Maths and Java Script any one tried it?

[JohnW2]

How about this version where you can select installation method? Not sure really helps and as yet only done for live cables not done earth so will likely be slightly out just an idea.

I think you really need to start by deciding what you want to achieve with this calculator - not simply calculating/displaying things 'because you can'.

AFAICS, entering installation method is only relevant to determining the CCC of cable (which one can just look up in the BGB, OSG or wherever) - and has no relevance to the calculation of VD, Zs or PSCC.

Kind Regards, John

 

[ericmark]

I am getting confused about the OSG does this also give a formula to correct the figures or is it a rule of thumb thing which is just near enough?

Can't see the point in making a calculator then using rule of thumb!

 

[ericmark]

How about this version where you can select installation method? Not sure really helps and as yet only done for live cables not done earth so will likely be slightly out just an idea.

I think you really need to start by deciding what you want to achieve with this calculator - not simply calculating/displaying things 'because you can'.

AFAICS, entering installation method is only relevant to determining the CCC of cable (which one can just look up in the BGB, OSG or wherever) - and has no relevance to the calculation of VD, Zs or PSCC.

Kind Regards, John

That was also what I was thinking so did not alter the original but with the comments about using Method 100 I started to wonder.

I think of a C32 RCBO and look at the 320A PSCC required and realise how this reduces the ring to 80 meters and wonder how many consider this when selecting a C type.

 

[JohnW2]

I am getting confused about the OSG does this also give a formula to correct the figures or is it a rule of thumb thing which is just near enough? Can't see the point in making a calculator then using rule of thumb!

It's not a question of 'needing correction' - as I said, they are just being very conservative. They are saying that even if the temperature of the conductor is only 10° when you undertake your Zs measurement, if your measurement is less than their tabulated 'maximum Zs' figure for the OPD concerned, this will guarantee that the Zs remains below the BGB's corresponding 'maximum Zs' figure even if conductor temp rises to 70°.

Kind Regards, John

 

[JohnW2]

.... AFAICS, entering installation method is only relevant to determining the CCC of cable (which one can just look up in the BGB, OSG or wherever) - and has no relevance to the calculation of VD, Zs or PSCC.

That was also what I was thinking so did not alter the original but with the comments about using Method 100 I started to wonder.

In terms of calculation of VD, Zs and PSCC (which I thought was the primary purpose of the calculator), none of the stuff about installation method, grouping or CCC is really relevant. I only mentioned 'Method 100' because, if you were going to display a CCC (even though I'm not sure I see the point), you really ought to say what installation method it refers to.

I think of a C32 RCBO and look at the 320A PSCC required and realise how this reduces the ring to 80 meters and wonder how many consider this when selecting a C type.

In a domestic setting, 80m is still quite a lot! However, I suspect that you would only very rarely find anyone suggesting/contemplating a Type C MCB for a ring, anyway - it usually arises in relation to radials (often dedicated circuits) supplying equipment with high start-up currents.

Kind Regards, John

 

[ericmark]

I think of a C32 RCBO and look at the 320A PSCC required and realise how this reduces the ring to 80 meters and wonder how many consider this when selecting a C type.

In a domestic setting, 80m is still quite a lot! However, I suspect that you would only very rarely find anyone suggesting/contemplating a Type C MCB for a ring, anyway - it usually arises in relation to radials (often dedicated circuits) supplying equipment with high start-up currents.

Kind Regards, John

I think the main reason for using a type C RBCO is because of lack of stock in suppliers of type B rather than being selected because they want that size.

I think you are right that now I know it all works some of the outputs used to test can be removed again.

 

[ericmark]

I have removed the non essential stuff and tidied up a bit must admit REM'ed out rather than removed so this I hope is final version unless you good guys see some errors I have missed.

Thanks for all your help without which it would never have been done giving (I hope) correct readings.

 

[EFLImpudence]

It seems to be fine, Eric.
Very good. Thank you.

I don't know (to save reading all again) if it has been covered and you did not want to do it but -

Would it be better to enter Zs and Zn instead of Zs and PSCC and
the calculation to include PEFC as well as PSCC?

