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Every time I fill in a form it asks questions like what earthing system and what is the supply fuse.
For forms made by non IET also seen questions like what type or size of cable.
Often one especially with an inspection has no idea of precise details. One knows the incoming fuse is => 100A but as to if 60, 80, or 100 one has no idea. As to fuse type one can guess at BS 1361 but one does not really know.
And looking at page 338 of BS7671:2008 when has one ever seen a 2-phase supply? Split-phase yes but it is still single phase with 460 volt between phases.
Should we not have the option to select TN as really it does not matter is TN-C-S or TN-S all that matters is the earth loop impedance. The only exception would be petrol stations, caravan sites etc.
What I think should happen in a perfect world is when the supply goes in one should receive a form from the DNO with all the information required under supply characteristics and earthing arrangements. But I have not seen such a form and unless you are on site when the DNO guy arrives it is guess work.
OK we know it's 230 v at 50 Hz and our meters give us the Ipf and Ze but once we enter under "Supply Protective Device Characteristics" BS 88, BS 3036, BS 1361, ect then likely this will be copied from form to form for all time. So should we really guess?
Maybe we should enter "Awaiting results of enquiry"?
OK with some supplies one can see it is a TT or TN-C-S but other than enquiry one can never be sure it's a TN-S supply. As to IT only every worked on it once in Hong Kong on a TBM and yes we knew what it was. Also seen it on a DC supply to cranes in a steel works with two bulbs to show neither leg has gone to earth. But industrial premises are very different to domestic. At Point of Ayr we had huge resistor between plant earth and DNO earth not a clue what code that comes under?
Yes most of us make an informed guess. But should we? Why ask a question on a form to which we can only guess the answer? Or should we draw the DNO fuse to write down the information which to be honest does not really matter.
As to
624Y Twin & Earth PVC Cable BS6004 A05VVH4-U
or
624B Twin & Earth LSZH Cable 300/500V BS7211
tell me who can after it is 10 years old hand on heart really tell which is which without removing some and putting a flame to it.
On commercial we have:-
6181XY Double Insulated Cable 600/1000V BS7889
6181Y Double Insulated Cable 300/500V
6181B LSZH Double Insulated Cable 600/1000V BS6724
6491X H05V-U Cable 300/500V BS6004
6491X H07V-R Cable 450/750V BS6004
6491X H05V2-U Heat Resisting Cable
6491B H07Z-R Low Smoke Cable 450/750V BS7211
Again tell me how with a standard inspection one can really know which is which? OK on installation cert one should know and enter the type. But once installed why would on an inspection and test one want to enter what type of cable? And if one thinks it's 624B and it's 624Y and then some one latter puts a 40A MCB on 6 mm sq cable (43A rating ref method 100) instead of a 32A MCB (34A rating ref method 100) there could be problems.
We all copy the information from last cert to ours and that is OK it is by enquiry. But that means 40 years after some one makes a guess it is still being entered as fact on the forms.
For forms made by non IET also seen questions like what type or size of cable.
Often one especially with an inspection has no idea of precise details. One knows the incoming fuse is => 100A but as to if 60, 80, or 100 one has no idea. As to fuse type one can guess at BS 1361 but one does not really know.
And looking at page 338 of BS7671:2008 when has one ever seen a 2-phase supply? Split-phase yes but it is still single phase with 460 volt between phases.
Should we not have the option to select TN as really it does not matter is TN-C-S or TN-S all that matters is the earth loop impedance. The only exception would be petrol stations, caravan sites etc.
What I think should happen in a perfect world is when the supply goes in one should receive a form from the DNO with all the information required under supply characteristics and earthing arrangements. But I have not seen such a form and unless you are on site when the DNO guy arrives it is guess work.
OK we know it's 230 v at 50 Hz and our meters give us the Ipf and Ze but once we enter under "Supply Protective Device Characteristics" BS 88, BS 3036, BS 1361, ect then likely this will be copied from form to form for all time. So should we really guess?
Maybe we should enter "Awaiting results of enquiry"?
OK with some supplies one can see it is a TT or TN-C-S but other than enquiry one can never be sure it's a TN-S supply. As to IT only every worked on it once in Hong Kong on a TBM and yes we knew what it was. Also seen it on a DC supply to cranes in a steel works with two bulbs to show neither leg has gone to earth. But industrial premises are very different to domestic. At Point of Ayr we had huge resistor between plant earth and DNO earth not a clue what code that comes under?
Yes most of us make an informed guess. But should we? Why ask a question on a form to which we can only guess the answer? Or should we draw the DNO fuse to write down the information which to be honest does not really matter.
As to
624Y Twin & Earth PVC Cable BS6004 A05VVH4-U
or
624B Twin & Earth LSZH Cable 300/500V BS7211
tell me who can after it is 10 years old hand on heart really tell which is which without removing some and putting a flame to it.
On commercial we have:-
6181XY Double Insulated Cable 600/1000V BS7889
6181Y Double Insulated Cable 300/500V
6181B LSZH Double Insulated Cable 600/1000V BS6724
6491X H05V-U Cable 300/500V BS6004
6491X H07V-R Cable 450/750V BS6004
6491X H05V2-U Heat Resisting Cable
6491B H07Z-R Low Smoke Cable 450/750V BS7211
Again tell me how with a standard inspection one can really know which is which? OK on installation cert one should know and enter the type. But once installed why would on an inspection and test one want to enter what type of cable? And if one thinks it's 624B and it's 624Y and then some one latter puts a 40A MCB on 6 mm sq cable (43A rating ref method 100) instead of a 32A MCB (34A rating ref method 100) there could be problems.
We all copy the information from last cert to ours and that is OK it is by enquiry. But that means 40 years after some one makes a guess it is still being entered as fact on the forms.
