[petefav]

When I replaced an old porch outlet with a GFCI the unit tripped as soon as I connected the downstream load wires.. There are no other outlets on the circuit, only a number of ceiling light fixtures in the two adjoining rooms. What should I look for? Also, is there any chance that an undetected ground fault could add to my electric bill over time?

[tkrussell]

There is no reason to have GFI protection for light fixtures, so the GFI should be connected that does not protect these lights.

There can be a accidental neutral ground connection in the downstream circuit causing the tripping.

[petefav]

Thanks for the reply. I know GFCI is not needed for lights... I just mentioned that for except one other outlet that tests "correct" the only other things on that circuit are ceiling lights/fans, one with a rheostat switch. Also, the wiring is old flexible metal bx without a ground wire. I assume the metal sheath provides grounding?

[tkrussell]

The metal sheathing of BX cable is allowed to be the equipment ground.

With those items, fans, lights, etc on a GFI circuit, clearly one has a ground fault.

[ballengerb1]

This is an exterior receptacle and if the area is subject to water The GFCI is appropriate. TK is correct, your GFCI is doing its job, you have a fault somewhere.