Difficult to provide general advice on this, because of detail and nuance, so I'll have a go by making some general observations and referencing standards from where requirements can help address the detail for a specific building.

Peter Read said:

We have a natural smoke vent system on a project where the main supply cable to the SVCP has been taken from a local DB and wired in SWA. These systems have a 72 hour back up for the life safety element and all power & control cabling from the inverter is wired in FP200. However, the AOV contractor has just informed us that the main supply should also be wired in FP and afford the appropriate protection.

What if the inverter fails, and there's a fire? n this case if the primary supply is not protected against fire, the system can't act as designed? Clause 37.2.3.1 of BS 9999 says that protection is necessary for the primary supply too.

The relevant references for supply to safety services are Clause 15.7 and Section 37 of BS 9999, and Chapter 56 of BS 7671.

Peter Read said:

My question is should the main supply be installed in FP from the main panel board or can the protection be from just the local DB, bearing in mind that should the system 'fall over' the battery system will still give 72 hours of protection. Any insight would be appreciated.

See Section 37 and Table 29 (item 21) of BS 9999, Chapter 56 of BS 7671

Generally, safety services requires substantially separate distribution from other electrical services (see BS 9999 Clause 37.2.3.2)

Overall, though, for a given building, a competent person ought to have a fire risk assessment of the premises which details the relevant measures to be taken?

Difficult to provide general advice on this, because of detail and nuance, so I'll have a go by making some general observations and referencing standards from where requirements can help address the detail for a specific building.

Peter Read said:

We have a natural smoke vent system on a project where the main supply cable to the SVCP has been taken from a local DB and wired in SWA. These systems have a 72 hour back up for the life safety element and all power & control cabling from the inverter is wired in FP200. However, the AOV contractor has just informed us that the main supply should also be wired in FP and afford the appropriate protection.

What if the inverter fails, and there's a fire? n this case if the primary supply is not protected against fire, the system can't act as designed? Clause 37.2.3.1 of BS 9999 says that protection is necessary for the primary supply too.

The relevant references for supply to safety services are Clause 15.7 and Section 37 of BS 9999, and Chapter 56 of BS 7671.

Peter Read said:

My question is should the main supply be installed in FP from the main panel board or can the protection be from just the local DB, bearing in mind that should the system 'fall over' the battery system will still give 72 hours of protection. Any insight would be appreciated.

See Section 37 and Table 29 (item 21) of BS 9999, Chapter 56 of BS 7671

Generally, safety services requires substantially separate distribution from other electrical services (see BS 9999 Clause 37.2.3.2)

Overall, though, for a given building, a competent person ought to have a fire risk assessment of the premises which details the relevant measures to be taken?