220/240 V extension cord

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  #1  
Old 06-18-09, 05:46 AM
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220/240 V extension cord

Ok - I'm probably going to get shot down in flames - but .....

I need 22A 240V for a 5HP 60G air compressor. I have no way of getting a hard wired circuit into the work shop at a reasonable price (distance etc). But I could run an extension from the good old 4-prong dryer plug - which is on the correct end of the house.

This would be 10/2+ground wire - 50 feet- with a switch/breaker box on the workshop end so I can cut off compressor there and not have to run back to house - for safety etc.

My questions is - can I use a RV 30A cable (i already have one of these) and replace the plug on one end - and wire the other into the compressor. it says it is #10 wire ?

Any better economical ideas ?

thanks - Stephen
 
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Old 06-18-09, 07:08 AM
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Cord

A 30 amp rv cord is for a 110 volt circuit. 3 prongs.

To connect to a 4 prong dryer receptacle, you would need a 10/3+ground.

I am not recommending you do this.

The proper thing to do is install a sub-panel in the shop.
 
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Old 06-18-09, 07:43 AM
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Originally Posted by Wirepuller38 View Post
A 30 amp rv cord is for a 110 volt circuit. 3 prongs.

To connect to a 4 prong dryer receptacle, you would need a 10/3+ground.

I am not recommending you do this.

The proper thing to do is install a sub-panel in the shop.
Plesae read my fairly detailed question carefully.

i said i would replace the ends - i do not need to use the white on the dryer as i won't have any 110v circuits - i just need the 2 x hots and the ground.

i explained why realistically i can't get a sub panel to the shop. - well i can for about $600.

That is why i did say i would install a box with breakers at the shop end.
 
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Old 06-18-09, 08:15 AM
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I am not a pro, but one thing I have learned from this site is that the easy way does not always meet electrical codes and may be hazardous. No pro is going to agree with a hookup that is iffy at best.

Listen to what Wirepuller 38 is trying to tell you.
 
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Old 06-18-09, 08:22 AM
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Originally Posted by goldstar View Post
I am not a pro, but one thing I have learned from this site is that the easy way does not always meet electrical codes and may be hazardous. No pro is going to agree with a hookup that is iffy at best.

Listen to what Wirepuller 38 is trying to tell you.
i did - and i understand he is not recommending this - but he ignored my question details and talked about wrong plugs and 4 core wire etc - when i had already descrivbed i knew the plugs needed replacing.. I am not trying to be difficult.

I was just trying to clarify the details.

I know this is not "ideal" - and maybe not to code - but is it 'temporarily-safe' and will it work ?.

If you search this site you will find a lot "worse" recommendations than i am suggesting

i guess my real question is

will the wire in the RV cord support 240V 22A - with out catching fire ?
 
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Old 06-18-09, 08:47 AM
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It sounds okay to me as long as the cord is #10 and you put the correct plugs on it. The neutral pin on the house end would not be connected. The breakers on the garage end are unnecessary as the plug itself is considered an adequate disconnect and the 30A breaker is already the correct size for the motor. Try to get the extension cord as short as practical. If you have extra cable, snake it along the floor instead of coiling at one end.
 
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Old 06-18-09, 09:17 AM
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Originally Posted by ibpooks View Post
It sounds okay to me as long as the cord is #10 and you put the correct plugs on it. The neutral pin on the house end would not be connected. The breakers on the garage end are unnecessary as the plug itself is considered an adequate disconnect and the 30A breaker is already the correct size for the motor. Try to get the extension cord as short as practical. If you have extra cable, snake it along the floor instead of coiling at one end.
excellent - thank you.

i'm surprised i don't need the breaker as the disconnect is in another building ?
 
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Old 06-18-09, 09:45 AM
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It's a temporary connection, so it is the disconnect. If you need to service the motor you can easily unplug it and pull the cord back to prevent unauthorized operation.
 
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Old 06-18-09, 11:01 AM
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thanks - and last dumb question

if an extension is 10/3 and rated at 30A @ 125V then the power is V * I = 3,750W

ignoring the plugs (i'm cutting those off) - can the same wire work at 30 A @ 240V - which is twice the power = 7,200W

...after all it is 10/3 ?
 
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Old 06-18-09, 11:16 AM
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The key is the gauge not watts. A #10 is good for 30a.
 
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Old 06-18-09, 12:57 PM
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Yes, it's only the current (amps) that contributes to the heating of the cable so 30A at 120V is effectively the same as 30A at 240V as far as the cable is concerned. You can get into an issue occasionally where the insulation is not thick enough for a higher voltage, but virtually all cables have at least a 300V rating (service junior) grade so it shouldn't be a problem.

Your cable may have a series of letters on it which indicate the rating. If you see an SJ such as SJOW then it is good for at least 300V (as well as exposure to Oil and Water).
 
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Old 06-18-09, 04:47 PM
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You may be ok with tempory useage that fine but down the road you may have to plan to make a subpanel anyway IMO that is the best route to go that way.

Is your garage is attached or detached ?

If attached it will be eaiser to deal with it.

If you going to use the air compressor pretty often then go with subpanel route.

I know you may bulk at the cost of mataerals but overall it is not too expensive compared how much time you have to slide the dang dryer out of it place.

I will give you a example which I did not too long ago the subpanel is under 50$ and there were short run of 16mm˛ { #6} and half dozen breakers both single and duex pole verison and the whole thing just for subpanel hook up plus ran two circuit for 240v's
The overall materals is less than 250$ { I will leave the labour rate out of this part for now }
And that person is very happy he did not have to drag hevey 10mm˛ { #8's} anymore.

Merci,Marc
 
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Old 06-18-09, 05:14 PM
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Originally Posted by french277V View Post
You may be ok with tempory useage that fine but down the road you may have to plan to make a subpanel anyway IMO that is the best route to go that way.

Is your garage is attached or detached ?

If attached it will be eaiser to deal with it.

If you going to use the air compressor pretty often then go with subpanel route.

I know you may bulk at the cost of mataerals but overall it is not too expensive compared how much time you have to slide the dang dryer out of it place.

I will give you a example which I did not too long ago the subpanel is under 50$ and there were short run of 16mm˛ { #6} and half dozen breakers both single and duex pole verison and the whole thing just for subpanel hook up plus ran two circuit for 240v's
The overall materals is less than 250$ { I will leave the labour rate out of this part for now }
And that person is very happy he did not have to drag hevey 10mm˛ { #8's} anymore.

Merci,Marc

trouble is my garage is 160 foot away from the sub panel and across a driveway

from the laundry room - is is only 30 foot - and fortunately the drier plug is not covered.

I will not use the compressor that often - i am restoring an old truck - but if i decide to swap my 110V welder in for a 240v one - then i will invest in the sub panel.
 
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