I am designing my first Foundation Fieldbus system and I want to use a conduit based system with small junction boxes along the trunk line to spur off for the instruments. I noticed the Relcom and other companies make terminal blocks specifically for Foundation Fieldbus. Can I just use a normal Phoenix stacked ternimal block with bridge bars? The only benefit I see is that the FF solutions have a LED on them to show they are powered.

 

If you go to the Foundation Fieldbus website ( "www.fieldbus.org":http://www.fieldbus.org ) you can download 2 or 3 application guides. In one of the guides it shows the method you described above as a valid option. In fact I was recently involved in a job that had several instruments that were located outdoors and we used an enclosure rated for the location and terminal blocks bridged together. There were no problems encountered at all. One provision, however, that the Relcom can provide is individual protection for each spur. I.E. if for some reason there was a short circuit in the cabling the chances that the entire segment would stay up is much improved.

 

Yes, you can use standard terminal blocks. I jumpered the blocks together with wire instead of
using bridge bars. It seemed to work OK, although I prefer the FF-specific products from either Relcom or InterlinkBT. The LEDs on Relcom products, such as the Spur Guard megablocks, actually indicate more than just power. If a short occurs on one spur that exceeds about 60mA (check the specs - I'm going on memory), that spur is tripped. A red LED indicates the shorted spur and the short is prevented from effecting the instruments on other spurs of the same megablock. You can't do that with standard terminal blocks...

Chris George
Southern Alberta Institute of Technology

 

Yes. No special equipment is required to connect FOUNDATION(tm) H1 Fieldbus. Current limiting or fuse for each device (spur) may be useful preventing a single short from bringing down the entire network although a current limit at near 60 mA may still be too high, affecting many devices.

You may want to check this book (mind the line wrap, you need the complete address):
"www.isa.org/Template.cfm?Section=Shop_ISA&Template=/Ecommerce/Product
Display.cfm&ProductID=3036":http://www.isa.org/Template.cfm?Sec...=/Ecommerce/ProductDisplay.cfm&ProductID=3036

Jonas
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