 

[JohnW2]

I have removed the non essential stuff and tidied up a bit must admit REM'ed out rather than removed so this I hope is final version unless you good guys see some errors I have missed. Thanks for all your help without which it would never have been done giving (I hope) correct readings.

It certainly looks tidier.

I have a suspicion that something is probably wrong with your 'temperature correction' calculations, since changing operating temperature from 70° to 30° (with 30° ambient), or even changing ambient to 0° and operating temp to 100°, has only a very slight effect on the calculated values of VD, Zs and PSCC.

You might also want to consider adding a note indicating that your calculations relate to conductors at their maximum permitted operating temp - since, although I think that is reasonable (as a safe/conservative approach), it is apparent that some (like EFLI) don't feel that this is always appropriate.

Kind Regards, John

 

[ericmark]

It seems to be fine, Eric.
Very good. Thank you.

I don't know (to save reading all again) if it has been covered and you did not want to do it but -

Would it be better to enter Zs and Zn instead of Zs and PSCC and
the calculation to include PEFC as well as PSCC?

I would seem I have moved from original so much. Stage one was from the reading auto taken with a ELI meter to give volt drop and cable length i.e. to verify volt drop with a EICR.

JohnW2 thought the reverse would be handy working out volt drop and prospective ELI and PSCC at cable destination from cable length and I would agree we see so often "I have a shed/garage at bottom of garden which is 100 meters from house can I use 6mm cable?" entering details would help but for house wiring to measure how much wire is going to be required not so sure really helps?

Also entering prospective short circuit current would also be another option rather than Ze and Zs as it will not involve the earth cables so not going to be messed up with parallel paths however although I know the old top of range Robin meter which also had the leads and test spikes to test earth rods without using mains power auto switched connections on the IEC 14 plug in test lead some cheaper version still connect line - earth when testing prospective short circuit current I know I was caught out then realised 240/ELI = PSCC with all readings it did not switch from earth to neutral but just did internal calculation.

Although the Cleaned up version does the three calculations I am not sure about removing the stages used to arrive at the answer as if I have made an error it's harder to identify. The old version does allow one to see any striking errors by showing stage information.

I think there is still a place for working out volt drop from loop impedance and also working out volt drop from PSCC when Part P first started I did wonder about what checks would be made with paperwork sent to LABC using a calculator like I have made it would be so easy for figures to be tested and I wondered if one would get pulled for missing items like volt drop.

I built an Excel program to print out results which also checked the results flagging up errors. However as time went on I realised Part P was just a money making exercise and very little if anything was checked. With a new form my son entered figures into wrong part which meant on paper 5 houses failed because of holidays he was not able to talk to right people to explain the error and expected a phone call when it was checked. It never happened so clearly never checked.

However I still wonder if some one in 9 years time could request copies of test results from the LABC and point out a design error and ask for it to be corrected free of charge? After 10 years then it should be checked so once that is done any faults is down to guy testing either he flags up fault and you are asked to rectify or he is now responsible.

This then asks the question could he be asked to foot the bill or design errors missed in the inspection?

Hence the idea of a calculator mainly for my own use to flag up errors. My old phone would work with excel but not the new one hence the move from Excel to Java Script.

It has certainly been an interesting exercise with faults which were in the Excel version being highlighted. Give it a year and I will not remember how it was done I will just use it. So did need your help getting it right to start with.

As to temperature and other factors correcting the results it will not alter the answer by much and I do question if it really needs all the inputs. Hence why set to auto enter standard answers. Unless I find some one else's version to compare with hard to really check. Since only to 2 decimal places the results in each version don't exactly match but I feel close enough not to worry about.

 

[JohnW2]

Would it be better to enter Zs and Zn instead of Zs and PSCC and the calculation to include PEFC as well as PSCC?

I would seem I have moved from original so much. Stage one was from the reading auto taken with a ELI meter to give volt drop and cable length i.e. to verify volt drop with a EICR. ... JohnW2 thought the reverse would be handy working out volt drop and prospective ELI and PSCC at cable destination from cable length and I would agree we see so often "I have a shed/garage at bottom of garden which is 100 meters from house can I use 6mm cable?" ...

