Perhaps more a case for abolishing the ring circuit, although the 'imbalance' is nothing to worry about.
The tripping would be the same on a 32A radial so not really relevant.
Wiring an induction hob and two ovens on a single cooker circuit
- Thread starter TeeKay
- Start date
The tripping would be the same on a 32A radial so not really relevant.
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No I wasn't particularly bothered about the imbalance, just the overload of the whole ring.
I don't see the need to abolish the ring but in this situation it was easy to give the 3 appliances their own ring, due to the cu being on the other side of the wall in a cupboard under the stairs.
OK, but it's not the terminology which is the issue but, rather, the concept - there is a big difference between a moderate degree of overload (everyday sense) which is technically called 'overload current' and a very large degree of overload (everyday sense), which is technically called 'fault current'. As you have described, in the former case it's not impossible that the current will be greater than the CCC of the cable but less than the rating of the OPD, but in the latter case it's inevitable that the current will be greater than both the CCC of the cable and the rating of the OPD.
We're down to probabilities (likelihood) again. I would say not unreasonably, the regs love the word "likely". The situation you describe would only be "within the regs" if, in the judgement of the designer, the load was not likely to (under fault conditions) draw a current in excess of the CCC of the cable. The existence of anecdotes (such as you are able to provide) does not necessarily mean that such events are "likely".
Kind Regards, John
Not in the sort of scenarios we are talking about.
However, it can theoretically occur if some 'small load' (with cable appropriate to that small load) is hard-wired to a 'high current circuit' (without any intervening FCU or whatever). If one did this because one's judgment was that the nature of the load was such that it was 'unlikely to result in an overload' then, if the 'unlikely' event were to occur (not impossible - since 'unlikely' does not mean 'never') then a current well in excess of the CCC of the load's cable might flow.
Kind Regards, John
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One theoretically does not need anything like that extreme a situation for there to be a possibility of the short leg of a ring being 'a little overloaded'.
With Method C 2.5mm, just one double socket within about 16% (of the total ring length) (32% of end of ring to midpoint) from one end of the ring could theoretically result in such an overload. If the cable had a CCC of 20A (the lowest permitted) one double socket within 37.5% (of total ring length) (75% of end of ring to midpoint of ring) of an end of the ring is enough.
If it were 'known' that the first three points on the ring were likely to be used for those appliances, then the designer could (should) not believe that it was "unlikley that any part of the cable would be overloaded for long periods of time" (which is what the regs requires of him/her) unless those three points satisfied the criteria intimated in the paragraph above.
However, it seems that most people do not seem to think much about, let alone worry about, such issues - as far as I can make out, the location of sockets on a ring is usually determined by 'where they are required, regardless of the electrical considerations discussed above,
Kind Regards, John
Is that still a cooker circuit?
What loads could do what is being postulated resulting in thee times the design current of that load with that being the rating of OPD?
I think so - but can't be sure
I'm not sure what you mean by "...with that being the rating of OPD".
Even in terms of a cooker circuit, I suppose it could happen if someone hardwired (i.e. without a plug/socket or FCU) the igniter of a gas hob (which I imagine is 'unlikley to result in an overload") directly into a 'cooker circuit'.
Kind Regards, John
I meant with the OPD rating being three times the CCC of the cable used.
Yes - exactly - surely not possible.
Even a 1mm² flex would mean the igniter had to draw 30A.
Have overload and fault currents been defined anywhere different to the brown book of 2008? To me any overload due to a fault is fault current whether it trips the OCD or not. The fact that the faulty 'oven' would work OK on its own hid the potentially hazardous situation (In fact it was their go to first choice as it reached temp quicker than the other 2).
Likewise overload current is down to incorrect circuit design or incorrect use of a correctly designed circuit.
From that I will not change my description from fault current regarding the 3 ovens as the overcurrent was wholly down to a faulty appliance and I'll describe the kitchen and breakfast routine as overload current as in a majority of houses the installation would not have been troublesome. Poorly designed or used but not faulty.
I imagine that the distinction was made long before 2008, and it's persisted in all editions of the regs since then.
As I said, it's not the terminology that is the issue. Whilst it's obviously the case that both 'overload' and 'fault' currents (as defined) result from faults (in the everyday sense), the distinction exists because the requirements of the regs are very different in the twoi situations - in particular, the regs explictly require very short disconnection times for 'fault', but not for 'overload' currents (as defined).
As above,you are talking about the everyday meaning of "fault", but that's a bit confusing in the context of a trade/industry which has a specific definition of a "fault current" (being the current due to a fault 'of negligible impedance').
As we have discussed, the existence of an 'overload current' can certainly be result from a fault (everyday sense) in the load. What you are saying is that the circuit design should take that into account - that makes total sense but, as I said, the regs (and even some people's idea of 'common sense') only require that if such an overload current is "likely" (which is an individual judgement)
You're obviously free to use whatever terminology you wish - but when there is an audience of people who are used to the reg-defined technical meanings of 'fault current' and 'overload current', you might cause confusion (and/or be poorly understood) if the terminology you use differs from what they are used to.
Kind Regards, John
How did you get the homeowner to accept the cost of notifying for this new circuit? Given you don’t have current regs, what do you test against?
Very valid questions. However, he seems to have a habit of quoting anecdotes from the fairly distant past, so maybe what he is describing happened at a time before the requirement for notification existed, and also at a time when he did have a copy of then then-current regs?
Kind Regards, John
Indeed. In a later post he referred to the brown cover in 2008. The last brown copy I recall was the 16th edition 2001. Out of date by 2008. I don’t come across any of the installations which are seconds from total failure he faces on every job. Then again up here we don’t see many AV engineers being called for electrical installation jobs.
I think you'll find that it was the 2004 version of 16th including Amd1 and Amd2 which was the last brown one - which would mean that it would, indeed have been out-of-date in the latter part of 2008, although I suspect that the 17th edition (first published in January 2008) will not have 'come into force' until mid-2008, so that the 'brown book' may still have been effectively 'current' in the first half of 2008.
I suspect that much the same is true 'down here'.
Kind Regards, John
Just checked and it was still in effect until mid 2008. Apologies to Sunray.
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