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I hope this practical question is not OT and not too trivial for this forum. I am renting an apartment in a duplex with a shared water heater and dryer. Turns out, both water heater and the dryer are connected to my meter. The neighbors seem willing to pay their share for the past 6 months, only how to estimate their fair share?

I tried to leave the apartment for a couple of days and take a reading from the electric meter before and after. It appears that in these 48 hours, my meter changed by 10KWH, i.e. $5/day, with everything but the fridge off. Realistic? There are 3 to 4 of them, and they seem to shower a lot! I know, because I don't get much hot water.

The neighbors are moving out in a month, so I don't have much time to experiment. There is no way to interrupt the electric circuit to insert a meter; so I am thinking, maybe an induction meter would be feasible? How reliable would it be?

EDIT: actually, turns out the dryer plugs into a standard 220V outlet. But heater probably takes much more electricity anyway, right?

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    $\begingroup$ Induction meters (clamp meters) work well and are pretty accurate but you must separate out the conductors and only clamp one of them. $\endgroup$ – Brandon Enright Feb 10 '14 at 2:18
  • $\begingroup$ You mean, get one of the 3 wires? Ouch! No, can't do that! Are you sure there is no other way? $\endgroup$ – Ruby Feb 10 '14 at 2:29
  • $\begingroup$ Not the physics answer you're looking for but... call the landlord? And failing that, got any lawyer friends? $\endgroup$ – chase Feb 10 '14 at 3:06
  • $\begingroup$ I think this actually is off topic here. We'll see what others say. $\endgroup$ – David Z Feb 10 '14 at 4:24
  • $\begingroup$ It can be physics: after all, it can be about energy it takes to heat a certain volume of water, and ways to measure electric current. Or it can be about the landlord. I could easily post this at some tenants rights forum, but I am afraid I would not get an answer, for the lack of people who understand these two subject matters. $\endgroup$ – Ruby Feb 10 '14 at 4:39
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This was a comment but it got too long..

With the level of information you can provide this is not a physics question at all.

10 kWh over 48hr may be very high or very low consumption, unless you have traced the circuits you don't know what that meter supplies.

The fact you run out of hot water tells us nothing useful at all about power consumption, it may suggest your tank is small or that your neighbours like to leave the hot taps running for fun.

If you want to pay the correct amount without getting another tank then you need to have a plumber install two flow meters on the water tank and install another power meter (your energy supply company will do that, It'll cost a fortune) then divide the bill based on the flow rate ratio. Anything else is just wild guess work.

Though, that'll probably cost more than a whole new tank.

You just need to come to some agreement with your neighbour and/or landlord, get advice from the appropriate forum. The usual method is that power is included in the rent (rent is still a flat rate).

If you were unaware of the issue before moving in, you've been deceived. If you were in my country the tenancy disputes tribunal would certainly rule in your favour and the landlord would have to pay your bill.

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amp meters would not work as they display the instantaneous current consumption...what you need is to monitor the integral of i^2*R where R is the resistance of the water heater

in Europe (UK or Germany), your electricity company would give you a so called smart meter. this has a clamp current sensor that can be connected around the power cable going to the electrical heater and used to continuously monitor consumption or energy. However, it is dependent on using a resistive load (which you actually have) and that the voltage remains constant (doesn't have a voltage sensor to simplify installation).

you could try procuring one of these energy meters but instead of attaching the clamp current probe at the energy meter terminal, attach it to the water heater side...some would even have wireless data transfer so one can see how much energy was consumed on its iphone or whatever...

very likely you can get these with $20 from ebay

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  • $\begingroup$ Hi, I don't know if the information provided by you is correct or not but if it is correct it is indeed a really good advice. $\endgroup$ – hsinghal Jul 1 '16 at 2:44

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