Split Bolts vs Wire Nuts on the Roof [RE-wrenches]

Ray Walters ray at solarray.com
Mon Dec 6 12:56:07 PST 2004


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Mark;

I too have seen splitbolts loosen over time. It causes problems too, as the 
volt drop across the connection can cause all sorts of erratic behavior 
(possibly fires). I've heard of PWM controllers causing vibration in 
connections that can loosen stuff, and stranded wire always needs to be 
retightened after a few minutes due to metal creep. I used to swear against 
wire nuts for DC because of John Wiles, but after years of tearing down old 
systems etc. I've seen more splitbolt failures than wirenuts. The only wire 
nut problems were not twisted together properly, etc. I use both, tighten 
the splitbolts with two wrenches, tape with cold shrink then a second coat 
of regular electric tape.  I like to use Polaris insulated splice 
connectors (a set screw for each wire), crimp connectors, insulated 
junction blocks, etc. instead.
Over the years, I've modified my system designs to avoid split bolt 
connectors whenever possible. An outdoor breaker box wired straight to the 
DC load center avoids those problems, and makes the system safer and easier 
to work on later. (Trying cutting apart a taped split bolt to get a voltage 
reading for instance)

Ray



>On another subject, we recently had a call back on a grid tied PV system 
>and found a split bolt in a raintight j-box on the roof that was slightly 
>loose.  I'm thinking the stranded USE-2 had relaxed with all the 
>temperature cycling up on the roof, and loosened the split bolt just 
>enough to cause an intermittent.  I know the drill, tighten and loosen the 
>bolt a few times before the final tightening, to get the strands to 
>compress as much as possible.  But I'm wondering, do you prefer split 
>bolts or wire nuts in this application?  Seems like wire nuts wrapped 
>securely with rubber tape might actually be more reliable than split bolts 
>for this small size wire (10-12AWG).
>Thanks
>Mark
>Cobalt Power Systems

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