An overview of the testing procedure for supplementary protective bonding. I also talk about "My' take on touch voltage. Comments on this most welcome, as I find it a complex issue.
This is the only video which clearly makes the distinction between the purpose of CPC and PBC respectively - one limits the duration of the fault and the other limits the level of the fault. This is a very important concept which is quite difficult to grasp but once understood makes sense. I must admit these videos are impressive - I suspect you have taught this subject ...if not you should !
Good explanation on Supplementary Protective Bonding and Touch Voltage. Good revision, especially as I don't work in bathrooms and the like. Back in about the late 80s we were involved in a refurbishment of some blocks of flats 12 storeys +, we had to bond the metal window frames throughout each flat. My governor at the time with technical teams argued against it, still had to be done 🤷♂🤦♂. Thank you. 👊😎👍💙
Thanks very much, really appreciate your comment. I have been trying to put a video together for a while on transposing formula. Something I still struggle with. Looking at your channel, you have some great content on that.
Thanks for the video. I've always struggled with this topic but the graphics using hypothetical resistances helped. Confused when you said at 17.39 you say you can "calculate the Volt Drop on the R1 leg", then realised you'd included the external element of 0.175 ohms. Certainly helps and I'll bookmark this video for future reference. Just a quick question, why 240 volts and not 230 volts as used in most other calculations?
Thanks for the comment. I used 240, because I was using the touch voltage scenario from Paul Cooks Comment on the wiring regulations book, and he used 240V.
Hi...Thanks for the video. I was under the impression that 230 volts multiplied by the Cmin, was to be used in this type of callculation. ... Also, that the 50 volts was for use on a TT system, and you should use 230 volts on TN systems which if used along with an RCD would give 1667Ohms with 59 volts but 7667 ohms with 230 volts?
Thanks for the comment. You only need to use Cmin, to account for fluctuation in the supply voltage when finding Zs values. 50 volts in the maximum touch voltage allowed. The 1666 reading --- Supplementary bonding test is 50V not 59V ( 50/ 0.03 is 1666.66666...) Often rounded up to 1667. And the 230 V is for the extraneous CP test so for a 30mA RCD that would be 6.67kΩ, as you take 1000Ω off for the impedance of the human body
@@JPElectric great video. So why is supplementary bonding test is at 50 volts? And extraneous bonding test is 230 volts? They both can indroduce a dangerous potential! I assume the supplemtary test is at 50 volts because water is more likely present! I.e water tap, radiator pipe etc.
Best to test with a megger as in insulation resistance test.. Put one lead of the megger onto a known earth in the bathroom i.e the earth in the light fitting and test it to the extraneous conductive part i.e the Tap in the bath. If the resistance is less that 1667 ohm there is no need to supplementary bond. If the resistance is between 1667 and 22000 ohms then it needs to be supplemtary bonded. Take a 2.5mm earth from light fitting and bond to tap. 50 volts is minimum touch voltage and resistance of human body is 1667 ohm approx. Divide 1667 into 50 volts result is .02 miliamps which is 20 miliamps. All bathrooms should be 30ma rcd protected. So that means rcd will trip as resistance has a low enough value for fault current to flow.
