Thermal Unit Selection Tables

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umagooma

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When calculating Thermal Unit Size, where do I find what table to use? I also get confused when one value, for example a B25, is 14.1 - 15.8 in table 2 and a B25 in table 3 is 12.8 - 14.3 Please help me understand how to choose the correct tables. :happysad:
 

kwired

Electron manager
Location
NE Nebraska
When calculating Thermal Unit Size, where do I find what table to use? I also get confused when one value, for example a B25, is 14.1 - 15.8 in table 2 and a B25 in table 3 is 12.8 - 14.3 Please help me understand how to choose the correct tables. :happysad:
Sounds like you are using Square D NEMA starters - you need to first read information that precedes the tables to find the correct table for your application. Number of thermal units, size of enclosure all make a difference in which table is to be used. This is if you are reading the selection data in the "Digest". If you have an enclosed device inside an enclosure specifically intended for the device - they generally only have the applicable table for that enclosure attached to the enclosure somewhere. If you purchase an open device it usually comes with more then one selection table and you need to read instructions to determine which one to use for your application.
 

Jraef

Moderator, OTD
Staff member
Location
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Occupation
Electrical Engineer
... If you purchase an open device it usually comes with more then one selection table and you need to read instructions to determine which one to use for your application.
But we all know, those table charts get thrown away with the cardboard box it came in...

Back in the day, I would have picked up my 3" thick 4lb. Digest and flipped to the right page in 20 seconds. Now if I want to find it on the Internet, I have to wade through a lot of garbage google results for every eBay junk dealer or parts house that says they will fond it FOR you and charge you for it. Then eventually I get to Schneiders website, explain to it that I DON'T want to know about the latest Telemecanique products, drill down through layers or superfluous advertising and wait for a slow server to deliver the selection guide, then start again to download the actual chart itself, taking 10-15 minutes all totaled. Progress...
 

kwired

Electron manager
Location
NE Nebraska
But we all know, those table charts get thrown away with the cardboard box it came in...

Back in the day, I would have picked up my 3" thick 4lb. Digest and flipped to the right page in 20 seconds. Now if I want to find it on the Internet, I have to wade through a lot of garbage google results for every eBay junk dealer or parts house that says they will fond it FOR you and charge you for it. Then eventually I get to Schneiders website, explain to it that I DON'T want to know about the latest Telemecanique products, drill down through layers or superfluous advertising and wait for a slow server to deliver the selection guide, then start again to download the actual chart itself, taking 10-15 minutes all totaled. Progress...
You obviously don't go to their on line digest often enough to have bookmarked it:) The online digest itself is a ad free and the current one gives you options of flip viewer in your browser window or abiity to open each chapter as an individual pdf file.Finding that page if you don't already have the correct address may mean needing to go through other pages though and being bombarded with whatever they may put on those pages.
 

tom baker

First Chief Moderator
Staff member
And going to on the online digest may not be possible in the field. My favorite is the Allen Bradley IEC starters the instructions are inside the box, but in the form of little icons, so its language free...
 
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