Hi, don't bother asking stuff on here, as most of the guys on here are twonks
Yes there is a point and that point is showing bas that he doesn't f*cking own the f*cking place.Looks like the OP has deleted his original text so no point in taking this further.
I've never really had any reason to think about or investigate it very deeply, but I've never fully understood what the 3-phase VD figures given in the tables in the regs (which are generally slightly (~15%) lower than the corresponding figures for single-phase) actually represent. Thinking simplistically, if a balanced 3-phase load drew 60A per phase, I would expect there to be "60A's worth" of VD in each of the three live conductors and hence, I would have thought, double that 'one conductor' figure for the reduction in each of the phase-phase voltages - but that 'logic' does not take the actual phase differences into account. I suppose my main problem may lie in my not being too sure as to exactly what is meant by 'voltage drop' in a 3-phase context. Is there a simple explanation?AIUI the "standard" rules for three phase cables assume there will be negligable volt drop in the neutral but if you are putting all the load on one phase that clearly will not be the case. So you'd have to treat the three phase cable as a single phase one.
Well if we assume a balanced resisive load and a perfect three phase source there sill be no drop in the netural. So the P-N voltage will drop by the volt drop in the live conductor.I've never really had any reason to think about or investigate it very deeply, but I've never fully understood what the 3-phase VD figures given in the tables in the regs (which are generally slightly (~15%) lower than the corresponding figures for single-phase) actually represent. Thinking simplistically, if a balanced 3-phase load drew 60A per phase, I would expect there to be "60A's worth" of VD in each of the three live conductors and hence, I would have thought, double that 'one conductor' figure for the reduction in each of the phase-phase voltages - but that 'logic' does not take the actual phase differences into account. I suppose my main problem may lie in my not being too sure as to exactly what is meant by 'voltage drop' in a 3-phase context. Is there a simple explanation?AIUI the "standard" rules for three phase cables assume there will be negligable volt drop in the neutral but if you are putting all the load on one phase that clearly will not be the case. So you'd have to treat the three phase cable as a single phase one.
Thanks. All agreed. So you're saying that when one talks about VD in a 3-phase context, that is in terms of P-P voltage?Well if we assume a balanced resisive load and a perfect three phase source there sill be no drop in the netural. So the P-N voltage will drop by the volt drop in the live conductor. ... Again assuming a balanced load the phase angles won't change, so the P-P voltage will drop by sqrt(3) times the ammount the P-N voltage dropped by. ... These assumptions would seem to tally with your statement that the three phase figures in the regs are about 15% lower than the single phase figures since sqrt(3) is about 15% less than 2.... I suppose my main problem may lie in my not being too sure as to exactly what is meant by 'voltage drop' in a 3-phase context.
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