I bought the EVGA SuperNOVA 1300 G2 power supply last year when it was on sale because I knew I'd need it for an upcoming computer build.  I installed the power supply in my system recently and I have been having an unusual problem.  If I put the back panel on, the computer won't boot.  While troubleshooting, I figured out that if I touch or move any of the cables that power the graphics card or the 8 pin connectors on the motherboard, the system shuts off.  When I put the back panel on the case, the back panel moves the cables inward and that's why the system won't boot with the back panel of the case on.  I tried moving the cables to bend at different angles and I still have the same issue.
 
Would I have to send in the whole power supply for RMA or can EVGA just send me new cables?

Call EVGA & ask Contact Customer Service
 
When installing cables - I push on the wires & not the plastic end ... this keeps wires from getting pushed into the plastic end instead of onto the components Pins

Time to contact support.

Similar to what sparetimepc suggested, are the cables stretched or overly tightened at any point for cable management reasons?
 
I'd concentrate by looking at the ends of the 24pin connector - on both sides - to see if a pin is backing/pulling out of the molex connector.  That could easily be the reason why it's shutting off.

Customer support wanted me to move the actual connectors on the power supply and see if it was an issue with the connections on the PSU.  The connections there don't seem to move, but I can get the system to shut down by touching the 8 pin cables where they bend closer to the PSU connectors. The last bend in the cables from being bent back and forth and tied up to fit in the box.
 
All the connectors on the motherboard, CPU, and PSU are in tight and clicked in place.  I can't wiggle them or pull them loose.
 
I changed the routing of the water cooling loop and added another coolant temperature sensor this past weekend(soft tubing), so I removed all the cables, checked them and put them back in.  I still have the same problem.
 
The case(Lian Li PC 011 Dynamic XL https://www.lian-li.com/pc-o11d-rog/) has 3 possible positions for the PSU.  I also tried the PSU in another location and still have the same issue.
 
Previous to this, I was using an older, lower wattage, Seasonic power supply.  Everything worked fine, expect that if the GPUs and CPU were under high load, it went above the maximum power the Seasonic power supply could handle and tripped overload protection on the PSU.  The Kill-A-Watt meter shows the system pulling 980+ watts from the wall when the CPU and GPUs were under full load with the EVGA PSU installed.
 

sparetimepc
So did you reroute the cables so the back panel doesn't even touch the cables, like don't even route them around the back side temporarily to make sure the back panel itself isn't grounding out something or the motherboard plug itself isn't defective? I believe that's a modular power supply, did you try a different cable. This seems like your not leaving enough room for cable movement. Make sure there is no solder point sticking out on back that when putting on the back panel it's pushing a cable hard enough to penetrate it.

When I have the back panel off the case, the cables aren't touching anything other than a rubber grommet where the pass through the rubber grommet to connect to the motherboard and GPUs.  There is plenty of room inside the case for the cables and they don't get pinched or pulled when I moved them by hand into the position they would be in with the back cover on.  Its just when the cables move toward the case, the system shuts off or won't boot if it was turned off even if the back panel isn't on at all. When I move the cables in toward the case, it changes the angle in the cables where the cables were bent back and forth and wrapped to fit in the box.
 
I can move the cables by hand into the position that they would be in with the back panel on and the system won't boot or shuts off its its powered up.
 
There are no different cables available.  The PSU comes with one 24 pin connector and two 8 pin CPU connectors.  So I have no cables to swap out.
 

EVGATech_LeeM
Similar to what sparetimepc suggested, are the cables stretched or overly tightened at any point for cable management reasons?
 
I'd concentrate by looking at the ends of the 24pin connector - on both sides - to see if a pin is backing/pulling out of the molex connector.  That could easily be the reason why it's shutting off.

The cables aren't stretched or pulled tight.  When the back panel is off, the cables stick out of the side of the case.  If I take the 8 pin CPU cables and move them toward the case with my fingers, the system shuts off.  They don't appear to be touching elsewhere when I do that.  I don't see any issues with the 24 pin connector.  No pins seem to be further in or other than others on that connector.  I can move the cables by hand into the position that they would be in with the back panel on and the system won't boot or it shuts off its its powered up.  Also, I don't have an issue when moving the 24 pin connector.
 

Hoggle
I would be taking it apart and finding out if I can spot the damage on any cable. Power cable issues can go very bad very quickly. I would also be looking for any part where a cable could have been near a case fan or the edge of something you might have moved like the side panel that could have caused damage.

This started when the PSU was new and recently taken out of the box.  Its difficult to have an unused cable damaged unless it happened at the factory.  The cables don't go near any fans.  I checked the 8 pin CPU cables and the 24 pin cable and don't see any wear externally.