amount of labor, but they are also a notable source of failure over the lifetime of the conductor installation. Even when initially installed with appropriate tension, it is common for tension in a span to change over time as poles settle/age, communication wires are attached to poles, or adjacent spans have poles replaced. Additionally, it is possible for momentary events such as car-versus-pole or fault currents to cause momentary reductions in tension as the conductors thrash about.

One possible compromise is to allow a maximum of 1 automatic per section of wire/guy wire. This allows for installing normal splices on the slack wire, while still allowing the easy installation of the automatic as the final splice as the wire is brought up to tension. If the span needs a subsequent splice, the original automatic should be replaced with a standard splice.

There can also be additional prohibitions against automatics for certain kinds spans such as freeway/railroad crossings as well as for extra long spans like river crossings.

 

[stevenal]

Bacon,
Regardless of the design tension, something happened to the once un-spliced span to cause it to get to 100% of its breaking strength. The fix seems to be to put this mechanical fuse in exactly the same place it broke the first time, ensuring future breaks will be in this location. I could see putting the 60% splice at the source end of the span, ensuring future breaks bring a de-energized conductor down. Unfortunately, that's not where the original break occurred.

Do you believe the momentary tension reduction below 15% might cause failure?

 

[waross]

Does the slice release without adequate tension or does it take a "one time" tension of at least 15% to "set" the splice?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[bacon4life]

A large utility close to me (BC hydro) did some forensic analysis a while back that found several kinds of problems with automatics. Forensic_Analysis_of_Automatic_Splices_Leads_to_Change_BC_Hydro

I haven't personally witnessed an automatic release under low tension, but my understanding from talking to crews was that occasionally they would find automatics where the conductor had fallen out after a car versus pole event. After reading the BC hydro paper, it may also be possible other kinds of failures occurred.

One other thing to note is that ancient copper conductors can fail at much less than 60% of RBS. It is unclear to me why the conductors have lost so much strength since being installed more than 70 years ago.

 

[davidbeach]

I’m aware of automatics in slack spans failing when a downstream fault causes conductor movement in the span. Just because that’s not what they’re intended for doesn’t mean they don’t get misapplied.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

-- Douglas Hofstadter, Jan 1982

 

[Chrisrc]

Lots of great info. here on this thread. You may find this article beneficial. Automatic Splices - The Inside Story:

https://classicconnectors.com/downloads/Automatic_Splices_-_The_Inside_Story.pdf

 

[Chrisrc]

You may also find this product useful. It was invented to protect and reinforce automatic splices.

https://classicconnectors.com/

 

[stevenal]

Chrisrc,

They've been here to present to us. We may be purchasing some of their products.

So far, the answer to waross' question above depends on who you ask. The the automatic rep says the internal spring keeps it functioning until tension goes negative. The Classic dude says the 15% must be maintained for the 30 year life.

 

[Chrisrc]

NOTE: Several utilities have banned the use of automatic splices on their systems. This usually happens after a catastrophic incident.
You guys may enjoy reading up on a few electrocution cases involving automatic splices:

https://abcnews.go.com/blogs/business/2012/12/jury-awards-109m-in-pa-power-line-death

https://www.nbclosangeles.com/news/...electrocutes-three-in-san-bernardino/1882746/

https://www.wfaa.com/article/news/l...ine-files-lawsuit-against-oncor/287-459931066

https://www.tampabay.com/news/publi...r-line-on-courtney-campbell-causeway/2285169/

https://www.arkansasonline.com/news/2016/nov/22/summit-man-36-electrocuted-by-power-lin/

 

[stevenal]

Thanks Chrisrc. All appear to be cases of downed conductors. The fourth one hit a pay wall, and out of the other four only the first one contained the word "splice." If the lawyer is correct and overheating caused the failure, this might have been any sort of splice. This one required some more research, since wire brushing is key in getting an automatic to hold mechanically even without overheating. I found [URL unfurl="true"]https://www.klinespecter.com/sites/www.klinespecter.com/files/goretzka-120712-3.pdf[/url] where the word "automatic" does appear.

 

[Chrisrc]

The Arkansas electrocution involved a copper compression splice, not an automatic. I should not have included it. All the others were the result of a failed automatic splice. I have much more detail including photos and court documents of all of these incidents, but not appropriate to post them here. According to the manufacturers, automatic splices are designed to last 30-40 years and many will last a lot longer, especially if they're installed according to the manufacturer's specifications and the line is not heavily loaded. Unfortunately, it's too easy to install them incorrectly. I have yet to meet a utility that has NOT experienced a wire-down incident resulting from a failed automatic splice.

 

[stevenal]

Chris,
I have a feeling we've met. Anything you are able to share, please do. Email works also. Even the compression story would be of interest for contrast. Thanks.

 

[stevenal]

Update:
Getting back to waross' question, this just in this morning:

15% is our minimum required tension. If it drops to lower than that, we can’t guarantee performance.

Not just the rep this time, but the manufacturer. As bacon4life indicated above, there are a lot of reasons tension might decrease. I'm beginning to believe the only acceptable use is for temporary emergency repairs, always returning soon afterward to reinforce it or to replace the automatic with compression.