Intrinsically safe circuit - surge protector

[nhee2]

A field installation has an intrinsically safe RS-485 communications circuit to a field mounted device. The proper IS barrier meeting the requirements of the control drawing is installed at the panel (non-hazardous) end of the circuit. At the field end (I.S.), a passive (non-powered) data line surge suppressor is installed.

The control drawing for the field device doesn't include any provisions for the surge suppressor - even though it is passive, does it need to be explicitly identified on the control drawing for it to be consistent with the approved configuration?

 

[petersonra]

A field installation has an intrinsically safe RS-485 communications circuit to a field mounted device. The proper IS barrier meeting the requirements of the control drawing is installed at the panel (non-hazardous) end of the circuit. At the field end (I.S.), a passive (non-powered) data line surge suppressor is installed.

The control drawing for the field device doesn't include any provisions for the surge suppressor - even though it is passive, does it need to be explicitly identified on the control drawing for it to be consistent with the approved configuration?

I would say yes.

PS you can't just move it to the other end of the wires either.

 

[nhee2]

yes, I agree, that is how I was leaning. This seems like one of those scenarios where the surge suppressor doesn't negatively change the circuit, but since it is not listed it can't go there. although I wonder if the MOVs or zeners or whatever is in the surge device would affect time-response of the barrier.

 

[paulengr]

yes, I agree, that is how I was leaning. This seems like one of those scenarios where the surge suppressor doesn't negatively change the circuit, but since it is not listed it can't go there. although I wonder if the MOVs or zeners or whatever is in the surge device would affect time-response of the barrier.

MOVs are ineffective at low voltage. It will be a PIN or fast recovery diode or a GDT or spark gap. Of those the diodes have some capacitance so technically a violation but it’s so small I’d ignore it. The spark gap is obviously a bad idea. That leaves the good old telco GDTs (gas discharge tube) which is essentially a hermetically sealed spark gap and what you probably should use since it won’t violate IS since there is no stored energy.