Hi All,
I am considering a transformer with emergency generator combination. I have read some threads of pros and cons of using a 3 pole vs a 4 pole ATS.
3 pole seems to avoid some issues with potential floating neutrals but usually comes with the warning that having genset and transformer on...
Hi All,
I am looking at some Schneider data sheets for fuse backup protection for breakers and switches.
One table notes the fuse as "BS88 or gG" in one column and "HRC DIN type" in another. I took this to mean a BS Bolt-in or clip-in fuse would be the first column and a NH type fuse would be...
Hi All,
I don't have access to IEC 60269-2. Can anyone tell me if the standard provides total I^2t energy maximum values for the various fuse types. I have IEC 60269-1 but it only specifies minimum pre-arcing energies, I need the total energies.
Cheers,
Healyx
Hi All,
Does anyone have a source for a numerical example of how to calculate the damage curve of a transformer using IEC 60076-5.
I have found heaps of examples for IEEE/ANSI curves, but no luck with the IEC calc.
Specifically I'm not understanding where the J term (current density) in the...
Hi,
For a LV generator (400V output) that feeds a TNC-S earthing system where 4 cables leave the generator (3 phases and 1 PEN (combined Protective earth and Neutral)). The neutral on the generator is also bonded to the earth electrode.
Is it correct to say that Line to Neutral faults in the...
Does anyone have a source/reference that shows that current sharing between parallel multicore cables is equal?
I am talking about 3 phase, unshielded multicore cables where the 3 phase cables are arranged in a triangle (triplex/trefoil) and have a consistent, constant twist rate (transpostion)...
Hi,
When sizing a cable fed by a fuse for temperature rise, do you use the "pre-arc I^2t" or the "total I^2t" (voltage dependent) for the actual let through energy the cable would see for a high current fault? I think it would be the "total I^2t" figure but I am surprised at how this results in...
Hi,
Is the published total let-through energy (not pre-arc)for a fuse the largest amount of energy that a fuse will let-through for a fault in the adiabatic region (0-5s)? or is it just the worst case energy that will be let-through for the worst case fault level (e.g. device rating)?
I am...
Hi All,
I was once told during a course that if you had high earth loop impedance, instead of increasing cable sizes, you could use an RCD. I can't find the reference in AS/NZS 3000 (Australian Wiring Rules) to say this is OK? Does anyone know where to find it? Happy to get opinions on other...
Hi All,
Does anyone know how to calculate reactance for 2 cables in a closed loop (e.g. phase and earth cable) where one cable is larger than the other?
I use the equation X = 0.0628ln(GMD/GMR).
Cable 1 (Phase Cable is 240mm2 - GMR = 7.7)
Cable 2 (Earth Cable is 95mm2 - GMR = 4.8)
Distance...
Hi All,
I'd be interested in some opinions on this:
Should a single phase circuit breaker in a 3 phase switchboard have a fault rating >= the maximum 3 phase fault at the board or the maximum single phase fault at the board. The single phase fault (phase to neutral or phase to ground) is...
Hi All,
I'm using Schneiders free Ecodial program to try and calculate some short circuit currents. I was doing a sanity check on the maximum single phase current (Ik1max) and am a long way off their calculated answer. Can anyone confirm I have this wrong?
The system is:
400V Phase/Phase...
Hi All,
I'm trying to work out how to calculate minimum fault current manually in the IEC domain (usually phase to ground fault is minimum). I know the Cmin parameter needs to be set to 0.95 but what I need to know is what temperature the various cable resistances should be calculated at...
Hi,
Does anyone know where it is stated that it is OK to use IEC60909 to conduct short circuit analysis instead of AS3851 in Australia? I haven't found a software program that states compliance with AS3851 but have found plenty that do IEC60909, and these programs appear to be in use in...
I know that if a circuit breaker is interrupting a known symetrical fault, you can find out the disconnection time by looking at the breaker's time-current curve (Given you have calcualted the prospective short circuit current (PSCC) using cable impedance etc.). Can you still calc disconnect...
Hi,
When sizing a cable you need to take into consideration among other things short circuit temperature performance. Here is Australia we use AS3008 to size cables for 600v or lower (apparently very similar/interchangeable to european standard IEC 267??? - I can't remember the number).
I...
