# CT Polarity in KW meter and Ammeter or Ampera Meter

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Hi all

Can anyone explain the reason pls?

Why kW meter is influenced by polarity of current transformer and why not for ampera meter." Basically we know that when we do wiring for ampera meter.. we don't need to worry about the CT polarity, but what is the reason.

Regards,

Saidaibala

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"Why kW meter is influenced by polarity of current transformer and why not for ampera meter"

Is it? . I think with alternating Voltage and alternating current a Wattmeter is not polarity sensitive.

Could somebody confirm this for me. I was waiting for somebody else to answer but what the heck!

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• 1 month later...

An ameter measures the average magnitude of the current and an AC meter is poarity insensitive.

A KW meter measures the instantaneous product of volts time amps and is therefore polarity sensitive.

The KW reading is the average of the products of volts times amps. If the current is reversed, the KW will be negative.

Best regards,

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Hello MarkE,

What is ampera meter, is it the same KWh meter...? If so, I had studied in my course years back that torque on the rotating disc remains positive irrespective of the magnitude of the current in energy meters, hence the case is not with the ampera meter...!

Don't mind with my small electrical knowledge...!

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Hello MarkE,

What is ampera meter, is it the same KWh meter...? If so, I had studied in my course years back that torque on the rotating disc remains positive irrespective of the magnitude of the current in energy meters, hence the case is not with the ampera meter...!

Don't mind with my small electrical knowledge...!

AMP meter measures current (AMPS) through the circuit VOLT meter measures Voltage across. Power (P) = I (amps) * V (volts). Analog Kwmeter has two coils doing just this.... Rotating Disc huh!! are you talking motors? T = f.d or maybe use po=2 pie n t / 60 re-arrange. n=rpm hence dividing by the 60 and t=torque.

Most 10 - 20 ft reefers have menu that will give real time current drawn from evap motors, compressor heating elements etc. Menu will be displayed on actual refrigeration unit itself (very easy to understand) As Marke pointed out, the amount of power consumed depends on overall eff.

Hope this helps. What are you actually trying to accomplish?

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