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4 comments
Commentator

Join Date: Nov 2008
Posts: 93

Temperature Classes

07/27/2011 4:54 AM

dear all,

I am confused about temperature classes of instrumentation in hazard areas , we have classes from T1 to T6 can any body explain to me what is meant but maximum surface temperature ?and how we can select type depending on hazard area classification?

for example does T6 instrument covers T3 ones or vise versa

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#1

Re: temperature classes

07/27/2011 5:20 AM

It's all to do with gas group. T1 will cover hydrogen and little else. T4 will cover most things except carbon disulphide and one or two other specials.

The T class is simply the maximum surface temperature that can be expected under fault conditions. It must always be below the autoignition temperature of the gas(es) present.

The article in Wikipedia gives more details.

Do not attempt to select, install, commission or modify hazardous area electrical circuits without having received beforehand suitable and adequate training.

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Commentator

Join Date: Nov 2008
Posts: 93
#2
In reply to #1

Re: temperature classes

07/27/2011 5:28 AM

thanks

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2
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Join Date: Feb 2009
Location: Houston, USA
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#3
In reply to #2

Re: temperature classes

07/27/2011 11:07 PM

Good answer has been given by PWSlack. I just would like to add more:

The temperature class defined in North America (NEC) and Europe (IEC) are:

Max. Surface
Temp °C
North AmericaEurope
450T1T1
300T2T2
280T2A---
260T2B---
230T2C---
215T2D---
200T3T3
180T3A---
165T3B---
160T3C---
135T4T4
120T4A---
100T5T5
85T6T6

The temperature class of the explosion-proof equipment ensures that the surface temperature of the equipment will never exceed this value, even in the worst condition (such as the motor burns, explosion occurs in a box etc). The lower is the temperature class, the higher is the price of the equipment. When selecting the equipment, make sure temperature class value remains almost 80% of the ignition temperature of the LEL (Lower Explosive Limit) of the surrounding gases. By this selection, it is guaranteed that there will not be any fire for the worst condition of the equipment.

- MS

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Commentator

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Posts: 93
#4
In reply to #3

Re: temperature classes

07/28/2011 4:45 AM

thank you so much

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a_m_shiha (2); msamad (1); PWSlack (1)

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