Grounded OUtlet?

I am attempting to put in a three prong outlet. How do I determine if an old two prong outlet is grounded? I have a volt meter. I put the red probe in the outlet and the black probe on the outside outlet screw and got a 120 v reading. However when I open up the outlet I do not see any grounding wire. All i see is four wires hooked up to both sides of the outlet. I thought my volt meter reading meant it was grounded but the absense of the ground wire is confusing me. Help please!

 

Is the box metal? Is the wiring in conduit?

 

the wiring box is metal and the wiring going in to the box is loose. However the wiring in the basement is in conduit. I checked all of the other outlets in the house and they are giving me the same reading. There are already a few three prong recepticles in the house. Thanks!!

 

if you can see that the wire comes in paired up with an overall sheath, then there is no conduit. If there is conduit, you need to bond the receptacle to the box. Without conduit, your only solution to gain a three prong plug is to install a GFCI outlet and put the sticker on that says "No Ground Connected" Otherwise, you are violating code and creating a potential hazzard (as well as liability)

 

The wiring has a pretty thick sheath around it. It looks as thought there is a sheeth, than a breakout, then the copper. It seem slike the actual electrical wire is wrapped in something. Is that just old wiring or is that some type of non metallic conduit? Will a GFCI protect electronics even though there is no ground connected? Why is my multimeter reading that the current outlet is grounded?

 

What we're looking for is whether the conduit is attached to the receptacle box in question. Inside the box you should be able to see individual wires coming into about a 1/2" hole with a locknut around the threaded conduit end. If you have metallic conduit from the breaker panel all the way to the receptacle box, and it's properly installed, that box is grounded by the conduit. That will give you 120 volts from hot to ground, as you have read.

Ungrounded GFCI receps are permitted but a surge protector for home electronics requires a ground to do its job. Generally, electronics fare better when electrical anomalies occur when plugged into a grounded recep.

If your recep box is grounded you must attach a bare of green insulated wire onto the green screw on the recep and run it to a green screw screwed into the recep box.

Hope that helps.

Juice