gkenyon:ProMbrooke:gkenyon:ProMbrooke:gkenyon:ProMbrooke:
Thats where CPCs come in, in that they would cause the fuse or MCB to open in 0.2 seconds or less.Doesn't that happen anyway ... in TN systems where the loop impedance ensures operation in 0.1 s?
The issue being, that, in TN-S systems (no RCD), you're limited in circuit length with Type C mcb's.
Also, interested where 25 V comes into the equation here? To do that, you've got to oversize the cpc, not undersize it ... and even then, may not be possible in TN-S due to the effect of the distributor's cpc ?
It does, but going by table 41.1 we are allowed a loop Z high enough to cause 0.4 seconds disconnection.
Type A, B, or C MCBs, fuses, or the like you are always limited in circuit length be it voltage drop or should the RCD become inoperative.
25 volts is the highest touch voltage under infinite time allowed by the IEC in wet locations according to Table C.1 in IEC 61200-413. Where higher touch voltage are found, disconnection is required. At 125 volts 0.17 seconds is required. With a reduced size CPC, even faster times are required.
IEC 61200-413 is now inactive. It's not a current standard.
As I've said repeatedly, you'd need to refer to something more up-to-date.
Latest versions of IEC 61140 and IEC 60479 series.
IEC 60479 still gives similar results. 30% decrease from 900 is 630 ohms. So assuming 630 ohms vs 500 ohms take us to around 0.2 seconds vs 0.17 seconds in the old standard.But that's for large contact area ... and hand to hand.
You'd probably be more realistic looking at small or medium contact area, hand-to-foot.
What about saltwater-wet conditions?
Why do all conditions need to consider water-wet?
And finally ... if you do have a serious concern ... you're not taking children into account, and at least 10 % of the population (but then again, IEC 60479 doesn't full stop really).
A handle on a fridge, tool, pole ect becomes a large contact surface area. Both feet on the ground with wet shoes. In fact with a power tool its possible to have both hands on it at the time of a fault.
IEC 60479 gives 850 ohms at 125 volts with salt water.
Water wet would be places where wet hands are common or likely to be found: pools, spas, bathrooms, greenhouses, sinks, outdoors.
Children are a difficult challenge as ethical issues are raised as to whether or not they can consent in scientific experiments. However, considering smaller hands and thus contact area the difference may not be so big. At least resistance wise. Whether or not children have a lower ventricular fibrillation threshold would be impossible to test for, for obvious reasons.
gkenyon:ProMbrooke:gkenyon:ProMbrooke:gkenyon:ProMbrooke:
Thats where CPCs come in, in that they would cause the fuse or MCB to open in 0.2 seconds or less.Doesn't that happen anyway ... in TN systems where the loop impedance ensures operation in 0.1 s?
The issue being, that, in TN-S systems (no RCD), you're limited in circuit length with Type C mcb's.
Also, interested where 25 V comes into the equation here? To do that, you've got to oversize the cpc, not undersize it ... and even then, may not be possible in TN-S due to the effect of the distributor's cpc ?
It does, but going by table 41.1 we are allowed a loop Z high enough to cause 0.4 seconds disconnection.
Type A, B, or C MCBs, fuses, or the like you are always limited in circuit length be it voltage drop or should the RCD become inoperative.
25 volts is the highest touch voltage under infinite time allowed by the IEC in wet locations according to Table C.1 in IEC 61200-413. Where higher touch voltage are found, disconnection is required. At 125 volts 0.17 seconds is required. With a reduced size CPC, even faster times are required.
IEC 61200-413 is now inactive. It's not a current standard.
As I've said repeatedly, you'd need to refer to something more up-to-date.
Latest versions of IEC 61140 and IEC 60479 series.
IEC 60479 still gives similar results. 30% decrease from 900 is 630 ohms. So assuming 630 ohms vs 500 ohms take us to around 0.2 seconds vs 0.17 seconds in the old standard.But that's for large contact area ... and hand to hand.
You'd probably be more realistic looking at small or medium contact area, hand-to-foot.
What about saltwater-wet conditions?
Why do all conditions need to consider water-wet?
And finally ... if you do have a serious concern ... you're not taking children into account, and at least 10 % of the population (but then again, IEC 60479 doesn't full stop really).
A handle on a fridge, tool, pole ect becomes a large contact surface area. Both feet on the ground with wet shoes. In fact with a power tool its possible to have both hands on it at the time of a fault.
IEC 60479 gives 850 ohms at 125 volts with salt water.
Water wet would be places where wet hands are common or likely to be found: pools, spas, bathrooms, greenhouses, sinks, outdoors.
Children are a difficult challenge as ethical issues are raised as to whether or not they can consent in scientific experiments. However, considering smaller hands and thus contact area the difference may not be so big. At least resistance wise. Whether or not children have a lower ventricular fibrillation threshold would be impossible to test for, for obvious reasons.
