240 extension cord questions...

[reinhardt]

i bought an air compressor recently that is 240v and draws 21 amps. i have no 240 in the garage but my dryer is 20 feet away. i have a piece of 50' 10/3 cord that i would like to wire to the motor directly and put a 3 prong plug on the other end to plug into the dryer outlet when i need air and roll it up when i dont. the dryer outlet is 240v, 30 amps 3 prong. i would prefer not to cut the cord shorter if i dont have to as this is only a temporary install until i can afford to run in a dedicated 240v outlet into the garage. but temporary may be a while so i dont want to burn up my compressor motor.

now for my two questions: do i need to cut the cord shorter? where can i find a 3 prong 240v plug? i checked hd and lowe's websites and didnt see one. i saw 6 ft long cords, but i dont wanna splice that into my 10/3 cord - that seems unsafe.

ben

 

[SPDMETL]

The store's websites are often less than helpful-you have to go there.

 

[mrb]

post a picture of the dryer outlet. if its really a 3 pin ungrounded dryer outlet its not safe to plug your compressor into it, if its a nema 6-30 then youre fine.

i wouldnt worry about the length of the cord at 50ft. the compressor doesnt know if you have 50ft of 10/3 cord on the ground or 50ft of 10/2 romex in the wall...

 

[reinhardt]

post a picture of the dryer outlet. if its really a 3 pin ungrounded dryer outlet its not safe to plug your compressor into it, if its a nema 6-30 then youre fine.

i wouldnt worry about the length of the cord at 50ft. the compressor doesnt know if you have 50ft of 10/3 cord on the ground or 50ft of 10/2 romex in the wall...

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10051&catalogId=10053&productId=202214665&R=202214665

it looks just like this. my concern with the cord length is voltage drop across the wiring from the main panel to the outlet to the end of the 50' cord. so you say there wont be any major voltage drop then? if this plug is unsafe, what do i do with that? thats what the outlet in my house looks like, the house was built in 1987.

ben

 

[ishiboo]

http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10051&catalogId=10053&productId=202214665&R=202214665

it looks just like this. my concern with the cord length is voltage drop across the wiring from the main panel to the outlet to the end of the 50' cord. so you say there wont be any major voltage drop then? if this plug is unsafe, what do i do with that? thats what the outlet in my house looks like, the house was built in 1987.

ben

Voltage drop on the cord is only 1.5% @ 30A. You'll be fine.

As mrb said, that is an older non-grounded dryer plug... you may have a ground present in the box but if the wiring is dated you will just have a neutral. (Our house had a 3-pin dryer plug with 10/3 NM so I was able to upgrade to a 4-pin receptacle.)

If you're concerned with not having a ground, you could run one separate of a higher gauge wire.

 

[sberry]

Is this a main entrance service panel that the outlet is connected to? If so the wire is grounded, if this circuit originates from a more modern 4 wire fed sub panel than the N is seperate.

 

[reinhardt]

Now I am slightly confused. Ugh... I know 110v has a hot (black), nuetral (white), and a ground(bare). I was under the impression 240v had 2 hots, a nuetral and a ground. Now if my 3 prong outlet only has three leads it is the nuetral that is missing? does that mean the ground has power on it? or does the power flow from one hot to the other with the ground present for ohh **** moments? the outlet is connected to the main entrance service panel as there are no sub panels in my home. i'm not quite following the difference of the 3 prong vs 4 prong plug. off to yahoo i go.

ben

 

[pattenp]

240V does not use a neutral. Dryers and stoves have a neutral because they have controls and or timers that use 120V so the neutral is needed to provide 120V. The old way of wiring for dryers and stoves was to use three wires, 2 hot and 1 neutral/ground. The neutral and ground was bonded at the appliance so technically the one wire was being used as both the neutral and ground. The new way is to use four wires, 2 hot, 1 neutral and 1 ground. The neutral and ground are now required to be separated. Your existing dryer circuit using three wires technically can be used for your compressor because the compressor does not need 120V so it doesn’t use a neutral. I don’t understand why it wouldn’t be safe to use the dryer socket to plug in your compressor because the neutral and ground should be bonded in the main service disconnect panel effectively making the third prong on your plug also a ground. I know for the purest on proper plug requirement the three prong dryer plug is the wrong plug to use because the third prong is thought of as being the neutral.

 

[mrb]

codes aside and practically speaking if the dryer receptacle is supplied from the main panel containing the n-g bond there shouldnt be a safety concern. but if the dryer receptacle is supplied from a 4-wire supplied subpanel then using the neutral as the ground for the compressor could pose a hazard during a fault condition

 

[35mastr]

I see alot of talk about bonding the neutral and ground. Anyone have a pic of this bonding? I have always run my 220 welders off the dryer plugs with just the 2 hots and the neutral.

Will this harm any of the equipment eventually.

 

[z28snksknr]

My new Eastwood 175 MIG has a 3 prong 220V plug. I plug it into a 220V 3 prong outlet with 10-3 wire to the box. I doubt i'm doing it any harm by not having a 4th wire in the outlet to the box. I also doubt that your dryer's 220V requirements are different from your air compressor's 220V requirements as long as they are aroudn the same amperage range.

 

[mrb]

I see alot of talk about bonding the neutral and ground. Anyone have a pic of this bonding?

this is at the main service only

 

[35mastr]

this is at the main service only

My house was built in 1954 so I dont think it has the bonding. Thats why I am asking for a picture of what it may look like. Still has the old 100 amp service with the really expensive Zinsco style breakers.

 

[pattenp]

I see alot of talk about bonding the neutral and ground. Anyone have a pic of this bonding?

In the main service panel there may be one or two bars to which your neutral and ground wires connect to. When there is one bar you'll see both the neutral and ground wires connected to the one bar in effect bonding the two together. Where the ground wires are connected to one bar and the neutral wires are connected to another bar the two bars are bridged by a mechanical connection which bonds the two together.

In a sub-panel there needs to be two bars, one for neutral and one for ground. But the neutral bar needs to be isolated from (not connected to)the ground bar.

 

[pattenp]

Will this harm any of the equipment eventually.

I assume your dryer outlet is wired off the main service panel so the neutral and ground are bonded so in effect your neutral in the case of your welder is actually a ground. So no, it won't harm your welder.

 

[pattenp]

Neutral and ground in same bar so they are bonded.


Isolated neutral and ground in sub-panel.


Isolated neutral bar. Whip would be attached from box to bar when bonded.

 

[reinhardt]

again, my neutral and ground are bonded in the main panel and the dryer outlet is ran off of the main panel (no sub panel). so i think i'm good to go on plugging the compressor in. good times.

ben