Flat cable for Devicenet

smiller

Member
Join Date
Aug 2003
Location
Arizona/Brazil
Posts
116
I am in the planning stages of a Devicenet upgrade on some Cutler Hammer switchgear lineups. Are there any issues that I should be aware of regarding the use of flat cable and vampire connectors instead of round cable and Tees? I wonder about the lack of a shield and possible noise from the 480 volt bus in close proximity. Please let me know either pro or con regarding flat cable.

Thanks.
 
I would stick with Round and Tees, personally. Costs more but I think a much better solution, and is inherantly more flexible, cable layouts/runs can be modified more easily to minimise possibility of EMI pickup.

Have you seen the range from Sutherland Shultz (i think) that incorporates power supply monitoring LEDs in the Tees and end-of-line resistors. There is also an LED tells you if you've had transient noise spikes on the signal wires.

I never did like the idea that there is no separate shield in the Flat cable, it goes against all the "good practice" and "absolute musts" that keeps a DN working effectively. And of course, the flat cable can't be bent up or down !
 
+1 on round cable thin or thick. In the US check Turck for the cordsets and connectors.

DeviceNet_Config.jpg


Enjoy!
 
Thanks for the input. I have been using Brad (Molex) fittings. They offer the diagnostic tees with LEDs and other diagnostic equipment like the Net tool that has been very handy. I also have an EnetDN unit on order that will constanly monitor and trend the D net network and offer remote monitoring over Ethernet.

Steve
 
I have never understood how some vendors use 300V insulated round cable in MCC wireways without running headfirst into NEC Article 725, but that's between them and their customers.

The knurled connectors in particular are alarming to me: a conductive, sharp, abrasive item in a wireway with unsecured wires carrying high voltage, AND it's the first thing you're going to grab.

Rockwell Automation, as you've probably seen, uses the flat cable extensively. Having the wires parallel to one another gives you noise cancelling that is almost as good as shielding. Placing the flat cable behind the wireway also makes it nearly impossible to damage.

The proximity of the MCC bus is less of a problem (at least in the MCCs I've used) because the bus generally carries nice clean sine waves, while the output of a VFD (which is going to be lower power but much closer to the droplines) has all kinds of harmonic and noise components.

In nine years of commissioning and troubleshooting MCCs with flat-cable trunks, I have seen only one noise-related problem, and that was with an unapproved power supply and untwisted power wires that ran 20 feet through the wireway past the output of Yaskawa drives.
 
Flat cable in itself is not a problem but mixing round and flat cables in a single system can be a nightmare. The main problem is ensuring contnuity of the shield between different segments of round cable. As a result we replaced all of our flat cable some time ago in the interests of a consistant plant wide approach.
 
We have done numerous startups on AB Intellicenter MCCs with devicenet factory installed. The MCC sections use flat cable throughout. We spec to run the latest thick round cable (Belden 7897A) from the Devicenet Scanner to the closest end of the MCC section. The thick round is easier to pull through conduit than flat. You just have to make sure the shield and DC- are jumpered together where the round meets the flat then shield is grounded to DNET power supply. After years of discovering what not to do, this is the best media configuration for us. No more wasted time troubleshooting media issues.
 
Inside panels and outside of machines with frames like skids or conveyors, the flat cable is great. I much prefer it over the round cable. The main reason, terminations. The flat cable connectors are rock solid and more water resistant than the round tees (get the ones with the o-ring). Just don't ever take one off once you've installed it.

I have used the thin cable inside panels in daisy chain and you spend a lot more time chasing bad terminations. It's ok if you only have a few devices.

The thick round cable is a PITA to terminate. Tee connector installation is tedious and must be done exactly as instructed. You'll still probably snap the net wires a few times before you get the hang of it. The cable is just so bulky and stiff. I'll never use it again unless forced to.

For making additions on the fly, nothing touches the flat cable. You can physically add connections while it is running. You still have to add devices to the scan list of course, but it can significatly reduce downtime during modifications.

Bottom line, real experience with all three says the flat is the easiest and most robust.
 
Last edited:
I have used the flat cable for a DeviceNet install behind a sulfuric acid pickling line and it has worked great for me. I also ran the flat cable for additional 24VDC power which I use to power DeviceNet Armor Block nodes. The advantage is if I need to add any thing I can just clamp down another vampire block. Never had any failures because of water or acid with the vampire connectors either.
 
I've got a few lines here each with a 600 foot run of flat cable, various limit switches and encoders along the way. To date, we've had no problems, even in a repetitive, medium vibration and sway application. I did drop the network speed down a notch though, but more to not have random headaches at night then any real need.
 
I'll jump on the flat cable bandwagon as well, working in a facility which has about 15,000 feet of it installed for nearly 10 years and working flawlessly. End devices such as armor blocks, bar code readers are constantly being moved around and the vampire connectors make this a breeze.
 

Similar Topics

Hi everyone, I’m constructing an electrical panel and I was wondering if 28 AWG Flat Ribbon Cables with 0.5 pitch ( 32 conductors ) will be able...
Replies
2
Views
1,432
Guys, It is about an AB ControlLogix 5555 processor communicating wth. a D-Net (Armor Block 1792D-8BVT8D) throgh a Flat Media Cable. Some of the...
Replies
1
Views
7,586
Hi All, Developing a new application and deploying a historian. In the past I mostly used the original Trend and had them setup with the...
Replies
4
Views
1,338
I’m using an AOI in a Rockwell PLC for a device but this older, (non-Archestra) version of Wonderware apparently doesn’t recognize “dot” tagnames...
Replies
3
Views
1,620
Hello, I was hoping you guys can help me with a issue I started having with trending from a Wonderware Historian Server The trending data just...
Replies
7
Views
3,484
Back
Top Bottom