Can I use Cat-5 for DH-485 cable?

[brstilson]

Here's the application:

I'm have Panelview 600 with two 485 ports I'm moving. On the Panelview there's a big connector like what's on the PIC box, and an RJ-45 connector. I'm running a cable from the big connector to the port on a SLC 5/03, but I think I'm going to need to lengthen the cable coming from the RJ-45 connector, which goes to a programming port on the side of the main panel (that's not moving). Can I use Cat-5 cable for this?

 

[Bit_Bucket_07]

I'd recommend a twinaxial cable with a characteristic impedence of 120 ohms, but CAT5 cable will most likely work -- especially if you aren't pushing the distance and/or baud rate limits.

 

[brstilson]

I'd recommend a twinaxial cable with a characteristic impedence of 120 ohms, but CAT5 cable will most likely work -- especially if you aren't pushing the distance and/or baud rate limits.

I'm not. We're talking a 20 foot run at the most, that will only be used on an extremely rare occassion (uploading/downloading/getting online)

 

[Bit_Bucket_07]

CAT5 is a twisted pair cable with a characteristic impedance of 100 ohms, so it isn't very far off of spec for RS485.

 

[TConnolly]

I've done it with the UIC, but only with a short 1 meter cable. Make sure the cable is not a cross-over. Don't use a pre-made CAT5 enet patch cable. These have crossed over pairs in them. If you are making up your own then it will probably work.


Edit to add: As a matter of practice, where ever I have a DH485 port using an RJ45 connector I put a big sticker next to the port that identifies the port and includes a do not plug in Ethernet warning. If someone comes along and plugs their laptop ethernet port into the DH485 port the laptop Ethernet port will loose and will be permanently damaged.

 

[Ken Roach]

I read this carefully and I agree that CAT5 twisted-pair cable is OK for this purpose as long as it's connected 1:1 and you don't plug anything other than a 1747-PIC or 1747-UIC into it.

This is a good time to add a label indicating that the plug is not Ethernet !

Remember that the "Peripheral" port on a DH485 device like a PanelView or a 1747-AIC has +24V DC on Pin 3... more than a few Ethernet ports have been smoked when people plugged into it with the wrong device.

 

[BobB]

I would suggest you use screened CAT 5.