Cable Specs
Cable Specs
(OP)
Anyone can give input about specifying instrument cables for power plants. The cables will be for:
-Analog input 4-20mA or RTD
-Digital Input/output
-Input/Output cables from Swicthgear to PLC for control and monitoring
I am looking specifically whether to provide shield on Digital input/output cables and whether to have them twisted pairs or simply control cables
Your input will be appreciated.
-Analog input 4-20mA or RTD
-Digital Input/output
-Input/Output cables from Swicthgear to PLC for control and monitoring
I am looking specifically whether to provide shield on Digital input/output cables and whether to have them twisted pairs or simply control cables
Your input will be appreciated.





RE: Cable Specs
We also use individually twisted shielded pairs for 24 Vdc digital contacts, etc. This is just for cable standardization. Assure that the cables are tray rated if any cable tray is used. I am a fan of 600 Volt insulation but this is left over from some old NEC issues.
Ethernet uses unshielded twisted pairs. Copper Ethernet is also limited to 100 meters.
If looking for a cable standard, consider specifying NEMA WC 57 (ANSI/ICEA S-73-532) Standard for Control, Thermocouple Extension and Instrumentation Cables.
Some people think that Instrument Cables are "power limited" cables. UL 13 applies to power limited cables. However, these signals are not NEC 825 power limited cables unless you use Intrinsic Safety Barriers. Intrinsic Safety would be very unusual in a power plant. Perhaps your fire alarm signals are power limited signals but not the 4-20 mA or alarm signals.
RE: Cable Specs
I.S. is actually pretty common in European plants, especially the younger generation of CCGTs because the installed cost is usually much lower than the flameproof Ex'D' alternative. The old stations built years ago 'when we built things things properly' have a lot of Ex'D' equipment. I.S. is the only option under the ATEX Directive for Zone 0 environments where a continuous explosion hazard exists.
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If we learn from our mistakes I'm getting a great education!
RE: Cable Specs
My point related to this topic is that novice engineers and designers want to apply NEC article 825 for DCS and SIS wiring. The overcurrent protection in such systems rarely qualifies as power limited circuits except when IS barriers are applied. Even those tiny 1/4 Amp micro-fuses can usually be replaced with a fuse closer to 10-Amp.
RE: Cable Specs
600 V insulation is a good thing - although you hear a lot of whining from some of the vendors.
Definitely individual twisted shielded pairs for signal cable.
RE: Cable Specs
single pair cables with shield for analog and digital signals
multipair cables with individual and overall shield for analog signals
multipair cable with overall shield for digital signals
I am new in the north american market and my colleagues are arguing that they only consider instrument cables for 4-20mA and RTD signals. For the rest alarm and signalling digital inputs, cables are considered to be control cables with multcore and without shields.
is this common way of doing it in power plants
RE: Cable Specs
RE: Cable Specs
http://www.tecnicable.com/productos/cable.asp
EOZ1 (ROZ1) - Z10Z1
RE: Cable Specs