- Joined
- 11 Jan 2004
- Messages
- 42,735
- Reaction score
- 2,633
- Country
But Ban likes arguing semantics, so let's go for it! 
Four Double Sockets on a 10A Radial.
- Thread starter APHSLTD
- Start date
Sponsored Links
True - but I think I'll leave that to you, should you feel that it's worth pursuingBut Ban likes arguing semantics, so let's go for it!
Kind Regards, John
As for the 2nd one - you frequently point out that DNOs do not work to BS 7671.
No, because that should not be used if the load is going to be greater than 13A, and it should not be used in order to ensure that a load (not a fault) of >13A gets disconnected.
No, it comes down to what 433.1.1 says, not to a study of meaning.
Sponsored Links
As I recently wrote, is that not one of the ways in which the 13A fuse prevents the cable being overloaded? Whilst one should not design, say, a fused spur from a ring final for a load which one thinks is 'likely to' exceed 13A, the designer obviously has no way of ensuring that loads totalling >13A will never be plugged into the sockets, so the fuse serves to protect the cable should that (deemed 'unlikley') situation ever arise.
Kind Regards, John
Stupid posts like that don't exactly help
433.1.1 merely says that the design current of a circuit should not exceed the In of the OPD. As I've just written, in the absence of a crystal ball, a designer who bases his/her design current on the belief that the current 'is not likely' to exceed In (13A fuse in the case under discussion) can (in the case of a sockets circuit) never be certain that this load will never be exceeded - hence the OPD will operate if that 'unlikely' scenario comes to pass.
In reality, it's difficult to see how a designer really can often be very confident that the load on a multiple-socket fused spur is unlikely to ever exceed 13A!
Kind Regards, John
If he is not confident then a 13A fused spur is clearly an inappropriate design.
Yes, of course a socket circuit has uncertainties, but in this case the OP has not designed a standard A1/A2/A3 circuit - he has struck out anew and created a new design.
Ib ≤ In ≤ Iz
You do not chose the value of In as a way to limit Ib.
Yes, of course a socket circuit has uncertainties, but in this case the OP has not designed a standard A1/A2/A3 circuit - he has struck out anew and created a new design.
Ib ≤ In ≤ Iz
You do not chose the value of In as a way to limit Ib.
As you say, the OP's 10A radial circuit is not A1, A2 or A3, but it appears to me to have been designed appropriately:
Indeed not, but that's not what the OP did. He estimated Ib as 7.9A ("certainly less than 10A") and took a view (I suspect conservative) that Iz was 13.5A, and on that basis selected In as 10A. Provided one accepts his estimate of Ib, then that sounds like a totally correct design process, doesn't it?
Kind Regards, John
No, it doesn't:
You don't seem able to let go of the fact that, in what you've quoted above, the OP probably chose less than ideal language. I suggest that you consider everything he has written, rather than focussing on one sentence. As I wrote:
If one accepts that the MCB is there to provide both overload and fault protection, and if one takes the OP's phrase "to protect the cable due to overheating because of the installation" to mean "to protect from overload a cable whose Iz has been reduced to 13.5A because of insulation", then I don't think that any reasonable person would have a problem with the statement.
Kind Regards, John
If it was me I would be putting a cable in that would allow me to plug in a 13A appliance like an electric heater.
Doing otherwise seems short sighted.
Doing otherwise seems short sighted.
So would I, but the OP seems pretty adamant that he would 'never' want more than 10A.
Mind you, although no-one actually commented on my thoughts, I do suspect that the OP may be being unnecessarily conservative/pessimistic in assuming that his 2.5mm² cable will have a CCC of only 13.5A. As I said, it would not surprise me if careful consideration of the installation method would allow for a 16A, or perhaps 20A, MCB.
Kind Regards, John
Yes I'm not sure whether the OP has made things worse by running the cable in conduit.
or
whether electricians don't work to the letter of the requirements when insulation is involved,
buts its a sad day when you can't have some sockets on a 16A MCB with 2.5mm cable
or
whether electricians don't work to the letter of the requirements when insulation is involved,
buts its a sad day when you can't have some sockets on a 16A MCB with 2.5mm cable
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
