HELP! commercial socket with type D rated fuse

[Rockingit]

Thanks for everyone's reply, to people/person saying it should be rethought about, it's an office space very very small 40sqm at most! Computers, small kitchen etc. So yes a domestic board was fine it's just that they've decided to put a piece of machinery in after the whole installation that I have no clue about and just been asked by the builder that it needs to be type D 16a with a commando socket. It's very unusual industrial equipment would be put in an office which is why you wouldn't put a industrial board on. But everyone else has been very helpful. I'm still scratching my head through this one. I'm actually going to try a RCBO C CURVE 20A, and see how we get on if needs be then I think I'll go down the route of another board

Technically that will be non-compliant - you can't have a 20A CPD protecting a 16A rated connector. Personally, I'd look to see where this socket needs to end up and fit it at that point with a small 1 or 2 module DIN housing containing your RCBO or RCD/MCB combo for D16 and look up what my max allowable Zs is at that point. I'd then get out my tape measure back to the incomer and use the Ze and cable R1/R2 figures found in the OSG to calculate a feed cable size that complies before fitting a KMF type unit with an appropriate sized fuse (for a 5s circuit....) off some Henleys.

 

[loz2754]

Technically that will be non-compliant - you can't have a 20A CPD protecting a 16A rated connector.

What about a 20 amp radial with 16 amp socket outlets in section H3 of the OSG?
Of course, for one 16 amp socket outlet it's normal to supply it from a 16 OCPD, but it could be supplied from a 20 amp OCPD and still be compliant.
In any case, BS7671 makes no reference to 60309-2 socket outlets being protected by an OCPD, the primary purpose of which is to prevent overloaded circuit cables.

 

[Rockingit]

What about a 20 amp radial with 16 amp socket outlets in section H3 of the OSG?
Of course, for one 16 amp socket outlet it's normal to supply it from a 16 OCPD, but it could be supplied from a 20 amp OCPD and still be compliant.
In any case, BS7671 makes no reference to 60309-2 socket outlets being protected by an OCPD, the primary purpose of which is to prevent overloaded circuit cables.

512.1.2 states that EVERY item of equipment is capable of carrying the design load. I've never understood why it's written in the OSG as it is, and as someone who's had to prise apart many welded overloaded 16a connections over the years I stand by that! My guess is that it's following the logic that says that you have 13A sockets on a circuit fed from a 20 or 32A MCB, however they all rely on the plug fuses for protection whereas 60309 series devices do not have that. I believe the BS EN 60309 standard itself has commentary that the provision for multiple 16A outlets on a 20A radial relies on low loadings and diversity.

As such, in this deployment where the manufacturer is specifying a D-curve device which implies excessive in-rush currents and the possibility of momentary arcing, I personally wouldn't.

 

[pc1966]

I'm actually going to try a RCBO C CURVE 20A, and see how we get on if needs be then I think I'll go down the route of another board

For the small cost of the Fusebox RCBOs you could try the 16A C first and see if it is trip-happy or works OK?

If not then going to 32A C and separate 16A D-curve MCB would give you the same 320A-640A instant trip but with the 16A overload curve.