Thank you Sir. I'd thought I'd trouble myself to make a general point. Agree about the Covid thing. I'd never thought I'd hear it from my Students, but every one of them all agreed it was better to be studying in College, than being on line on TEAMS....and I've got a right collection of pimps and bedwetters. Fingers crossed for the exams this month.Thank you for that I've been teaching this most of today and really couldn't be arrsed to type the formula to explain it.
It's obvious that you understand Electrical Science and principles. You have put im far more eloquently than I could.
As well as helping L1, L2 and L3 through thier practical assessments due to no fault of there own ( covid has really limited the time they have for practical).
Thank you Sir. I'd thought I'd trouble myself to make a general point. Agree about the Covid thing. I'd never thought I'd hear it from my Students, but every one of them all agreed it was better to be studying in College, than being on line on TEAMS....and I've got a right collection of pimps and bedwetters. Fingers crossed for the exams this month.
Yes, and that's why the IEE specify the characteristics of a CCU to make sure you meter monkeys ( with the exception of live cable jointers, speaking of which you could not pay me enough to bugger around with 33-11KV live) just put int the supply. As mere tamer of Electrons, who shits solid gold and piss's perfection. Are trusted and qualified to take over from the cut out ( ohhps did I say cut out?. I've never cut a meter seal in my life honest Guv). ( however the kits amd the seals are avaliable on a certain auction site for around £15).Of course the real giggle is that the feed to the house is only 10mm, but 25mm tails to the consumer unit so nothing to worry
Part P is building regs not BS7671 amd don't apply to special loactions Don't try to be a smart arrse ot will not end well. Both my self and @lecky Could rip that supposed argument apart with a few paragraphs.Plumbers, tend to be Part P certified, if they fit boilers.
Well I got a plumber and he fitted the same shower and he was qualified.
How to design an Electrical Circuit:
1) Find out the Wattage of the intended load/s that are Resistive and divide through by 230v if single phase. If its a three phase it's; Wattage/Line Voltage(400) x 1.732 (square route of 3) x Power Factor (if there is one) x Efficiency ( if there is one). If It's Gas Discharge Lighting it's; Wattage x 1.8 For In rush Current/ 230V. End of step one. You've found the Load Current Ib. ( The "I" is the symbol for Current and the "b" stands for "Burden" as in burden on the Circuit) You now know that Current is going to be dragged through your Circuit and can rate your Switches, Junction Boxes and Terminals to exceed Ib, or you'll eventually melt them, or weld them shut.
2) Now choose a Protective Device that equals or preferably just exceeds Ib. Cb types are; Type B for Resistive Loads, Type C for Resistive/Inductive mixed Loads and Type D for mostly Inductive loads. The rating of that Device ( i.e.32 Amps) is now your "In" or nominal current rating for your device
3) Next, calculate IT. IT = The Tabulated Current Carrying Capacity for the Cable, so called because you have to gather information on what could increase heat on a Cable, along your intended route for the Circuit. Heat is the enemy of cables, particularly PVC and Copper cables, as Copper has a Positive Temperature Coefficient, meaning it's Resistance goes up with heat ( and Current carrying ability subsequently goes down), whilst PVC has a Negative Temperature Coefficient, meaning its Resistance goes down in increasing heat....neither of those effects are what you want in a Cable Conductor or Insulator! There are Correction Factor Tables in the Regs, or the On Site Guide: the commonly used ones are Ca= Ambient Temp Correction Factor, Ci= Insulation Correction Factors (through insulated cavity walls, not the Insulation in Lofts and Ceilings, Cg= Grouping Factor for cables heating each other up, Cc is for cables buried underground in Soil, whilst Cf is for the old Semi enclosed rewireable Fuses, which can be too slow to clear Overloads effectively ( don't use them.) Once you've gathered the data ( there are more correction factors than this but these are the most common) then calculate IT. IT= In ( CB Rating)/ Ca x Ci x Cg x Cf x Cc. Now you've found IT make a note of it.
4) Establish the Installation Reference Method? Are you clipped Direct? Are you in Conduit or Trunking? This too has a heating effect to a lesser extent and effects the ability of the Cable to carry the Current. It comes out of a Table in the Reg's in the Form of a letter Code from the Alphabet.
5) Now chose a cable type and look it's Current Carrying Capacity Table up for its particular table in Appendix 4, tables 4D onwards of the Regs. Look for the Column on the table with the Letter code you found earlier for the Installation Reference method and look down the Column of figures until you reach a number that's the next size up from IT, that you calculated earlier. You've just found the IZ for your cable. IZ Is the Current carrying capacity of your cable. "Z" As a reminder that it's the last letter of the alphabet and the last thing you should be deciding is the cable size...not the first. Now look across from the IZ number on the table and read off the cable size in mm sq that you should be using.
6) Measure your length of run in Metres. Now calculate your Voltage Drop by reading the corresponding milli V/Amp ( of Ib)/ metre in the IZ tables. Multiply all those values and check your chosen cable comes under the Voltage Drop Limits in the Appendix 4, the Voltage Drop table. If the Voltage Drop exceeds the percentage limit listed, try the next size cable up and see how you get on for Voltage drop with that ?
7) Now look up the R1 and R2 prospective resistance rating of your Line and CPC in milli Ohms/metre and calculate that for your run. You'll find the tables in the on Site Guide, or in the back of Guidance Note 3 Appendix B. Add it to your Ze (0.35 for TNC-s, 0.8 for TNS and less than 200 for TT). Then adjust for temperature as the Resistances in the table were calculated at 20 degrees c. Inside ambient is 30 Degrees C using the multiplying factor tables in the On Site Guide. You've now got your Theoretical Circuit Zs in Ohms. Go to the Protective Device Zs tables in Part 4 of the Regulations and check the Zs you've just calculated, comes under the maximum Zs ( x 0.8 for indoor circuits) listed in the table for the In you chose in step 2. ( The Max Zs tables in the On Site Guide are already Temperature corrected for indoors, so don't multiply by 0.8 if you are using these tables.) If it doesn't then your fault current isn't going to be cleared in time by the Protective Device, before the Fault Current starts thermally shocking the Conductor. You might have to fit an RCD to the Cb, just to get it cleared in time. but beware, some Special Locations require an RCD and a Zs lower than the Max. In this case, fit a Distribution Circuit of a larger CSA cable from the Consumer Unit, to a Distribution Box of a Discriminatory Protective Device, to reduce Zs and shorten the length of run to the Final Circuit. This should reduce the Zs.
If any of that didn't make any sense, or you don't have the means to do the Cable Calcs, then you really have no business Installing Circuits...especially the ones in your own home?
Hope this informs?
Mr R Sole and I currently have identical employment. I teach JTL and On Site Apprentices the basics in level 3 Design amongst other things.
Install a power shower, they will rip you to the bone.I’m a little surprised that there are still electric showers, not only are they dangerous with 240 volts in the shower with you they are not really a shower as such, just a dribble of hot and cold water. After living in Canada I realised on a trip back to blighty just how appallingly bad they were.
A shower should be capable of tearing off the top layer of skin with water pressure and lots and lots of lovely hot water with no danger of death ‘going for a shower sir? Well take this piece of leather to bite on’
Safest solution is get your missus to hook-up a Kärcher to a hot water tap and and give you the good news at 140Bar. No danger of electrocution!