ECN Forum Forums Photo Discussion Forums Photos for General Discussion Multiple feeds, One Service

Submitted by renosteinke:



Close Up

Hmm,
I always thought that PoCo's were all for saving every cent possible?.
{I know the one I work for does!!}
The extra wires wouldn't by any chance be for future expansion would it?.
Is this a Residential or Commercial installation?.

{Message edited to add some missing letters}

[This message has been edited by Trumpy (edited 07-05-2005).]

The location is commercial, with separate meters for two stores. Below the mast is a gutter, with taps to four meters (each business has separate meters for the hot water), so this service has been there a while.

Despite there actually being two services, the practice here is to use a gutter to tap off of one set of wires. That is what was done here.

Future expansion? The PoCo would upsize the transformer, and run larger wires.
Parallel feed? The PoCo would run wires of the same size. Different sizes run in parallel are, well, a really stupid thing to do. (If someone out there doesn't understand 'why," speak up and we'll explain it!)
The method of connection is concealed by the tape over the splices. The usual connector here is a "parallel groove" type, with grooves for two wires, not three. PoCo rules do not allow the use of split bolts.

The PoCo itself is a little confused as to how this happened. When they fix it, I'll have a Sunday service change to do.

Its easy to figure out, the PoCo is stealing electricity from itself!!!

(If someone out there doesn't understand 'why," speak up and we'll explain it!)

Ok, I'll bite because I don't know everything.

I understand that it's wrong, but why?

Btw, what does POCO stand for?

[This message has been edited by ShockMe77 (edited 07-22-2005).]

PoCo = Power Company

Got me for a few weeks when I first joined the forum too

Did'nt 'sparky 66' coin the word POCO?

The reason this is wrong is because of voltage drop.
Ohm's law tells us that voltage equals the current times the resistance.

Let us assume, for the sake of this discussion, 200 amps flowing, at 120 volts (to ground) over 100 feet.
For #2 wire, table 8 in the NEC give a value of 0.0194 ohms resistance for this length. 200 amps x .0194 = 3.88 volts "dropped". Of the 120 volts that leaves the pole, only 116.12 makes it to the meter.

For 2/0, the value given is 0.00967. 200 x .00967 = 1.934. So, at the meter, 118.066 volts are received.

Wait- one wire is delivering 116 volts, and the other is delivering 118? Right- there's a 2 volt difference.
And, since voltage flows from higher to lower, two volts (400 watts) will flow into the smaller wire.

400 watta is a significant amount of heat generated where these wires meet.

That is why we use identical size- both in diameter and length- for parallel feeds. We eant to avoid setting up this type of situation.

Reno, I don't understand your explanation.

You've described 200 A flowing in each wire, but in fact, the 200 A would be divided between the two according to the ratio of their impedances.

Given your example, that ratio is (.0194 / .00967) = 2:1, so 133 A of that 200 A would flow in the 2/0, and 67 A in the #2. The voltage drops therefore are equal, and there's no power "flowing" from one wire to the other.

Argument #2: A 2/0 wire is made up of 19 strands. Isn't that the same as an 18-strand wire in parallel with a 1-strand wire?

That's the way the PoCo used to do years ago when they were doing away with residential 3 phase around here and we were replacing the old 3 pase A/C's with new single phase units.
They would parallel the two old service drops into one single phase drop.



[This message has been edited by SparksNmore (edited 07-24-2005).]