240V Heater wire guarge on long run

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Old 11-01-05, 05:48 AM
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240V Heater wire guarge on long run

I want to install an outlet for a portable construction heater in my attached garage. You've all seen the orange box fans with a stove element inside? It draws 240V/4800W and will be situated about 75-100' from the breaker box.

Do I need special wire for a heater? What guage would I need for the draw and length of run? If I did the calculation properly, 4800w/240v=20a then a 20 Amp breaker should cover it but what about a safety margin or if my house is running on 220v?

Thanks in advance. Again, I'm in Ontario if that makes a difference when it comes to personal safety and not burning my house down.
 
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Old 11-01-05, 06:12 AM
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Is this heater hard wired? Does it have a cord and plug?

If it is to be hardwired, then the nameplate will specify the current rating and/or the breaker size needed. You will need a cutoff located in the garage to remove power without having to go all the way back to the main panel.

If this heater has a cord and plug then the plug will dictate the necessary electrical connection. You may want 10 gage wire, even if the breaker would allow for 12 gage.
 
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Old 11-01-05, 11:36 AM
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The heater has a plug and two fins turned 90 degress to a normal plug but other than than it looks like a normal 110V grounded plug . This is the orientation of the plug -.-

I did the connection in my old house to the socket but the breaker panel was two feet away so it didn't concern me as much. I used a 20A breaker and everything was fine but due to the length of the run I wanted to make sure of things. I heard somewhere that runs around 100' require lower guage wire due to heat or current loss.
 
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Old 11-01-05, 11:49 AM
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Your description could show a 15 amp plug or a 30 amp plug. Based on your description of the heater, I am thinking that it is a 30 amp plug. Does the documentation that came with the heater, or the name plate on the heater tell you anything? if you don't have the documentation, have you looked for it on-line?
 
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Old 11-01-05, 11:53 AM
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Is the plug any larger than a normal 120V plug? The blade orientation that you are describing is either a 6-15P (240V, 15A) or a 6-30P (240V, 30A). If it is the size of an ordinary plug then it will be the 6-15P.

I would use a 6-20R receptacle, 12ga wire, and a 20A breaker for this device.

Does the heater have any sort of 'nameplate' with a current rating? With a 6-15 plug, it should not really be able to draw 4800W...I was wondering if this was some sort of specification game, and what the 'proper' nameplate says.

Finally,
I heard somewhere that runs around 100' require lower guage wire due to heat or current loss.
Is a partial truth. Longer runs of wire do need thicker wire, however this is do neither to heat nor current loss. As the wire gets longer, you have more _resistance_ in the circuit. Current flowing through this resistance means a _voltage_ loss; the voltage delivered to the load will be lower if the wire is longer. None of the current is 'lost', but the 'push' behind the current is reduced. The power lost _is_ converted to heat, however because the wire is longer, you never see this heat as increased temperature. The distance at which you must increase wire size depends upon numerous factors, including supply voltage, sensitivity of the load to voltage drop, load current, etc.

For the heater that you describe, 100feet with #12 wire results in a 2% voltage drop, which is totally fine.

Given your problems with understanding 'voltage drop', I strongly suggest that you review a book or two on electrical wiring. There are many details that you can get wrong in a wiring project, and no way that you will be told everything that you need to know on a discussion board.

-Jon
 
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Old 11-01-05, 01:39 PM
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The construction/milkhouse heaters I've seen sold use a 6-50 plug, and are wired into a 30A circuit with #10 wire.
 
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Old 11-02-05, 05:19 AM
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The heater's plate only reads 240V 60 Hz 4800 W. The plug cords which is about 5' long reads 60 degrees 12/3. The prongs and plug itself are about twice the size of a normal plug.

Maybe I used a 30A breaker when I wired it in the old house? I'm not sure anymore.
 
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Old 11-02-05, 07:59 AM
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Okay, what you have is a 30A 240V plug. You should install a matching 30A receptacle, wire this with #10 wire and use a 30A breaker. Because the heater does not require a neutral, you could use '10/2' cable, which has two current carrying conductors and a ground conductor.

Since you are making the effort of running the cable, you might consider running a 10/3 cable and then leaving the neutral unused; this will give you more flexibility in the future to use this circuit for additional applications. It is not necessary for your heater, and adds extra expense now, so you should only do this if you envision doing something else with this circuit later on.

-Jon
 
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Old 11-02-05, 08:43 AM
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Thanks for everyone's help. At this point I'll use the 10/2 since I can't think of anything else but the heater ever using 240. All of my tools run on 110 for now. It's an easy fix in the future anyways since I now live in a bungalow with a suspended ceiling in the basement and the box is a straight run across the basement to the garage.
 
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