Last week Mrs B bought a Russell Hobbs travel kettle from Argos. Test boiled it once successfully then refilled for second boil/rinse per instructions. Shortly afterwards noticed every socket in house had gone off. Checked in garage to find RCD tripped. So far pretty normal.
Quickly traced kettle as culprit. Surprising bit though was it tripping RCD immediately it was plugged in and with socket still switched off.
How does that happen?
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I believe that household sockets are single pole, so they only break the live supply. If there is a short between the neutral (blue wire) or somewhere internal and earth it could trip the breaker. Cookers and showers have double pole switches that completely isolate the device.
Last edited by: Old Navy on Sat 11 Nov 17 at 13:15
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Perhaps it has a neutral to earth short, maybe in the plug. Have you tried it in another socket though?
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Thread drift a bit...
Just wired up a new mid price range British made cooker. The block a the back of the cooker is barely large enough to accommodate the thick electric cables and the cable grip does not accommodate the cable.
Its clear money saving and annoying and potentially dangerous.
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>> Perhaps it has a neutral to earth short, maybe in the plug. Have you tried
>> it in another socket though?
Yes and tried other items in the socket it was initially connected to. Definitely kettle causing the trip.
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Take it back. It will have a moulded plug so no user serviceable parts inside - it's dangerous. I often wonder about this - Bought a DVD player for the Office in my old job. Failed PAT testing out of the box. Expensive proper make.
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>> Take it back. It will have a moulded plug so no user serviceable parts inside
>> - it's dangerous.
It went straight back and was replaced without quibble even though she couldn't find receipt.
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Assuming that the house is correctly wired, and all earth bonding has been done correctly.
Probably a N to earth connection - probably a a direct short inside a failed heating element. It will only cause an RCD to trip if the neutral is floating up above Earth potential enough to generate sufficient current to exceed the trip current . This can happen if the neutral is bonded to earth some distance away eg at a substation and there is a sufficient other load resulting in a voltage drop on the neutral. Use a DVM to check the neutral voltage wrt to earth. This could also be the result of large loads on other premises from the same supply.
It could also happen If the neutral - live are reversed somewhere, you need to get this checked!
It could also happen if the socket is wired incorrectly.
Some sockets are now equipped with DP switches but I believe that this relatively recent innovation.
Last edited by: sherlock47 on Sat 11 Nov 17 at 15:36
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>> Assuming that the house is correctly wired, and all earth bonding has been done correctly.
>>
>> Probably a N to earth connection - probably a a direct short inside a failed
>> heating element.
Thanks. I'd sort of thought through the possibility of a live/neutral difference but couldn't quite rationalise how it happened. Your explanation fills the gaps.
>> It could also happen If the neutral - live are reversed somewhere, you need to
>> get this checked!
Pretty sure that's not case. No other appliance has caused a problem and it was checked last year when our blown oven was replaced.
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>> It could also happen If the neutral - live are reversed somewhere, you need to
>> get this checked!
>>Pretty sure that's not case. No other appliance has caused a problem and it was checked last year when our blown oven was replaced.<<
1. Did they check every socket? and all wiring? - I doubt it.
2. That fault would not show up when plugging non faulty items into the same socket. So nothing is proved.
Last edited by: sherlock47 on Sun 12 Nov 17 at 10:20
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Bromp, as a caravanner who goes foreign, haven't you a Martindale?
Just read that and it sounds a bit Masonic.
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>> Bromp, as a caravanner who goes foreign, haven't you a Martindale?
Been on my going to do list for ages. Now on order from Amazon.
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>>
>>
>> Probably a N to earth connection - probably a a direct short inside a failed
>> heating element. It will only cause an RCD to trip if the neutral is floating
>> up above Earth potential enough to generate sufficient current to exceed the trip current .
>> This can happen if the neutral is bonded to earth some distance away eg at
>> a substation
Aha, I presume you are an electrical expert Holmes?
I have never found anyone who can explain what is going on here in a way I can understand:
Our house is in open coutryside and gets its mains from our own transformer on a pole in a field, carrying the 10KV transmission lines. Two wires lead to another pole just by the house, and at the insulators mounted on the eaves one of the wires branches, becoming the Neutral and Earth which run, with the Live, to the fuse box.
So it seems to me that in our house, Neutral and Earth are the same thing. It would make no difference which way round the sockets were connected, as they are joined together anyway, the junction on the pole being earthed by a wire running down to the foot of the pole.
From what you seem to be saying in this thread, we have a permanent, intentional, situation which an RCD would detect as a fault?
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Martindale arrived today and sockets that tripped RCD with errant kettle test OK.
Instructions make clear that device cannot detect Earth/Neutral crossover. N & E at supply from pole transformer are in some ways same thing as your description sets out. Earth on appliances is there to ensure that if a fault exists allowing user touchable conductive parts (eg Washing Machine's steel case ) to become live current will go directly to earth and blow fuse/trip CB.
Reply to my post says *I think* that in urban situations loads can behave so that there is a potential difference between Neutral and Earth which could trip RCD but cause no other problem.
Last edited by: Bromptonaut on Mon 13 Nov 17 at 21:22
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>> Two wires lead to another pole just by the house, and at the insulators mounted on the eaves one of the wires branches, becoming the Neutral and Earth which run, with the Live, to the fuse box.
I am not sure I understand your description;
Are you saying that there are 3 wires from that post nearest the house. one of which is the earth ? Live & Neutral from the street, and earth from the bottom of the pole?
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>
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>> Are you saying that there are 3 wires from that post nearest the house. one
>> of which is the earth ? Live & Neutral from the street, and earth from
>> the bottom of the pole?
