Macgyver-ing DeviceNet

I show up on site today to commission a smalll DeviceNet network, only problem is instead of Devicenet cable, cat6 ethernet cable was run. Seems like it will take two weeks to get the spec'd cable on site from Allen-Bradley. So my question is do i need this cable or will other cables work; i.e. 4-wire shielded "belden" cable, cat-6 cable, linked paperclips, rubber bands, etc? I'm not looking long distances here, tying in 3 vfds that are 10ft away from the PLC.

Try it and tell us.

Any reputable cable supplier should be able to supply "DeviceNet" spec cable, you don't have to buy it from Allen-Bradley.

Don't forget you can use the "Thin" cable for the trunkline, it just limits the current capacity to 3A, and for short runs inside enclosures it can look neater.

And don't forget the 120ohm terminating resistors at both ends of the trunkline.

BillRobinson said:

I show up on site today to commission a smalll DeviceNet network, only problem is instead of Devicenet cable, cat6 ethernet cable was run. Seems like it will take two weeks to get the spec'd cable on site from Allen-Bradley. So my question is do i need this cable or will other cables work; i.e. 4-wire shielded "belden" cable, cat-6 cable, linked paperclips, rubber bands, etc? I'm not looking long distances here, tying in 3 vfds that are 10ft away from the PLC.

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I wouldn't recommend it, as Ethernet Cable is not shielded as a general rule. I am not sure if Cat 6 is though. As Daba pointed out, Termination Resistors are mandatory. The Thin Cable should be fine for that length. The Devicenet Cable we use here is Belden, and is available from a number of sources. I generally use the Thick Cable for Trunk lines, and put a Tap in each Cabinet, and then use the Thin Cable from there on.

Stu....

From a signal standpoint, I'd give it a 75% chance of working well enough to start the drives, and a 50% chance of handling the induced noise from the drives.

I have two warnings in the "can't hurt to try" category:

1. Even DeviceNet thin cable has 22 AWG wire for the power pair and as a Class 2 current-limited circuit is rated for only 3A. Category 6 twisted-pair cable is typically 23 or 24 AWG, so depending on how it was installed you might have to put a very small overcurrent protection fuse in place. For a load of only a few hundred milliamperes this might work, depending on how closely it is inspected. For my own peace of mind I would put in a 1 A fuse.

2. A more general warning: If you make this work, you decrease the probability that the contractor will supply the proper cable, and increase the probability that they'll make the same mistake again.

Maybe I'm having deja-vu from an infamous "Show us where in the spec it says we can't use wire nuts" project.

So when they say "I doesn't say we can't do it" is that a bad sign? I told them that my performance standard would be compromised and so they have a light warranty. When my taillights are gone so is the warranty. They changed their attitude.

JeffKiper said:

So when they say "I doesn't say we can't do it" is that a bad sign? I told them that my performance standard would be compromised and so they have a light warranty. When my taillights are gone so is the warranty. They changed their attitude.

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Many places tell you the spec for DeviceNet cables...

You can probably get away with any shielded cable especially for short distances. In a bind I once used shielded thermocouple extension cable and it worked well.