HELP! commercial socket with type D rated fuse

[charliespark]

Hi guys,

Rewired a unit where they make dentures, builder today has asked to install 16a commando socket with isolator (no problem) however stated the company fitting the machine has required a type D breaker, the whole board is RCBOs and the company 'Fusebox' is what I fitted the board with but they don't do type D. I know if I put in a MCB of another brand then it will be a C3 or C2 depending on who you are however I don't see an alternative other than to fit another small CU, but would that be tripping the RCD as its only rated 40A and these type D go 10 to 20 times the amps on start up? Also would I need to run this in some type of SWA or SY cable for the jump in Amps or would normal 2.5 T + E Suffice? I'm generally just Domestic so any help would greatly.be appreciated

 

[charliespark]

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

 

[charliespark]

I believe the maximum size of device for these boards is 40A, he is considering this to supply another board. I agree though never fit a CU considered domestic in a commercial setting.

Small office space no more than 40sqm. He has an adjacent unit, other sparks fitted exact same. All it's got is computers, sockets, small kitchen, lights etc. Don't think a commercial board would be necessary do you?

 

[charliespark]

I wasn't aware fusebox made any devices suitable for commercial installations, are you sure this is a suitable unit?


It doesn't matter who you are it will not be a C3 or a C2, it will be a non-compliant installation.
The C codes are only used for reporting on an existing installation on an EICR. They are not applicable to new works as new work should fully comply with the regulations (subject to any justifiable departures, which this would not be)

Mate it's a 40 sqm tiny office. Do you really think you need a commercial board In there? Every single other unit has a 4 way board. You could barely swing a cat around in it. It's sockets and lights basically. I didn't know they was putting in a machine at a later date. That was never discussed, just a builder saying it needs this and that as they usually do without knowing its very complicated and that can't be done just like that. But thanks for your help

 

[charliespark]

Bad news, Fusebox don't make a 16A D-curve MCB.

One option would be to use a Fusebox 32A C-curve RCBO in the main CU and then add a 16A D-curve MCB in a separate DIN box so you avoid the issue of non-matching manufacturers. Not ideal in terms of fault selectivity, but if they are both adjacent to each other and not serving multiple circuits then not too hard to rest both if needed.

Thanks this has really helped

 

[DefyG]

Had a similar problem with some pumps where manufacturer specified D type breakers which for the existing DB were unobtainable so agreed to try C type before upgrading/adding to switchgear. They worked fine without tripping on start so were left in circuit.
You may find C type will satisfy the connected load there without upgrading the installation further?

 

[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.