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I think so, I need to dig back through my notes. I think that they apply cable factors to a ring final circuit, to ensure that the cable is able to carry 20A, so in some cases 4mm2 is used.

:LOL::LOL::LOL:

Hi Dave, the OSG says In is the overcurrent device rating and the factors, Ca Cg etc are applied ( In is divided by the factors ) and this gives a number It, the tabulated current capacity of the cable. You find the next value up from this to get Iz in the cable tables. This is what the book...

Just run through a past exam paper June 2022. The last question is, as usual, a cable calc. I was pretty close to the right answers on most of it. However two things threw me, when I checked the anwer sheet. We've been taught that for a basic radial power circuit, You find the Ib (design...

good to see I'm not the only one confused...

I'd go so far as to say that any conduction of heat in an electric fire was a fault, leading to parts that could get hot enough to start a fire or burn people... but hey what do i know? Maybe the resultant house fire, is the third method of heating the room...

Yeah this course has just one written exam for the whole course, no MCQ at all, sadly. Even the course notes don't mention conduction... For good reason too IMHO.

C&G seem to think an electric fire heats a room by conduction? Surely it only heats by convection and radiation? They ask for three ways an electric fire heats a room. Electric underfloor heating would certainly use conduction but an electric fire? Maybe there is conduction after the radiated...

Our level 3 lecturer seems to be confused on how to use the tables in appendix I, for calculating Zs. They said that you look up the resistance in Table I1 and if the ambient temp is below 25°C, use the factors in Table I2. If over 25°c, use table I3. I don't think this is right. Table I2 is a...

Blimey, that was quick! :LOL: I'll have a look and see if I can find the original source of the question.

No, the fault condition where there is an earth to neutral fault in one applicance which only trips the RCD when a different applance(s) are switched on, bringing the total current up high enough that 30mA goes via the fault... I asked our lecturer about this (my original question) and they...

Ha! Well thanks for persevering! We've just been given our level 3 synoptic to do. Its the complete wiring plan for a bungalow, so there are at least 3 ring finals. I've just gone with 4mm2 as the cables are under a lot of insulation so Ref Method 101. 2.5mm2 is only rated to 17A according to...

I assumed the impedance of the earthing system would have an effect on this. Interesting fault condition to have. I wish I'd measured the voltage between earth and neutral at the socket I was working on now.

Thanks! So a parallel path is created for the neutral current thus creating the inbalance in the coil and tripping the RCD.

OK. Will the type of earthing used will have a bearing on this?

Just wondering why there's any current able to flow. (Not sure what the earthing arrangment was)

I assume that a main RCD tripping while working on an isolated (at the breaker) circuit, means neutral to earth current. Is it a sign of a fault somewhere else?

Yeah, had a look and found a few that work on a 13A socket, but I think they are all induction so they're only really running one ring at a time! Must take ages to cook a bit dinner!

A friend of mine has an electric hob which, they tell me, is plugged into a 13A socket! I didn't think that would be possible... Anyway I had a look at a typical ceramic hob online and the specs seem to show 3x rings at 2.8kW and 1x rings at 2.4kW. Further down the specs list it says total...

OK, still struggling to find any values for let through on datasheets. They just refer to type B curve.