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#198974  02/09/11 10:43 AM
Re: Long control circuit
[Re: sabrown]

Member

Registered: 12/12/02
Posts: 298
Loc: Ogden, Utah, USA


The control circuit is just a pump mag, the 208 VAC is not isolated from the load at all. 14 gage gives a surge voltage drop of 9.2 to 9.4% (results from two different programs, slightly different wire assumptions). Droping the power factor as expected in a coil to an assumed 0.5 bring the drop t0 4.9% (beyond the capability of one program). I other words I am crossing the line between threory and practicality.
Using loose math, we take the coil and assume that its X/R ratio is 11 (my first likely bad assumption): thus R = 11X, Z=V*V/VA=(208)(208)/311=139 Z=sqrt(X*X + R*R)= sqrt(121(X*X) + X*X), so X=12.6 (reactance) R=138
The 14 gage wire (from Table 9) for 2100 feet X=.3 R=13
for a final X=13 R=151
Z= 152
This gives a circuit flow of 1.36 amps when compared with the 1.5 amps of the mag at its rating, is a 10% drop in current. The mag should be rated for proper operation from 20% to +10% thus we are with in the operational parameters even during the initial surge with 14 gage.
But none of this takes in account the capacitve component of the 2100(*2) of wire. C=0.225AK/tE12 where A is the area, K is the dielectric constant (Vacuum K=1, air greater than 1, solids and liquids may be 2 to 14000), and t is the distance in inches between plates, E12 means 10 to the 12 power.
Making a boat load of bad assumptions: K=2, t=0.133 (the diameter of XHHW2), A=(diameter of 14ga)(one way length in inches)=(0.024)(25,200)=604.8
so C=2 nanofarads (and could be off by a factor of 1000 larger) reactance of wire would be X=1/2(3.14)fC = 0.2 to 200 micro which is insignificant.
I am probably over analysing this, but it seems with all my bad assumptions that this would not be an issue, but in the real world??? Such as I did not take into account the power factor effect, and all this may be just pulling the wool over your eyes making it seem like an EE is needed. Besides, I may have mistakes in here besides the poor assumptions.
The compound relay situation is what I want to avoid, for I would go beyond that to likely a Gems Sensor such as the series 26M. No issues there other than surge protecting the line if desired, they can sometimes see the surge protection as a closed contact.
Shane

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