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Today I have the checked the meter. It was showing 0.650 kW (instantaneous power) while just four appliances were running. i.e two ceiling fans of 60 W each and two refrigerators of 150 W and 180 W respectively. Total power consumption 60 + 60 + 150 + 180 = 450 W. Why these readings are not same? Why there is a difference of 200 W?

Transistor
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Waseem Khan
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    Measuring such things is rather complicated. You may be encountering different types of power measurements (especially with motor loads), inaccuracies.... or there may be additional equipment you are unaware of. Try turning on and off the known loads one at a time and compare the resulting figures. See what you measure with none of them on. – Chris Stratton Aug 22 '20 at 12:08
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    I doubt your meter was reading 650 kW (not 'KW' which would be kelvin-watts. Also 'Ws' would be watt-seconds. It's just 'W' for watts.). Check it again. Is it 650 W? What exactly is "the meter"? – Transistor Aug 22 '20 at 12:11
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    A clear photo always helps. – D Duck Aug 22 '20 at 12:16
  • 0,65 Megawatts is beyond your average home capacity. Are you located near a nuclear reactor? (lol) I hope you have deep pockets. This is going to cost alot until you fix this, Are you forgetting kW vs kWh? – Tony Stewart EE75 Aug 22 '20 at 12:24
  • So your two ceiling fans and two refrigerators use about 30 times the energy used in the university where I work and the max consumption in kW I have recorded there is about 23kW. I suggest you have a unit error. – Solar Mike Aug 22 '20 at 12:26
  • You're still reporting 650 kW which is 650,000 W when you're expecting 450 W. I think the photo of the meter and readout is a good idea. Add one in. – Transistor Aug 22 '20 at 12:28
  • Updated the question – Waseem Khan Aug 22 '20 at 12:47
  • sorry it was 0.650 kW – Waseem Khan Aug 22 '20 at 12:48
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    Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design. This is a site rule and not something I've made up. Your meter is regarded as an electronic device in this context. In other words, without explicit design knowledge of your meter it is guesswork at best. – Andy aka Aug 22 '20 at 12:56
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    This seems to be the same basic question as: Consumption of automatic electric voltage regulator or stabilizer When you try to improve or add to a question do that by editing the original question not by posting another question or adding information in comments. –  Aug 22 '20 at 13:50
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    Where are you getting these figures of 60, 150 and 180 watts? – Harper - Reinstate Monica Aug 22 '20 at 14:16

2 Answers2

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Possible reasons:

  • The ratings on the appliances are wrong or optimistic.
  • The meter is not accurate at low ranges. (You have posted no information on the meter so we don't know what its full scale reading is and what accuracy and precision it can give.)
  • You are running the appliances at a voltage other than their ratings. This will cause the power to deviate from specifications.
  • You have additional load somewhere that you have not taken into account. (What is the reading when you switch off the four appliances?)
Transistor
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Nameplate power draw is about provisioning

Most mains equipment has a nameplate or placard specifying its power draw, either in amps or VA. VA being coarsely analogous to watts. This data is for the mains power electrician or EE (the person who plans circuit breaker layouts, branch circuit wiring, conduit runs, and buys Leviton, Eaton, Square D etc.) to figure out how many devices can go on individual branch circuits, and how to size the overall service for the loads.

The nameplate is arrived at based on rules, and factors for things like startup current and power factor, to reflect the practical burden it places on the branch circuit. For instance an appliance consisting of a diode+resistor in series (thus 50% PF) that draws 30 watts will be nameplated for 60 VA.

Of course the nameplate data is only as good as the manufacturer: if it doesn't have a UL Listing or other NRTL equivalent, and it's just cheap Chinese, then it could be anything.

So nameplate power will not reflect what you see on a variety of measuring devices. how does it deal with power factor, RMS, reactive load etc. For instance many meters would observe 30W from that hypothetical 60 VA diode+resistor load. Which is accurate is a subject for debate!

Another classic problem is people overlooking loads that are attached to the electrical system.

Harper - Reinstate Monica
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  • This clearly states exactly I Answered Actual / Rated (for breaker rating) yet Voltage Spike fails to understand my brevity of wisdom for the test condition of rated with Vin tolerance. He forgot to ask for clarification and acted improperly. -1 – Tony Stewart EE75 Aug 24 '20 at 00:50