No voltage drop? Why?

Status
Not open for further replies.
growler said:
Larry is right and if there is nothing in the shed but an air compressor why not convert to 240V. You can probably buy another air compressor cheaper than you can trench 200 ft.
Click to expand...

One could make an argument that 210.52(G)(2) would require a 125v receptacle in that location.
 
1902128-2233 EST

I retract my previous statement that it might not get smoking hot.

I ran an experiment on a 250 ft coil of NM-B in a plastic package laying flat on my bench. This was #14 copper. Tested at 5 A 60 Hz. Room temperature 80 F. Thus, 26.6 C. Initial DC resistance 1.20 ohms. Ran test for about 1 hour at the 5 A AC. Highest outside surface temperature was about 190 F, cooler at the bench top. DC resistance at end of test 1.60 ohms. This calculates to an average internal temperature rise of about 81 C. Maximum hot spot will be higher. Actual temp = 81+27 = 108 C, hot spot is higher.

If we ran at about 10 A one might expect about 4 times the temperature rise.

Surpising how poor the thermal confductivity is.

What happens to Romex when buried in insulating foam?

.
 
Cirus said:
I understand voltage drop has to do with wire size, voltage and distance. I've got experience in running underground lines long distances. I have a customer that has a small shed with a 200'run of 10/2G UF running underground. It's a 120 volt circuit that feeds nothing but an air compressor. Spec plate says it pulls 15 amps on 120. Someone else ran the underground line. Voltage at the receptacle is about 122 with no load. With the compressor on voltage drops to 114 and the amperage is 16.7. Sometimes it trips the breaker which is understandable. I'm running a new #6 line to it to resolve the voltage drop. I have a compressor of the same size in my shop and I thought I would perform a test just out of curiosity. I'm had a roll of 12/2g Gomez and put a cord cap on one end and receptacle on the other and plugged the compressor in while taking a amp reading. Amps never got over 14. The romex was still in a 250' coil. My question is would I get the same reading if the romex was stretched out to 250'? Why was there no voltage drop yet there was significant drop on the 10/2 underground line?
Click to expand...
You were drawing 14 amps at your shop, but what was loaded/no load voltage? Air compressor likely is going to draw a higher current when near cut out pressure than when there is low pressure as well. On top of that, you may or may not have voltage drop issues on what supplies your house/shop/etc. and even the size/impedance of the source can have some impact.
 
Status
Not open for further replies.
Top