Proper lightning/surge protection of fieldpoint network

[bob_miller]

I am in the process of adding a second, remote, FP1001-based node located
2000 feet away from my existing cFP2020-based node. Communication will be
via RS-485 over buried cat5e. Additionally, this second node will acquire 4-20mA
data from a two-wire pressure sensor located a third location 1000 feet further
away, loop-powered off of this fieldpoint's PS-4 power supply. All fieldpoints and
transducers are inside buildings.

I am concerned that I properly protect all fieldpoint hardware from lighining-induced
surges. To this end:

1) Both fieldpoint nodes' 120VAC power is fed through industrial surge protectors.

2) I plan to install appropriate industrial surge protection devices at both ends of the 2000 foot
    RS-485 link between the fieldpoint unit

3) The two-wire 4-20mA link will also have industrial protection devices designed for 4-20ma loops
    at both the fieldpoint end and at the transducer end (the connection will be made via one pair of
    another buried cat5e line).

All protection devices will be robustly bypassed to the local ground.

Is this scheme adequate? Should I be independently powering the remote sensor? Any
additional recommendations or corrections? Lightning is a significant risk in this 7000-foot
Colorado location (Got a hit in my backyard yesterday).

If it matters, the planned protection devices are MTL ZoneBarrier devices.

Bob

[Otis]

Hi bob,

First off, here are the specs for the FP-1001 (see Appendix A).

As far as other recommendations go it won't necessarily be anything specifically related to FieldPoint and just general information that you would need to know for isolating any sort of instruments.

• You may want to contain the FieldPoint controller in an shielded and grounded box of some sorts.
• Keep leads as short as possible to avoid the leads from getting too much noise or being susceptible to strikes.
• If those leads can be struck try to isolate the leads or try to arrange them so that they are less likely to be struck.

If anybody else has dealt with a system that is similar feel free to reply and let Bob know what you did and how you did it.

Regards,

[bob_miller]

Thanks for your reply; your suggestions are good -- so good I was already doing them

The connection distances are unfortunately unavoidable; this installation is monitoring and controlling
a small drinking water plant and its associated distribution system with remote tanks, pumps, valves,
etc. But the connections are all buried (the neighborhood all pitched in with shovels and railroad picks
and a backhoe last summer) and the fieldpoints are all in grounded steel control boxes.

My data-gathering has suggested that a lightning strike anywhere near one of the three building
locations could generate a transient ground surge between the sites of up to several thousand volts;
hence the concern about additional surge protection and proper location and installation of this
protection on any wires linking these sites' fieldpoints and/or sensors.  The FP-1001's rs-485
isolation is probably not good enough to rely on alone and the cFP2020's isolation will be inescapably
defeated by the need for rs-485 biasing not built-in.

I would have gone wireless but none of the three sites has line-of-sight to either of the other two --
and antennas are themselves lightning targets...

The general philosophy about lightning protection seems to be "protect for the near misses and try to
prevent a direct strike; a direct strike will fry everything!"... But I want to make sure I don't overlook an
unnecessary vulnerability due to my lack of experience with this problem.

Bob