MTL FNICO Power Supply, Live-work on trunk

[Vettori]

Hello

We are into automation field. One of our customer want to use FNICO concept in Zone 2 (IIB) for few segments. We proposed MTL FNICO PS solution, wherein live-work on both trunk & spur is possible.

Surprisingly, MTL 9112-NI datasheet shows certification code as -
II 3 G EEx nA[L] IIB T4, which means trunk is rated nA and spur (associated appartus/device - in bracket) is nL certified. If so, how live-working on trunk is possible, as it's rated nA?

[aagostin]

What makes you believe the trunk is nA and the spur is nL?
This is the certificate of the FNICO supply, not a megablock, and not a segment consisting of supply and megablock.
nA relates to the electronic of the supply (meaning you can put the unit into Zone 2), and [nL] refers to the associated apparatus, meaning the wire that comes out of the FNICO supply. And so far, the wire that comes out of the FNICO supply is a trunk, and not a spur. So the trunk is nL, and hence also the spurs, once you connect spurs to the trunk.

[IanVerhappen]

To add to what Andreas states above, Spurguard is intended to protect against a short circuit on a single spur from causing the entire Fieldbus segment to short (because FF is wired in parallel). If however you are asking about Surge protection, then this is certainly on a case-by-case basis.

[Mike ONeill]

The surprise is that you think that working on the trunk 'live' is a 'good' idea - you would disconnect or disrupt every device on that segment to what benefit.
Far better advice is to accept that, in reality, working on a live trunk is not feasible and to then step away from the outdated and inefficient FISCO/FNICO package supported by (only) MTL and move to the high power trunk design supported by everyone else (and MTL). In this design, you can have the highest segment capacity/best supply performance, and mix any combination of I.S./FISCO/Entity/Exn/Exe/Exd devices that you need.