12.5A compressor & 10 ga ext'n cord

[rick carpenter]

I have a Husky 8 gal/12.5A/120V compressor with ~6' of 14/3 power cord. Of course the lit says don't use an extension cord, but if you do, use 10 ga and not over 25'. Any ideas why they might spec 10 ga over 12 ga? Seems like overkill. I'd like to wire in 25' of 12 ga (or 10 ga if I have to) outdoor extension cord to the switch and never use an extension cord.

 

[stage20]

the amp draw on start up. the longer and smaller the cord, the more it hurts the motor on start up, even more when the motor has to overcome pressure in the tank.

the right way is to buy more air hose. granted ive plugged mine into a 16ga 100ft in a pinch, but this is why compressors fail over time.

im in construction and i see compressors used everyday. all of them are out plugged directly into the temporary pole outside.

 

[sberry]

Its the total length of the circuit, cord, wire but as you said, number 14 cord. I would simply add a 25 ft 12 if I needed it. They will run farther than that depending on service. If it has a home port I tend to run a wire for it, may not always need a cord.

 

[theoldwizard1]

Any ideas why they might spec 10 ga over 12 ga? Seems like overkill.

It probably is over kill. It is common to de-rate extension cords.

I'd like to wire in 25' of 12 ga (or 10 ga if I have to) outdoor extension cord to the switch and never use an extension cord.

That is EXACTLY what I did. Used 12 gauge. It has been running fine for over 10 years.

Shop around, you CAN find black 12/3 SJOW extension cord.

 

[alfredeneuman]

From the Southwire Voltage Drop Calculator:

"A maximum distance of 137.23 feet will limit the voltage drop to 3% or less with a #10 Copper conductor delivering 12.5 amps on a 120 volt system."

"A maximum distance of 82.942 feet will limit the voltage drop to 3% or less with a #12 Copper conductor delivering 12.5 amps on a 120 volt system."

and

"A maximum distance of 53.735 feet will limit the voltage drop to 3% or less with a #14 Copper conductor delivering 12.5 amps on a 120 volt system. "

3% is the generally accepted maximum voltage drop.

 

[wyliesdiesels]

The one thing no one brought up is that cordage has a lower ampacity than building wire...this is the reason for the manu. saying to use a larger gauge cord. #12 cordage is rated 15a and #10 20a...with in rush current and the continous load of a motor, a 12ga cord isnt rated for that load...

 

[rick carpenter]

Thanks y'all! A lot to think about. Now the question: Are plugs typically capable of handling more amps/volts than their rating? A 10 or 12 or smaller ga cord will all use 5-15 plugs. That's why I wondered if a 10 ga cord is overkill.

EDIT: Thanks Wyliesdiesels, you posted while I was composing/editing my second post so I didn't see your post til I hit send.

 

[alfredeneuman]

The one thing no one brought up is that cordage has a lower ampacity than building wire...this is the reason for the manu. saying to use a larger gauge cord. #12 cordage is rated 15a and #10 20a...with in rush current and the continous load of a motor, a 12ga cord isnt rated for that load...

According to NEC Table 400.5(A)(1) Allowable Ampacity for Flexible Cords and Cables:
Column "B" because only 2 wires are current carrying.

#14 has an ampacity of 18 amps
#12 has an ampacity of 25 amps
#10 has an ampacity of 30 amps

When you apply the required 125% to the motor load it comes to 15.625 amps. I left that out of the previous calculations
The voltage drop calculations are the same regardless of it being cord or building wire

A #12 cord will carry the load for 66.354 feet
A #10 cord will carry the load for 107.784 feet
It was calculated at 3%

btw (NEMA suggests a maximum voltage drop tolerance of 10% for motors

Which would be 221 feet for #12, 365 feet for #10) I chose to figure at 3%

#12 would definitely carry the load

 

[theoldwizard1]

Thanks y'all! A lot to think about. Now the question: Are plugs typically capable of handling more amps/volts than their rating? A 10 or 12 or smaller ga cord will all use 5-15 plugs. That's why I wondered if a 10 ga cord is overkill.

