240V extension cord with dryer adapter

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  #1  
Old 12-18-14, 09:31 AM
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240V extension cord with dryer adapter

For only occasional use, I'd like to use a 240V air compressor in our garage, but I don't want to pay the likely pretty high cost of running a dedicated 240V line.

Our washer/dryer room on the main level of our bungalow is about 20 feet from the attached garage's personal-entry inside door.

Would it be possible to fabricate a say 20 to 30 foot long 240V extension cord that would plug into the dryer's outlet? (I'm assuming that the typical electric dryer for US and Canadian homes is 240V, so please tell me if I'm wrong. Below is the style of outlet and plug/wire that we have.)
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(A lower-amperage-type 240V-compressor would plug into the other end which would reach into the garage. Perhaps this one:
SANBORN® 60 Gallon Oil Lubricated Belt Drive Air Compressor | Princess Auto
or maybe with a bit more capacity
SANBORN® 80 Gallon Hi-Flo Single Stage Air Compressor | Princess Auto)

Thanks for any advice.
 
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  #2  
Old 12-18-14, 09:36 AM
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Every air compressor I've ever seen said not to run on an extension cord.
 
  #3  
Old 12-18-14, 09:55 AM
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I wouldn't recommend a cord less than #10 AWG, and #8 AWG would probably be a better choice (both for safety and health of the compressor motor). Other than that I don't see a problem with either of the two listed compressors.
 
  #4  
Old 12-18-14, 04:00 PM
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Thanks, guys.

First, I found this older thread about practically the same subject.
http://www.doityourself.com/forum/el...need-help.html

Here's our dryer's plug that I just this moment photographed:
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Here are the two breakers in our home for the dryer that are unified (and therefore operate as one) by a metal bar that runs between the breakers' two handles:
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As long as it is properly sized for the load, why is an extension cord not recommended for an air compressor (as opposed to say a welder that usually already has as long cord)?

Wouldn't installing an in-the-wall, or surface-mounted, dedicated 240V line from the main panel in the basement to the garage be essentially the same as an extension cord (by design anyway, but not location within a wall)? If shielding/protection is the objection, I suppose I could use a say 25-ft length of this stuff
Southwire | Armoured Electrical Cable – Copper Electrical Wire Gauge 8/3. AC90 8/3 - 75M | Home Depot Canada
and have the garage end terminated in a surface-mount, but in this case free-floating, 30-amp box like the following (but this would depend on the design of the specific compressor plug, of course):
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Speaking of plug styles:
How to wire 240 volt outlets

Wow! When you enter the 240V world, things change.

What is the likely plug-design of either of those two aforementioned 240V compressors, and, if it is a three prong plug, what kind of cord should I be using and will an adapter be needed somewhere in this mix (say at the dryer outlet, if one wanted to go from there with a cable that has three prong plug like the following
20 ft Pro Grip® STW Welding Extension Cord | Princess Auto
or a 4-prong "RV extension cord" like the following
NU-CORD 94561E 50-Feet 50-Amp Rv Extension Cord - Electrical Cables - Amazon.com)?

Thanks.
 
  #5  
Old 12-19-14, 06:24 AM
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why is an extension cord not recommended for an air compressor
Extension cords cause voltage drop. You add hose, not add extension cords. Just change the plug end of the cord provided with the compressor and plug it in rather than using an extension cord.

be essentially the same as an extension cord
No.

I suppose I could use a say 25-ft length of this stuff
Not outside a wall as an extension cord.

Dryer receptacles are meant for dryers. If running a separate 240 volt circuit, use a 30 amp dedicated 240 volt receptacle and the existing plug on the compressor. No extension cord needed.
The welding cord you refer to is 40 amps and has a different configuration plug on it. The RV cord you refer to is 50 amps and still another plug configuration on it.
 
  #6  
Old 12-19-14, 06:55 AM
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An air compressor has a high startup current draw. Most panel breakers can take this draw without tripping because it's for only a few seconds, but a marginal extension cord or marginal circuit wiring (in terms of wire gauge) for the circuit length will impose a voltage drop at that moment that will impair compressor operation. Welders are not impaired by this.

