Discuss Why does AFDD protection need to be per circuit? in the UK Electrical Forum area at ElectriciansForums.net
True and I absolutely agree with maximising selectivity for minimising inconvenience during a fault and facilitating easy fault finding, but I was under the impression that AFDD protection HAD to be per circuit?Probably for the same reason RCBOs are preferable to split RCD boards... we should be looking to minimise disruption in the event of a fault. Plus, it makes fault finding a hell of a lot easier if you know which circuit you're looking at to begin with.
Thanks for this SparkyChick, So its confirmed then, the regs definately want us to install per circuit, but I just wonder why? Is it purely to do with Selectivity or is there a more practical/technical reason for it?And.....
421.1.7 Arc fault detection devices conforming to BS EN 62606 are recommended as a means of providing additional protection against fire caused by arc faults in AC final circuits.
If used, an AFDD shall be placed at the origin of the circuit to be protected.
NOTE: Examples of where such devices can be used include:
• premises with sleeping accommodation
• locations with a risk of fire due to the nature of processed or stored materials, i.e. BE2 locations (e.g. barns
woodworking shops, stores of combustible materials)
• locations with combustible constructional materials, i.e. CA2 locations (e.g. wooden buildings)
• fire propagating structures, i.e. CB2 locations
• locations with endangering of irreplaceable goods.
What SC saidFrom the regs:-
532.6 Arc fault detection devices (AFDDs)
Where specified, arc fault detection devices shall be installed:
(i) at the origin of the final circuits to be protected, and
(ii) in AC single-phase circuits not exceeding 230 V.
Very good point. At the origin of the circuit is positioning, not Selectivity Light bulb moment!RCD's are also at the "origin of the circuit" I don't take that as necessarily individual to each circuit. It may be more to do with the operation of the device itself, but cannot see why split load AFDD's would not work
Sorry don't understand?So you would not protect the sub main circuit to a barn but would protect the individual final circuits from the barns consumer unit??
Just reading all of this topic I’ve been installing new CCU’s since 18th came into force and noticed couple of changes one being the new rcds have an earth fault indicator on the rcds another being the Rcd trip times on the Hager fuse boards are rather high although complient typical values are x1 89.5 and x5 40.0 these readings are far higher than the old Hager fuse boards which i typically would get x1 19.8 x5 10.5 these are just averages but changed dramatically since the new fuse boards came outIt is possible that multiple circuits may have too much noise on them, the unit has to decide what is an arcing fault and what isn't, take your vacuum motor or fridge, it needs to know the arcing on the brushes is not a fault so I expect the more it is looking at the harder it is and possibly nuisance tripping thus follows.
This is my theory anyway, don't take it as gospel but it would make sense.
that would mean all of us having to replace our MFTs with ones that do 200-250mA instead of 150mA.Hager released a memo on their required test currents. Need testing at 200 or 250 mA for 5x I think from memory
Use the VAR setting. Sad but truethat would mean all of us having to replace our MFTs with ones that do 200-250mA instead of 150mA.
VAR? what's that?Use the VAR setting. Sad but true
It’s the variable setting on your MFT to allow you to select desired trip test current.VAR? what's that?
Reply to Why does AFDD protection need to be per circuit? in the UK Electrical Forum area at ElectriciansForums.net
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