electricalforum.nz

"2.6.2.3 Protection against initiation of fire
Although not a mandatory requirement of this Standard, to provide
additional protection against the initiation of fire caused by current leakage
across insulation, a Type S RCD with a rated residual current in the range
100 mA to 300 mA may be used as a main switch in a domestic electrical
installation, in addition to the requirements of Clause 2.6.3.
NOTE: Protection is not afforded to separated circuits typically used for extra-
low voltage (ELV) lighting or against the initiation of fire from equipment
operating at elevated temperatures."

Has anyone actually installated or used such a device? Anyone with knowledge around this is it something that would be worth it for the customer?

Never used one, but from what I understand they are usually rated for 100mA and suited towards the protection against fire. They are not suitable for personal protection (like the A, B, II type) as they have a built in time delay to allow for nuisance tripping.

Off the top of my head, I think the delay is still within the time requirement for personal protection, but obviously the 100mA doesn't comply.

The longer delay of Type S is for discrimination purposes, with the downstream RCD closest to the final subcircuit providing the personal protection required by ESR 2010.

The use of a 300 mA RCD can in most circumstances also provide discrimination between the upstream and downstream RCDs.

Yes the RCD closer to the load will provide the personal protection, but for things like mains and submains, anything other than a 30mA RCD won't comply as a protection method for the cabling, so mechanical protection would still be required.

So I understand this solution is for fire protection mainly and is not one that is commonly used by the sounds of it. Anyone have any idea how they stack up vs AFDDs? Is one better suited for the purpose? Would using them in conjunction provide even better protection or would one effectively make the others purpose redundant?

All the AFDD devices I have seen are only rated at 25 A max and you need one for each final subcircuit.

Whereas an RCD can have a higher current rating and can be applied to multiple final subcircuits with a single RCD.

All the AFDD devices I have seen are only rated at 25 A max and you need one for each final subcircuit.

Whereas an RCD can have a higher current rating and can be applied to multiple final subcircuits with a single RCD.

I see, so the Type S RCD could provide an option that can be provided to a whole installation where as AFDDs are more suited to individual subcircuits

Does anyone know if this clause comes as an AS/NZS thing or is it taken from the IEC standard that 3000 is based on?

You have already shown the clause about an RCD as a main switch above.

There is some information about AFDDs in 3000:2018 appendix O

Otherwise, possibly manufacturers information?

I'm pretty sure that the way they operate, won't provide protection if they were used as a main switch.

The only way to get reliable discrimination between RCDs is by having a time delay (ie upstream device is Type S). That's because RCDs do not limit the current, they only react to it; and the max trip times for any Type of RCD do not vary depending on residual current rating - an 100 mA Type A must still operate within the same 0.3 sec as a 30 ma Type A.
True if the residual current was , for example, 40 ma, a downstream 30 mA unit would operate while an upstream 100 mA wouldn't, but we have zero control over what the residual current will be in any particular circumstance. And for a direct contact on 230 V, the fault current will be in order of 230 mA; enough to trip both so no reliable discrimination.

An AFDD can be used for one or several circuits, provided the max demand for the group is no more than the current rating of the AFDD. The fact AFDDs are not available above 25A limits their suitability as main switches; and in any case you do not want the entire installation blacked out due to one fault.
Same applies to RCDs

The 25 A 'limit" is simply because you can only fit so much stuff into the standard 2-module (36 mm) format, and for higher ratings everything has to be bigger.

Some AFDDs have an overcurrent function. Just as an RCBO combines RCD & overcurrent functions, these AFDDs have dual function AFDD + overcurrent. These AFDDs can be used without an mcb - but as all overcurrent devices are DMRAs and DHRAs, they need both SDoC & Approval.

Most if not all AFDDs have a 100 mA or 300 mA RCD function built in, so there's little point having an upstream RCD as well.

At some stage I would expect triple-function (overcurrent, 30 mA RCD, and AFDD) to be available, but not aware of any yet. and again they would need SDoC & Approval for both the personal protection and the overcurrent functions.