As stated, cords are de-rated, so 5-15 on a 10 gauge cord would be correct.


Stop over-thinking ! Throw away that 14 gauge pig tail and put a 12 gauge cord on it ! Keep it to 25' and you will be fine.

 

[alfredeneuman]

He wouldn't even have to throw away the pigtail.
Just make an extension cord and call it done!

 

[rick carpenter]

OK, no more overthinking, 12 ga & 5-15P @ 25' it is. I want a hardwired 25' power cord is so that it will be less tempting to use an extension cord on it. The stock 6' power cord just begs for an extension cord, and if it comes from other folk on a disaster or construction worksite when I'm not around inevitably they will use one too small and/or too long.

 

[rick carpenter]

After some delays, I finally wired in 25' of 12/3 SJOOW with a P&S Legrand waterproof plug (filled with roofing cement for kicks) and a Halex 1/2" strain relief at the pressure switch. No one should be tempted to use an extension cord on it now. Thanks for the advice, y'all.

 

[wyliesdiesels]

According to NEC Table 400.5(A)(1) Allowable Ampacity for Flexible Cords and Cables:
Column "B" because only 2 wires are current carrying.

#14 has an ampacity of 18 amps
#12 has an ampacity of 25 amps
#10 has an ampacity of 30 amps

When you apply the required 125% to the motor load it comes to 15.625 amps. I left that out of the previous calculations
The voltage drop calculations are the same regardless of it being cord or building wire

A #12 cord will carry the load for 66.354 feet
A #10 cord will carry the load for 107.784 feet
It was calculated at 3%

btw (NEMA suggests a maximum voltage drop tolerance of 10% for motors

Which would be 221 feet for #12, 365 feet for #10) I chose to figure at 3%

#12 would definitely carry the load

Thx for delving into the code, though i have it in front of me and crunching the numbers(which i love to do as well).

However, what i was referring to is how manufacturers rate their cords for lower ampacities than what code dictates.

Take for example the link below which is a 12/3 cord made by Cerrowire(who also makes building wire) sold at home depot. If u open the specs tab, u will notice the manufacturer has rated it(and obviously U/L listed it) for a MAX OF 15a.

Every #12 extension cord I have seen has been rated at 15a. Obviously, the listing (and warranty) would be violated if it was used at a higher ampacity.

In the case of NEC 400.5(a)(1), i think thats the maximum allowed possible rating but manufacturers are using lower ratings...

What do u think...

http://m.homedepot.com/p/Cerrowire-25-ft-12-3-Stayplug-Extension-Cord-Yellow-630-36037AR/204735826/

 

[sberry]

Listed at 15 due to the plug that comes on it?

 

[rick carpenter]

Listed at 15 due to the plug that comes on it?

You can find 20A 12/3 cords with 5-20P's & 5-20R's if you look for them. A generic "12/3" or "12 ga" search will come up with the 15 amp variety.

I meant to include my plug is 15A. Among the factors in choosing my compressor is that 125V & 12.5 running amps make it more readily usable on worktrips/etc since 5-20R's are less common to find out and about. I figure at start-up it will bump to +/- 14A maybe, so that's why I hope that 5-15P's can carry a little more than 15A (tho no mfr would ever admit to that!) for a safe margin over that bump.

 

[sberry]

At start this comp probably pulls near 60A. There is very little use for true 20A and not for the DIY crowd, its mostly used on truly dedicated circuits usually in industrial and institutional and not always due to a 20A demand but to keep some equipment from being plugged in to general circuits where one never knows what is on them.
Think of it this way, the janitor comes along with the floor machine and hook on to a general in a lab, trips it and kills the rats or fish or turns off sensitive equipment. Keeping the floor cleaner on a dedicated circuit keeps this to a minimum.
The 20A isn't really for the load but to keep the operator from plugging it in somewhere it shouldn't be or from adding another too light cord, I beliece some 20A can be found on 14 cords going to specific machines, keeps the dipstick from plugging a 16, or any other cord with a 15 end between it and the wall.

