Yep. RCD's tripping with the "wrong" polarity strikes me as an big indication that something isn't quite what it should be with the caravan wiring.
I should hope it places a resistor between L and N and across the current transformer. So that it actually tests what it is supposed to be doing rather than relying on another path that might not exist.
L ------ CT -------+--->
| +-- R -- TB --+ LOAD | N ---+-- CT ----------->
Whether the wiring is radial or ring makes no difference. What is important is that fused plugs allow circuit protection at a higher rating than would be permitted for individual appliances.
We have 20A and 32A radial circuits as well as 32A ring circuits; both need fused plugs as appliance flexes are only rated up to 16A (now, was
3/5/13/15A).If we didn't have fused plugs then circuit protection would have to be at 16A and we would have the problem that they do have in the USA that if you plug two high power appliances into the 'wrong' combination of sockets on various circuits the MCB trips.
Owain
I disagree; with a radial system it is possible to protect the appliance cord at the distribution circuit breaker. That is not possible with a ring main.
The fact that an MCB might trip does not demonstrate the system is unsafe.
Tony
There's plenty of it around. Their deaths per capita arising from electrical causes is significantly worse than UK and much of Europe. This is nothing to do with a radial system (which is implemented very safely in many places). It's to do with the poor quality of their wiring accessories, connections, breakers, etc, combined with higher current heating effects due to lower mains voltage. This is also amplified by the more significant use of entirely timber (flammable) building construction in many areas.
Why not? If you protected your circuit with a 16A MCB (be it radial or ring) then the appliance flex would be protected at the origin of the circuit.
You would of course also end up with a bunch of piddly little circuits not at all well suited to today's pattern of usage.
No, just that the design is not really fit for purpose.
You also could have suggested 32A appliance cords.
However putting a 5A fuse into the plug of a 2kW kettle in the UK does not prove that the architecture of the wiring system is not fit for purpose.
Tony
Frankly I've found it doesn't, in practice, matter what you use. Sister took about four different cables to cover all 'reversed wiring' possibilities, along with a tester , and took about an hour to figure it all out to her satisfaction. We just plugged in and that was it.
We know for certain that one of the sites was reverse polarity, so all we did was not leave stuff, phone charger etc, plugged in!
s'easy ... ;)
snip
Uses the Earth (the real solid one you stand on) for the return. Works well most of the time except when the weather is very dry then you get brown outs ................ (well you would if there is no rain!)
-- Mark BR
UK plug fuses are there to reduce (but not eliminate) the risk of fire caused by an appliance. They don't protect people, as you would be dead long before a fuse blew.
Mainland European installations have relied on RCDs for many years. An RCD protects people, not appliances, so you aren't likely to be electrocuted thanks to a flimsy plug, although there may be a slightly higher fire risk (or so I am told).
Fuses/circuit breakers are quite independent of RCDs and the use of one does not affect the need or the efficacy (or danger of fire) of the other).
Tony
Actually, they are there to protect only the appliance flex. If an appliance needs fusing for safety reasons, it is required to have a fuse within itself, and it isn't permitted to rely on any plug fuse.
Depends which risk you are considering. They protect you from a fire which might otherwise result.
I won't claim a vast experience across all mainland European installations, but I have never seen an RCD to protect people against electrocution used in the premises wiring (except for the occasional RCD-protected outdoor socket). RCD's are common in mainland Europe because TT and IT installations are more common than they are here, but those are normally 500mA RCDs in the areas of Europe I've seen them, and they are part of the supplier's works (like the meter is).
Not really, ignoring the impracticability of the size of the flex required, there is the problem that the socket and plug are not rated for the current.
Did anyone say it does? A 5A fuse in a 2kW appliance is an error. A 16A MCB on a general purpose power circuit is a design choice. However it would be a poor design choice for a circuit designed for a diverse load pattern, that can serve 100m^2 of floor area, and is cabled to handle in excess of 7kW of load.
Exactly, as was the reason mentioned in the post I was following for those circuit breakers tripping and that you characterise as a design not fit for purpose.
I am disappointed that my remark about plug fuses being needed in the UK because of the use ring mains in the UK has turned into arguments over whether any particular architecture is superior or unfit for purpose.
Tony
Unless a radial circuit is restricted to the current of the smallest flex likely to be plugged into it - which would be silly - a fused plug remains a good idea, regardless of the type of circuit.
I was not arguing that one architecture is superior to another (I believe there are pros and cons to both circuit types and one needs to chose which to use based on circumstance). However I was questioning your assertion that fuses are required *because* of the use of ring circuits.
I was highlighting that the requirement for the fuse is nothing to do with the circuit architecture. A 32A radial wired in 4mm^2 T&E would also require fused plugs for exactly the same reasons.
The crux of the issue is that if you have a circuit capable of supplying a current significantly in excess of the rating of the appliance flex, then you need a overcurrent protected plug. So its not really anything to do with the circuit being a ring or not, even if that is the most commonly encountered 32A circuit in the UK.
Easy to contradict - just find any examples of wiring codes that use ring mains without fused plugs or any that use fused plugs on a radial system.
Tony
If no national wiring code adopted that design how can you prove it's good?
Tony
I agree, but most of the world doesn't have fused plugs. So is there a major problem with, say, those 3A flexes running to laptop power bricks, plugged into a radial circuit limited to (say) 16A??
Ergo, you can never introduce a new way of doing things because no national code has specified that way therefore there is no way of proving it's good. At least, that appears to be where you are with that question. Doesn't make much sense to me.
Well the second is easy, as I mentioned before, a 4.0mm^2 T&E 32A radial, a standard circuit as described in BS7671.
Other countries don't tend to have comparable circuits since they don't have plug fuses, and hence can't provide adequate protection for the appliance flexes at the circuit origin.
To say that you can't find ring circuit designs that don't require plug fuses seems to rather miss the point that the need for the fuse arises out of the high current capacity of the circuit and not its topology.
Turn it round the other way, can you justify the need for a plug fuse just on the basis of having parallel connection paths to the circuit breaker? (or for that matter any other unique characteristic of a ring circuit other than its high current delivery capacity)
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