I have a new Legrand dimmer switch. It has a connection for a ground.
However the box it needs to go into appears not to be grounded.
The dimmer is model LSCL453P. The load is an LED light about 30 watts. This is not in an office (not bathroom or kitchen). The switch cover is plastic.
The voltage between the two wires is about 100V AC. The voltage between one wire (left in the picture) and the box is about 50V AC. The voltage between the other wire and the box is about 40V AC.
Is it going to work ok if I just connect the two wires?
Is that going to be any less safe than the alternative of just putting back the old on-off switch?
Edit: Some more investigating, it seems that the box is at about 40 volts AC relative to ground. So the basic premise of the question ( that the box is not grounded) is correct, but not in the way I assumed (i.e. that the box is not electrically connected to anything else in the world). I fear this has gone beyond a DIY project and calls for on site help from a qualified electrician.
Another edit. Putting an ammeter between the box and a trusted ground gives 0.2mA at about 40V. Resistance between the box and a trusted ground is very high. So I'm fairly sure the 40V is a parasitic voltage caused by capacitative coupling (and maybe some inductive coupling too) between the BX armour and the hot wire running through it. Likewise, past a certain point everything else on that circuit that should be grounded isn't. So now I'm back to where I started. The box simply isn't grounded. The lesson for me is to check both the voltage and amperage against a trusted ground. Just for safety's sake, not to mention getting the dimmer to work, I'm going to ensure that everything that should be grounded is.