Excessive voltage loss

[Terry]

Ok electrical gurus....can't figure what I am doing wrong here....

I have my camper near my barn....my well power line went bad so while they were there I had them trench a power line to my camper. I wanted 8, but all they had was 10....fine I figured it would work fine for what I am doing.

Well......

Length: ~120 feet (maybe 110) direct bury #10
Starting voltage: 114
Current: 14 amps
End voltage: 102
Voltage drop: 12 volts

By my calculations I should have no more than a 4 or 5 volt drop. I have checked and cleaned all my connections, yet I can make no improvements.

I have measured in various places and it is not in the camper...in most campgrounds, it barely drops a volt or two at that load.

I figured I was not going to get a full 30 amp...but at least wanted to run the ac on occasion when working on it or packing up. With this drop my EMS is shutting down.

Any thoughts or other suggestions?

[Flytyer]

Did you take in account its really 240 feet of drop ? Pure coper would be 0.9989 ohms per thousnand seems about right...

[pfin38]

Normally you would have to use the next bigger sized wire for runs over 100' to combat the vd.

[Terry]

I used several of the online voltage calculators and came back with similar results. They all ask for the length of the cable, so I didn't think you had to double it.

That just doesn't intuitively seem right to me....in a large house wired with #12 you could easily have 75 to 100 feet of wire from the breaker panel to the last circuit in the branch and you don't see nearly that kind of loss at 15 amp.....

Would not be such a big deal but I am way rural and during the really hot days my voltage overall is lower than normal. Had the power company out, but they don't seem to be able to do anything so far.

[Mainenebula]

Is 120' the entire distance from the service panel? Anything else on the circuit?

[Terry]

Only thing. I ran it directly from the breaker panel. It enters the outbuilding where there is a junction box then out to a weatherproof 30 amp RV receptacle - so one splice is all it has and it is good and tight. 2x checked the receptacle as well an all looks good.

[2edgesword]

I'm wondering if the buried wire is heating up (ground temperature and self-heating) causing a change (increase) in the resistance of the wire.

[pfin38]

I still believe (NEC) code dictates larger wire size for anything over 100' just for this reason (voltage drop).

[rwilley]

Originally Posted by pfin38

I still believe (NEC) code dictates larger wire size for anything over 100' just for this reason (voltage drop).

I was having the same problem at my sons house this year. The AC couldnt start we think because the wire was to long and not heavy enough.

[clubhouse]

I am learning a lot from this thread. I am learning about things I never thought I wanted or needed to know about...watch out Jeopardy :-)

Terry I hope you are able to get this figured out easily with much additional expense and/or labor.

After reading this I did a google search on Votage Drop and read several articles. Then I searched for a calculator, the first hit was from "South Wire". When I input your data from the original post, it determined #8 wire if direct buried was required to maintain <3% VD. They calculate actual VD to be ~2.32%

[David472]

Terry,
Here are some numbers from the electrical engineering book;
10 gauge wire has a resistance of 1.018 ohms per 1000 feet.
Your 120 foot run should be 0.12216 ohms for each wire, so, you are correct, there should be only a few volt drop, not 12 volt drop for a 14 amp draw.
To get that 12 volt drop, it's behaving like 14 or 16 gauge wire.
I suspect the copper wire was nicked or partly cut when buried, or does not have the circular-mil area in its cross-section that it needs to have to be true 10 gauge.

[29BHS ECO]

When you got the 102V reading did anything else turn on or was running like a water pump? That will effect your overall voltage. You have got to be carefull with that 102, lots of old elect gagets would run +-10% to 20 % of the rated 120, but this new electronic stuff will get hurt at anything less or more than the 10%. Sorry I don't have a fix . Larry