As I’ve said, I think that you really need to start by deciding what is the ‘purpose’ of this calculator. If it is intended for design purposes, then one clearly will not be able to enter any measured values relating the circuit which has not yet been designed/installed (e.g. Zs/PEFC, PSCC or Zn at the end of the circuit). If it is for design purposes, one needs to be able to enter details about the cable (particularly length), together with Ze (or PEFC at origin of installation) & PSCC (at origin of installation), and thence use the calculator to estimate VD and Zs at the ‘end’ middle for a ring) of the circuit.

If the calculator is intended for some purpose other than design, then it obviously needs to be structured accordingly. If one is talking about an existing circuit, then what obviously matters (for an EICR etc.) are the values of Zs/PEFC (and maybe PSCC) measured at the ‘end’ of the circuit. About the only thing to be left to be calculated is the VD, and that it a pretty trivial arithmetical exercise once one has the other required measurements.

Also entering prospective short circuit current would also be another option rather than Ze and Zs as it will not involve the earth cables so not going to be messed up with parallel paths ...

Indeed - if one only wants to calculate VD and PSCC. Again, however, if one wants to use the calculator for design purposes, one won’t be able to enter either Zs or PSCC of the circuit.

Although the Cleaned up version does the three calculations I am not sure about removing the stages used to arrive at the answer as if I have made an error it's harder to identify. The old version does allow one to see any striking errors by showing stage information.

I agree totally - it is frustrating not having the intermediate figures there. I think you’re trying move far too quickly. IMO (it’s certainly how I would do it) I think you should leave as many as possible (‘diagnostic’) intermediate results there until you are totally sure that you have a final and correctly-working version. Then, and only then, should one remove all the ‘unwanted’ outputs.

I think there is still a place for working out volt drop from loop impedance and also working out volt drop from PSCC ....

As you have observed above, one cannot accurately estimate VD from measured Zs/EFLI/PEFC, since those measurements are all affected by ‘parallel paths’. You could do it from L-N loop impedance (or PSCC) if you had measurements both at origin and end of the circuit. The best way, of course, is to calculate VD from an R1+RN (or R1+R2, plus the appropriate adjustment for live/CPC csas - since such ‘dead’ measurements would not be affected by ‘parallel paths’).

Talking of ‘parallel paths’, it’s probably worth remembering that when the calculator is used in ‘design mode’, the calculated estimated Zs will be that which would apply in the absence of parallel paths - if such paths exist, the Zs would obviously be lower, but that wouldn’t matter.

As to temperature and other factors correcting the results it will not alter the answer by much and I do question if it really needs all the inputs. Hence why set to auto enter standard answers. Unless I find some one else's version to compare with hard to really check. Since only to 2 decimal places the results in each version don't exactly match but I feel close enough not to worry about.

I will write separately about the temperature business.

One other issue. For reasons that have been discussed, you use the 26A ‘effective design current’ for calculating VD for a 32A ring final, but I wonder how acceptable this is for ‘official’ purposes (such as an EICR), given that I can find no reference to it in the BGB (which essentially regards the Ib of a 32A ring final as being 32A). This is also of (albeit fairly trivial) relevance in terms of your ‘temperature correction’ calculation, since ‘Equation 6’ calculates ‘Ct’ as a function of Ib/It. I presume/suspect that, for a 32A ring final, your calculator is using the 26A figure for Ib in this equation, and I’m not sure how appropriate/acceptable that is.

On a related issue, as I’ve discussed before, what value of Ib are you intending should be entered for a radial circuit?

Kind Regards, John

 

[JohnW2]

As to temperature and other factors correcting the results it will not alter the answer by much and I do question if it really needs all the inputs. Hence why set to auto enter standard answers. Unless I find some one else's version to compare with hard to really check. Since only to 2 decimal places the results in each version don't exactly match but I feel close enough not to worry about.

The first point is perhaps more for EFLI than you. Prior to the corrections discussed below, your calculator is seemingly estimating VD and Zs at maximum permissible conductor temperature (70°C) - i.e. by using the (70°C) mV/A/m figures from BGB Table 4D2A or 4D5. EFLI feels that this is not necessarily appropriate.

