Strain relief's sold by Northern Arizona Wind & Sun

Are the strain reliefs Northen Arizona Wind & Sun sell for the 1/2" PV junction box knockouts actually water tight? They don't appear to have any gasket. I have seen other dealers sell strain reliefs for PV's that cost 2-3 times as much but have Buna-N seals.

Comments

  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Strain relief's sold by Northern Arizona Wind & Sun

    Not really watertight, not as they come. You can add an o-ring gasket.. BUT

    Our experience over 30 years has been that unless you can get an absolutely total airtight seal that you do NOT want water tight seals.

    The problem is that in very many places the junction box (or whatever) heats up in the daytime. At night it cools off and pulls in cooler - and damper - air. This often causes condensation inside the box. And it seems that condensation is a LOT harder to get out than to get in.

    We have seen j-boxes that were "almost" totally sealed in the Texas desert that had several spoonfuls of water in them, and they were totally corroded inside.
  • System2System2 Posts: 6,290 admin
    Re: Strain relief's sold by Northern Arizona Wind & Sun

    Thanks for the insight!
  • System2System2 Posts: 6,290 admin
    Re: Strain relief's sold by Northern Arizona Wind & Sun

    I usually drill a small hole in the bottom of the boxes if they contain a terminal strip or anything else that can be harmed by water that gets in due to condensation.

    An interesting aside is the National Electric Code's definition of "water proof" and "water tight".

    A water proof enclosure is one in which the entrance of water will not effect the operation of the enclosed device.

    A water tight enclosure will prevent the entrance of water.
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Strain relief's sold by Northern Arizona Wind & Sun

    The problem with many enclosures and seals is that they might be "watertight" - that is won't allow water in, like from rain, but will allow enough air in and out to get the condensation. You don't need much, as over a period of time it builds up as it can't get out.
  • System2System2 Posts: 6,290 admin
    Re: Strain relief's sold by Northern Arizona Wind & Sun

    We are about to install the strain relief on a new 130w panel and now, after reading your notes it appears we should not use a silicone sealer....is that correct??
  • BB.BB. Super Moderators, Administrators Posts: 31,337 admin
    Re: Strain relief's sold by Northern Arizona Wind & Sun

    It really seems to be counter intuitive, but as Wind-s2 says, you really do need a vent hole to keep moisture problems down.

    I would seal up the box on all of the gaps and such--BUT--leave the lowest corner open (just a small gap or hole--no gasket or sealent). If the lowest point in the box is not at a gap--then take a 1/8" or so drill and poke a hole there. Also, try and install any cable and such with drip loops (cables exit from bottom or side down from box so that water wants to drain away from the box instead of into the box).

    On my solar install, the vendor tried to make everything water tight--and I ended up with water dripping out of my conduit connections in my garage until I made an place for the water to drain.

    Years ago, I helped install a short wave radio transceiver on the exterior bridge of a ocean going research vessel, and had to drill a small hole in the lowest corner of the plastic enclosure (was an active antenna load matching coil)--sure felt strange to do it, but it worked fine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Strain relief's sold by Northern Arizona Wind & Sun

    bb,
    that's interesting on the antenna coil. was it hf or vhf(assuming hf as you state short wave)? if hf how did they allow for multi bands?
  • BB.BB. Super Moderators, Administrators Posts: 31,337 admin
    Re: Strain relief's sold by Northern Arizona Wind & Sun

    Neil,

    Oh boy--I was afraid that somebody was going to ask me the details... It was back around 1983 and I worked a summer as and electronics tech for the USGS... Part of that was working on the SP Lee, a multi-channel sonar mapping ship.

    I don't even remember the bands now that it covered. It was a HAM unit that had the antenna tuning coil outside near the whip (as I recall). The unit was a multi-band HAM transceiver and even included AM/FM and other receive only bands too... To tune the antenna you would set a frequency and hold the mike for a couple of seconds--the radio would then broadcast at low power and tune for a low SWR value.

    We installed it as a backup to a satellite radio phone (was like a 5' dome with some serious hydraulics driving it)... The longest distance I talked on it was from the coast of Alaska to Redwood City CA (I was in Redwood City--not on the ship). I only went on two shake-down cruises south of San Francisco towards Monterey Bay.

    Here is a picture of her...

    http://defoenet.com/shipbuild/boats/usns_splee.htm

    T-AGS-31 S.P. LEE
    Length 208' 4"
    Job #441, Keel laid 7/12/67, Launched 10/19/67
    Dock Trial 9/21/68, Builders Trial 10/22-30/68
    P.A.T. 11/6/68, Depart Bay City 11/14/68
    Arrived Boston 11/24/68, Delivered U.S.N. 12/2/68
    Commissioned 12/13/68

    http://www.navsource.org/archives/09/1031.htm Fixed Link-BB

    It was a fun time, that summer. Learned a lot and helped quite a bit too... It was an interesting time in my life. The research was just converting over to computers, the satellite systems were just getting used by us--we still had dead a reckoning system (sonar beams directed down fore and sidewise to measure track in water)... She had a round bottom so as to be acoustically quiet for intelligence gathering (as would be expected for a sister ship to the famous USS Pueblo that was captured by the North Koreans). With a good wind behind her she could probably break 11-12 knots with her twin 500 hp diesel electric motors (again, quiet drive).

    We towed a multi-channel hydrophone array that was probably about 0.6-0.8 miles long with about 5 air guns (make a bang of a 1/4 stick of TNT every 10-40 seconds). Plus a bunch of other instruments to gather data as she cruised around.

    Looks like her last cruise was in 1994:

    http://walrus.wr.usgs.gov/infobank/programs/html/platforms/html/Samuel_Phillips_Lee.html

    Haven't thought much about them for years.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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