What is the amperage rating of the plug that the compressor came with? Or what is the maximum amperage circuit that the compressor may be wired into (stated in the instructions)?

It is okay to construct an adapter with a (female) receptacle of a higher rating and a plug with a lower rating. Not vice versa. However, for a compressor, you will not get good performance if the circuit you plug into has a lower amperage rating than the compressor needs.

If the dryer circuit is rated higher than the compressor maximum circuit rating or the compressor plug rating then you may not connect the compressor to that circuit without a subpanel with appropriate breakers in between.

You may not cut off a plug and substitute a plug with a higher amperage rating.
 
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Old 12-19-14, 07:40 AM
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As long as it is properly sized for the load, why is an extension cord not recommended for an air compressor (as opposed to say a welder that usually already has as long cord)?
It is okay if it's properly sized, but that often gets really expensive because flexible cords have lower ampacity than in-wall wiring. It is better to err on the side of too big than too small. Welders are different because they use power in a different way than motors, and are also usually designed to operate with long cords.

Wouldn't installing an in-the-wall, or surface-mounted, dedicated 240V line from the main panel in the basement to the garage be essentially the same as an extension cord
Yes and no. If you use a big enough cord and good quality receptacles and plugs, yes. A flexible cord needs to be larger than equivalent ampacity wall wiring, for example my recommendation above to use #8 cord. There is also an issue of wanting to have the fewest connection points possible. It's all about reducing the potential for overheating.
 
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Old 12-19-14, 09:01 AM
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Thanks, all, for the advice.

The recommendation for longer hose, rather than longer cable, is a good one, but my wife will not allow a big compressor in either the tiny main-level laundry room or the basement room in which the main panel is located, and I don't particularly like those options either.

In order to reduce the total number of connection points by ONE, I suppose I could remove the cord that is supplied with the compressor and replace it with a much longer one of the proper gauge -- one that would reach the dryer outlet/receptacle "on its own". After all, the compressor has to plug into an outlet/receptacle somwhere, whether that receptacle is in the garage possibly 10 feet away, or the dryer outlet 25 feet away.

The first thing I must do is go to princess auto and see what the appropriate compressor's plug looks like and see how long its cord is. If I'm lucky, maybe it's already 25 feet long.

I really don't need a higher air capacity than this one:
SANBORN® 60 Gallon Oil Lubricated Belt Drive Air Compressor | Princess Auto
which has the following specs:
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I'll consider the options, do more study, and do both what makes sense and is perfectly safe.

Thanks again.
 
  #9  
Old 12-19-14, 09:08 AM
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I'd want the dedicated line, anyway - I'd hate to not be able to use the compressor when the dryer is running because that's exactly when I would want to use it.
 
  #10  
Old 12-19-14, 10:03 AM
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Generally the bigger compressors don't come with a plug in cord, they are intended to be wired up direct. I'd definitely consider installing a dedicated circuit for the air compressor! It might not cost as much as you think.
 
  #11  
Old 12-19-14, 12:04 PM
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By the time you buy the SO cable, two connectors, and wire it all up, you're probably looking at about the same cost of hard-wiring it yourself. Then you don't have to worry about running and re-coiling the cable every time you want to use it, those inevitable times where you want to use the dryer and the compressor at the same time.

If you've done some DIY, it shouldn't be a difficult project. At first glance, it looks like you simply need to run a 12/2 NM-B cable from a dual-pole 20A breaker at your panel to the garage, connect to a 20A/240v receptacle (or 4x4 box to hardwire). I'm sure we'd all be willing to help out if you decide to go that direction.
 
  #12  
Old 12-19-14, 01:06 PM
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I would prefer one of the solution mentioned over, but if this are a compressor ran from time to time I would tried with e 20 ft awg 12 or greater dimension extension cord. Unplugged when not in use, and not left unattended.
This are based on experience in Norway. 20 ft are pretty short, and an extension cord in free air will not be to hot at 15 amps even as an awg 14. In hence of the breaker size we would have a code demand of at least awg 10 extension cord.

