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Old 01-20-2012, 07:54 PM   #1
br1dge
 
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Im getting close to starting to buy parts for my electric build. I am just trying to go over everything before I start putting out the cash. I have a couple questions Im hoping you might be able to help me out with. Currently I am planning to run off of my dryer outlet and for now just run one element at a time. Eventually I would like to bump up to a 50A setup but in the short term I would like to set it up with a Spa Panel running off of the dryer outlet. This way it is portable to anywhere that has a dryer outlet (friends house). The main restriction that I can see is that my dryer plug in is about 50 ft from where I normally brew. I found this extension cord on Craiglist. its 100' 30A 12/3. Do you see any problems plugging this into my dryer outlet and then running this to my Spa Panel. Then 4 wire cord from Spa Panel to Control panel? Let me know if Im missing anything.

Shore Power Cord 100 ft. 30A Mil-Spec

Rig will be 5500W element, PID, RTD. Happy to answer any questions if I left something out.


 
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Old 01-20-2012, 08:33 PM   #2
audger
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the only thing a 50+ foot cord does is cause a voltage drop, which will decrease available power to the element. everything should still work just fine, but if you measure a solid 240v at the dryer element, you will measure around 231v at the end of that 100ft extension cord. if you cut the cord in half and used 50 feet, voltage would drop by half as much, or to ~235v.

that is assuming you have a full 240v at the dryer plug, which often isnt the case. if you are starting out at only 230v, you will only have 221v at the end, etc. a heating element is a resistive load and really doesnt care what voltage it gets. if you are trying to run a pump or other controls off one of the 120v legs, you may only have 100 or 110v, which could be a problem.

a 5500w element draws 5500w at 240v. at 230v, it will only draw 5270w. at 220v it will only draw ~5000w. so you can see how the element power is derated as you decrease voltage. as long as you are aware of that, there is nothing else you should worry about.

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Old 01-20-2012, 08:54 PM   #3
br1dge
 
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Quote:
Originally Posted by audger View Post
the only thing a 50+ foot cord does is cause a voltage drop, which will decrease available power to the element. everything should still work just fine, but if you measure a solid 240v at the dryer element, you will measure around 231v at the end of that 100ft extension cord. if you cut the cord in half and used 50 feet, voltage would drop by half as much, or to ~235v.

that is assuming you have a full 240v at the dryer plug, which often isnt the case. if you are starting out at only 230v, you will only have 221v at the end, etc. a heating element is a resistive load and really doesnt care what voltage it gets. if you are trying to run a pump or other controls off one of the 120v legs, you may only have 100 or 110v, which could be a problem.

a 5500w element draws 5500w at 240v. at 230v, it will only draw 5270w. at 220v it will only draw ~5000w. so you can see how the element power is derated as you decrease voltage. as long as you are aware of that, there is nothing else you should worry about.
Thanks audger!! That doesnt sound like too much of an issue for the elements. Starting with 5500W gives me some room to lose wattage and still be fine. I was planning on eventually running my whole control panel off of the Spa Panel (after the extension cord) which would include my pumps at 120V. You said this "could" be a problem. Can you elaborate more on this?

Does this mean that if I want my full control panel to eventually run 100' from the breaker that I would need to either buy a 50A breaker to start with or maybe run heavier guage wire permanently to the Spa Panel?

It would be nice to have the whole thing portable but maybe thats just not feasible??

 
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Old 01-20-2012, 10:13 PM   #4
jeffmeh
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IANAE (I am not an electrician), but I thought 30 amp required 10 gauge wire.

 
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Old 01-20-2012, 10:33 PM   #5
rollinred
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Quote:
Originally Posted by jeffmeh View Post
IANAE (I am not an electrician), but I thought 30 amp required 10 gauge wire.
What he said.

 
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Old 01-21-2012, 12:14 AM   #6
Hoosier-Brewer
 
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12/3 is good for 20 amps.

 
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Old 01-21-2012, 12:17 AM   #7
NoCornOrRice
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For that price, you could probably get 50' or more of the really good stuff: 10/4 SOOW.

 
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Old 01-21-2012, 12:35 AM   #8
Hoosier-Brewer
 
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Quote:
Originally Posted by NoCornOrRice View Post
For that price, you could probably get 50' or more of the really good stuff: 10/4 SOOW.
You're probably right on that. I have a 30 amp RV cord on my camper that was ~$45 and it's 50'. Similar to this, but I got a much better price. Walmart.com: Road Power 30-Amp RV Extension Cord, 30': Computers

 
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Old 01-21-2012, 07:45 PM   #9
yjfun
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Extension cords don't follow the same rules as regular wiring sizes in a home. If you are going to hook up anything that requires 120 volts in your control panel then you will need 4 wire cord and the allowed amp loads are as follows. #12 20amps, #10 25amps, #8 35amps, #6 45amps, #4 60amps. The reason for this is heat buildup. The breaker may not trip because the amp load isn't high enough to show a short but the cord can essentially turn into a heating element and burn your house down. Using a longer cord increases the resistance and causes even more heat.

 
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Old 01-22-2012, 04:32 AM   #10
Dert
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I have #8 Cu running out to my detached garage with a 50 amp breaker...inspected and passed by the state of MN.

And, I just ran 2 50 amp circuits using #6 Al wire (XHHW-2, rated for 90 degrees C) that is rated for 55 amps at 60 degrees C. yjfun, the numbers you listed are wrong...a lot of the ampacity depends on the type of wire and how it is run.

 
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