Wiring trick for KWH meter running on 115V?

System

HI gang, new to the forum here. I am working on completing a grid tied system here in sunny (OK rainy today) pennsylvania.

This system is 1600 watts of PV connected with an older SMA 1800U inverter. The output of the 1800U is 115 V AC, which is apparently kind of an oddball these days.

Anway we've installed a meter socket between the inverter and the main panel of the house, so that we can track the PV production independent of the inverter. I installed a similar system a few years ago, and when we ran the single leg from the inverter through the meter, it only ended up reading half of the watt hours produced by the system (the inverter always read about double).

I'm told there is some trick to wiring a KWH meter so that it will read the full watt hours. Does anybody know this trick?

If it helps, here is my system configuration:

1600W PV at pole > DC discon at pole > DC discon at house > Inverter > AC discon > PV meter socket > 115 volt breaker in main panel > Main Panel

Thanks for your suggestions and best wishes,
Farmer

BB.

Re: Wiring trick for KWH meter running on 115V?

Note, I am not an electrician or utility meter specialists--the following is my understanding of how the "generic single phase 120/240 VAC" meter works. Before you make any changes based on the following, make sure you understand what your are doing and are save doing it (turning off power, double checking before working on circuits, etc.).

Assuming you are using a standard 120/240 VAC single phase "home type" utility meter (showing socket wiring)...

1. How are you making the connections?

a) connecting home breaker Hot/Neutral to the two meter lugs on the "Load Side", then connecting the meter "Utility Side" lugs to the Hot/Neutral of grid tied inverter (or you have reversed the Utility/Load side connections)?

b) connecting a double pole breaker (Hot A/Hot + neutral to "utility side" of meter, and connecting to meter "load side" Hot/Neutral lugs (leaving the second meter Hot Lug disconnected?

c) connecting a double pole breaker (Hot A/Hot + neutral to "load side" of meter, and connecting to meter "utility side" Hot/Neutral lugs (leaving the second meter Hot Lug disconnected) to 120 vac grid tied inverter?

d) or something else?

2. if you are doing A--I would guess that you would read 1/2 the true power transferred (and depending on Utility/Load side to Inverter Connection, the meter may read forward or backwards).

3. if you are doing B--This would emulate the normal Utility Meter connections and should work fine--the one downside is the meter will read backwards (count down)... Not a big problem unless your meter cannot read backwards.

4. if you are doing C--would be similar to the utility meter connection (should work fine). Meter should count up for kWhr reading. The "disconnected" 240 VAC connection is needed so the meter measures the correct 240 VAC voltage (however, only 1/2 of the meter is reading current--the other 1/2 240 VAC connection reads no current so readings should be accurate as the meter assumes 1/2 voltage between the two Hot Phases is 120 VAC and the current you are measuring).

5. if D--tell us what you are doing (I have an old single 120 VAC utility meter that I use to measure power--and that works well).

Or, you might just get a standard industrial kWhr type meter (here are some rated at 120 VAC @ 50 amps).

-Bill

jacobs

Re: Wiring trick for KWH meter running on 115V?

If you are using a 120/240 volt meter, it must have 240 volts leg to leg to operate properly. If you don't have 240 volts available, you can install a simple 120/240 volt step up transformer in the meter box. Wire the primary leads of the transformer between the neutral and the 120 hot leg. Wire the secondary leads to the two 240 volt legs.

Small inexpensive transformers are available from Mouser Electronics or Digikey.

jacobs

Re: Wiring trick for KWH meter running on 115V?

One more item.....At least some meters won't operate properly unless mounted on a vertical surface.