XL spreadsheet intended recipients: ELECTRICIANS and/or ELECTRICIANS DIYERS
XL spreadsheet purpose: To calculate approx SOCKET WIRE diameter (EG 2.5mm or 4.5mm) to use in a RING ELECTRICAL CIRCUIT, from approx "calculated" amps drawn through socket wire from appliances / electrical sockets, in that RING ELECTRICAL CIRCUIT (Eg: KITCHEN).
NOTE: ELEC current is drawn from nearest source, hence current amps is highly unlikely to be drawn consistently through socket wire, hence the need for this calculation.
Also RINGing a CIRCUIT (Definition below) as some may presume INCORRECTLY, that this DOUBLEs the AMPs (Or to put in other words halves the AMPs drawn through the RINGed circuit socket wire) that can be drawn through the RINGED CIRCUIT, that is NOT RIGHT. RINGing is not consistent like this in reducing AMPAGE drawn through the RINGED CIRCUIT, hence the need for this calculation, "commonly" known as the KIRCHOFF [Blocked Image: http://www.electriciansforums.co.uk/images/smilies/wink.png]equation.
RING DEFINITION: In electrical circuits of significant load, such as KITCHEN, normally socket wire is supplied from main fusebox to kitchen sockets/appliances, then onto the NEXT kitchen sockets/appliances, then FROM LAST SOCKET/APPLIANCE in KITCHEN ELEC CIRCUIT a length of socket wire is connected back to the fuse box socket, the purpose of this is to distribute the electrical load. You might think why not use thicker socket wire, INSTEAD of RING circuit, well for a number of reasons: UK 3 pin plugs terminal holes could only accommodate 1.5mm to 2.5mm, and also the terminals of appliances without leads the terminal hole is normally between 2.5mm to 4mm, at the most. The only terminal holes greater then this are cooker switch sockets, and obviously commercial switches.
Hi ELECTRICIAN DIYers, the following are equations/xl formulas (SPREADSHEET [Blocked Image: http://www.electriciansforums.…mages/smilies/biggrin.png]) of what SKT WIRE would you use for RING MAIN example with a known MAX in AMPS (Given recognised KIRCHOFF equation with 3 SKT EXAMPLE1 below, D is the SUPPLY/SOURCE/START of CIRCUIT/FUSEBOX MCB).
As per the example given in the NICEIC TECHNICAL MANUAL [Blocked Image: http://www.electriciansforums.…ages/smilies/rolleyes.png], of a RING circuit, calculated using the KIRCHOFF [Blocked Image: http://www.electriciansforums.co.uk/images/smilies/wink.png]equation.
Here is a SPREADSHEET with formulas for the example in the NICEIC TECHNICAL MANUAL.
EXAMPLE1:
SKT D to A: 32A(TOTAL OF A+B+C), 20m's
SKT A: 12A, AtoB 15m's
SKT B: 14A, BtoC 20m's
SKT C: 6A, CtoD 5m's
SIMPLY, "IF" this was a RADIAL CIRCUIT were the WATTS/AMPS MAXIMUM was known (32A), the SKT WITE to be used/spec'd would suggest 4mm SKT WIRE.
Obviously the KIRCHOFF equation doesn't actually reduce the actual WATTS/AMPS used, it calculates the AMPAGE spread over the RING MAIN, as an approximate. But isn't the KIRCHOFF equation the recognised standard equation for calculating a RING MAIN.
ALSO I realise in addition to KIRCHOFF, the IEE 17th Edition Pg44 quotes something like:
1.5mm (20A not ringed) or 2.5mm (27A not ringed) is approx 32A Ringed, <less then 100m's (# 20A x 1.6 or 27A x 1.2).
Hence on the 3rd tab of the spreadsheet, I guess this is how IEE reached 32A, or a sliding scale of multiplication as you can see in the pattern #, or unless they destructively tested socket wire in collaboration with socket wire manufactures such as Prysmian, and the suggested figures were thought reasonable for permanent use for a great many years, well socket wire isn't going to twist and bend behind plastered walls.
LONG HAND OF EXAMPLE1 with KIRCHOFF short hand:
SKT D to A: 32A(TOTAL OF A+B+C), 20m's, Cumlative Count 0A
SKT A: 12A, AtoB 15m's, Cumulative Count 12A
SKT B: 14A, BtoC 20m's, Cumulative Count 26A
SKT C: 6A, CtoD 5m's, Cumulative Count 32A
i) Metres of Skt wire X Cumulative Count of AMPs from skts in circuit:
20 X 0 = 0
15 X 12 = 180
20 X 26 = 520
5 X 32 = 160
0+180+520+160=860
TOTAL i) / LENGTH TOTAL - Cumulative Count of Amps in circuit = AMPs of SKT LENGTH
D to A = 860 / (20+15+20+5) - 0 = 14.33A
A to B = 860 / (20+15+20+5) - 12 = 2.33
B to C = 860 / (20+15+20+5) - 26 = -11.67
C to D = 860 / (20+15+20+5) - 32 = -17.67
SEE NICEIC TECHNICAL MANUAL Pg 5
Given this example if RADIAL then 32A would use 4mm SKT WIRE. So if RING circuit what SKT WIRE would you use, given the above? Please show workings.
If the above are totalled together: 14.33A + 2.33A + -11.67A + -17.67A = 19.3A
Does this equate to the AMPAGE spread over the SKT WIRE?
Hence 1.5mm SKT WIRE? 1.5mm SKT WIRE is rated to 20A. OR since the figure is very 20A, then the next biggest 2.5mm SKT WIRE which is rated to 27A? (Bigger is always better). [Blocked Image: http://www.electriciansforums.co.uk/images/smilies/cool.png]
Cheers
Stephan Rands
www.srands.co.uk
MPG autocalc
[URL="http://www.srands.co.uk/Weight,Length,Temperature,Speed&MetresM2_AutoCalc.xls"]METRIC autocalc[/URL]
MTB routes in/near Hull, Humberside
ELEC GAS WATER autocalc: 1st tab, scroll down
FUSEBOX MCB autocalc: 3rd & 4th tab
RING AMP autocalc: 1st tab
