You have probably noticed that some neighbors have multiple electric meters. Just on my street, about half the homes have two meters and one house actually has five! The Federal Electric Commission (CFE) offers much lower rates for low usage subscribers. So if you have a house that can claim to have multiple dwelling units (for example, a maid’s quarters, guest house or rental area), you can have more than one electric meter. The difference can be very substantial, so this possibility is worth looking into.
CFE residential billing uses two rate structures. Tarifa 2 consists of a fixed charge and a single rate. The fixed charge and the rate change each year or so, but for simplicity I have used the November 2016 values in the following example. Tarifa 1 is a different structure that does not have a fixed charge but uses three increasingly higher rates as the consumption increases. If the average consumption over a 12 month period exceeds 250 kWh per month under tarifa 1, yet another structure called DAC (De Alto Consumo) is triggered. This consists of a fixed charge and a much higher rate.
When looking at your electric bill, be sure to remember that it is for two months. So divide the consumption by two when comparing it to the examples below.
To make comparison of the rates easier, we can assume that all monthly consumption is the same. Then the DAC rate becomes just another segment of the tarifa 1 rate structure.
The above graph shows the cost for the two rate structures. This chart is for a single meter and includes the 16% IVA and 10% DAP taxes.
Note that tarifa 1 provides a lower cost than tarifa 2 as long as the consumption is less than 250 kWh per month. That is a relatively low threshold which corresponds to an average load of about 350 watts running continuously. A small San Miguel home with a refrigerator and lights that are not left on when not needed should meet this. A larger home would typically run 2 to 3 times this much. This is why many homes use multiple meters. By keeping each meter below 250 kWh per month, the DAC threshold is avoided and the much lower rate shown above applies. For example, suppose you use 375 kWh each month. If you have tarifa 2, the monthly bill will be 1,500 pesos, but if you have tarifa 1, the DAC rate will apply and your bill will be 2,000 pesos. So one possibility would be to change to tarifa 2 and save about 25% on your bill. If you were to install two meters and continue with tarifa 1, each meter would record 188 kWh which would cost about 350 pesos each or 700 pesos total. That is only about 1/3 of the single meter cost under tarifa 1 and 1/2 that under tarifa 2!
It is interesting to see how sensitive these calculations are to the balancing of the load between the two meters since the only way to guarantee an even balance would be to connect the two meters in parallel. (CFE might object to this). The graph below shows the total bill for three levels of consumption as a function of the load balance. The dip in the center of each of the three curves corresponds to the standard tarifa 1 rate while the higher values are where the DAC applies.
The orange curve shows that for a total energy usage of 375 KWh, the balance needs to be between about 33% and 66% to avoid the DAC. For higher usage, say 490 KWH, the balance needs to be much closer to 50% while for a lower usage like 260 KWH the range is much wider.
If you are living in an area served with 3-phase power, your meter may be marked either 1F2H, 2F3H or 3F4H, where F means Fase (phase) and H is Hilo (conductors). If you are in an area served by 2-phase power, the meter will be marked 1F2H or 2F3H. These may be either analog or digital. In any case, if you decide you want to replace your existing single meter with two meters, you want to request having two of the 1F2H meters. This will involve changing meter sockets as well as requesting CFE for the new meters.
A simplified schematic of how a 2 or 3 phase meter is wired is shown below.
A two meter system should be connected to the main entry panel as indicated in the figure below. (If your distribution is 3 phase, line 3 is not connected). The black, red and white rectangles represent the two line side buses and the neutral bus inside the main circuit panel which connects to the branch circuits or to the sub-panels.
Installing a second meter is definitely a job for an experienced electrician because it involves dealing with the live wiring on the CFE side of the meter(s).
As discussed above, it only makes sense to have two meters if your total average usage is between 250 and 500 KWh per month. But to realize the full savings, the loads on the two meters must be evenly balanced. Once the meters are installed, just write down their readings over a period of say 1 week and see if the usage is about equal. If it is not, you will need to swap one or more branch circuits between phases. This is easy to do but requires some work to figure out which ones to swap.
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