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Demand charges are related to the maximum kW drawn during a particular time window, typically 15 or 30 minutes. The single largest window sets the demand charge for the month. While the average kW may be much lower, the utilities must install transmission and distribution systems to handle the much higher peak kW drawn during certain periods. The demand charge is supposed to compensate the utility for the added cost of the larger lines, Transformers, etc. needed to handle the peaks.

Simply recording the maximum demand would mean that just starting a large electric motor could send your demand charge sky high (remember that some motors draw 7-10 times their running current on start up!), yet the momentary spike in current draw would not require a distribution system that was 10 times larger.

On the other hand, say you used a 100kW motor for 50 minutes an hour. Your neighbor uses a 1000kW motor for 5 minutes an hour. You both consumed the exact same kWh, yet the utility would have to install a distribution system that was 10 times larger to serve your neighbor. That is the type of consumption a cumulative demand window is designed to capture. Your neighbor would be paying for the extra cost involved in the 1000kW distribution system, even though he only needs it for 5 minutes an hour.

Demand charges are an excellent incentive to do load leveling, or so-called peak shaving, and a huge industry has grown out of that reason.

Cumulative demand is the addition of each billing period [average over the window] maximum demand as described above. This value can be used to assure that no reset of billing period data has been missed - no missing billing periods. The utility can use the cumulative demand collected with the previous billing, and add to that the current billing period's max. Dmd., and the result should be the meter's current maximum demand. If the values do not match, a maximum demand for some billing period has not been collected correctly. If someone broke the seal on the meter, and caused the meter to start a new billing period to attempt to avoid paying for an earlier maximum demand, it would be detected.

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Definition of maximum demand?

MAXIMUM DEMAND (M.D.): -It is the greatest demand of load on the power station during a given period.I.e. The maximum of all the demands that have occurred during a given period (may be a day, may be an hour etc.).Need of maximum demand in Electricity bill?When the rate of electrical energy is charged on the basis of maximum demand of the consumer & the units consumed, it is called two-part tariff.In this total charge is divided into two.A) Fixed charge à depends on maximum demand of consumerB) Running charge à depends on no. of units consumedIt is measuring by installing maximum demand meter. Charges are made on the basis of maximum demand in kVA & not in kWMaximum demand used to be measured by a demand needle on the meter, that would actually store only a peak demand. When you start an electric motor, this peak can be very high for a second or two. For this reason, more modern meters calculate an average demand over some period of time (often 15 minutes), and the maximum of those average demands is used as the maximum demand for billing purposes.Billing by maximum demand allows the utility to bill for the cost of installing better wiring and transformers for customers with a large active demand (KW).Values other than KW can be measured the same way for other demand values.


What does the acronym CUM stand for?

CUMulative CUbic Meter


How do you read my email meter type em 3330?

This EMAIL EM3330 electricity meter is highly programmable. Therefore, depending on your electricity supplier and location, the information below may or may not be relevant. (For your information, we are located in Perth, Western Australia, and our electricity supplier is Synergy / Western Power.) There are basically 3 sets of "registers" (or data storage areas) inside the EM3330. Normally, the meter slowly scrolls through the "Standard" set of "registers" automatically. The "register" number is on the left hand side of the LCD screen. If you are patient, this is what you will see in turn: (and if you are impatient, you can step through them quickly by pressing the "RESET" button.) 04 - Current time from the internal real time clock (this clock determines what tariff Synergy charges you if you use a SmartPower scheme) 05 - Current date 07 - Cumulative kWh imported from the grid - this is what appears in your bill 10(A) - Cumulative kWh imported from the grid during "On Peak" period 20(C) - Cumulative kWh imported from the grid during "Off Peak" period 30(B) - Cumulative kWh imported from the grid during "Weekend High Shoulder" period 40(D) - Cumulative kWh imported from the grid during "Weekend Low Shoulder" period 107 - Cumulative kWh exported to the grid - this is what appears in your bill 110(A) - Cumulative kWh exported to the grid during "On Peak" period 120(C) - Cumulative kWh exported to the grid during "Off Peak" period 130(B) - Cumulative kWh exported to the grid during "Weekend High Shoulder" period 140(D) - Cumulative kWh exported to the grid during "Weekend Low Shoulder" period 99 - Error code (if applicable) 188 - Display test screen The "ALT" button allows you to access additional registers for diagnostic purposes. "ALT-1" gives you the voltages and currents measured on each electricity phase coming into (and going out of) your house. "ALT-2" gives you maximum kWh demand and maximum kWh exported within each of the 4 SmartPower periods (ie On Peak, Off peak, etc - region specific information!) "ALT-1" registers: 51 - Phase A voltage 52 - Phase B voltage 53 - Phase C voltage 59 - Power Factor 61 - Phase A current 62 - Phase B current 63 - Phase C current "ALT-2" registers: (this is guess work, but seems to be reasonable assumptions - but the information is region specific) 15 - Maximum recorded kWh demand during "On Peak" period 25 - Maximum recorded kWh demand during "Off Peak" period 35 - Maximum recorded kWh demand during "Weekend High Shoulder" period 45 - Maximum recorded kWh demand during "Weekend Low Shoulder" period 115 - Maximum recorded kWh exported during "On Peak" period 125 - Maximum recorded kWh exported during "Off Peak" period (this should be zero as you cannot export power in the dark, which is what "Off Peak" is!!) 135 - Maximum recorded kWh exported during "Weekend High Shoulder" period 145 - Maximum recorded kWh exported during "Weekend Low Shoulder" period Hopefully, this information is of some use to you!


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