GEM track voltage on both legs of split-phase?

[wci68]

I found this previous thread but it seems to be old so I thought it better to start new: Measuring both legs at 240 volt vs just one leg at 120 volt?

I am interested in being able to monitor the voltage of both legs of a standard residential split-phase service, independently.

It is not unusual for the two legs to have slightly different voltages to ground. Measuring a single leg to ground, or measuring leg-leg as a single value makes the assumption the potential is the same for both legs. If monitoring a single leg, then at least all those circuits on that leg will have accurate power measurement. If monitoring across both legs (hot/hot) then the average would be the voltage reference and neither set of circuits would be completely accurate.

It is not clear from the earlier post whether using two PTs allows the monitoring of both legs independently or if the two potentials are simply averaged (added, then halved), but it appears to be the latter.

Is it possible for the GEM to monitor/track voltage (potential) independently for each of both legs?

[mwareman]

GEM only has one voltage measurement input, so I suspect it cannot on its own. In my case, I'm using all 32 channels - and may be adding some new circuits in the next few months. I'm planning on getting a second GEM and having it feed the same Dashbox. I wonder if this allows the Dashbox to separately track leg voltage.

[ben]

You can't track each separate leg with 1 GEM. It uses one voltage reference.

I'll have to check with Paul when he's in, but I think you'd be able to with 2 GEMs. You just need to make sure the outlet of the 2nd GEM is on the 2nd leg of your panel. The DashBox will show a voltage load for each GEM.