Is a 300mA RCD main switch a requirement or recommendation on a 3phase DB with 30mA RCBO protection on the outgoing ways except for the fire panel feed and SPD?

Unless the building is part of an agricultural installation, or maybe a fuel depot or ammo dump, or in some other way an unusual fire risk, probably not a requirement to have the TD RCD at the incomer at all. But what makes you think there might be ? is there some other documentation or requirement you have been given ?
Customer and insurance requirements often have requirements that exceed minimal regs level ;-)

In terms of the SPDs, when they eventually reach end of life, the elements will go dead short circuit so something will need to clear that LN fault, but given the solid earth, a suitable fuse or MCB maybe just fine.

Is there anything special about the fire panel supply?

Mike.

Thanks for the reply. 

The building contains two separate sauna/steam rooms with wood fired boilers.  The DB is located in a third mechanicals room, so should be fairly well protected from the moisture in the rest of the building.  

There is ventilation makeup air ducts connecting the mechanicals room to the changing rooms, and since the changing rooms are adjacent to the steam rooms, when the sauna users go back and forth, the changing rooms get some steam in them.

The fire panel is a Morley Zx1se, connected to a campus wide fire panel network, so faults are monitored and if it lost power that would be noticed within a few hours even if the building was unoccupied.  The supply to the fire panel is all surface run, nothing special.

The project is in the design phase and the customer initially requested 300mA RCD main switch, but in discussions about pricing they couldn't point to a reg that made it mandatory to have that.

Regards 

Good afternoon; 

Is there any recommendation to have a 300mA RCCB main switch for fire protection for the distribution board itself?  The out going ways as described have the 30mA RCBOs, but in the unlikely event of moisture from the sauna / steam room making its way into the mechanicals room where the distribution board is, or a failure in the heating system pipework in the mechanical room that would result in water spray or steam, would an RCCB main switch limit the risk of fire in the panel?

Also, could the fire panel fail and initiate a fire itself, like if the batteries overheated, that a 300mA rcd might react to and prevent?

Or is an RCCB main switch still unnecessary in this scenario?

Regards,

If you're worried about ambient conditions then the incomer of the DB probably isn't the right place for protection - as it won't cover the incoming terminals or the RCCB itself - which is probably half of the highest current carrying components. I would have thought the usual recommendation would be to select equipment that was suitable for the conditions (or locate it somewhere else where the conditions are more favourable) - that's presuming there is a problem with the current location, which seems unproven at least so far.

Likewise if you needed a 300mA RCD for ADS (e.g. in TT systems) it would more likely want to go at the origin of the distribution circuit, rather than at the far end a few inches before the next tier of protection (the only common exception I can think of is where the system is TT and the DB is at the origin of the installation, and double/reinforced insulation can be provided for the incoming cables).

Secondary batteries can indeed overheat and go into thermal runaway (one place I worked had the lead acid battery in a UPS fail that way - it was spotted in time and left outside for a couple of days before it cooled down). If it gets to the point of frying the charger electronics it may wall get to the point of tripping the CPD - but by that point disconnecting the supply doesn't help that much as the energy from the fire is coming from the battery. The solution to that sort of thing really should be down to the equipment standard for the panel (possibly why many panels have reasonably substantial steel enclosures) - it only really becomes a supply side issue if the manufacturer's installation instructions call for additional protection - and if that were the case you might be better putting an RCD on the fire panel final circuit - so to have better discrimination  and not loose power to the whole building due to one small fault.

But if that's what the customer wants and the customer is willing to pay for...

   - Andy.

If you're worried about ambient conditions then the incomer of the DB probably isn't the right place for protection - as it won't cover the incoming terminals or the RCCB itself - which is probably half of the highest current carrying components. I would have thought the usual recommendation would be to select equipment that was suitable for the conditions (or locate it somewhere else where the conditions are more favourable) - that's presuming there is a problem with the current location, which seems unproven at least so far.

Likewise if you needed a 300mA RCD for ADS (e.g. in TT systems) it would more likely want to go at the origin of the distribution circuit, rather than at the far end a few inches before the next tier of protection (the only common exception I can think of is where the system is TT and the DB is at the origin of the installation, and double/reinforced insulation can be provided for the incoming cables).

Secondary batteries can indeed overheat and go into thermal runaway (one place I worked had the lead acid battery in a UPS fail that way - it was spotted in time and left outside for a couple of days before it cooled down). If it gets to the point of frying the charger electronics it may wall get to the point of tripping the CPD - but by that point disconnecting the supply doesn't help that much as the energy from the fire is coming from the battery. The solution to that sort of thing really should be down to the equipment standard for the panel (possibly why many panels have reasonably substantial steel enclosures) - it only really becomes a supply side issue if the manufacturer's installation instructions call for additional protection - and if that were the case you might be better putting an RCD on the fire panel final circuit - so to have better discrimination  and not loose power to the whole building due to one small fault.

But if that's what the customer wants and the customer is willing to pay for...

   - Andy.

Thank you Andy, 

That gives me a better understanding of my options for this installation.

Regards.