greatings all. i live in an rv and everything runs on 120 volts. 240 volts didn’t even come into the rv until recently. but i got this new heat pump and it required 240 volts so i ran a 240 line into the rv and put in a breaker box. now the old 120 lines goes into this new box, so everything is connected to just one leg. i also have a 240 grid tie inverter connected to this new box.
i was over in the “learn” section reading and i kind of got the idea that this isn’t the best way to do things. i think that i should go to the original rv breaker box and move half my lines to a new wire and run it up to the new breaker box. try to split things up 50/50.
is this worth the effort ?? i just order a shield so that i can start monitoring my electrical input. right now if i put a ct on both lines ones going to have a lot more usage than the other.
Kindly explain what you mean by “rv”.
It probably is worth moving your loads around. It means that you’ll get less voltage drop under high load conditions, which is good - especially if the voltage drop happens your side of the meter. As you’re getting an emonTx Shield (?) and two c.t’s, check the current under various conditions and make a best effort to balance the two legs. You’ll never succeed in getting a perfect balance under all conditions, but the nearer you can get under “average” and “high load” (interpret those as best you can) conditions, the better.
thanks, rv = recreational vehicle
If it’s mobile, one perhaps obvious point is that you need to make sure that all wiring is secure and cannot move and chafe. In the UK, there are additional rules for mains voltage wiring in vehicles, but I’m not familiar with the details. It might be worth checking your rules, as avoiding a problem now is a lot better than correcting it later.
I have some experience in this area, and indeed it’s better to split your loads 50/50 if you intend to use a 50 amp service, otherwise you’ll pop the breaker with all the loads being on one side. IF your RV has two air cons then definitely so. As other people have mentioned ‘if in doubt seek expert help!’
Dave.
yes i’m looking into the best way to split things up. its kind of amazing how little electricity i use except for heating and cooling. and i have high hopes that this new heat pump will take care of most of that. i’ll really get a good idea this week. its going to be cold here in arkansas.
Probably not, as that was his configuration before he brought in the second leg.
(he’s in the US on a split-phase supply)
If the heating and cooling are 240 Volt loads, then given your 120 Volt consumption is so low,
(and your had no issues prior to adding the second leg) you’re more than likely OK with things as
they are.
I can relate to that, I’m in Oklahoma. 
Thanks Bill, I had a trailer (30AMP) and then a motorhome with a 50amp service - we toured all over the US and Canada in both over a few years. Incidentally the motorhome (we had it new) was wired incorrectly with both AC’s on one leg. The generator kept popping it’s breaker until I figured out the two were on one pole of 50amp in the fuse box and in turn the generator - swapped it over and it was fine.
Dave.
PS. we stayed twice Oklahoma City and Elk city looking at my GPS tracks
That’s not the first time I’ve heard of a bad factory wiring job on an RV. 
You weren’t too far away then. I’m in Granite. ~30 miles S of Elk City.
One consideration there: if your low current loads (lighting in particular) can be shared between the two legs, you won’t be left completely in the dark if you do trip the breaker.
He’d have to trip the main breaker for that to happen, but nonetheless, it is a good point! 
what a small world, i was born in altus AFB oklahoma.
maybe i should start a new thread for this, i’m looking at the specs of this shield i got coming. if i understand this correctly i need 2 ct’s for the 240 and one for my grid tie inverter. ?? the grid tie inverter is 240 volts surely i don’t need a ct for both sides ?? i would think the output from the grid tie inverter would be even across both legs . i only ordered 2 ct’s.
Small world indeed. I work in the Radar Shop there.
Have you had a look at this?
https://learn.openenergymonitor.org/electricity-monitoring/ac-power-theory/use-in-north-america
(the sub-section titled Measuring Whole-house Power)
If you were going to monitor/measure only your 240 Volt loads, then one CT would be fine.
But, since you want to m/m your 240V and your 120V loads, you’ll need CTs on two of the three wires.
The link above has a detailed explanation.
Correct.
now thats just crazy, my father was in the air force and worked on b52 radars systems there in 1959.
yes i read that, im just not sure i understand. “in theory it does not matter which voltages and currents are measured, but in general, it will be more convenient to arrange the voltage transformer to measure the voltage of one leg to neutral, and to attach a current transformer to each leg”. so one ct on L1 and one ct on L2, the voltage transformer connects between L1 or L2 and neutral. then only 1 ct needed for the grid tie inverter ? if so i need to order another ct.
That’s a bit before my time. in '59, I was but three years old. I was USAF active duty from
1973 to 1980, and though I never worked on 52s, I did work on KC-135s.
Although I have worked on airborne radar (and nav aids) my current job involves a
Digital Airfield Surveillance Radar and a Pulsed Doppler Weather Radar which are ground-based.
OK, back on topic…
Indeed you do.
Your 9V AC-AC wall wart will connect to a 120V outlet and you’ll have a CT on each hot leg,
(facing opposite directions) and one CT on the GTI output.
okay i got it, will order today.
Hi Michael!
Thanks for helping explain how to monitor US power. I’ve been reading over the guide in “Learn” section and came across this equation:
V × ICT1 + V × ICT2 = V × (I1 + I3) + V × (I2 + I3) = V × I1 + V × I2 + 2 × V × I3
The voltage being constant for both legs, I1 being current through leg one and neutral, I2 being current through leg two and neutral, and I3 being current through both legs 1 & 2.
I’m wondering if there is an error in the third part:
V × I1 + V × I2 + 2 × V × I3
Wouldn’t we only take half the current of the 240v loads here? The same current that travels through L1 travels back through L2, is my understanding. Any feedback / yey/ney would be appreciated! Getting ready to configure feeds for whole house monitoring. Thanks
Andrew
Do you accept that the total power is
V × ICT1 + V × ICT2 ?
Then the rest is algebra.
The other way to look at is: What is V?