Wire gauge calculation

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abaco108@yahoo.com

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Mike,

I was wondering if you could give me some assistance with a wiring issue that we have come across . This in tells the marine industry. The problem that we are facing is the manufacture of a power cord recoiling unit refers to the NEC code to proper electrical installation. The boat manufacture installed this unit with 14 gauge wire. I had done the math and I calculated it needs to be 10 gauge wire. Here are the measurements a minim of 20 feet long is the distance that it needs to travel from breaker panel to D/C motor. The motor is 12 volts and under normal load it should require 7 to 9 amps according to the recoil manufacture. However on the motor specs it shows 13.1 amp. The problem is when I tighten up the pulley to grip the power cord better do to the cord slipping on the pulley the voltage drops down to 7 to 8 working volts and high amps. If I use a jumper wire 10 gauge from power supply to motor it reads 12 volts at motor and around 8 amps of draw. The boat manufacture claims that it is wired correctly yet I have a huge voltage drop and higher then normal current draw. The boat builder did have another company go to boat to evaluate the problem they to agreed wire is under gauge. Will you do your calculations to verify minim wire gauge required. Thank you for you time.
 
What is the current after the pulley is tightened? Maybe you do not have enough reduction and need another pulley loop. Are the cord tensions consistent between tests?

With #14 wire (just using 20ft of regular stranded at 80 degF) I drop from 12 volts to 7.8 volts at 40 amps. The same power output with #14 yields 10.8 volts and 28.9 amps. 40 amps of current with #10 yields 10.4 volts. Either way, that sounds like way too much current.

Going the other way:
With #10 wire, I drop from 12 volts to 11.7 volts at 8 amps. The same power output with #14 yields 11.1 volts and 8.4 amps.
 
I was thinking of some type of boat lift. I re-read and see you seem to be taking about some kind of extension cord. Maybe the pully is pinching the wire too tight and causing a high-impedance fault.
 
Well iam and old navy electrician we kinda rolled up a few cables in our time its a simple issue but a reel cable can have inductance when rolled up but when unrolled it does not have a inductance issue .

And under a load it can heat up by being rolled up which can change the resistance of wire .

Just a suggestion load and current use bigger wire .

But in you case its unrolled bad connection or wire has broken stranding inside !

Motor cant get full voltage current goes up
 
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