Violating codes are not commanded, but we do it temporarily from time to time. Here we are not allowed to run a cord trough a door or window.

dsk
 
  #13  
Old 12-19-14, 01:22 PM
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............................................
 
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Old 12-21-14, 01:28 PM
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  #15  
Old 12-22-14, 05:54 AM
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Darwin's Child,

The compressor you want to buy is a 15 amp 240v device.
And you want to plug it in to a 30amp 240v dryer plug??

Listen to the guys, they give great advice.
Run a new line and do it safely/correctly.
It is time consuming, but not expensive.
 
  #16  
Old 12-22-14, 06:14 AM
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>>> I assume that this would be the correct plug ... 14-30

You can construct an "extension cord" with 10 gauge wire for the 30 amp plug. At the "female" end run the wires (hot, hot, neutral, ground) or cable into a small 120/240 volt panel with, say, two to eight breaker slots. Mount the panel and the 15 or 20 amp receptacle that the compressor's existing plug fits, on a piece of 3/4" plywood. In the panel install breakers suited for the receptacle(s).
 
  #17  
Old 12-22-14, 08:53 AM
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The compressor you want to buy is a 15 amp 240v device.
And you want to plug it in to a 30amp 240v dryer plug??
Compressor motors can be installed with breakers up to 200% under most circumstances and 250% in some circumstances. The breaker size itself is not a problem as long as the cord is sized correctly and quality connectors are employed. The motor has a thermal overload protector built-in and the breaker is effectively providing only short circuit protection.
 
  #18  
Old 12-22-14, 03:15 PM
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Like ibpooks, I also think that breakers in home breaker-panels were designed and put there more for overload protection of wiring in homes rather than the protection of the device being plugged into the circuit.

For example, we have plenty of 120V electric devices in our home that are just a few watts and a fraction of an amp of draw, yet they are plugged into 15-amp breaker/circuits. I assume that this is a perfectly normal, acceptable situation/"design".

I believe that the ability of a circuit/breaker combination to deliver far more power than electical devices "need" has very little to do with whether or not these devices can be safely plugged into it, as long as the amperage/wattage of the device does not exceed the safe carrying capacity of the circuit. (A short circuit or using say a 13-amp electric hedge trimmer with an extension cord of inadequate gauge for its length might very well trip/open a 15-amp breaker.) Is this belief correct?

Therefore, I believe that it would be perfectly safe to install on the aforementioned 240V, 15-amp-rated compressor's swtich-box (if it in fact has an integral switch box) a 25-foot, 8 or 10 gauge metal-armored cable that has the previously-linked plug installed on its far end. This cable could then be plugged into the dryer outlet/receptacle whenever needed, and then the compressor's power switch could be flipped on and off just like any other electrical device. (Of course one would, as with any electrical device, make sure that the compressor's switch is in the OFF position before plugging into, or removing the plug from, the dryer outlet/receptacle.) From a strictly safety aspect only (not a statutory or code aspect), as long as the cable's wires are connected correctly to the compressor's switch box and the plug at the other end, is there absolutely anything unsafe about this design?

Thanks.
 
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Old 12-22-14, 03:30 PM
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13-amp electric hedge trimmer with an extension cord of inadequate gauge for its length might very well trip/open a 15-amp breaker.) Is this belief correct?
Not really. If the OCP is higher than the cord used to carry the current, the wire will become the fuse, and will cause fires before they burn in two.

It looks as if you are determined to use a cord and plug to the dryer. It is compliant as long as you use the proper cable and plug. If your dryer is wired with 4 wires, you most likely will just cap off the white wire in the compressor junction box, as it won't be needed.
 
  #20  
Old 12-22-14, 05:27 PM
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.......It is compliant as long as you use the proper cable and plug. If your dryer is wired with 4 wires, you most likely will just cap off the white wire in the compressor junction box, as it won't be needed.
Thanks.

