On Mon, Jan 2, 2017 at 4:49 AM, Bill Byrom <t...@radio.sent.com> wrote: > Most US homes and small businesses are powered by what is commonly > called a "split-phase" 240 V feed. The final distribution system > transformer has a 240 V center-tapped secondary. The center tap is > grounded, and three wires are fed to the building (actually it might be > up to around 6 houses): > (1) Leg L1 or phase A (red wire) -- This wire will measure 120 V to the > neutral or 240 V to Leg L2. > (2) Neutral (white wire) -- This wire is grounded at the distribution > system and at the service entrance to the building. > (3) Leg L2 phase B (black wire) -- This wire will measure 120 V to the > neutral or 240 V to Leg L1.
When someone here previously mentioned observing high voltage, one possible cause for this in this common "split-phase" configuration is that if the neutral wire is overloaded, damaged, poorly connected, or otherwise has high resistance, the voltage on the two legs will swing wildly and in opposite directions depending on load. So, e.g. if you put a 1kw load on L1 while L2 is nearly unloaded then perhaps L1s voltage drops to 108v while L2 rises to 132v. The reason for this is that, e.g. imagine that the neutral were removed completely you would effectively be connecting your appliances in a parallel-series circuit (all on L1 in parallel, all on L2 in parallel, the both in series) across the 240v feed. I've had issues with neutrals several times in the past, and in one instance, temporarily dealt with it by moving as much of the load to 240v as I could, manually balancing the remaining loads, and then using a digital multi-meter to dynamically control some additional load to keep the voltage sane on each side. I think the fact that you can end up with a much higher voltages at the outlet if the neutral has problems is one of the more unfortunate properties of the split-phase approach. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.