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RS485 Modbus cabling

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Mick Jefcoate

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A question on RS485 Modbus cabling on electrical meters. We are progressively connecting the Modbus cable to 3Ph Ct meters which will be powered up as we go. The next point may have a short line to line or screen as it is a cut cable.

Can anyone tell me if it is usually an issue for RS485 if it has a short circuit between lines or screen ?

I know it operates from around -5 to +12vdc and the meters have galvanic protection to 4Kv but this is for transient spikes.

Any help appreciated.

Mick
 
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A short to screen is usually a problem, depending on setup......RS485 consists of...Data in...Data out..+5v...and ground/screen. If the screen is shorted to any data line, then data is not transmitted.
 
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Rs485

tazz said:
A short to screen is usually a problem, depending on setup......RS485 consists of...Data in...Data out..+5v...and ground/screen. If the screen is shorted to any data line, then data is not transmitted.
Click to expand...

Thanks Tazz. Should have stated that the system isn't collecting data. This is more from a view of if damage might occure to any connected meters or equipment.
 
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Agree with Tazz - obviously if a data line or power supply line is shorted to either the screen or another line then it ain't gonna work.
I don't understand why you say it 'may have a line to line or line to screen short'. Surely if the cable is damaged it will be replaced?? Am I missing something? Daz
 
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DPG said:
Agree with Tazz - obviously if a data line or power supply line is shorted to either the screen or another line then it ain't gonna work.
I don't understand why you say it 'may have a line to line or line to screen short'. Surely if the cable is damaged it will be replaced?? Am I missing something? Daz
Click to expand...

Yep, this is a new install of RS485 modules into a mixture of new and existing Socomec meters. Each location requires us to finish the cabling and connections completely and power the meters up, but because it is a large job over quite a few nights, the new cabling may have a short because it is just a cut off end. Data collection is not an issue here.

Mick
 
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Ah, with you now! Must admit I don't know how resilient RS485 is to shorts whilst power is applied. It might be wise for you to do a bit of Googling. Daz
 
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