Upgrading from ring to radial?

[EFLImpudence]

27 x 1.13 = 30.51

 

[JohnW2]

27 x 1.13 = 30.51

It is - my apologies, and thanks for noticing. I then read my typo and used it to miscalculate the power as 8kW, rathervthan 7kW. All now corrected and, as I say in that correction, it does not really alter the gist of what I was saying.

You will be aware (since I don't always notice and correct!) of the fact that my (essentially two-finger) typing often results in 'character transpositions', two of my most common being "taht" and "obvioulsy". I suppose that typing "35.1" (truncated "35.10") when it should have been "30.51" can be explained in the same way (contains the right characters, but not in quite the right order!).

Thanks again.

Kind Regards, John

 

[ericmark]

I think

27 x 1.13 = 30.51

makes not difference, a 32A MCB will allow more current than a 25 amp MCB, it really does not matter at what point they will trip. What matters is they will trip before damage.

 

[EFLImpudence]

I was only correcting John's typo.

 

[JohnW2]

I think makes not difference, a 32A MCB will allow more current than a 25 amp MCB, it really does not matter at what point they will trip. What matters is they will trip before damage.

My point was that the CCC tables we use take into account the fact that an MCB should allow 1.13 x In to flow continuously and indefinitely without ever tripping.

Since I was talking about a cable with a tabulated CCC of 27A (Method C) I talked about a hypothetical 27A MCB (which I presume doesn't exist), since that would be deemed to be satisfactory for protecting a cable with a tabulated CCC of 27A. However, as I said, that implies that the cable (with a 'tabulated' CCC of 27A) is deemed to be perfectly safe with a continuous current of up to 27A x 1.13, i.e 30.51A.

Kind Regards, John

 

[JohnW2]

I think there is a mistake in the title, it should say down grading ring final to radial.

I agree with eric, it would be downgrading!

This is really a mixture of semantics and personal opinions!

Given that there are at least some people around who believe that ring finals are undesirable (and unnecessary), in some cases to the extent of suggesting that they 'should not be allowed', I would think the fairest thing would be to be non-judgemental and just talk about "changing", rather than "upgrading" or "downgrading".

As for whether ring finals "should be allowed", it's very probable that they wouldn't be if someone had thought of the idea for the first time in 2018 (or any other recent time). However, that's not a simple argument, since it could apply to lots of other things - I would imagine that tobacco, alcohol and maybe even caffeine-containing drinks would be banned (in the same way as cannabis etc.) if they had first appeared in 2020, and even the likes of things like aspirin and paracetamol would probably not be regarded as safe enough (at least, for very widespread use) if they had first appeared in 2020 (or any time in recent decades).

Kind Regards, John

 

[flameport]

Theoretical only, not permitted in reality.

 

[ericmark]

I have to agree with @JohnW2 I think if the gas cooker was invented today it would be banned, I look at the safety features of my induction hob, and think how can anyone consider gas?

But during WW2 when the ring final was invented it was well ahead of it's time. There was no 1/3 rule on drilling beams, and no insulators on the live pins so the 13 amp plug could supply 13 amp and the fuse cool enough for as long as one liked, there was no reduction in heat removal due to insulators on the live pins, and 7/.029 was nearly 3 mm so even it the ring was broken there was really no problem.

The problem arrived when insulators were put on live pins and the cable size reduced to 2.5 mm² and the protective device changed from 30 amp to 32 amp, the combination resulted in the potential for an overload of an extended duration. The limit of 2 KW for fixed appliances in the main removed the problem.

So the washing machine, tumble drier, immersion heater, oven and other fixed high power users were removed from the ring final load. However it seems people do not read the appendix to BS 7671 and the washing machine, and tumble drier are still connected to the ring final, if we had radial we could not do that, it would trip.

As to if having a radial that forces one to follow the appendix guidance is good or bad is up for debate.

 

[JohnW2]

Theoretical only, not permitted in reality.

Does not the "unlikely" in the regulation render it 'permitted' (at the discretion of the designer)?

If one were not prepared to take that view, then the regulation you quote would mean than no sockets circuit, of any design, would be permitted if Iz < (1.13*In) wouldn't it? - For example, although the regs, as usually applied, would theoretically allow a Method C 1.5mm² 20A radial, it would not be allowed if one did not accept the "unlikley" statement you quote.

Kind Regards, John

 

[winston1]

I have to agree with @JohnW2 I think if the gas cooker was invented today it would be banned, I look at the safety features of my induction hob, and think how can anyone consider gas?

But during WW2 when the ring final was invented it was well ahead of it's time. There was no 1/3 rule on drilling beams, and no insulators on the live pins so the 13 amp plug could supply 13 amp and the fuse cool enough for as long as one liked, there was no reduction in heat removal due to insulators on the live pins, and 7/.029 was nearly 3 mm so even it the ring was broken there was really no problem.

The problem arrived when insulators were put on live pins and the cable size reduced to 2.5 mm² and the protective device changed from 30 amp to 32 amp, the combination resulted in the potential for an overload of an extended duration. The limit of 2 KW for fixed appliances in the main removed the problem.

So the washing machine, tumble drier, immersion heater, oven and other fixed high power users were removed from the ring final load. However it seems people do not read the appendix to BS 7671 and the washing machine, and tumble drier are still connected to the ring final, if we had radial we could not do that, it would trip.

As to if having a radial that forces one to follow the appendix guidance is good or bad is up for debate.

First there is no limit of 2kW limit for fixed appliances in the regs. It is guidance but not regs.
Second washing machines and tumble dryers do not trip on radials. I know several people in Europe with such setups and no problems.

 

[JohnW2]

So the washing machine, tumble drier, immersion heater, oven and other fixed high power users were removed from the ring final load. However it seems people do not read the appendix to BS 7671 ...

WEll, they might read it, bit since it isonly guidance, many choose not to to 'adhere'to it.

... and the washing machine, and tumble drier are still connected to the ring final, if we had radial we could not do that, it would trip. As to if having a radial that forces one to follow the appendix guidance is good or bad is up for debate.

I don't get that. Whether or not 'it trips' depends upon how many, and which, high-powered appliances one has running simultaneously on the same circuit, and the rating of the OPD of that circuit. If one ran multiple high loads on a 32A radial, it would be no, or more, less likely to trip than if they were on a 32A ring, would it?

In reality, I actually doubt that a WM and dryer on the same 20A radial would often, if ever, trip the OPD....

Kind Regards, John