In general what NEC section (table) best describes how to derate SOW type cable. I am unable to verify voltage drop calcs. The application is for (temporary) power disto from smaller portable generators (15kw). The cord reels are specified with 200' SOW cable, 3cond+G #10AWG 1phase, 240V. The continuous load is one 1.5 hp 230V motor (10A), and two 750W-120V lights. Ambient 30degC. Just looking for less than 5% on the 230V motor. No electronics so the overall circuit VD doesn't concern me. Would anyone be able to verify my calcs?
Derating SOW cable
- Thread starter dinkelja
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petersonra
Senior Member
- Location
- Northern illinois
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- engineer
The NEC charts are for derating to protect the insulation from overheating, not for VD.
The way I see it is this.
It is temporary.
It is not in an unusually hot area.
Chances are even if you load the cable to 100% of its ampacity, you won't be able to harm the insulation.
<added>
1.5 hp 230V motor (10A), and two 750W-120V
If you have 10A L-L for the motor, and 6.25 A L-N for the lights, that is a total of 16.25 amps on each line, with the neutral being close to zero (assuming one light on each L-N). One of the Internet VD calculators claims that you will only have about an 8V drop. That seems pretty realistic, so I did not double check it.
That is about 250W that you will need to dissipate in the cord reel IF it is all wound up, but if you have a 200 foot reel, presumably most of it would be unreeled when it is actually in use.
The way I see it is this.
It is temporary.
It is not in an unusually hot area.
Chances are even if you load the cable to 100% of its ampacity, you won't be able to harm the insulation.
<added>
1.5 hp 230V motor (10A), and two 750W-120V
If you have 10A L-L for the motor, and 6.25 A L-N for the lights, that is a total of 16.25 amps on each line, with the neutral being close to zero (assuming one light on each L-N). One of the Internet VD calculators claims that you will only have about an 8V drop. That seems pretty realistic, so I did not double check it.
That is about 250W that you will need to dissipate in the cord reel IF it is all wound up, but if you have a 200 foot reel, presumably most of it would be unreeled when it is actually in use.
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- Location
- Illinois
- Occupation
- retired electrician
You will if you leave much of the cable on the reel.
Don
petersonra
Senior Member
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- Northern illinois
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- engineer
don_resqcapt19 said:
One would expect that if one needed a 200 foot reel at least a substantial part of it would be unreeled.
- Location
- Massachusetts
petersonra said:
I don't think he means a coil, but a cord reel.
Todays job you need 75' tomorrow you need all 200' and another day you may only need 25'
How about temp?
How about temp?
I agree with Bob you should be just fine with the #10 sow. In fact even when calculated at 125% you are still fine. Using the '02 NEC here; 400.4 tell you about the cord. 400.5(A) says its good for 25 amps(3 cond). Chapt9 table eight says #10 stranded is 1.29 ohms/1000 1.29x16.25x400feet/1000= 8.4vd 8.4-240= 231.6 volts at your load. 3.5% drop at 100% load with your 200 ft. My question, what about temperature, would you go to 310.16 for correction factors if not 30c? I dont see any correction factors in art 400.
How about temp?
I agree with Bob you should be just fine with the #10 sow. In fact even when calculated at 125% you are still fine. Using the '02 NEC here; 400.4 tell you about the cord. 400.5(A) says its good for 25 amps(3 cond). Chapt9 table eight says #10 stranded is 1.29 ohms/1000 1.29x16.25x400feet/1000= 8.4vd 8.4-240= 231.6 volts at your load. 3.5% drop at 100% load with your 200 ft. My question, what about temperature, would you go to 310.16 for correction factors if not 30c? I dont see any correction factors in art 400.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
S'mise said:
A long time ago I ran this down. If I recall correctly, the cord reel is actually listed for the maximum amperage it is allowed with the cord completely reeled in.
Take a look at these examples.
http://www.durohosereels.com/series_2750.htm
http://www.durohosereels.com/tech_info.htm
adj cords for temp?
adj cords for temp?
Thanks Petersonra, It makes sense to follow the instructions of any listed equiptmint (cord reel) but I was wondering about temperature adjustment for cords in general. Say, I am running that SOW cable in a cable tray or somewhere else that is not 30c. Where are the temperature correction factors for cable?
adj cords for temp?
Thanks Petersonra, It makes sense to follow the instructions of any listed equiptmint (cord reel) but I was wondering about temperature adjustment for cords in general. Say, I am running that SOW cable in a cable tray or somewhere else that is not 30c. Where are the temperature correction factors for cable?
- Location
- Illinois
- Occupation
- retired electrician
They could very well be listed for use at full load while coiled, but the ones on our rescue truck for portable lighting would overheat at the center with a 1000 watt 120 volt load on 20 amp rated cord reel. They were 200' cords and often only about 100' would be pulled off. When we need the full length, we found that we could not unreel the last 50' of so. The jacket of the cord was "fused" to the adjacent wraps. After I replaced the cords, we always took all of the cord off the reel when we used it and never had any more problems.
Don
Don
Temp correction cable?
Temp correction cable?
Temp correction cable?
No takers?S'mise said:Thanks Petersonra, It makes sense to follow the instructions of any listed equiptmint (cord reel) but I was wondering about temperature adjustment for cords in general. Say, I am running that SOW cable in a cable tray or somewhere else that is not 30c. Where are the temperature correction factors for cable?
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