MC Connectors instide junction box?

newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
When you transition from PV wire to standard wire in a junction box (even if it's a disconnect) you are wiring with hot (often around 500V) wires. We often make short jumpers coming out of the box and put an MC connector on one end and then a mating MC connector on the home run from the array. We generally just do this for the ungrounded side. This makes it so that you can wire the junction/combiner/disconnect with non-live wires and you can test and then disconnect the MCs to wire the inverter with non-live wires as well.

Now, if you put the MC connectors on inside the junction box, on the one hand you would have the problem that they pretty much couldn't get out of there w/o cutting the wire, but on the other hand you would be eliminating another wire connection/splice and protecting that MC connection.

What do you think?

Comments

  • TnAndyTnAndy Solar Expert Posts: 249 ✭✭✭✭✭
    Re: MC Connectors instide junction box?

    When you say you put an MC connector on the end of a wire, do they MAKE MC connectors that are field installable ? and by that I mean JUST the connector.........Who sells them ?

    Thanks !
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: MC Connectors instide junction box?

    I get them from a solar distributor. They are competition for the site here, so I don't know if it's kosher to mention them. It isn't that hard to find the connectors though.

    In order to make your own connections you have to buy a crimper. I bought one that works for MC3 and MC4 and it cost about $600.
  • BB.BB. Super Moderators, Administrators Posts: 30,642 admin
    Re: MC Connectors instide junction box?

    Here is a thread with a few MC crimp kit vendors listed... (you can ignore the whole solder/crimp argument if you want).

    Given that it may cost around $600 for the first connector crimp--for small/one time systems--just getting a pre-made male/female cable to finish up with wiring a string may be more cost effective for most non-professionals.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: MC Connectors instide junction box?

    But BB, what do you think about the OP?
  • BB.BB. Super Moderators, Administrators Posts: 30,642 admin
    Re: MC Connectors instide junction box?

    I am not the person to ask if the suggestion would meet code...

    My two cents--I would not go out of my way to put the MC inside of the box. As mentioned before--may become an issue if the connector cannot be removed from the box without cutting the wire (what does the MC buy you)--and you may already have a dozen (plus or minus) exposed MC connectors on the solar array anyway--so one more or less is just not an issue.

    I would suggest that the MC connection not be made/broken under load. The arcing would probably damage the contact surfaces and support structure and lead to possible future failures.

    And if you interrupt the current to prevent contact damage (switch, breaker, pulling a fuse, disconnecting at night, etc.)--then you can pretty easily break the connection anyway (assuming bolt/screw type connection)--and the extra MC may not be needed.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GreenerPowerGreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    Re: MC Connectors instide junction box?

    What I did was to use the 3-foot MC extension like these from NAWS, cut it in half and use the other ends to make connections inside the combiner box. Cheap and easy to disconnect to dismount the panels also, in case of hurricane.
    GP
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: MC Connectors instide junction box?

    When we connect and disconnect the MC's there isn't a load - we just connect them to measure voltage in the conductors in the inverter, then disconnect and wire the inverter, then reconnect - but the inverter disconnect is off at this point so there is no complete circuit. Not that you were saying we connected/disconnected under load, just explaining our procedure.

    It wouldn't really be out of the way. Either the connectors are adjacent to the box or inside it. It's really that it seems a bit hokey to put them inside vs. prevents another splice connection which could be a source of resistance and takes time to do.

    The extra MC is another disconnect, but the purpose is to make wiring the box safer. Regardless of what type of fuse/breaker/DC disconnect you have, you are handling the live wires with potential to something close by (another wire/bus bar).

    Greenpower, that's pretty much what I do. I just make my own since I have a crimper.

    p.s. I've received a few shocks (through gloves - not too bad) but last week I got a whopper with about 440V from one bare hand to the other (through my chest) that made me jump back and give a good shout. I want as safe a protocol as possible.
  • GreenerPowerGreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    Re: MC Connectors instide junction box?

    Ouch ! (especially when you are on a roof). I kept the carton boxes of the panels and use them to cover the panels whenever I work on the wires.
    GP
  • BB.BB. Super Moderators, Administrators Posts: 30,642 admin
    Re: MC Connectors instide junction box?

    Newengery,

    Not a problem--because there are so many people that read the posts here--I try to be really clear when talking about potentially hazardous (such as breaking connections under load).

    Glad you are OK after your 440 hit--Many times it is not the shock itself, but the results that harm (fall of ladder, fall/drop tools on others, fall in wet area with current still flowing, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: MC Connectors instide junction box?
    newenergy wrote: »
    When you transition from PV wire to standard wire in a junction box (even if it's a disconnect) you are wiring with hot (often around 500V) wires.

