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

 

[nicebutdim]

You are where you are with this and while fusebox might not be the ideal choice for a commercial application, I'm not sure why you wouldn't split the incoming tails to fit another small, suitable board?

I'm guessing the RCD rated at 40A isn't fitted upfront?

Edit: just read op again and see that you've fitted a full rcbo board. Where exactly is the 40A rcd?

 

[westward10]

You are where you are with this and while fusebox might not be the ideal choice for a commercial application, I'm not sure why you wouldn't split the incoming tails to fit another small, suitable board?

I'm guessing the RCD rated at 40A isn't fitted upfront?

Edit: just read op again and see that you've fitted a full rcbo board. Where exactly is the 40A rcd?

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.

 

[pc1966]

You will be hard pressed to find anyone who makes D-curve RCBOs, realistically your best bet is a 16A D MCB and then an RCD in either a separate enclosure, or if plenty of spare ways in the CU, it can go in there.

You only need the RCD's current rating to exceed that of the MCB's thermal trip (i.e. 16A here). Under hard fault conditions the RCD typically can break 1-1.5kA so you also need the MCB to be breaking before that point on the magnetic trip (which is almost always the case as 50A * 20 = 1kA, 63A * 20 = 1.26kA)

Same for the cable, it need only be rated for the MCB's rating (i.e. 16A under installed method). With a RCD you have very little to worry about in terms of Zs for disconnection.

 

[nicebutdim]

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.

They offer a 50A SP RCBO, which gives more headroom, but still likely to be taken out by inrush current through a 16A type D.

 

[pc1966]

I would add though that the I2t let-though of a D-curve MCB might be a bit high for something as weedy as 1.5mm T&E (1mm CPC) which meets 16A usually. So you might want to use at least 2.5mm T&E (1.5mm CPC) or look at something with 2.5mm CPC as well, for example NYY-J

Edit: Also note many places will sell you NYY-J by the metre which keeps cost down if you know what you need. And a little extra, the one thing more expensive than buying too much cable is buying too little!

 

[davesparks]

the whole board is RCBOs and the company 'Fusebox' is what I fitted the board with but they don't do type D.

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

I know if I put in a MCB of another brand then it will be a C3 or C2 depending on who you are

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)

 

[pc1966]

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.

 

[ipf]

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.

I too agree but isn't it a bit difficult getting hold of a single phase industrial Con Unit these days, with 10k rated c/b's? Even Schneider are 6k. (and not in the same class as the 10k gear, nor the same price range).
We just used to use metal clad CU's but these days.....
Could get a 3 phase and convert to single but it seems a bit over the top.
Solve the D type problem though.

 

[Risteard]

You will be hard pressed to find anyone who makes D-curve RCBOs, realistically your best bet is a 16A D MCB and then an RCD in either a separate enclosure, or if plenty of spare ways in the CU, it can go in there.

You only need the RCD's current rating to exceed that of the MCB's thermal trip (i.e. 16A here). Under hard fault conditions the RCD typically can break 1-1.5kA so you also need the MCB to be breaking before that point on the magnetic trip (which is almost always the case as 50A * 20 = 1kA, 63A * 20 = 1.26kA)

Same for the cable, it need only be rated for the MCB's rating (i.e. 16A under installed method). With a RCD you have very little to worry about in terms of Zs for disconnection.

Many commando sockets have DIN rail for an RCCB (assuming installation method permits of course).

 

[davesparks]

I too agree but isn't it a bit difficult getting hold of a single phase industrial Con Unit these days, with 10k rated c/b's? Even Schneider are 6k.

I've not had any difficulty getting them, they are on the shelf at the wholesalers.

I use schneider and the MCB's are definately 60947/60898 dual rated 10kA devices

 

[Rockingit]

Sounds to me that this whole thing needs a rethink and that the results of that thinking is that inappropriate equipment has been used so far and will need replacing. It may also decide that the Zs for a D type radial is un-achievable for standard ADS which may place other considerations on reliance of an RCD for protection.

 

[ipf]

I've not had any difficulty getting them, they are on the shelf at the wholesalers.

I use schneider and the MCB's are definately 60947/60898 dual rated 10kA devices

Course, the acti9.

 

[loz2754]

isn't it a bit difficult getting hold of a single phase industrial Con Unit these days, with 10k rated c/b's?

Ask for a single phase distribution board, not a consumer unit (which is made primarily for the domestic market).

 

[ipf]

Ask for a single phase distribution board, not a consumer unit (which is made primarily for the domestic market).

As above, cheers.