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# equation

Hi All, I think I have confused myself somehow and feel I am spiraling into further confusion. When I am doing the equation, it is saying the longer the cable is, the smaller the CPC has to be. My calculations are below. 20A radial BS61009-1 Curve C Install method type B using 2.5 singles...
2. ### Adiabatic Equation - why only for CPC?

Why adiabatic equation is used only for sizing of CPC? Why not for phase conductors too?; As the fault current also flows through the phase conductors
3. ### Earthing equation 3P 100A

Hi guys I carried out an EICR a while back on a property with 3P 100A incomer and it only had a 16mm earth. I thought this was undersized, I made contact with the local DNO and had 2 replies, one said it was fine, the other said it should be 25mm. Im trying to do the adiabatic equation for it...
4. ### Help with Adiabatic equation

Hi, Could anyone check my calculation please. Protective device 60A 1361 E.S = TN-C-S Cable 16mm T & E CPC 6.0mm Zdb = 0.43ohms Multiplier temp 1.20 0.43 x 1.20 = 0.52ohms 230/0.52 = 442A SR 442 squared x 2secs/115 = 5.43mm Cheers
5. ### Adiabatic equation infinite loop

So I'm looking into the thermal constraints of every cable in my 2396 project. I've used the adiabatic equation in a spread sheet and 99% of them are fine with the CPC I have selected. However, there are a few really short circuits with very low earth fault loop impedance. Because of this the...
6. ### Using adiabatic equation for CPC on SWA

I want to use the armour as my CPC but need to check it complies. The cable will be run from a SP Distribution panel to CU. As per Selection and Erection Guidance Note 1 table D10a I can see a 10mm XLPE SWA requires a 31.1mm csa to comply, but only has 26mm on 2-core. 20171231_114229828_iOS.jpg...
7. A

Hi all, been trying to work this out now and carnt get my head round some of the calculations. please see where im going wrong. voltage drop: so 63amp mcb supplying electric boiler, run is approx 25 meters in 16mm twin & earth. so Mv/a/m x length x amps divided by 1000= 2.8x25x63 divided by...
8. K

### calculating csa of earthing conductor with BS1361 fuse

Maybe I'm overlooking the obvious but how would you calculate the min. csa of an earthing conductor of say a tn-s system when there is no time/current graph for a 1361 fuse in the BGB? Do you just obtain If from Uo/Ze and then use this in the adiabetic equation. Ta
9. H

### help on pirs

Hi all, Completed my first pir yesterday (: now this client has got a three phase supply, TNS which feeds a ground floor shop and a flat above, the flat has a on peak and off peak supply. With the tails for the flat going into two kmf switches with a sub main cable of only csa of 10mm T+E for...
10. ### Knowledge is Power

First the basics Knowledge is Power Time is Money and as every electrician knows, Power is Work over Time. So, substituting algebraic equations for these time worn bits of wisdom, we get: K = P (1) T = M (2) P = W/T (3) Now, do a few simple substitutions: Put W/T in for P in equation (1), which...
11. S

Hi guys. Just wanted to ask what code you would give an old wylex fuse board with wooden enclosure. It does have the plastic (plexolin I think it's called) plate at the back. Also 2.5 T+E with 1.0mm CPC used for a ring main on a 3036 fuse. Thanks in advance. Steve
12. C

### Domestic Voltage drop on a ring?

Morning, Just a quick question? In the OSG (2008) (page 44), it says that you can have 106 metres of 2.5 T&E with a 32A type B cb. Any ideas how they are working this out? My understanding of vd on a ring is mvam x half of length x half of ib / 1000 So 18 x 53 x 16 / 1000 = 15.2 v?? I assume...
13. H

### Size of Conductor for TT Installation

I am hoping to use my own house for my assessment to join either NICEIC/Elecs/NAPIT however I have a question over the size of the earth conductor. Most people give me the stock answer of 16mm as the Tails are 25mm however I do not believe that this has to apply to a TT system although I am...
14. ### Building Control

Hello, got my Elecsa assessment on 4th january, going to change the cu in my house and use that as assessment job, its simple as only 3 circuits, sockets, lights and shower. But shall i tell building control?? Elecsa said upto me, they dont request it but they will let building control know...