Those are classic signs of a loose neutral. Check where this circuit originates for a loose wire on the neutral buss.

What are you using to measure this with.

Between want and want are you measuring it.

What size and type of cable is this.

You said ONE of the 120 volt leads.

Is this a 240/120 circuit? And is this a 3 wire or 4 wire circuit.

A GROUND FAULT means that there is current flowing from a hot to the ground. You may or may not have that in this case.

But that is not what is causing this symptom. It is series resistance.

Measure of each hot to neutral, and hot to hot. Also if this is 4 wire also measure from neutral to ground.

Sorry about the limited info. This is a 3 wire utility, ran from the transformer at the pole to my barn. The wire size I dont know but it is big, each wire almost an inch in diameter. It has been buried for almost seven years and there has been no recent digging or excavation around the line path. I measured the voltage at the fuse box in the barn. One leg is fine, measures 120 volts to the ground cable. The other leg as I said was 97-100 volts a few days ago but is now 199 volts. So, half the breakers are usable and I don't have any 240 service because of the one faulty leg. As one suggested, if the ground was bad, wouldn't both 120 volt legs be faulty. Thanks very much for your help and I look forward to you guys helping me

You did not indicate how you tested it?

I still suspect a bad neutral.

Turn EVERYTHING OFF. Then connect a known resistive load on one side.

1000 watt heater would be good.

Then measure the two legs to neutral and hot to hot.

Then plug the load into the other leg.

But really the whole question is mute.

You need to fix/replace that cable.

Call around for an electrican that has a TDR (time domain reflectometer). And ask them how much luck they have had in pinpointing the problem in a case like yours.

I did all the voltage testing with a digital multimeter. I put a load on the good leg, tests 120 volts. I put a load on the bad leg, 0 volts. Hot to hot unloaded is 126 volts, loaded 120 volts. So, which cable is at fault?

Thanks in advance,

Tom

The good news is that it appears to have failed completely which makes it easier to find with a TDR.

But it does not matter which wire failed, although it appears to be the one hot. The cable needs to be dug up.