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| Big Clive's "Trashy" meter, unboxed ( Duratool D03047 multimeter ) |
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| AVGresponding:
--- Quote from: IanB on April 30, 2023, 04:32:17 pm --- --- Quote from: AVGresponding on April 30, 2023, 01:00:36 pm ---4mm2 can be used for particularly long runs, but this is not ideal, and would be unlikely to be necessary in a domestic setting, and would be discouraged in any case, due to the negative impact on tripping times. I have seen 6mm2 used on a 20A radial socket circuit; it barely passed muster under testing. --- End quote --- How and why does cable size affect tripping times? For example, a 12 m run of 6 mm2 is going to have the same resistance and voltage drop as an 8 m run of 4 mm2 or a 5 m run of 2.5 mm2. Run lengths are going to vary a lot between a large house and a small shed. --- End quote --- You're thinking in terms of DC resistance; this is an AC circuit... |
| AVGresponding:
--- Quote from: themadhippy on April 30, 2023, 05:16:52 pm --- --- Quote --- I have seen 6mm2 used on a 20A radial socket circuit; it barely passed muster under testing --- End quote --- how come? the R1 R2 for 6mm is going to be lower than the same length of a bit of 2.5/1.5,meaning your fault current will be higher leading to a faster disconnection time,the only failure i can think of is the fault current being to high for the protective device --- End quote --- It was a very long run. I can't remember the exact length (this was 10 years ago), but I remember expressing some doubt. Funnily enough I was in the building yesterday, doing some fire alarm and emergency lights testing. It was for some sockets on columns, in a conference hall. They had to go up and over the ceiling, rather than in the floor; istr there were 4 columns and they used 2 circuits, so 2 columns per circuit. Only 2 double sockets per circuit, but the length would be over 60m I should think. |
| IanB:
--- Quote from: AVGresponding on April 30, 2023, 06:25:00 pm ---You're thinking in terms of DC resistance; this is an AC circuit... --- End quote --- The calculations for 50/60 Hz AC are the same as for DC where resistance, voltage drop and maximum fault currents are concerned. |
| AVGresponding:
--- Quote from: IanB on April 30, 2023, 07:00:39 pm --- --- Quote from: AVGresponding on April 30, 2023, 06:25:00 pm ---You're thinking in terms of DC resistance; this is an AC circuit... --- End quote --- The calculations for 50/60 Hz AC are the same as for DC where resistance, voltage drop and maximum fault currents are concerned. --- End quote --- The PFC is based on the impedance, not resistance, of the CPC. As for RCD trip times, it's the capacitance of long cables that affects the trip time. |
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