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Old 11-20-11, 09:42 AM
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I am trying to wire a construction heater into the 50 amp plug at an RV campground. The connections are NEMA 14-50R on the outlet and I want to plug in a heater with NEMA 6-15P can this be done safely?
 
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Old 11-20-11, 09:56 AM
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You cannot use a 15 amp device on a 50 amp circuit.
 
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Old 11-20-11, 10:13 AM
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Hey pcboss...just for my edification...why not? Isn't it like plugging a 1A lamp into a 15A outlet?

Couldn't you just wire the plug to only use the 2 hots and ground?


Different rules for high amp 240V? Or is it because you aren't using the neutral somehow?
 
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Old 11-20-11, 10:21 AM
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oops

So I messed up it is actually a 14-50R to a 6-30P. Is there a safe way to do this? If not please explain why?
 
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Old 11-20-11, 10:46 AM
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As to why not 50 amps...

What would appear as a short circuit to a 15 amp breaker might appear as a normal load on a 50 amp breaker!

So instead of a 50 amp breaker tripping in the event of a short circuit with a 15 amp device, it might "think" that short circuit was a "heating element" and continue to supply power to it! Then you have some very hot wires heating up and then causing a fire.

The following goes into how you would calculate how much "resistance" a heating element would have for example. A "short" would have an amount of resistance. Actually just a long run of wire has resistance...
How Much Resistance Should a Hot Water Heater Element Have? | eHow.com
 
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Old 11-20-11, 11:08 AM
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Mount a 30a fused disconnect and a 6-30 receptacle to a board. Output of disconnect goes to the receptacle. Connect fused disconnect and receptacle box with a nipple.

Run #6 3-conductor SOW from the input of the 30a fused disconnect to a 14-50 plug. Assuming this is a 240v heater no wire is connected to the neutral of the 14-50 plug.
 
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Old 11-20-11, 11:14 AM
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Ahhh I see now, guess I just wasn't thinking of the protection aspect...thanks Bill.
 
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Old 11-20-11, 11:32 AM
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Originally Posted by Gunguy45 View Post
Ahhh I see now, guess I just wasn't thinking of the protection aspect...thanks Bill.
Yes. And at some point you could take an 18 gauge extension cord say 100 ft. long and short the ends together. And that would appear as a normal load to a certain high amperage breaker. Too early for me to figure that out - what amperage... 100 amp breaker? 200 amp breaker?

Anyway here is resistance per foot of various size wires...
Resistance of Wire (Wire Resistance Calculator)

Then also as a wire heats up, the resistance increases.
 
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