From my understanding if you had an installation with large inductive loads, well the reactive part of the loads is not registered on the incoming meter and so the wattless current is free of charge, and so the supply company likes to fine you for having poor power factors. My question is why does the meter not see the wattless current, the meter does not know the current is going towards inductive reactance.the only vairable to work off at the metre is the current. any help would be much appreciated

James, The reason the Watt-Hour meter does not register Reactive power, is because the reactive power does no real work but it still has to be allowed for in cable calcs. Only True Power (V x I) does work, ie: creates heat or light, this is what the watt-hour meter is designed to indicate

Although the reactive power does no real work there is still its current flowing in the supply cables, now if the metre uses current to work out a watt rating the metre is going to read the wattless current. i suppose the question is how does the watt meter measure watts?

Reactive power is the product of a negitive multiplied by a positive factor. If you consider a sine wave with the voltage and current in phase the product of the two will yield a positive value + time a +, for one half cycle then a - times a - the next half cycle. this will always equals a positive product.

When reactive loads are installed the current and voltage are not always in phase and at times the instantanious valuesare of opposite polarity, this will yield a positive and negitive factor of which the product will have a negitive value( + times - equals a - product).

Negitive watts does not record on a watt meter. thus phantom power

[This message has been edited by cpal (edited 10-21-2004).]