Overloading one side of ring circuit
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Pensdown said:
andy said:
andy said:
I find the lack of understanding of basic electrical theory in both of you disturbing...
Please remember that next time you need any work done...Pensdown said:
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The former.
T
toasty
Adam,
Nice explanation, I agree totally.
However I wonder in real life how this would actually work....
The shorter leg would carry more current and therefore heat up a bit, which would in turn increase it's resistance resulting in more current flowing through the longer leg.
I wonder how much of a balancing effect this would actually have?
I guess as well as the resistance of copper we also need its temperature coefficient as well!
Nice explanation, I agree totally.
However I wonder in real life how this would actually work....
The shorter leg would carry more current and therefore heat up a bit, which would in turn increase it's resistance resulting in more current flowing through the longer leg.
I wonder how much of a balancing effect this would actually have?
I guess as well as the resistance of copper we also need its temperature coefficient as well!
0.004041
T
toasty
...and how it is ran (i.e clipped in free air, conduit, under insulation etc...)
Ambient temperature etc...
I guess you could never really calculate it reliably...
Anyone have any real life experince of an unbalanced ring causing any damage?
Interesting post BTW.
-Dan
Ambient temperature etc...
I guess you could never really calculate it reliably...
Anyone have any real life experince of an unbalanced ring causing any damage?
Interesting post BTW.
-Dan
That affects how well it can shed heat, and therefore what current it can carry before getting too hot, not how much its resistance changes with temperature.toasty said:
That affects how much hotter it can get before it reaches its maximum operating temperature, not how much its resistance changes with temperature.
You may assume an ambient temperature of 20ºC, and that the cable has been installed such that at Ib it reaches 70ºC.
I look forward to seeing your calculations.
A very good Q.
in some situations it can be almost as bad as a broken ring* and whether broken rings cause damage to the cables is a bit hit and miss, depending of course on the load applied to a single bit of 2.5 and the way the cable is installed (more insulation, the heat can't excape from the cable and it takes on a lower rateing) would be interesting to see if anyone has found a badly damaged cable caused by an overload as a result of a broken ring
*I'll calculate it a bit later, but in the kitchen at home, the ring starts from the CU, goes about a third of the way along the wall, feeds an outlet for the tumble dryier and the washing machine, goes another third along the wall and there are outlets for the kettle and dishwasher, then it carries on to the end of the wall feeding outlets with very little load, goes into the loft (and quite a bit of cable there - weird building construction), then comes along the opposide wall, a few outlets with very little loads, then along the end wall with no outlets and back to the CU - clearly not a clever design
I dare say when I calculate it, if we assume all appliances are working together, then there will be an overloaded piece of 2.5, how likely this to occur is a slightly difficult thing to factor in, though (there is an issue of 'wiring matters' from the iee which has charts of how the cycles of white goods overlap, but even this assumes they all start at the same time, which doesn't happen in practice)
Maybe one day I'll do an experiment using a clamp meter and see just how bad it works out inpractice with our kitchen ring...
sorry if I've digressed
Adam_151 said:
I have a ring circuit serving one side of the kitchen, as follows (number of === approx. proportionate to length of cable)
CU
Outward leg:
========== sockets and spurs for minor appliances === m/wave (2600W) === sockets and spurs for minor appliances (hob ignition, cooker hood) === sockets (kettle) === dishwasher (2550W) == socket (toaster)
Return leg (following same route):
Unbroken cable run back to CU
I think from what's been said above that I have no reason to be overly concerned about an unbalanced load. I can see how it may have been marginally better to feed some of the fixed appliances from the return leg but even if alternate sockets had been fed from the return leg, whether the high load non-fixed appliances (kettle and toaster) end up being supplied from one leg or another is only down to chance.
Anyway, interesting debate and another little nugget of understanding.
Of course Adam's right, (you break the laws of physics) anyone who is in doubt should try putting a clamp meter on a ring cct next time they are testing. Both conductors gives the total, and the two legs if measured will equal this.
Years ago there used to be rule of thumb for postioning sockets on a ring when one ring was used for a whole house. Most sparks now divided the house up enough not worry about leg loads. Also, not many houses have the electric heating loads they used to have with central heating so it's normally only the kitchen you need to worry about.
Anyway. Good to see your on the ball Adam
Years ago there used to be rule of thumb for postioning sockets on a ring when one ring was used for a whole house. Most sparks now divided the house up enough not worry about leg loads. Also, not many houses have the electric heating loads they used to have with central heating so it's normally only the kitchen you need to worry about.
Anyway. Good to see your on the ball Adam
I think the next debate we should have is "when is shower not a shower"
We've just completed re-wiring a large kennel and in the Kitchen they have a shower attached to sink tap like in commercial Kitchens. They use this not only to wash up but they have a floor drain and use it to wash the dogs coat if they roll in crap. During our last NIC inspection the inspector said that as the hand shower was being used for dogs, the kitchen should be classed as "Shower Room", with all the implications.
...I would like to hear your opinions.
We've just completed re-wiring a large kennel and in the Kitchen they have a shower attached to sink tap like in commercial Kitchens. They use this not only to wash up but they have a floor drain and use it to wash the dogs coat if they roll in crap. During our last NIC inspection the inspector said that as the hand shower was being used for dogs, the kitchen should be classed as "Shower Room", with all the implications.
...I would like to hear your opinions.
Pensdown said:
I'd be inclined to agree with the NIC inspector, if we consider that the reasons shower areas are classed as special locations is due to decreased body resistance due to lack of clothes and wetness...well the dogs don't have clothes anyway, but the wetness point is valid, putting saftey of animals on the back burner for a moment (not very PC, but what the hell, its the real world), what about the person doing the washing, well they are unlikely to naked (or at least I'd hope they arn't
) but their hands and arms at the very least may well be quite wet, possibly their feet if water runs off and forms a pool on the floor (I don't beleive animals are as easy to wash as dishes), in in the the extreme they could end up drenched if the animal objects to the washing... which brings us on to the other point, the issue with wetness in a shower area is not just the people using the shower will be wet, but that water may get splashed into electrical fittings if they are nearby, I'd say the risk of this would be even bigger in the situation you describe than in a normal bathroom and certainly higher than one would consider normal for a kitchen (well my dishes don't tend to jump about and shake themselves dry!)I'd be very tempted to treat this as if it was a shower that is installed in a room thats not strictly a bath or shower room (think en-suite shower installed in a bedroom)
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