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I installed a GFCI receptacle yesterday, the instructions were saying that if you see more than 4 wires in the box (excluding the ground) call an electrician.
In my case everything you see to the right of the brown dotted line was connected to one box (4x4)
I have seen those instructions, I thought it was funny at first but after thinking of the number of times DIY folks get line and load mixes up with just 4 wires and all the rat’s nests I have repaired over the years it may make sense for those that do not understand what they are doing.
The line terminals connect to the feeder from the panel normally black on brass and white on silver then a receptacle that is fed from this would be on load same color combinations.
Where things can get sketchy if there happened to be 1 additional red wire for a switched outlet as GFCI receptacles do not have a tab to break the top receptacle feed from the bottom one (if there is not a wired light in the room additional work needs to be done to maintain a switched receptacle as code has required for decades if no wired light fixture)
Other things like multi wire branch circuits can be there with an additional wire normally red again , this circuit has 240v between the red and the black and is a way to have an additional circuit while running less wires (saves $) .
Last as you have multiple feeds to other circuits, so it is not as easy as this goes there and the reason the MFG suggests a pro this way if you hook it up wrong the mfg is not liable for damages. 4 wires can be messed up but as you can see it may not work but with a multi wire branch circuit you could be shorting the 2 legs of your service together if done wrong and that is about the worst thing that can be done especially if you find yourself in the circuit some way.
This has to do with the device's UL listing. UL only approves devices for certain applications; i.e. you can't use an Alumiconn to splice 9600V wiring. Two things assure you stay within those applications: First NEC 110.3(B) which requires you obey the labeling and instructions, and second, UL also approves the labeling and instructions as part of the listing. That is because, generally, they only test for conditions described in the instructions (e.g. they don't test Alumiconn for 9600V splices). Anyway, if you wonder why some instructions are so stilted and weird, that is why.
When a manufacturer writes instructions likely to be read by amateurs, UL gives it extra scrutiny. It is UL who is imposing the "See electrician for >4 wires" issue. You have to hook up the two LINE terminals or the device won't function. With only 2 additional wires, UL feels comfortable with the instructions. >4, there become several wrong/dangerous ways to hook it up.
Anyway, for you, it is simplicity itself. Everything goes onto LINE. Don't even remove the warning tape from the LOAD terminals. So you would just pigtail.
Do not use the LOAD terminals at all unless you have a specific reason to do so, and only for the pairs of wires where that reason exists. The instructions will say something else; they want you to ignorantly protect parts of your circuit without realizing you are doing so, and because of the side-effects, that's something I do not agree with.
Why not use LOAD for everything? Well, you're perfectly allowed to; and you're advised to by the instructions. That will place everything downline into the GFCI protected zone. That seems oh, so clever: Free protection! And that is the purpose of having LOAD terminals! However, this has a dark side, if those downline loads don't need GFCI protection. Any trivial leakage from those things will stack i.e. cumulate, increasing your risk of nuisance trips. Nuisance trips drive people crazy. Do people do a laborious bug hunt on each leg of the downline that wasn't even part of the project in the first place, to suss out every last dirty contact or NM wire that's getting wet, or stick isolation transformers on their refrigerators? No, they don't; they rip out the GFCI.
So "GFCI everything" is a grand theory, but not something you can really live with. UL doesn't care about that. They say "you should do the bug hunt". UL can come and do the bug hunt, IMO.
What is a good idea to not protect?
