Foundation Field Bus Wiring


Thread Starter



I have a small concern and I want to get your opinion on it.

We had a problem in the wiring for one of our instruments "Pressure Valve". In the “Relcom megablock” terminal number "2". We saw the wires for this one are switched. The “+” wire connect to the negative side and the “-“ wire connect to the positive side. Also, we checked the wires going to the valve itself and it were connected very well.
The big problem was the loop is working well without any trouble.

My question is, is there any explanation for this?
Is it normal with the Field bus foundation?

This is my first time experience with this technology.

I hope it's clear to understand.

Not all field devices are polarity-sensitive so the fact the device is working is not unusual.

You might however want to reverse the wires so that anyone doing maintenance/inspection on the installation in the future doesn't ask the same question again.

If you are new to Fieldbus technology, you can download some background reading material from our web site.

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Thank you Steve for replying to my message.

You said it maight be not polarity-sensitive.
How can I know this type is a polarity-sensitve or not? We are using this type "FCS-MB10-SG-T".
Anyway, can you explain this idea? How can it happen "the polarity-sensitive"?



To know whether an FF device is polarity sensitive, refer the manufacturer's manual. The method is to connect the device and try it out.

Even though a device is not polarity sensitive, it is not a sound practice to reverse polarities. Follow the polarity marking on the mega block as well as the device.
It is the Field Device that may or may not be polarity sensitive, you will need to check the Instruction Manual for whichever device you have. I checked a Beka Associates Fieldbus display and that has 2 terminals marked 1 and 2 rather than + and -, the manual clearly states that these are "non polarised".

I personally agree. It is more prudent to assume devices are polarity sensitive because many still are.

To learn more about fieldbus installation take a look at the yellow book "Fieldbuses for Process Control: Engineering, Operation, and Maintenance"
buy online:

Aha good point Steve
I didn't get it at the beginning.
Anyway, our field device at that time was Control Valve and the wires were connected to a Fisher Positioner that has + and - signs.
Also, the megablock has +, - , and shield signs.

Our FISHER type is DVC6010F.

I’ll look for the manual and hope I can find something.
Thank you so much, gentlemen.

I've just checked the manual for this postioner and it's not polarity sensitive as you said.

Thanks a lot again.

Anyone can tell me how polarity sensitive idea works?

I verified this idea for my problem, but still want more information about it.

Thanks in advance for any help.