I am trying to install a gfci receptacle in my offfice( replacing the existing regular receptacle) I have two black wires that were wrapped together , two gray wrapped together, one single blue and one green. I followed the directions and think I got all the wires to the right place. The test light comes on but the reset button will not stay in. Can you help me get this wired and operating correctly. Thanks

Well now you have gone and done it, took all the wires off the existing duplex and forgot which go where?

Because of the colors you noted, sounds as if you have conduit with pulled wires instead of the typical two wire cable with black, white, and green wires.

The green is the grounds and goes to the green screw on the GFI. The gray may be the neutral for the 120 volt outlet circuit, but I caution you that many times gray is used as a neutral for 277 volt systems, which , if you have conduit, it is very possible that a 277 volt circuit an be passing through the outlet box.

Did either of the black and gray splices have a short wire coming off the splice , these , if 120 volt would be going to the GFI, black on brass Line terminal, and gray on the silver Line terminal.

I have no idea what the blue wire is. You really should have noted where each wire was connected to, now some troubleshooting and testing needs to be done to determine the purpose of each wire, before connecting to the GFI. If connected wrong, well, I don't have to remind you, the GFI will not operate properly.

If the black is the hot wire for the 120 volt and went to the brass on the old outlet, it is possible the blue connected to the other brass terminal on the old outlet.

Any combination is possible, since commercial wiring is done , custom, so to speak at each job. This is an odd arrangement with odd colors.

If you have a voltage tester, we can go from there,otherwise your guess is as good as mine. Not sure if I helped, get back if you have a tester, or have any other questions.

Thank You, I do have a tester. I realize the green is the ground, there are two black, two grey, and one blue wire. Can you help me from here.. Many Thanks!

With the power off, measure ohms between the ground and everything else. Near 0 means the incoming neutral. The rest should be open. Next, turn the power back on. You should have 120 between the incoming neutral and one other wire, the incoming hot wire. If the incoming neutral is one of the gray ones, you might try scraping it. Could be a dirty white wire. The blue could be discolored green. With metal conduit all the boxes should be grounded. If the blue wire is a ground, it may be grounded. All those extra wires go somewhere. Are there more outlets on this circuit? Pull one out and note which colors of wire go to which screw.

If as TK suggested there is some pass through 277, you need to shut it off too. Maybe you need a voltage detector. Don't know how I stayed alive for nearly 60 years without one. I came across the niftiest gadget for trouble shooting, a voltage detector. They work through the insulation of wires. There are several brands. I have a GB Instruments GVD-505A, less than $15 at Home Depot. Touch it to a hot wire, and the end glows red. Find the doodad that lights it on one side, and not the other, and you have the culprit. You do not have to open up housings and expose electrical contacts. You are looking at where your hand is, not where the meter is. Most people are capable of doing repairs and will get it going and not get hurt if they use a little sense. The voltage detector makes it even easier.