Wiring Midnite Solar Combiner

lzhome

Could someone please explain the wiring on Break #3 and Breaker #4 counting from the left?
#3 has the common positive output into bottom of breaker and looks like feed to controller out the top? Is this a overall breaker for entire PV strings with a larger amp breaker? Necessary?
#4 has ground in at bottom of breaker and what looks like a jumper on the side linking bottom to top? totally lost on this one.


Photo from Amazon: https://www.amazon.com/Midnite-Solar-Photovoltaic-Combiner-6-Position/dp/B0041OJ2J6/ref=pd_sbs_86_2?_encoding=UTF8&pd_rd_i=B0041OJ2J6&pd_rd_r=WMR509XRQ823V973039H&pd_rd_w=qIvxI&pd_rd_wg=pxzgg&psc=1&refRID=WMR509XRQ823V973039H

Estragon

I think you're right on breaker 3. Yes, I think you need a breaker protecting the wire carrying the combined current to the controller. I'd prefer it close to the controller myself to make for a more convenient shut-off, but different strokes.

I'm unsure about #4. It looks to me like it ties DC negative to ground through a 1/2a breaker, with polarity oriented for fault current coming from ground, which is a new one for me. Put current across it to open the breaker, and now DC- is at floating potential to ground? Maybe someone else can explain that one.

lzhome

And I just noticed #3 and #4 are not on the bus bar...

Estragon

The + side of #3 appears to be connected to the buss with the red wire to the square screw-in nut. Can't see what, if anything, is connected to the other (-) side of #3. Presumably, it would go to the charge controller.

Connecting #4 to the buss strikes me as a bad thing.

mcgivor

Looks like from left to right, breakers 1& 2 are PV strings, breaker 3 is a main shut down which is redundant because 1 & 2 would protect the conductors down stream and would trip before breaker 3,  effectively shut down everything if turned off or tripped.. Breaker 4 looks to be a means to isolate negative to ground bonding, for testing purposes perhaps  ??

BB.

The two breakers on the right are normal PV string breakers. Too much current on the PV string, and the breaker opens (15 amps or so?). Connects to a single positive bus.

The two breakers on the right make up a "ground fault detection/shutdown system". The breaker on the left is the main PV shutdown breaker, and it is tied to the 0.5 amp breaker trip lever. And the right breaker is connected between the PV return line and safety ground. If there is >~0.5 amp current flow between the neutral bus and ground bus, the 0.5 amp breaker trips which then shuts down the PV main breaker.

This ground fault breaker pair was an attempt to reduce the chances of arc fault between a short of the PV lines and earth ground.

I do not like this system and believe it is both unsafe and not code compliant--It was just a quick and dirty method to try and prevent some arc fault fires using existing UL Listed components.

-Bill

lzhome

Thanks for the responses. I will have 4 PV strings so I'll use 1 fuse for each string (15 amp). Now will I need to place a fuse closer to the CC for the PV combined positive feed or will these individual string fuses be sufficient?

mcgivor

@BB. Are you seeing a link bar between the two breakers on the right, the extreme right connected physically to the main shut down, from the image I can't see a tie bar, resolution permitting. 

Estragon

@mcgivor - I missed the tie as well, but now that Bill mentioned it I think I can (barely) see a brass tie bar between the breaker handles. Sort of makes sense to me now, in a nonsense sort of way.

Estragon

Personally, I would use the box as intended, with 4 breakers, one per string, to a common bussbar. It looks like the buss original was cut, so may need a replacement. A fault should open string breakers, but I would put a breaker near the controller for the combiner to controller circuit anyway. If nothing else, that lets me be certain the pv circuit isn't (and can't be made) live while I work on controller etc.

BB.

I cannot see the breaker tie rod--But it is the only way that this configuration would "work".

If the tie between the two breakers on the right is missing--Then it is not doing its job (owner can confirm if the two breakers on the right are tied together or not).

-Bill

westbranch

that picture is taken right from MidNite Solar's instruction manual  ... http://www.midnitesolar.com/pdfs/DC-GFP.pdf
the install is apparently NEC 2008 approved
This Link  lists TORQUE Specs for CB screws  ... http://www.midnitesolar.com/pdfs/torque_values.pdf