I was using a voltage drop calculator and it asked for 1/2 the total circuit length. I have a meter and main breaker on a pole the sub panel is 225 feet away. What is the total length a circuit mean?

There and back, it takes 2 conductors to make a circuit.
450 feet is the length of the circuit.

Quote:

---

Originally Posted by felicesnow

I was using a voltage drop calculator and it asked for 1/2 the total circuit length. I have a meter and main breaker on a pole the sub panel is 225 feet away. What is the total length a circuit mean?

---

If this is strictly a main breaker to a panel in a residence, you would not use standard VD calculators. The wire between a main breaker and a main distribution panelboard in a dwelling do not use the same size wire as other feeders.
If there are other breakers at the main disconnect then that is different.

Quote:

---

Originally Posted by donf

If it is then you must use the standard voltage drop calculation because the main panel in the residence is treated the same as if it were a subpanel. ........

......

At the main panel, .............
and cable sizing must be done using Table 310.16.

---

Don, this is wrong. What you are describing is a main power feeder.


Please see 310.15(B)(6):

(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. For individual dwelling units of one-family, two-family, and multifamily dwellings, conductors, as listed in Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service-lateral conductors, and feeder conductors that serve as the main power feeder to each dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder between the main disconnect and the panelboard that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit. The feeder conductors to a dwelling unit shall not be required to have an allowable ampacity rating greater than their service-entrance conductors. The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.61, and 230.42 are met.

What difference does anything make for voltage drop calculation?

Standard voltage drop calculation ?

Is there a non-standard calculation?

Table 310.15(B)(6) and Table 310.16, which ever applies to the situation, will list the minimum size wire for the amperage rating of that circuit or feeder.

Table 310.15(B)(6) is allowed to be used for the feeder to a dwelling.

Either may be increased in size due to excessive length and to reduce voltage drop.

So can I use the voltage drop calculator, and was the first answer of

There and back, it takes 2 conductors to make a circuit.
450 feet is the length of the circuit.


Be the right answer? I have a meter and main breaker on a pole and my sub panel (guess that is what it is called)in the house. I have 4/0-4/0-2/0-4 wire buried in the ground both boxes 200 amp.

I gave an answer here:

https://www.askmehelpdesk.com/electr...it-553506.html

If you already have #4/0 in the ground, too late to be asking the question.

#4/0 Aluminum at 225 feet will allow 125 amp load with a voltage drop of 2.74%.

Asking the power company is not the correct thing to do to size conductors the customer owns, as they use large derating factors to size their cables.

My plans called for a 125 amp box but the cable was to big so the electrican told me to go with the 200 amp box with lugs so that the cable would fit. Now a different electrican that I had a conversation at work with is telling me something totally different. Thank you for your help.

Voltage drop is one of those topics that can be easily misunderstood, or not studied enough to fully understand, and have several intangible variables that can affect it.

And even when understood, still takes a bit of art to arrive at a reasonable wire size.

And it depends on which on line calculator to use.

I used one that takes reactance into consideration to arrive at the #250 MCM.

When I used the IEEE formula, Amps x Length x 2 x ohms per foot, a simple formula that does not assume any reactacne, such as heavy motor loads and the capacitance of the wire run, I arrived at using 4/0 at 160 amps at 225 feet will result in exactly 3% voltage drop.

Poor power factor is not a problem in a home, and direct burial cable or in PVC conduit, capacitance is low. The IEEE DC formula is sufficient.

In my judgment, chances running 160 amps for any great length of time is unlikely, so getting close to 3% Vd is unlikely.

Sorry to mislead you with the conservation size of 250 mcm.

I would say your #4/0 in the ground will be fine.

felicesnow... Stratmando gave you the answer to your question.

Thank you so much everyone was so confusing, but you made it easy to understand with this answer. Again THANK YOU TK!!

felicesnow, Missouribound gave a good response reminding you this had been answered, Others added more. He would have provide good info if it wasn't already presented.

You guys kept changing the answers and made it so confusing, but Thank You for answering my orig question.

Did you use this calculator:
Mike Holt
Length is the distance of the run(L)
and where you see a X2 in a formula for single phase, the X2 is the there and back.
For 3 phase, the multiplier is the square root of 3(1.732)
1.732 is a handy number to remember.