 

[sberry]

In theory once we add a tap for multiple outlets the cord needs to be a 12 or have ocpd like a power strip has. The 15A end will feed thru 20A on a 20A circuit but there is the chance of overloading the additional cord.
There is some safety for this by a couple methods but mostly to design and you need to bear with me on it as I am not an expert and all this is some generalization and there are or may be specific exemptions but,,,,,,,,,,,,,, we can assume for the most part we are talking about UL listed with factory ends.
You were not the genius that picked your comp, someone did this for you in some respect. The engineer loaded all the pieces to this system to their legal design limit, figuring motor factors near 13A on a 14 wire, others load it to 80%, some can be 100 for non continuous and some are calculated like lamp cord, there is some headroom for error but any one device cannot overload either a 14 or a 12 wire. You can put 2 devices of 15A each and it will simply trip the breaker but once the operator adds a cord he is sposed to recognize the fact that it needs to be as big as the appliance needs if there is one outlet like the end of a common cord, or we use a 15 or better cord. We could in theory keep adding outlets forever if the wire is a 12.
Since the common power strip plugs to a 20 theru a 15 circuit they add a breaker just like some fan that has a duplex on it, has a breaker and 16 wire or cheap 4 way with cord. A simple hard 3 way will feed thru 20A.

 

[sberry]

Your comp really doesn't need a 12 cord and sometimes it makes them trip close to a good sturdy service panel. The factory cord has been designed for this to somewhat act as a choke. By adding a longer cord you may balance some of this out.
Good cord is more of an issue away from good service, long extensions etc.
I write this in pieces in and out of my office so,,,,,,,,,,,,,
It would likely allow installation on 14 wire in pipe and normally they assume some existing distance for the avg outlet. While its great to be on a 12/20 if its at the other end of a horse barn at 200 ft pretty much anything a guy adds is downhill and adding another chunk of undersized cord doesn't help.
I was in a building converted to a body shop, not that they knew how to use the 140 but the existing outlet served the lights and recepts at 15 and they are not smart enough to have a clue so I get them to use a 12 cord to a 20A near the panel and bypass the building wire and all is well.

 

[rick carpenter]

SBerry, I guess I really don't get your last two posts. You went into a lot of considerations that I never intended to do. But if that was to be helpful to others, then well done. The driving thought for this thread was to avoid the "need" for an extension cord by lengthening the comp's power cord to get it comfortably away from an outlet, allowing it to be easily moved out of my and other people's way, while retaining the 15A plug. The stock ~6' cord just begged for an extension cord. The factory lit said to use a 10 ga extension cord if I did use one. I looked at that then looked at the factory 14/3 cord, again it's ~6' in length, and decided to ask about a 25' 12/3 power cord as a solution.

I picked this comp for its specs based on the working conditions I expect and modded it a little for an even better fit. Pics are in the "Show your compressors" thread in the general tools forum. No claim of genius was made, though I am pretty happy with the choices I've made.

Thanks.

 

[sberry]

Yes, you did well. I simply embellish a little on theory as to the why and how they do what they do. There is a ton of stuff most of us don't even consider about common plugs and the design behind them. Some of the stuff really amazes me.
It tends to force the user to do the right thing in most cases. I am not familiar with European design but believe much of the over current protection is in the cord or cap which really makes sense as it could really have tailored fusing.

 

[sberry]

The code makes a lot more sense if one knows a little as to why. Pretty soon you will be referring to wires as grounded or ungrounded conductors.

 

[Charles (in GA)]

Listed at 15 due to the plug that comes on it?

Absolutely the reason! Its got NEMA 5-15 ends on it, so its a 15 amp cord.

 

[Jlarson]

(filled with roofing cement for kicks)

That may be the worst thing I ever heard.