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Old 10-01-2010, 07:31 PM   #31
Bobby_M
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Quote:
Originally Posted by nostalgia View Post
Call me paranoid, but I would never run undersized wire without protection. As you've probably seen in my build thread, the 6 gauge main supply is protected by the 50A breaker in my main panel. The 10 gauge wires for my elements are protected by 30A breakers in the control box. 14 gauge is protected by 10A breakers in the control box.

We're talking about a lot of amperage, 240V circuits and liquids. Yes, it's a short run. Yes, I'm supervising it. But I still don't want the wires melting because they're not protected by an appropriately sized breaker. The breakers were $16 each for the 30A and $8 each for the 10A. So $48 is cheap insurance when amortized over the time I'll be using the rig.

Edit: the DIN rail was $6.50 for 2 meters worth.

For the record, codes never entered into my thinking. Just protecting wires from burning up in a worst case scenario.

-Joe
I won't too adamantly defend my position of "not really necessary" on the branch breakers that you've installed. Given the prices I found for similar breakers, I wouldn't do it but at your pricing I would consider it if not go the fuse route. What I would like to chat about is what situation would cause the 10/3 SJ wires to overheat but still stay under the 50amp total load on the main supply? I'm not saying you should know, but I'm wondering if anyone can speculate. It's a narrow band between the amperage that would cause physical damage to 10/3 (what, realistically 40+ amps or so) and the 50 amps on the main. Something really odd and really specific would have to happen to get the element to draw 48amps.

Again, not argumentative at all, just fueling some conversation.
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Old 10-01-2010, 07:39 PM   #32
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10/3 is rated to 55A??? That wire is protected by the 50A breaker. The internal breakers and/or fuses are for the branch circuits. I don't think any standard situation would cause a failure of the 10/3 power wire as long as a 50A breaker was somewhere in that circuit...

 
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Old 10-01-2010, 07:41 PM   #33
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Argg.... I'm an idiot... 10AWG is good to 40A... realistically, you would not likely melt it, by why risk it?

 
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Old 10-01-2010, 07:55 PM   #34
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Quote:
Originally Posted by Bobby_M View Post
I won't too adamantly defend my position of "not really necessary" on the branch breakers that you've installed.
Nor was I attacking your position Just stating mine.

I don't know what situations can cause a sustained 40A load on a 30A circuit. Maybe my heatstick element chafes and grounds to the pot, but isn't enough of a dead short to trip the breaker. Maybe something breaks down inside the element, lowering its resistance just enough to draw 49.4A continuously and melt the 10ga wires. /shrug

I do know that even if the chances are slim, I don't want it to happen to me. I've put enough time and money into the system (there's a spreadsheet I should never have started ) that skimping on safety for $50 would be silly.

YMMV.

-Joe
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Old 10-01-2010, 08:33 PM   #35
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Quote:
Originally Posted by Boerderij_Kabouter View Post
Argg.... I'm an idiot... 10AWG is good to 40A... realistically, you would not likely melt it, by why risk it?
I'm pretty sure SJ and other flexible cords reduce it even more. 10/3 SJ is 30amp I think.
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