When measuring amps of probably all single phase motors with clamp-on ammeters, I notice slight difference in current readings between current measured on phase wire and current measured on neutral wire (ex. 1.5 Hp motor shows 6.4 amp on phase wire and 6.1 amp on neutral). Several a/c clamp on meters were tried, all had same reading difference. Why are the line and neutral current readings different? Is there a problem which I need to fix (and how), and which reading is the true current draw?
Are you using a True RMS clamp meter?
No, not using True RMS meter, but it should make no difference because: (a) True RMS relates to waveform affecting voltage readings and not current, and (b) ordinary clamp-on meters are calibrated for sine wave and measurements were taken on utility (WAPDA) power and not on UPS or generator. Furthermore, any meter error should cancel out because current reading of both line and neutral is done with same meter.
I could not understand this + & - with AC
AC mean alternating current so both the wires should have positive and negative charge on them in alternating manner.
Like for one second red will be positive and black will be negative ?
and next second red will be negative and black will be positive ?
For your question: one of your wire has more load because may be ground charge is leaking down from your motor !
I also see difference on nearly every neutral and live wire in my home, I thought it was due to RMS difference because every load is not ideal (inductive or resistive). Or maybe due to unbalanced neutral. Or maybe the current is somehow induced due to other wires fields.
Sort of, yes. Think of DC as a waterfall and AC as a oscillating transfer of energy.
Someone else said it better though: Direct current is like a chainsaw - the sharp bits travel in one direction doing work (slicing wood) and then return to their original location. The motion of the chain is constant. … Alternating current is like a hand saw - the sharp bits travel in one direction, then briefly stop, then travel in the opposite direction.
In end both transfer energy. Like so:http://stream1.gifsoup.com/view6/3719324/ac-vs-dc-o.gif
Yes i know alhamdoLILLAH why this is happening , when you see at your good quality clamp meter u will find + and - signs on it . although it is for DC but it also matters for AC , when you want to measure with phase line cross the wire from front to back in the clamp of your meter , and when you want to measure with neutral then cross the wire from back to front .
u will find no difference then
And why does direction matter?
because of the electrical field - The meter cant read properly if the field is in reverse direction .