    I'm not. I may be depressed sometimes, but I'm not ACTUALLY suicidal.

    G-d invented the blanket for this very reason. Get several on hand and use them.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MC Connectors instide junction box?

    I suppose someone could make an "MC 4 connector bus bar" that could go inside a weatherproof box and allow the panels to be plugged directly into it. There'd have to be some fairly substantial screw connectors to connect the cumulative panel load to some down lead. If you wanted to get really creative it could incorporate individual panel fuse holders too.

    It's late, I'm tired, and I'm spewing gibberish right?
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: MC Connectors instide junction box?
    ...I'm spewing gibberish right?

    I can't tell. Gibberish is not my first language. My wife and offspring may disagree. ;)

    K
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: MC Connectors instide junction box?

    The job I got shocked on had 102 panels on a tall, steep and slippery roof. Covering the panels would have been difficult and doing anything extra on that roof was at least a little dangerous. If I would have just followed the procedure I'm talking about I should have been safe.

    In this case I was shocked wiring the inverter, so I was already on the ground.

    winery1.jpg
  • KamalaKamala Solar Expert Posts: 452 ✭✭
    Re: MC Connectors instide junction box?
    newenergy wrote: »
    In this case I was shocked wiring the inverter, so I was already on the ground.

    Still... HOLY MACKEREL!
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: MC Connectors instide junction box?

    nice array. envy. i guess if you got to get bit you at least did it first class!;)
  • PhotowhitPhotowhit Solar Expert Posts: 5,222 ✭✭✭✭
    Re: MC Connectors instide junction box?

    OK, I'm hanging with the "Tall Girl" here.

    Even with a minimal system, I don't wire anything thats running a lot of amps, dusk and dawn are your friends, rubber mats are available to isolate while working.

    My combiner box has such short runs inside, I don't see any way to create a short unless you did it intentionally. If it was hot(mid day), I'd turn off the breaker at the power center, pull the fuses, make the connections(checking the orientation), tighten the wire reliefs, put the fuses back in and I'd even wait until dusk to throw the breaker, unless I was in great need.

    Perhaps I'm missing something.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: MC Connectors instide junction box?

    Most of the time were not combining strings outside of the inverter. In fact, in many systems the terminals in the inverter's disconnect are not rated to handle the current of combined strings. So, it's generally just transitioning from PV wire to regular nylon jacketed wire.

    Anyway, in a combiner if you touch one of the ungrounded wires and anything that's grounded, like the combiner box itself - after you land the grounded conductor - that's a shock. It wouldn't really require long runs.

    It's not impossible or anything to make the connections at dusk or dawn, but I'm wiring one of these up about once a week and have a ton of stuff to do so it would be somewhat difficult to not just do the wiring when it's ready.

    I'm thinking the procedure:

    Make jumpers with MC connectors for the ungrounded conductors
    Check voltages with grounded conductors and MC connectors on home runs
    wire junction/combiner box
    plug in MC connectors
    check voltages at inverter
    unplug MC connectors
    wire inverter
    plug in MC connectors

    is foolproof?

    It doesn't really take as long as it sounds because we have more than one person.
  • PhotowhitPhotowhit Solar Expert Posts: 5,222 ✭✭✭✭
    Re: MC Connectors instide junction box?

    I'm off grid so my world's a bit different, but don't you have a breaker between the panels and the inverter? so once you had the box wired you could leave the outside MC connection connected, I would think the breaker would be better designed to handle a hot connection.

    I thought MC connectors were only designed for 10 and 12 gauge wires? I'm running 6 or 8 from my box to the breaker. Likely NP for a grid connect with the higher voltage.

    Yeah, I have a nema box and the connections are actually closer than the grounded plate, I guess not a typical design but a good one! If it came with compression connections you'd never have to have enough wire inside the box to get to a ground. I'll shut up now as the NEC guys will get new ideas to save us from ourselves...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: MC Connectors instide junction box?

    I'm almost entirely on-grid. Typically strings are only at like 8 amps and we use 10 gauge for that.

    Regarding getting shocked with the ungrounded conductor and the ground, you could touch an ungrounded conductor with your hand and your leg could be touching some part of the racking system or conduit or a module frame and you could get hit.

    If you need to break a hot connection, i.e. turning a system on or off, you should have a breaker, a fuse or a disconnect switch. But, when we are connecting and disconnecting those MC connectors the system is still disconnected somewhere else in the circuit, like at the inverter.

    Whether we need some kind of disconnect between the panels and the inverter (well, the DC disconnect of the inverter) depends on the city and the accessability of the conductors.
  • PhotowhitPhotowhit Solar Expert Posts: 5,222 ✭✭✭✭
    Re: MC Connectors instide junction box?
    newenergy wrote: »
    (well, the DC disconnect of the inverter) depends on the city and the accessability of the conductors.