Equation 6 in 6.1 of Appendix 4 of the BGB appears to work on the assumption that a cable carrying it’s full ‘tabulated CCC’ (e.g. per Table 4D5) will run at the maximum operating temp (i.e. 70C), but will run cooler if the current is less than the ‘tabulated CCC’. It therefore introduces a correction factor which is a function of Ib/It. In other words, if ‘It’ is higher than ‘Ib’, then the tabulated mV/A/m resistivity figure will be reduced a little. However (although I haven't checked) I suspect that this correction will not have anything like as much effect as would using a 30°C resistivity figure (which I think is what EFLI might favour)

This begs a question as to what values for Ib and It your calculator is using (and should be using) for this ‘Equation 6’ calculation. One of the previous versions of your calculator displayed the CCC (i.e. It) as 42A for a 2.5mm² ring - was that 21A x 2 (per 4D5)? If so, is that necessarily ‘fair’ given that the current may not be equally divided by the two sides of the ring? (that’s almost a rhetorical question, since I’m not sure what other figure you could use!). As for Ib, as I recently wrote, I suspect that your calculator is probably the using the ‘effective design current;’ (AFAICS, intended for VD purposes only) of 26A for a ‘32A ring final’. Again, I’m not sure that is necessarily appropriate/acceptable for the Table 6 calculation (which perhaps should use 32A?) - the difference in Ib/It is ‘appreciable’ ... 26/42 = 0.62 and 32/42 = 0.76. In fact, Equation 6 uses the square of Ib/It, which makes the difference even greater - 0.38 vs. 0.58.

Having said all this, I rather doubt that (m)any electricians ever utilise 'Equation 6'! That's not really a problem, since 'not using it' is more conservative.

A few things to contemplate!

Kind Regards, John

 

[EFLImpudence]

i.e. by using the (70°C) mV/A/m figures from BGB Table 4D2A or 4D5. EFLI feels that this is not necessarily appropriate.

I don't think it makes a great deal of difference but it surely must be so.

Equation 6 in 6.1 of Appendix 4 of the BGB appears to work on the assumption that a cable carrying it’s full ‘tabulated CCC’ (e.g. per Table 4D5) will run at the maximum operating temp (i.e. 70C), but will run cooler if the current is less than the ‘tabulated CCC’.

Again, it does not really matter but ...

if there is a safety allowance or tolerance in the maximum CCC stated, is there any way of knowing what the actual temperature will be of, say, a 2.5mm² conductor carrying 27A?

Having said all this, I rather doubt that (m)any electricians ever utilise 'Equation 6'! That's not really a problem, since 'not using it' is more conservative.

Quite.

 

[JohnW2]

,...if there is a safety allowance or tolerance in the maximum CCC stated, is there any way of knowing what the actual temperature will be of, say, a 2.5mm² conductor carrying 27A?

I don't know. We have often agreed that there is undoubtedly a generous safety margin in the 'tabulated CCC' figures in terms of how high a current a cable can safely carry without damage, but I'm nowhere near as sure that there is any such 'margin' in relation to what conductor temperature will result from a given current - i.e. the 'safety margin' may be in terms of what conductor temperature (beyond it's 'maximum operating temperature') the cable can safely tolerate, not the conductor temperature which results from a particular current.

As I said, 'Equation 6' appears to assume that the 'operating temperature' specified in the BGB's CCC tabulations (e.g. 70°C for Tables 4D** and 4D5) will be achieved if the specified current ('It', CCC) flows through a cable with a particular csa and installation method. The equation then effectively attempts to estimate what temperature will be achieved (hence what conductor resistivity will be) if the current flowing is less than the 'tabulated CCC'. Unless you can think of something I've overlooked, I don't think that there is any way we can tell whether there is any 'safety margin' built into that - as above, the 'safety margin' could be in relation to what conductor temperature can be safely tolerated, rather than what conductor temp is achieved by a given current.

Whatever, 'safety margins' are just that, and we are theoretically constrained to work with the 'maxima' which are stated in the regs, even if those limits are deliberately conservative'.

Kind Regards, John

 

[ban-all-sheds]

In terms of calculation of VD, Zs and PSCC (which I thought was the primary purpose of the calculator), none of the stuff about installation method, grouping or CCC is really relevant.

Not quite.

The installation method affects the CCC of the cable for a 70° operating temperature. So its resistance is always the same, but a lower current means lower VD.