>>
>>
No, I am saying that 2 wires leave the transformer in the field, but just before they reach the house one of the wires (obviously not the live one, because that is thicker, having an insulated sheathe) divides, and from the junction two parallel wires run to the fuse box. One connects to Neutral, the other to Earth.
At the top of the pole another wire from that junction is stapled down the pole and is buried in the ground.
So both Neutral and Earth are earthed, and appear to a bear of little brain to be identical and interchangeable.
Yes - it's an isolated house. No one else uses the transformer on the pole.
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>>At the top of the pole another wire from that junction is stapled down the pole and is buried in the ground.
>>So both Neutral and Earth are earthed, and appear to a bear of little brain to be identical and interchangeable.
I don't think so. Perhaps you're assuming a connection that isn't there.
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Cliff, take a look at John Ward's videos on YouTube, explains about all types of earthing and bonding on UK supplies.
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CP
Not an expert, but have a good grounding. Hence can be guilty of not necessarily using the correct terminology - particularly wrt discussion on earthing systems!
The system you have described (known as TN-C) is common where overhead distribution is used. An RCD will detect a fault where there is an inbalance in the currents flowing in the'Live' and 'Neutral wires'at the consumer unit. (ie some current is flowing directly , possibly via you, to earth).
>>>It would make no difference which way round the sockets were connected,<<<
This is a misapprehension -because to provide RCD protection the neutral current must return through the consumer unit and RCD!
Broken neutrals on the supply side can give rise to nasty problems. However from what you say, you are an individual property fed from the transformer?
I suggest you read en.wikipedia.org/wiki/Earthing_system for a fairly comprehensive understanding. However there are a couple of points in that article that I do not fully understand.
Last edited by: sherlock47 on Mon 13 Nov 17 at 22:01
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>>
>> An RCD will detect a fault where there is an inbalance in the currents flowing
>> in the'Live' and 'Neutral wires'at the consumer unit. (ie some current is flowing directly ,
>> possibly via you, to earth).
>>
That's my point - Neutral IS earth - the two wires start from the same connection outside the house, and are earthed.
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Again, I confess a lack of complete understanding of this point, but Neutral and Earth are the same thing.
The National Grid 400kV transmission only has live. As it's three phase, there is nothing to return as the three phases cancel out. Neutral is added in at the local substation by sticking a plate in the ground. So neutral is taken from the earth. And then earth is finally added in at the property. In your case you don't have a substation so neutral comes in at the transformer and as it's earth anyway...
The point Sherlock is making is, AIUI, that the RCD - which is either plugged into the wall or is part of the CU - counts the number of electrons going through the live wire and the number going through the neutral wire. If those numbers don't agree then it assumes something is leaking to earth, probably through you, and so interrupts the supply.
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Mm
I hope that in your 3rd para you have clarified it so that CP understands. The only other way is to draw pictures!
CP
the 2 wires (ie E & N) have a completely separate purpose inside your house. One is to carry the current of the 'load', the other is to ensure your safety. To that end you will find that they are different sizes.
As a result of this thread I have googled a few things, and on so called professional forums find a worrying lack of understanding of even very basic principals from people who are apparently 'qualified' tradesmen. Qualifications are not what they were! In many cases nowadays just box ticking exercises with multiple choice answers.
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>> The point Sherlock is making is, AIUI, that the RCD - which is either plugged
>> into the wall or is part of the CU - counts the number of electrons
>> going through the live wire and the number going through the neutral wire. If those
>> numbers don't agree then it assumes something is leaking to earth, probably through you, and so interrupts the supply.
>>
It's important to note that you are only protected downstream of the RCD, where the earth, and neutral are separate.
Though how does this relate to the OP's point? I'm not sure that it does other than as I said before the kettle or plus probably had a N to E short.
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>> other than as I said before the kettle or plus probably had a N to
>> E short.
>>
Kettle or PLUG ...
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Having thought a little further, CP, you are misunderstanding, I think, the role of an earth.
It is at exactly the same potential as neutral - i.e. 0 Volts. The two are therefore always attached to each other.
Forget for a moment that it is called earth, as that can be a bit confusing, and call it Bob. Let us call the neutral Charlie.
You have three circuits in your house. Live, Bob and Charlie. You are completely correct that you could wire up your whole house using either Bob or Charlie as the neutral wire and you wouldn't notice any difference. (Ignoring for a moment the fact that the earth cable is thinner than the neutral.) BUT, you would have to do this consistently such that you allocate either Bob to all the neutrals, or Charlie to all the neutrals - and the other one is consistently allocated to earth.
The function of the Bob wire is to detect faults in metal cased equipment. It does this by being attached to the metal case. If a live wire touches the metal case then – if you have an RCD - this causes electrons to
The neutral/earth fault to which you refer only matters inside the house, i.e. on the human side of the CU and its associated RCD. Because as I said the RCD counts the number of electrons going through the live and the neutral and if they are different in number then it trips.
That, when it reaches the outside of your house, the electrons all end up in the same cable is irrelevant – as it’s the other side of the RCD.
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>> Though how does this relate to the OP's point?
Sorry, it doesn't, except that it's about RCDs and the relationship between N and E.
So as I understand it simply, the E wire to the pole is really just a fail-safe for the parallel N wire, connected to the same point. Once when working on the wall close to, I did observe that the two wires appeared identical, although slightly thinner than the Live.
Many thanks all.
Posted just before I saw your reply mapmaker.
Last edited by: Cliff Pope on Tue 14 Nov 17 at 17:45
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RCD Question How Does this Happen - Old Navy
