I have often wondered... who writes these regs'??? 

Hi Tomgunn, yes, understand it was tongue-in-cheek, but a fair question all the same.

Tomgunn said:

It just amazes me, without upsetting anyone... you understand, the confusion that many electricians' find... trying to work out what some of the regs' actually mean

Appreciate that. I guess it starts early on .. school and college, when we learn 'V=IR' ... when in BS 7671 speak (well, in electrical engineering in general) it should be taught as U=IR.

We are constrained by standards drafting rules these days, and in fact have been for some time - Regs have been a British Standard for over 30 years now! But I guess that's one of the reasons the IET and other organisations produce guidance to help.

gkenyon said:

Appreciate that. I guess it starts early on .. school and college, when we learn 'V=IR' ... when in BS 7671 speak (well, in electrical engineering in general) it should be taught as U=IR.

R or Z? 

(Edited for typo.)

It may be better in terms of teaching, or more accurately learning, as it is the usually recipient of the knowledge that has to do most of the thinking work,  if instead of agonizing over the choice of Roman letters (or Greek symbols in some cases) for a specific quantity as if rigidly defined and then learning formulae by rote, more effort went into the understanding of the concepts.

Far more use to know the orientation of magnetic flux about a current carrying conductor or  line of moving charges, and how its alternation only introduces currents in suitably aligned adjacent conductors, rather than memorising that " B equals mu zero Mu R times H, without a feel for the units or direction of either.

That particular one avoids worrying about 'eddy currents' in thin steel boxes with exit holes, when the problem is one of magnetic hysteresis.

Mike

The first question in my C&G 2360 exam required me to use a pencil to draw the magnetic flux about a current carrying conductor on a piece of paper without any clues or hints, that is not possible with on-screen multiple choice exams in which the correct answer is always one of several possibilities presented to you.

In my mind... "errr, Tom. Run a 4 core 16mm SWA from the 6" x 6" trunking / busbar / switchgear, etc... to a TP&N CCU." OK... job done but HOW can this be??? Experience, perhaps? Learnt from some college works, and great foremen.. in the past? 

OK, I'm not having a go but, there seems to so much confusion how to interpret the current, (NO 'pun' intended),  IEE regs... somewhat 'ambiguous,' to say the least, at times. A simpler, haha, (am I asking for trouble here), set of regs that everyone can understand? 

All the best! 

Folk do like an easy life at all levels, even in cases when it may not be 'right'.

Hmm

novel and original questions are favoured neither by the students nor the examiners, and are to be avoided.

Or something like that - I remember finding it funny - one of my university lecturers, then a keen and new chap to that institution, now probably long retired from the job if not the planet, was 'very disappointed' when his proposed new exam question for inclusion finals papers was rejected, not for being a bad question, but for being too novel - what they wanted was a question more like ones from the previous years.

So he told us all about the letter from the chief examiner, and then set us the question anyway. And yes, we had to go and look a few things up we had not covered in the coursework, so we grumbled, but looking back it was good practice - after all real life sometimes poses problems that do not have all the answers at the back of the  book.

Mike

The magnetic visualization, and maybe a bit of gazing at the bathroom ceiling though a warm fog after a beer to relax the mind, is helpful to see the pros and cons of the internal external CPC thing,

Well that is the command to a wire-man, installer or technician. Somewhere calm, someone, and it may be the same chap doing it, but now with his 'design authority' or 'senior engineer' hat on.

 Maybe he now puts on a hat with the steel dome and the 'Viking horns' perhaps, instead of the baseball cap ? (*)

 The rated load, the route length and what it passes through on the way has been digested and a decision made if that 16mm cable is the best thing for the application.
That decision needs quite a lot of understanding and experience of environments and things like how cables get damaged, and not that much maths. But it is easy to set exams that ask about maths, and hard to test depth of understanding.

Mike

(*)We have a chap at work who really does this when he is editing the library of approved parts and their design rules in the CAD that could affect everyone's designs...  we know not to interrupt him then.

Chris Pearson said:

R or Z?

Interesting. Definitely at it's most basic U=IR, but of course later on, when we are considering more complex problems, U=IZ

If anyone's wondering why U is used for potential difference or emf, it's because V is volume.

Some electrical engineers differentiate between AC and DC quantities using lowercase for AC, but this is definitely not the right approach because u represents velocity at time 0, v being velocity at time t, and i representing √(-1), so we ought not to write u=iZ.

... although that in itself is a segway into another useless fact ... The use of lowercase i for AC quantities is why electrical engineers use j to represent √(-1) in complex number calculations for phasor quantities ... a habit I find it difficult to break, purely because it's a little more distinguishable in a line of text than i.

but then V and v may be used for the DC and AC voltage components of a composite signal when you move next door into electronics land.

I and i are then the DC bias and small signal oscillating currents associated with V and v, HFE and hfe the current transfer ratio and its local value.

For the physics chaps U is as likely to turn up in considerations of heat flow, and velocity v.

Now j maybe root -1, or i, or i and j may be a counting variables, but then so might k, or n.

Really the solution is to put

'where

x is in units of gezonkas per arc second,

y is change of position with time, or velocity expressed as units of furlongs per fortnight'

and similar as required beneath the formulae - the chosen squiggles for shortform of any  given concept, are truly arbitrary. We should not rely too heavily on any 'agreed' definition, as generally it is only agreed within a small clique who wish to use the meta-language to keep the magic to themselves.

M.

mapj1 said:

We should not rely too heavily on any 'agreed' definition, as generally it is only agreed within a small clique who wish to use the meta-language to keep the magic to themselves.

So, I'd agree with that in terms of academia.

To that end, BS 7671 determines the symbols to be used in the standard (which generally aligns with BSI and IEC basic principles). This makes the definitions very public, and removes the 'magic' (again, that is a function of the BSI and IEC principles).

The guidance relating to BS 7671 necessarily aligns with BS 7671 for the same reason.

Why education deviates from industry practice is a key question, though. It's not just this branch of the IET's portfolio either.

mapj1 said:

We should not rely too heavily on any 'agreed' definition, as generally it is only agreed within a small clique who wish to use the meta-language to keep the magic to themselves.

So, I'd agree with that in terms of academia.

To that end, BS 7671 determines the symbols to be used in the standard (which generally aligns with BSI and IEC basic principles). This makes the definitions very public, and removes the 'magic' (again, that is a function of the BSI and IEC principles).

The guidance relating to BS 7671 necessarily aligns with BS 7671 for the same reason.

Why education deviates from industry practice is a key question, though. It's not just this branch of the IET's portfolio either.