Why MC connectors?

I have not purchased the latest edition of the NEC so I don't know what they say about it. But does anyone know why they require MC connectors on PV panels?

I usually don't try to second guess the code because in my career as a construction electrician I have found the code to be sensible and the requirements to be based on actual fact. But this one makes me wonder.

I insist on my panels being wired with #10 conductors pulled through Liquid tight flexable conduit to the first junction box. This is because of the problem with squirrels and chipmonks chewing everything they find.

This means I'll have to cut off the connector and saw a 7/8 hole in the panel's j-box.

What's going on with this?


  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Why MC connectors?

    why? i can guess it's because:
    1 they don't trust us at wiring in a junction box and :grr
    2 they are pushing those specific german connectors. :grr
    3 possibly it pays wiles well. :grr

    edit to add:
    the pv manufacturers also made it a violation of warranty to not use the mc connections as further incentive and this includes cutting them, bypassing them or invading the little jbox as violations.
  • rickeolisrickeolis Solar Expert Posts: 110 ✭✭✭✭
    Re: Why MC connectors?

    I'm so glad I live in the middle of nowhere...
    Screw all that code cr%$
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Why MC connectors?

    Are you suggesting that your method violates the NEC or just not happy that all new modules come with MC or equivalent connectors?

    If your method is a violation, why?

    690.32, to me, says that MC type connectors are allowed rather than required and 690.33, to me, says that if they are accessible they must be the new locking type (MC-4 or equivalent).

    I think the demand is clearly for the quick connections rather than wiring in a junction box.

    Also, are you really going to cut holes in the sealed jboxes of new modules?
  • RoderickRoderick Solar Expert Posts: 253 ✭✭
    Re: Why MC connectors?

    It sounds like you have panels with MC connectors, and instead want to break into the junction box of the panels, and run your own wiring, which can be enclosed in flex conduit.

    If it were me, there would be several things I would consider:

    1) How to plug the existing holes that the + and - leads come out of? I would not want to just leave those holes exposed to the elements.

    2) Mechanical stress on the junction boxes. I don't remember the boxes being tall enough to bore a 7/8" hole into the side, so you would have to cut into the top of the junction box. Is the material strong enough to support a screw-in flex conduit connetor? Is there enough depth there so that something can be screwed in? Would there be stress on the box throughout the life of the panel? I'm envisioning what I would say to the manufacturer if the panel failed before the 20-25 year warranty, and they found out I sawed a hole into the junction box.

    3) Access to the actual power leads once the box is opened. Can both leads be routed out one 7/8" hole? Is it encapsulated or otherwise coated with a sealer inside the box?

    I'll have to trust you on your rodent problem. I will say, we have rats and squirrels on the roof in our area, but they don't seem to gnaw on the panel leads, despite them hanging temptingly under the array. Maybe the leads taste or smell bad? I know there are squirrels, because they leave apple cores on the array.
  • Lefty WrightLefty Wright Solar Expert Posts: 111 ✭✭
    Re: Why MC connectors?

    I haven't got a copy of the new code so I don't know if it says mc connectors are manditory or if they are used the locking type are mandated.

    I based my info on the fact that it is hard to get large pv panels with jboxes instead of mc cables. NAWS says that the code mandated mc cables and when present stock of terminal box panels is gone it will be mc only.

    If the outlet boxes on the new panels are the same size as the old ones the hole won't be a problem. The Liquidtight connector has a rubber O ring that seals the connection against water.

    If the boxes are too small or potted, that will be a problem. But there are things that can be done.

    The rodents here also like to chew underground PVC conduit. The trick is finding the spot where they chewed through the conductor.

    If your car won't start after being parked for an extended time the first thing to check is the acorns stuffed in the air cleaner.
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Why MC connectors?

    For one thing MC is a brand and they don't require MC specifically.

    My reading anyway is that they require connectors that require a tool to disconnect *when* the cables are accessible. Inside a conduit should not count as accessible.

    I don't think any of the new jboxes (though they really aren't jboxes) will make this easy for you.

    The manufacturers went mostly to MC type connectors, just not locking, before the 2008 NEC. It's for convenience. A lot of their customers will be installing 1000 modules at a time and can't have electricians doing the connecting.

    Can you maybe do something with metal screening?
  • PhilSPhilS Solar Expert Posts: 370 ✭✭✭
    Re: Why MC connectors?
    If your car won't start after being parked for an extended time the first thing to check is the acorns stuffed in the air cleaner.

    After years of acorns in the air cleaner, chewed wires, and nests in the heater core housing I finally tried something that seems to work well:

    leave the hood partially open.

    We haven't had a problem in the two years since I've been doing that (only necessary for the vehicles that aren't used daily).

    And I went ahead and used the MC connectors on my last set of panels solely to avoid warranty problems.

  • Lefty WrightLefty Wright Solar Expert Posts: 111 ✭✭
    Re: Why MC connectors?

    Interesting about keeping the hood up. The little darlings removed all the isulation from under the hood of my pickup and filled the glove box with it.

    I guess I'll have to buy the newest copy of the NEC and get the straight scoop.
  • BrockBrock Solar Expert Posts: 633 ✭✭✭✭
    Re: Why MC connectors?

    I have been looking and can’t seem to find them, but can you get just the connectors (ends) and make up you own cable or connection? I ask because how are you supposed to get from the panel to a box at some point? You aren't supposed to run MC cables back to the MX-60 are you? I have #4 running up to the roof with the current panels wired in at a box. In the future when I add more panels and get back to that box with the new string via MC, do I just buy a long one and cut it in half and wire it in?
    3kw solar PV, 8 L16's, xw 5548, Honda eu2000i, iota DLS-54-13, Leaf EV, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    Re: Why MC connectors?

    Yep--just buy a cable and cut it in 1/2 (or whatever)... From what I remember before about MC's, I believe you have to take "training" before you are allowed to purchase the components to make-up the connections.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Lefty WrightLefty Wright Solar Expert Posts: 111 ✭✭
    Re: Why MC connectors?

    No problem after all. I found a site with the 2008 NEC and found out that MC cables are permited but not required.

    The phase out of panels with jboxes is something the PV industry is doing on their own.

    If you are not hooking up 20 panels I don't see the need to spend money on these cables and connectors.

    The site with the 2008 NEC is http://http://www.nfpa.org/freecodes/free_access_document.asp
  • System2System2 Posts: 6,290 admin
    Re: Why MC connectors?

    Could you please recheck the link?
    Would love to look through and learn, but "Page cannot be found" for:

  • System2System2 Posts: 6,290 admin
    Re: Why MC connectors?
    newenergy wrote: »
    For one thing MC is a brand and they don't require MC specifically.

    In the solar wiring world, MC is an acronym for multi-contact, not a brand name.


    Bad Apple
  • System2System2 Posts: 6,290 admin
    Re: Why MC connectors?

    This link should work NEC 2008

  • mike95490mike95490 Solar Expert Posts: 9,363 ✭✭✭✭✭
    Re: Why MC connectors?
    Dan Zemke wrote: »
    This link should work NEC 2008

    For a price:

    If you are not a subscriber, you can click here for a free one-day preview or subscribe now $9.95/month.

    I guess if you need to look one thing up, you can try the 1 day preview.
    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 ,

Sign In or Register to comment.