It is good to know that there's nothing obviously unsafe that I'm overlooking.

FWIW, I'll probably open the dryer's breaker in the basement before unplugging or plugging-in anything. This completely eliminates the remote possibility of touching live prong/contacts during the plugging and unplugging of either the dryer or compressor.

I'll post again when I've got the compressor, cable and plug all in hand, ready to assemble.

Thanks again.

(BTW, I was speaking from experience with the 13-amp hedge trimmer. For some reason, if I use the trimmer for more than say 10 minutes of continuous operation, the breaker in the basement trips/opens. I reset it and continue until it trips again. I figured it was tripping because of the rather long cord, but maybe I'm wrong. Maybe the 36-year-old breaker is simply getting old and tripping earlier than it did when it was new, or maybe the trimmer draws more than it is rated as it cuts larger/thicker material. Regardless, neither the cord nor the outlet it is plugged into are hot to the touch and the breaker resets immediately the moment I close it.)
 
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Old 12-23-14, 11:52 AM
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I believe that the ability of a circuit/breaker combination to deliver far more power than electical devices "need" has very little to do with whether or not these devices can be safely plugged into it...Is this belief correct?
No, in North American designs the breakers protect both the premises wiring (built into the building) and the devices plugged in. Appliances are listed by a nationally recognized testing lab (NRTL), most notably UL, for use on a particular type of circuit. The style of plug and cord for that type of circuit is manufactured into the product; or the manufacturer's installation manual lists the approved field wiring for appliances without molded cords.

I believe that it would be perfectly safe...is there absolutely anything unsafe about this design?
There's no such thing. Every design is a balance of risk, reward, cost, safety. Codes define for us a minimum level of risk that will generally be acceptable in society.

I believe that your plan to use a 25' #8 or #10 cord is compliant with the code. I don't believe that using metal clad is a better choice given that you can buy some really tough flexible cords which probably perform better than metal, and unlike metal clad, are listed for the purpose of flexible, temporary power supply.
 
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Old 12-24-14, 09:10 AM
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No, in North American designs the breakers protect both the premises wiring (built into the building) and the devices plugged in. Appliances are listed by a nationally recognized testing lab (NRTL), most notably UL, for use on a particular type of circuit. The style of plug and cord for that type of circuit is manufactured into the product; or the manufacturer's installation manual lists the approved field wiring for appliances without molded cords.
I think I understand what you're saying.

My point was that just because a circuit can provide far more power than a device needs does not necessarily mean that it is unsafe to plug it into that circuit.

OTOH, from what you say about molded versus non-molded plugs, etc., I also cannot assume that just because a device requires far less power than what a circuit can deliver does not necessarily mean that it is absolutely safe to plug it into that cirucuit (because of plug or cable design, for example).

While I'm typing, I also believe that when a 120V or 240V device is initially switched on, it can momentarily draw far more power than when "running". It is partially for this reason that I will choose a say 15-amp "running power" compressor rather than a higher-amperage one. What is the maximum amperage compressor that can safely be run on our home's dryer circuit with a 25' length of say 8 or 10 gauge exetnsion cord with that aforementioned plug?

I don't believe that using metal clad is a better choice given that you can buy some really tough flexible cords which probably perform better than metal, and unlike metal clad, are listed for the purpose of flexible, temporary power supply.
Would one of those aforementioned "RV" cables fit the bill? (For example, a 25' length of this:
NU-CORD 94561E 50-Feet 50-Amp Rv Extension Cord - Electrical Cables - Amazon.com)

If not, would you be kind enough to suggest a suitable flexible cable?

Thanks.
 
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Old 12-24-14, 09:40 AM
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My point was that just because a circuit can provide far more power than a device needs does not necessarily mean that it is unsafe to plug it into that circuit....
Correct on both points.

