Replacing a bad power cord

SDE

Well-known Member
I save cords from bad electrical devices. I now need to replace a cord on a 1hp motor. The cord is so old that the end is split in two. How do you know if the replacement cord is heavy enough to carry the load, before it starts a fire? I have some 220 cords and I could cap off the wires I would not need.
SDE
 

1 HP = 750 Watts / 120 volts = 6.43 amps * 1.5 = 9.4 amps, so I believe 14 gauge is heavy enough, but welcome other comments.
 
That's based on 100% efficiency.

In the real world, a 1 HP motor draws about 16 Amps at 120 Volts or 8 Amps at 240 Volts.

If there's a nameplate on the motor, it will spell that out.

Here's a generic chart if a nameplate isn't present.

<img src = "http://i.imgur.com/IsN0YGC.jpg">
 
If it where me I would use nothing less then #12 wire but I do tend to prefer to use bigger then what code calls for
 
SDE, you ask " How do you know if the replacement cord is heavy enough to carry the load, "

You do that by 1) Knowing the Full Load Current (may be present on nameplate of device) or obtain from tables, then

2) Consulting the NEC ampacity tables for the conductors you have (such as copper or aluminum) and how many
and in what type of enclosure or jacketing or in free air or direct buried or buried in conduit etc etc.

3) I always select wire so that the max continuous current is no more then 80% of the conductors ampacity.

EXAMPLE: If the max continuous current is say 16 amps, I would use a conductor having an ampacity of NO LESS THEN 20 amps as 80% of 20 = 16.

NOTE I would NOT want to use any less then 3 conductor cable. for 120 VAC loads that's the Ungrounded Conductor (Hot/Black),,,,,,,,,,,,the Grounded Conductor (Neutral/White),,,,,,,,,,The Equipment Grounding Conductor (Green). For 240 VAC single phase motors that's Red Hot L1, Black Hot L2, Equipment Gropundign Conductor.

I been retired a longgggggggggg time but belive thats still NEC code proper and how I was trained to compute it but no warranty, Billy Bob and Bubba may do it differently lol

Keep safe, post any questions, hope this helps

John T
 
Grrrrrrrrrrrrr Im sorry, I got in a hurry and I forgot something, we usually say some prayers at 3 PM and the wife was paging me lol

To know what size conductors are required, after and in addition to my post below, YOU COMPUTE THE VOLTAGE DROP and if its excessive you increase the conductor size. If youre passing 16 amps through 12 Gauge copper conductors it don't take too long of a run to yield excess voltage drop so you may have to go to 10 Gauge?????????

Don't forget overcurrent protection for your conductors and thermal overload protection for the motor also!!!!

Nowwwwwwwwww if I forgot anything else (may well have) perhaps the other fine sparky gents here can add to all this

PS I often hear an old wives tale that "By Golly 220 always requires 12 or even 10 gauge wire" NOT NECESSARILY SO Typically at 220 there's less current draw (maybe 1/2 as much) then operating the same device at 110 !!!!!!!! If you had a load that draws say 5 to 10 amps at 220 volts YOU SURE DONT HAVE TO HAVE 10 OR 12 GAUGE WIRE NOW (subject to long runs and voltage drops) but hey do as you please, far less harm in oversizing then under.

John T
 
When it comes to power tools horsepower didn't mean crap. I've yet to see any 110 volt tool use more than 15 amps. Rarely will they go over that. Most homes don't have more than 20 amp outlets.

I like to buy 12 gauge extension cords with molded ends. Cut off one end. Make sure you leave the right end. I have nerve seen 12 g cord that wasn't 3 wire too. Not staying they don't exist.

Many powered tools have under sized cords.
 
Maybe I'm missing something here. And I'm not knocking John T's expertise. To keep it simple, it seems to have done the job for a long time, so replace it with the same size wire. Or for a few pennies, go one size larger. If unable to determine what size wire is there now, take a short sample along to the store to match up. Of course use 3 wire cord & hook up the green grounding wire for your protection.

Willie
 
willie in mn,

Good advice, Most of the time the manufacture uses 14g wire when they should use 12g. It's a short cord and the tool doesn't run for hours on end. Look at vacuum sweepers, 15a, 14g and wires do get a little warm. Never catch on fire or melt the insulation.

Why use 10g wire? Good luck putting an end on 10g wire. Then what size extension cord will you plug it into? 12g at best unless you make a special extension cord. Then when you plug the extension cord into your garage or house outlet, what size wire is in the wall? 12g at best.

Why make answers so complicated, KEEP IT SIMPLE, use a pre made 12g extension cord. Do it all the time. Some of my smaller tools I use a 14g cord, never had a problem. geo.
 
Willie, good thoughts, no offense taken, SIMPLE is great, replace with at least same size wire is ceratainly good advice, but being an Engineer AND an Attorney, short n sweet is just not in my DNA, I cant help myself lol lifes made me that way.

Best wishes, God Bless, Happy Fourth of July

John T
 

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