Re: voltage drop calculation question

Posted by John T on January 01, 2020 at 16:17:27 from (107.77.215.178):

In Reply to: voltage drop calculation question posted by Ray Tractor on January 01, 2020 at 07:01:00:

Ray, you asked an electrical question so don't be surprised to see all sorts of answers, it goes with the territory on here. Here's the real deal as I best recall, but I've been retired from electrical power distribution design for years and rusty on the latest codes and NEC so NO WARRANTY …………..Things may change you know...…..

If you have two 120 volt fans and each draws 6 amps, two of them will draw 6 + 6 or 12 amps.

If one is on one leg L1 of a typical residential 120/240 Volt Single Phase Three Wire Service Transformer fed panel and the other was on the opposite (180 out of phase) leg L2, THE NEUTRAL CURRENT (transformer to panel Neutral buss) WOULD BE ZERO because L1 is 180 out of phase with L2 and they cancel each other out.....

If BOTH were on the same leg L1 or L2 and each drew 6 amps, the NEUTRAL CURRENT (transformer to panel Neutral buss) WOULD BE 12 AMPS

NOTE regarding the above two examples: Each fans individual branch circuit Neutral would carry its own 6 amps of return current, but the Neutral current from the transformer to the panel Neutral buss is what would be zero or 12 !!!!!!!!!!!!!!!!!!! The individual 120 volt branch circuit (Line and Neutral) to supply a 120 volt fan that draws 6 amps would have 6 amps of current flow in each conductor WELL DUHHHHHHHHHHHHHHHH.

A 240 Volt appliance WOULD DRAW ZERO AMPS OF NEUTRAL CURRENT, there's NO NEUTRAL even connected to it, only two Hots L1 & l2 plus an equipment ground (typically).

The way a typical residential 120/240 Volt Single Phase Three Wire service is obtained is by use of a transformer with a 240 volt end to end L1 to L2 Secondary winding. That transformer is tapped in its center (Neutral) such that its only 1/2 or 120 from either end to the center tap (Neutral), thus you have two legs of 120 from the outer end to the center tap (Neutral) but 240 volts single phase from end to end L1 to L2

There are a gazillion line voltage drop calculators on the net, choose one. Line voltage drop is a function of Current,,,,,,,,,,,Wire gauge,,,,,,,,,,,,Wire length. Add up all the loads,,,,,obtain the wire gauge,,,,,,,,,obtain the wire length THERES YOUR ANSWER

Hope this helps, post back any questions

If in doubt where fire or life safety is concerned consult competent trained professional electricians and engineers, local authority and the NEC, don't risk your life or a fire on opinions posted here, mine included.

John T

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