extension cords: length vs amps

Question

My Ariens snowblower engine manual has this to say about using an extension cord for electric start:

Use appropriately sized extension cord (a minimum of 16 gage, 3-wire, 13 amp, no longer that 25 feet, and suitable for outdoor use) to prevent damage to electric starter.

I would have thought that, at the end of the day, the only thing that matters (apart from the "outdoors qualified") is the amp capacity of the cord.

I have a 3-wire cord rated for 15 amps, but it's a lot longer than 25 feet. Can I use it in this instance?

Answer 1

(note: this post assumes that by "gauge" you mean AWG)

I expect the biggest issue with longer leads is likely to be volt drop, especially during startup when motors can draw substantially more than their normal running current. Volt drop during startup may cause slower startup or even failure to start which in turn can lead to overheating.

I would suggest that if you need to use a longer cord you should aim to keep the resistance of the cord no greater than that of the cord the manufacturer recommends. So if you double the length you should also double the cross sectional area (which in american terms seems to translate to reducing the AWG number by 3).

Answer 2

The longer the cord, the higher the voltage drop across the cord. If you used a longer cord, the starter could potentially see a voltage lower than the minimum tolerance. Which could cause damage, or poor performance.

If you want to keep the equipment running well, you should follow all of the manufacturer's instructions.

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After doing some math, it looks like the manufacturer is trying to limit the voltage drop to ~2.5% (VD% = (2 x 25' x 13A x 0.00489 ohms/ft) / 125V = 0.025428).

If you increased the length of the cable to 50', you'd have to use 12AWG cable to maintain the same 2.5%. 100', and you'll have to use 10AWG.

It's doubtful that a typical homeowner (or anybody for that matter), would have a 100' 10AWG extension cord.

Answer 3

The manufactures' instructions are written for the purpose of keeping the item you purchased running well and with the least amount of maintenance. They also know what limits and capacities the machine is able to tolerate.

You should abide by the instructions if only to keep you investment running for as long as possible.

Having said that; if the cord isn't "a lot" longer than the recommended length AND is 12-14 gauge copper wire I don't think the starter will be harmed if used for short intermittent engine starting.

Answer 4

Well according to the voltage drop calculator here: http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=13.17&voltage=120&phase=ac&noofconductor=1&distance=50&distanceunit=feet&amperes=13&x=48&y=11

A 16 AWG cord 50 feet long at 13 amps drops 5.22 volts on a 120 volt circuit. This exceeds the 3% voltage drop recommended by the National Electrical Code.

Voltage drop: 5.22 Voltage drop percentage: 4.35% Voltage at the end: 114.78.

It will probably still work but you may shorten the life of your starter motor. As Tester and ojait said it is best to follow the manufacturers recommendations. Or you could pull start it. 😉