I also believe that when a 120V or 240V device is initially switched on, it can momentarily draw far more power than when "running"
Motors draw much higher current during start-up, not nearly as much for other kinds of devices like lights or heaters. Compressors in particular are "hard starting" motors meaning they can draw huge start up current.

What is the maximum amperage compressor that can safely be run on our home's dryer circuit
The compressor manufacturer should specify two values: max OCPD and min circuit ampacity. They will be listed in the manual and/or stamped on a metal plate on the motor. The max OCPD tells you the largest breaker you're allowed to connect that compressor to. The min circuit ampacity tells you the least size circuit you can connect the compressor to. The dyer circuit is 30A for both. So you're OK if you find a compressor with min circuit ampacity less than or equal to 30, and a max OCPD greater than or equal to 30.

If not, would you be kind enough to suggest a suitable flexible cable?
You want to look at the insulation type. The linked RV cord is STW which is a "mid/light duty" cord with plastic insulation. A heavy duty cord would be something like SJOOW which has a durable rubber insulation and is oil resistant. The codes can be tough to decipher, here's a chart to help: Glossary and O.D. Range Generally anything rated as service or hard service will be a very durable long lasting cord for residential conditions.
 
  #24  
Old 12-24-14, 12:43 PM
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Thanks very much for your advice, ibpooks!

I'll be looking in/at potential compressor candidates' manuals and labels for the OCPD ratings you mentioned. From what you say, I seems possible that I might actually have to pick a compressor that might be larger than one I might otherwise select.

I'll also carefully consider which cable to buy according to the specifications link you've provided. I'll probably go well beyond what's needed in terms of ruggedness, and probably gauge, too.

FWIW, before I retired, I used to work as a laboratory tehnician in various power plants -- one of which was a nuclear power plant that was under construction. At one point during the latter's construction, there were 10,000 contract workers building the place and, as you might be able to imagine (but probably not), the number and variety of temporary high-voltage cords, power/junction boxes, etc. that were literally all over the place -- on bare earth, concrete floors, through puddles, overhead, etc. etc.-- that were being run over by trucks, carts, you name it, was astronomical

I have to assume that, the place being what it was-- a place where a large number and variety of safety regulations were continuously and strictly enforced by a large number of safety officers/enforcers who were crawling all over the place -- all of this clutter was in complete conformance with those regulations.

It is because of working in that place that I sort of smile and shake my head as I read the objections/concerns to running a 25 foot extension cord for one compressor that plugs into one dryer outlet. (Which reminds me..... I should add that the total length of the wire shown below that runs from the main panel to the dryer outlet is maybe 20 feet, but probably less.)
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I know that 120V or 240V can easily kill a person, but I also know that there are safe solutions availble to run temporary electric power to just about anywhere, in just about every environmental condition imaginable. One could argue that this particular situation may not in fact meet the strict regulatory definition of the word "temporary", but, to be prefectly blunt, that is of no concern to me. Safety is.

Thanks again.
 
  #25  
Old 01-10-15, 02:22 PM
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Just followed a similar thread here somewhere only the guy had a welder he was attempting to do the same thing with. I was surprised by the number and intensity of the "naysayers". Quoting irrelevant electrical code rules, using scare tactics and I suppose saying exactly what is politically correct as they should. Sounds like you are on the right track here and not developing a permanent solutions for commercial use so it should work.
 
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Old 01-10-15, 02:36 PM
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Quoting irrelevant electrical code rules,...
Electrical codes are not irrelevant, in most cases they are a matter of LAW. Don't want to follow them? Fine by me but DON'T advocate others to ignore laws.
 
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Old 01-10-15, 03:35 PM
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But Furd, he is an accountant according to his profile so certainly he must no all there is to know about wiring.
 
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Old 01-10-15, 03:56 PM
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An accountant who lives in Illinois, where, for the most part, you must run everything in conduit, anyway
 
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Old 01-10-15, 07:09 PM
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Ohhhhh, a beancounter. That would certainly qualify him for knowing the cheapest way to perform electrical work safely.
 
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