    Well there is always the NEC code which is the base threshold for the tax credit...

    For my system I'd have to be barefoot and dealing with a whole lot of amps to short through me as my panels are free standing and I'd be 12 feet from grounding rod...

    I'm not big on NEC code, before I purchased a couple new panels this year I had installed with a combiner box, then took the box out and sold it since the stand alone panels have vertually nil chance of fire damage, glass and silicon even tedar are pretty fire resistant after the combiner box they run less than 10 feet into a breaker. But to qualify for the Taxc credit the panels had to be installed to code. I read no where were I couldn't change it afterwards.

    They were hooked into a distrubution block the same way I had my smaller system running safely for several years.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: MC Connectors instide junction box?

    This thread points out the difference between a grid-tie array that runs hundreds of volts and an off-grid array which is typically less than 60.

    Just an observation, which I admit doesn't seem to have any actual purpose.:p
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: MC Connectors instide junction box?

    Photowhit, not sure if you're saying a separate disconnect is required by the NEC, but the NEC requires a means of disconnect of the PV source and all other conductors in a building or structure. Many grid tied inverters come with an attached (but often removable) disconnect that satisfies this requirement.

    Some cities require a disconnect before entering a building (not an NEC requirement as long as the PV conductors are in metal raceways or enclosures) because they want the fire department to be able to switch off the PV source before they start chopping holes in the roof.

    I'm not sure what happens on a low voltage system if a wire gets pinched and there's a short, but on a high voltage system the insulation can catch fire instantly.

    Is NEC a threshold for tax credit, or is it a final permit? They aren't necessarily exactly the same requirements.
  • PhotowhitPhotowhit Solar Expert Posts: 5,222 ✭✭✭✭
    Re: MC Connectors instide junction box?

    I'm honestly not sure about the requirement.

    I have a Trace PC250 power center which has an integrated C60 charge controller and the Array comes straight into a breaker, there is no other shut off for the Charge controller. The inverter, ProSine 1800 has a shut off inside and outside, and at the Power Center, both as a battery and AC breakers.

    As the Power Center was made to make meeting code easier perhaps I made an assumtion, I'll check it out when I have some time.

    BTW - This also has genset, AC from inverter, Battery, and Array Disconnects in the same box, I think in the latest revision of NEC they don't want AC and DC disconnects in the same box... lol. I think this makes it easy and straight forward for fire dept if the need arises.

    The Power Center acts as the main Breaker Box with the inside breaker box as a sub panel.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: MC Connectors instide junction box?

    I don't think there's anything in the NEC about AC and DC not being in the same box. I was pretty much quoting all the NEC disconnect requirements for PV in the 2008 NEC. Also, most of the major manufacturers claim that their AC/DC disconnects meet NEC.

    You aren't supposed to mix AC and DC wiring in a conduit or even a box, but the disconnects have a divider between the AC and DC sections.

    Your system sounds interesting and complicated. I haven't even done a real off-grid system yet, just fooling around on battery chargers for a truck and boat.
  • PhotowhitPhotowhit Solar Expert Posts: 5,222 ✭✭✭✭
    Re: MC Connectors instide junction box?

    Just a basic off grid system.

    Never worried about code until I wanted to run AC and added @800 watts to my system. I never had any fear of my panels spotaniously ignighting (I've seen the photos circulating of some homemade solar panels mounted on plastic burning, and have seen some photos in Home Power of glass modules shorting out, but nothing much in the way of fire.

    The breaker is there in the box so I use it, never even had that much before I wanting to get a tax credit on the panels in '06. always used a distribution block basically backwards, joining the panels into one heavier wire. Many Solar suppiers still sell them, though I doubt they discribe what to use them for...

    I can understand a combiner box if you have roof mounted panels, and I guess they aren't required for some instalations though I'm not sure what the threshold is.

    Anyways I got a couple cheap combiner boxes (that had the wrong type fuses in them ie; ac rated) that are the same vintage as my Power Center. I have no one enforcing code where I am in rural central Missouri. I'll leave one in place for my standard setup, and use the other to check on idibidual strings if I have problems, or likely switch to a MPPT charge controler.

    I think they are quickly moving toward panel type boxes with no exposed connections, not sure my combiner boxes will fly though they have thumb screws to open.

    I think they would have required it with the last changes in the NEC as applied to solar, but no UL listed fuse holder with no exposed connections existed at the time.

    Many times I think the NEC tries too hard to protect people. I wonder if people loose the respect for the danger if they are too protected.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
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