12 gauge 25amps?
- Thread starter Saywatt
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Actually you can fuse it higher depending on the application, read 240.4(D) and go on to the other sections mentioned for the whole picture.
Roger
ptonsparky
Tom
- Occupation
- EC - retired
Motors
Temperature
conduit or raceway fill
Temperature
conduit or raceway fill
The first part of your statement is only partially correct. 12 can be rated for 30, 25, or 20 amps, depending on the insulation.
In most cases, you will be limited to 20 amps by 240.4(D). But in some cases, you can use the ampacity listed in T310.16 per 240.4(G).
- Location
- Massachusetts
Nope and not a great idea due to voltage drop.
VD wasn't a problem. Just shy of 20 amps for long periods is my concern.
It's a short run and there wasn't much in the way of dimming at the end of the line. My concern is 19.8 amps on 12 for long periods.
I could put a 20amp inline fuse in, but how long would it hold?
- Location
- Logan, Utah
- Location
- Massachusetts
Oh you have voltage drop, it is just a mater of if it concernes you.
1.2 volts lost on a 12 volt circuit is 10% and 19 amps on 12 AWG will drop 1.2 volts in just a very short run.
As far as the loading, if you think it is going to be run for periods exceeding three hours it is a continuous loads so you have to use at least a 25 amp fuse and conductor.
No one answered the why.
ptonsparky
Tom
- Occupation
- EC - retired
Perhaps he didn't phrase the question correctly.
The real answer is "Because the NEC says so!!" We gave him exceptions to that general rule. I have been told on here before that the NEC doesn't have to make sense.
The real answer is "Because the NEC says so!!" We gave him exceptions to that general rule. I have been told on here before that the NEC doesn't have to make sense.
ptonsparky
Tom
- Occupation
- EC - retired
WAG would be that most terminations, (devices) will not handle the temperatures of the smaller conductors operating at the higher current levels.
- Location
- Logan, Utah
The 'small conductor rule' first shows up in 1956, at the bottom of Table 1, Chapter 10 (it's now T310.16):
"The current-carrying capacities for Type RHH conductors for sizes 14, 12 and 10 shall be the same as designated for Type RH conductors in this Table." This put 14, 12 and 10 RHH at 15, 20 and 30 amps respectively. RH was a 75?C conductor, and RHH was a 90?C conductor.
Why? I don't know... he's on third.
I found a little information here http://forums.mikeholt.com/archive/index.php/t-118527.html
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