3A MCB/RCBOs

[mikhailfaradayski]

Any idea why such an animal isn't readily available for the domestic market?
I know they are produced by a few manufacturers, but they seem to be a bit like rocking horse plop when I talk to local suppliers.
Given the modern way of splitting up a domestic install into greater number of parts coupled with some appliances requirement (from MIs) to be protected at 3A, i really am surprised that most if not all CU manufacturers have not jumped on the band wagon.

Or am i missing something?

 

[Taylortwocities]

The CPD is supposed to be there to protect the fixed cable installation, not the appliance at the end.

So 6amp for 1.0mm cable
20amp for 2.5mm cable etc.

If you need to comply with MIs for a 3amp protection then you installan FCU or a plug with a 3amp fuse at the end of the fixed wiring.

Meerkat

• Taylortwocities
• 11 Dec 2009
• 53

 

[holmslaw]

..

 

[mikhailfaradayski]

I guess that means the designers at MK and ABB are utter idiots for designing stuff which has no purpose?

no so

Meerkat

• Taylortwocities
• 11 Dec 2009
• 53

Seriously though, I have personally seen a few situation where having a 3A trip would have been easier and neater than faffing around installing an ugly FCU

 

[holmslaw]

..

 

[mikhailfaradayski]

Because the minimum size cable used for circuits is 1.00mm. As its rating is above 6 Amps there is no point in having a lower value fuse/mcb.

I can see how a lot of people would think that, but maybe the logic is a bit back to front.
As a 5/6A fuse/trip is the smallest commonly available size that would be installed in a CU, it make 1mm cable the smallest csa that could be safely connected. If a 3A trip was available, then its conceivable that a 0.5/0.75mm cable could be connected directly into the CU(not taking rating factors into account)

In this age of low energy everything, it may be a way forward

 

[mikhailfaradayski]

But you can't just do away with a fcu as it also functions as the local isolator.

agreed, that may be the case in some situations, but I can't disregard what my own eyes have seen which has led me to think about it.
1 example - cooker ext. hood calls for 3 amp fuse - the usual stuff. Does not say DP switching. CU is in kitchen, 3ft away from ext.hood. Nowhere nice to put an FCU, except high on wall over kitchen units. Customer needs to stand on a stool to reach CU, no problem, but she can't reach that height of wall over kitchen cabs due to the distance away from the wall of the stool (due to base cabs)
If a 3A MCB had been available, it would have been just lovely

 

[JohnW2]

Any idea why such an animal isn't readily available for the domestic market?

TLC are currently offering an MK B3, with no indication that it is not in stock.

Kind Regards, John.

 

[JohnW2]

Given the modern way of splitting up a domestic install into greater number of parts coupled with some appliances requirement (from MIs) to be protected at 3A, i really am surprised that most if not all CU manufacturers have not jumped on the band wagon.

One problem .... as we've seen, some people feel that they have to be incredibly pedantic in obeying the letter of MIs. There are a good few things for which the MI explicitly require connection via 'an FCU with a 3A fuse', and I've never seen one which says that this requirement is waived if the circuit is protected by a 3A OPD!

Kind Regards, John.

 

[mikhailfaradayski]

Any idea why such an animal isn't readily available for the domestic market?

TLC are currently offering an MK B3, with no indication that it is not in stock.

Kind Regards, John.

Yep, spotted them, but there not local, not same day availablity, not cheap when you throw in delivery cost, not a great deal of use if you abide by the whole type testing issue with mixed CPD and you are not working with an MK board.

Now try the same search for RCBO's. It gives slim choice (some C curve, but not much B)

 

[mikhailfaradayski]

..../snip/... There are a good few things for which the MI explicitly require connection via 'an FCU with a 3A fuse', and I've never seen one which says that this requirement is waived if the circuit is protected by a 3A OPD!

Kind Regards, John.

Can you see any sound engineering reason why that should not be the case?

Do you think the wording has come from lack of availablity of such an MCB? Or maybe the manufacturers find it easier to be complacent, not have to think about it and bother to have their documents up-dated? (On occasion, I still see reference to the 16th ed)

 

[JohnW2]

Can you see any sound engineering reason why that should not be the case?

Definitely not.

Do you think the wording has come from lack of availablity of such an MCB? Or maybe the manufacturers find it easier to be complacent, not have to think about it and bother to have their documents up-dated?

I suspect the latter.

Kind Regards, John.

 

[JohnW2]

Yep, spotted them, but there not local, not same day availablity, not cheap when you throw in delivery cost, not a great deal of use if you abide by the whole type testing issue with mixed CPD and you are not working with an MK board.

Fair enough - I was merely answering your question, as written - without any qualifications about make, delivery times and delivery costs

Now try the same search for RCBO's. It gives slim choice (some C curve, but not much B)

I know - I had a quick look. I'm not sure that poor availability of Type B ones is much of an issue - the Zs requirement for a C3 is hardly demanding.

Kind Regards, John.

 

[phatboy]

I would think another good reason to have a 3amp MCB or RCBO would be for a smoke detector circuit.... 5amp for a couple of smoke alarms is excessive, and I don't think there was a fuse in the detector!

 

[EFLImpudence]

Can you see any sound engineering reason why that should not be the case?

There is none.

Do you think the wording has come from lack of availablity of such an MCB?

No. It is totally irrelevant and pointless.

Or maybe the manufacturers find it easier to be complacent, not have to think about it and bother to have their documents up-dated?

Perhaps, but was it ever necessary? More likely ignorance or the 'May contain nuts' syndrome.


Also, if kai's post in another thread, saying that the manufacturer of his immersion element demands a 13A SFCU, is truly the case then 134.1.1 will have to be amended and preceded by "If necessary" or, logically, deleted.