80% Auto-Ignition Temperature

[fifty60]

I am trying to find in the code where it discusses the temperature of sheathed heaters in hazardous environments.

I know the temperature of the heaters have to limited to 80% of the AIT of the hazardous material, but is the 80% in Celsius or Fahrenheit?

 

[zbang]

I know the temperature of the heaters have to limited to 80% of the AIT of the hazardous material, but is the 80% in Celsius or Fahrenheit?

Percentages don't have units. For instance, 80% of the temp. where water boils is 170 deg F or 80 deg C, but they're both 80%.

 

[fifty60]

80% of 100 C gives a different result than 80% of the equivalent of 100 C. The NEC would have to mean 80% of one or the other but it cannot be both...

.8 * 100 C = 80 C.

100 C = 212 F

.8 * 212 F = 169.6 F

169.6 F =76.4 C

 

[ggunn]

80% of 100 C gives a different result than 80% of the equivalent of 100 C. The NEC would have to mean 80% of one or the other but it cannot be both...

.8 * 100 C = 80 C.

100 C = 212 F

.8 * 212 F = 169.6 F

169.6 F =76.4 C

What if it means Kelvin?

 

[Smart $]

80% of 100 C gives a different result than 80% of the equivalent of 100 C. The NEC would have to mean 80% of one or the other but it cannot be both...

.8 * 100 C = 80 C.

100 C = 212 F

.8 * 212 F = 169.6 F

169.6 F =76.4 C

All references I've seen to AIT use Celsius.

FWIW, when converting to Farenheit, you also have to take into consideration the zero offset of the different scales, i.e. 0?C = 32?F... so it's actually .8 * 180 + 32 = 176?F.

 

[david luchini]

I am trying to find in the code where it discusses the temperature of sheathed heaters in hazardous environments.

I know the temperature of the heaters have to limited to 80% of the AIT of the hazardous material, but is the 80% in Celsius or Fahrenheit?

501.135(B)(1)(1) says "80% of the ignition temperature in degrees Celsius"

 

[fifty60]

All references I've seen to AIT use Celsius.

FWIW, when converting to Farenheit, you also have to take into consideration the zero offset of the different scales, i.e. 0?C = 32?F... so it's actually .8 * 180 + 32 = 176?F.

You first have to multiply the 180 * 9 / 5 before you add the 32.

 

[Smart $]

You first have to multiply the 180 * 9 / 5 before you add the 32.

I don't know where you are getting that. 180?F is the span equivalent of the range 0-100?C... i.e. the equivalent range is 32-212?F.

Conversion:

?C = (?F-32) ? 5/9
?F = ?C ? 9/5 + 32

Essentially the delta ratio of the scales is 9?F to 5?C, while the zero offset is +32?F.

To figure the equivalent of a temperature percentage in ?F based on the same percentage to 100?C...

?F = (% ? 100?C) ? 9/5 + 32

We can shorten that to...

?F = % ? (100?C ? 9/5) + 32
?F = % ? 180 + 32

 

[rbalex]

I am trying to find in the code where it discusses the temperature of sheathed heaters in hazardous environments.

I know the temperature of the heaters have to limited to 80% of the AIT of the hazardous material, but is the 80% in Celsius or Fahrenheit?

If you asked this question in the Hazardous Locations forum you mike have gotten the "Code" answer a bit sooner. It's in the same Section you learned that it was 80 percent of the AIT. [501.135]