wire nut question

wxh3
wxh3 Solar Expert Posts: 70 ✭✭✭✭
I saw in another thread that wire nuts are not recommended for low Voltage (<50V) DC connections. Just curious, why is this? Might they be ok to use in a small, low Wattage system? What type of wire connector should be used instead?

Somehow I missed this information in all my reading about PV systems...

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,398 admin
    Re: wire nut question

    My guess is that wire nuts are frowned on in wet locations... They are not sealed against water / humid environments (for example, this warning on a boating site)...
    The worst of the problems with DC system add-ons comes with improperly installed wiring and the use of wire splices of all sorts. Typical of these are the use of electrical taped connections which, when the tape gets warm (as in the engine room) the tape glue gets soft and the tape falls off. Or the use of wire nuts or crimped butt connectors in locations that get wet. Wire nuts (those twist-on cones) are not approved for marine use. When connections get wet, the wire corrodes, creates high resistance, usually resulting in equipment damage or failure for reasons which the owner will never discover. He'll think just that damned lousy piece of equipment crapped out, when in fact the lousy wiring job is the culprit.

    And, one would assume that splicing in DC solar panel usage would tend to be outdoors. And, from what I have seen, there is probably no such thing as a sealed exterior electrical box--and in fact, you should probably drill a small hole at the bottom of each one to let water drain out.

    What is the correct answer for splicing wires?... I have used self vulcanizing tape (soft rubber tape that "seals" together over time, and then soaked in an electrical sealant--available from your local hardware/electrical store). Crimping of joints is usually considered the most secure and reliable--but in the above link, they don't even like crimps.

    -Bill :confused:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • aj164
    aj164 Solar Expert Posts: 122 ✭✭✭
    Re: wire nut question

    My guess is that a splice made with a wire nut has some low resistance, and the low resistance is significant enough at low voltages (implying higher currents) to heat up the splice and cause a problem.

    At voltages over 50, the current is likely to be too low, and the small resistance in the wire-nut splice is negligible.
  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
  • cizzi
    cizzi Solar Expert Posts: 109 ✭✭✭✭
    Re: wire nut question

    You can use marettes and then an exterior weatherproof PVC junction box with proper connectors, look at the picture of my junction box.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: wire nut question

    For yard/lawn sprinklers, they have wire nuts for the low voltage wireing, that has dielectric grease in them, keeps moisture out. These are systems that pull less than 1 amp. https://yard-boss.com/store/store.php?crn=222

    But, wire nuts are rated for the number of conductors, and their outer insulation(600V). As long as you only use the proper quanity of the right size conductors, I don't see what would be wrong, as 14ga wire is only rated 15A, so a wire nut for 3-14 should be able to serve up to 15A. I don't know if there is legal grease to add to them to seal moisture out.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • sam c
    sam c Registered Users Posts: 16
    Re: wire nut question

    AM I missing something.? I use solder and heat shrink tube on any weather exposed connection, then tape the whole thing.:confused:
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: wire nut question
    sam c wrote: »
    AM I missing something.? I use solder and heat shrink tube on any weather exposed connection, then tape the whole thing.:confused:
    Not everyone knows how to solder, and I don't think soldered joints even appear in code, way too variable, but properly engineered wire nuts, and split bolt splices work.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,