Hi, folks - wondering if someone can help me out. I'm getting an "open ground" reading on a wall outlet which is being fed by 12/2-grounded romex cable. The cable is grounded at the panel, so I'm not sure why I should be getting an open ground reading.

This line is for an electric baseboard heater, and someone tapped into it to put in a wall outlet. Is it possible that this is a 240 volt circuit, and would that cause an "open ground" reading on a Sperry 3-prong tester meant for 120V?

By the way, the outlet works with a fluorescent light plugged into it, but I haven't tried using any other appliances/devices in it, and I'm worried about doing so if it's possible this is a 240V line.

Most baseboard heat is 240 volts. Tapping into this 240 volt circuit for a 120 volt outlet is not allowed, so if someone did that, they probably did a few other things wrong, such as use the ground for the neutral at the outlet, and not use it as a ground at the outlet.

I cannot tell you how the outlet tester will act if connected to a 240 volt circuit, it would probably burn out quickly.

You need to stop using this outlet until you are sure how it is wired. Find out if the heat circuit is 120 or 240 volts. Look at the heater for a nameplate that lists the voltage, or find the breaker that serves it. If the breaker is a 2 pole, then it is 240 volts.

If it is a 1 pole then it is 120 volts. Then you need to find the junction box the outlet is tapped into and repair the ground.

Most baseboard heat is 240 volts. Tapping into this 240 volt circuit for a 120 volt outlet is not allowed, so if someone did that, they probably did a few other things wrong, such as use the ground for the neutral at the outlet, and not use it as a ground at the outlet.

You got that right. It could be a full time job just going around and fixing all the things the previous owner did wrong: 20A circuits with some 12/2 and some 14/2 wiring on the same circuit, with 15A outlets to boot; Romex cable incorrectly "grounded" to the box (i.e. the ground wire bent back and clamped under the NM connector, but not grounded, or wrapped around a screw on the box, but without the box being grounded... the list goes on and on.

I've checked the heater and panel as you suggested, and it looks like it's definitely 240V. Not sure why the fluorescent light still works, but maybe it's rated for up to 240V. Anyway, looks like I'm going to have to remove that outlet.

Cheers,
LDR