Recent content by christof22

Hi John, i didn't quite grasp what you were saying :) Conversely, one can have satisfactory MPB (and maybe also SB) but without satisfactory ADS (e.g. if Zs was too high) - in this case 'not safe'. Notwithstanding thermal constraints, you can, it would be a challenge and you would...

:? I'm getting confused now :D Yes, the first part of your post is the point i am making, maybe i misunderstood your previous post( that one can exist without the other) [/b]

Hi John It does depend upon the installation as you say, though if MPB is required then for ADS to be safe MPB needs to be installed. Hadn't read the full thread, missed the SB bit :) Cheers Chris

Hi John Sorry i will have to disagree on that note, you need both, disconnection and MPB for ADS to be safe. Cheers Chris

I think you are all confusing the matter lol ADS is one of the requirements for protection against electric shock(BS7671), and it comes as a package, Protective Equipotential Bonding is part of that package. Cheers Chris

Hi John In your example you have the (500)2, and a time of 0.01, a non limiting device would have a I2t of 2,5 kA, with an energy limiting class what the time current graph doesn't show is how the device limits the peak current, which in turn effects the I2t. So in my example we have the...

Hi John I believe i have answered your question, down to 0.1 seconds you will derive the same answer, below 0.1 there are other factors, energy limiting, asymmetrical faults. Example 32 amp type B, 500 amp fault current, I2t = 1.69(kA2S) Disconnection time = 0.01 Your method would...

Hi John At around 15 kA the fault current will contain a DC component, the fault current is no longer symmetrical, its now asymmetrical, this makes direct calculation difficult and will differ from one device to another. Cheers Chris

I think it may be difficult to meet parts (iii) and (iv) of 543.2.6 Cheers Chris

Hi John, the Time current curves in BS7671 will be the same as the manufacturers I2t down to the 0.1 second disconnection times. Cheers Chris

Hi John Manufacturers info on I2t starts much lower than the 10 kA, if you are looking at low fault current levels then i doubt there will be much of a difference between BS7671 and the manufactures info, as fault currents increase energy limiting kicks and manufactures CPD will differ in how...

With disconection times less than 0.01 you need to refer to the manufacturers A2S/I2t, where large fault current exist, these figures are derived through test and measurement, though its still definitely an adiabatic process. cheers chris

The adiabatic assumes all heat is contained within the conductor, this is relatively true for disconnection times upto 5 secs , upto ten seconds with certain cable sizes if memory serves me right. Beyond these times we have no adiabatic, now heat is lost into surrounding insulation, if we...

Hi You need to assess the fault current levels, front end and far end. Then you will either have a disconnection time or a I2t to use within the adiabatic. cheers chris