Came back from the pub quiz last night to find the downstairs in darkness.
The RCD had tripped. It would not reset unless we had all the light
The lights are on a 6A RCBO with an 80A 30mA RCD
Strangely though we found out that I can have a small number of lights
on, but beyond that point, the RCD or RCBO goes. It doesn't like
fluorescents, they will trip every time, yet 5 incandescents on a dimmer
in the front room are OK. Although some of the lights that will stay on
are are energy savers (so fluorescents!)
The Megger shows live earth and live neutral OK! (With all light
switches turned off - so is it a fitting?)
This has me puzzled.
That suggests that some of your light switches are switching the
neutral? or is that you have a neutral earth leak that is insufficient
to trigger the trip as well as some other leakage path which is switched
in by some of your lights. Have you got enough real lamps to use for now
in place of the crap CFLs. Might buy you some peace and quiet over the
An interesting one, not least for the totally illogical way that the
previous owner had wired it! (He was a builder, so I should have
expected it I suppose!)
I live in an 1890s terrace. From front to back we have 2 lights in the
hall, one in the living room, two in the dining room, one in the
kitchen, one in the utility room one in the cloakroom and one outside.
With the Megger I quickly established that the back of the house (from
the kitchen was OK). I had to get most of the upstairs bathroom and
landing floors up to work out the feed from the fusebox goes to the
living room first (5 incandescents on a dimmer and worked fine) then to
the dining room (one three arm fitting that only worked with one energy
saver fitted) a double fitting that tripped with anything in) then
splits back to the hall and forward to the kitchen etc.
To cut a long story short and after about 4 hours of testing (removing
wires, Meggering etc.) it turned out to be an overheated chocolate block
(poor connection?) in the three arm fitting in the dining room that was
shorting earth/neutral (yes the one that was working!) and once that
repaired, all was OK)
What a sod to find though, not helped by the fact it "seemed" OK!
Anyway all sorted and a Happy Christmas to all on UK DIY
Train set at www.lmandwr.co.uk
Dogs at www.whissgig.co.uk
I'm in the US and it sounds like you're in the UK or some other European
country so I know our wiring is different, but ... maybe you can clarify my
confusion in this post; always interested in things different from my own
I fail to see how a neutral/earth short could cause any visible problems.
Depending on resistances back to the electrical panel, they should simply
share the neutral current, or if the resistances are different, the lowest
resistance path would carry the current back to the panel. Normally Earth
leads should carry zero current.
I suspect my confusion is due to things like
"The lights are on a 6A RCBO with an 80A 30mA RCD",
which are absolutely meaningless to this yank<g>! So apparently the key
words you're using are not ckt breakers, but some other form of protection
that relies on other than simple current overloads; right?
Hmm, I may have worked it out. Google was no help with its gazillion hits of
Roman Catholic ... , but Wikipedia seems to have filled in the blanks! And
here I thought I understood your ring ckts and all that! lol.
I know for instance that RCBO = Residual Current Circuit Breaker with
Overcurrent Protection. THAT sounds like a ckt breaker but Residual Current
fits in there how?
Wikipedia seems to indicate that RCD stands for "Residual Current Circuit
Breaker "; is that right? Now that sounds like what we might call a GFCI or
Ground Fault Ckt Interruptor, a product that keeps a measure of the current
in the hot and neutral lines and if they vary by more than a few milliamps,
opens the ckt., assuming there is a fault at some point.
Would RCBO be the same thing, the only difference between the two being
that one is located at the point of use, and the other at the Mains
Thanks for any clarification anyone is willing to provide,
RCD's, or Residual Current Devices (fomerly known as earth
leakage circuit breakers,) are very common in 240V areas.
Remember much of your electrical supply is 110V - sometimes even
55-0-55 - with 240V across phases used for higher power
equipment. In Europe we use a (nominal) 230V single phase supply
for everything - nominal because we are supposed to be
standardised across the EU. In practice Europe mainly uses 220V
and the UK and Ireland use 240V but both fall within the
permitted tolerances on 230V.
In the UK domestically we use a single phase supply which is
usually single pole switched and carries a small cartridge fuse
in the plug to protect the cable and appliance. The plug is
three-pin with earth, although the earth spike may not be local.
It has to be said that most domestic electrical kit - brown goods
such as hi-fi and TV, portables such as hairdriers and shavers,
and many electrical tools such as drills - are these days fitted
with two-core cable and are double insulated with a double pole
switch. This is because there is no polarity awareness in most of
the EU - they often use two-pin Schuko plugs which can be
reversed on insertion. IME even if the outlet has an earth pin -
as often found in France - there is still no standard wiring for
the polarity of the other two pins. This is a problem if
three-pin weatherproof connectors are used - which are supposedly
standard across Europe (we know them as BS4343 in the UK) - which
we use with our touring caravan: they are clearly polarity marked
on the body but I have only experienced three (out of many) sites
correctly wired. I often wonder if they are even earthed!
A RCD is basically a pick-up coil through which the L and N
cables both run. If the current through both cables is the same
then there will be nothing induced in the pickup coil. If there
is a current imbalance - some is flowing through you - then there
will be a current imbalance in the main cables which the pickup
coil will detect and trip the supply. Normally that current
difference is 30mA, but for 'at risk' places such as an
electronics work bench 10mA is often used. It is usual for the
RCD to be on the main supply - it is often also the main supply
switch as it is double pole - so if it is tripped everything goes
off, not just the one circuit. More modern installations have
split rings so that wired-in appliances and lighting are not
protected and you don't get plunged into darkness for a simple
Incidently, if you wonder why our electrical outlets are such it
is a historical cost thing. Most European wiring is radial - i.e.
every outlet has it's own cable back to the supply board and is
individually fused (or breaker) and some places (such as Germany)
have outlets that are mechanically slightly different and are
supplied at 6A rather than the 'normal' 16A. British and Irish
wiring is almost always in a ring so the ring is fused or
switched at 30A or 32A but the plug carries a fuse which may be
1/2/3/5/7/10/13A, although the Great British Public, being
generally thick and unknowing, use moastly 3A or 13A.
Hope that clears your understanding?
You gave a rather good answer right up until your "the Great British
Public, being generally thick and unknowing, use moastly (sic) 3A or 13A).
Does that make you the only intelligent Brit out of 65,000,000 or so then?
I think not, and I would be interested how you have managed to come to that
conclusion without inspection every piece of domestic electrical equipment
in the country
My last paragraph should have read:
I think not, and I would be interested how you have managed to come to that
conclusion without *INSPECTING* every piece of domestic electrical equipment
in the country.
Have you ever seen any equipment on sale or tried to buy a plug
retail with anything other than a 3A or a 13A fuse? Equally have
you ever tried to buy fuses retail other than 3A or 13A? Ergo
most (non-understanding) people will use 3A or 13A fuses as they
either know no better or don't have the knowledge to go buy
From a personal standpoint I tend to use 2A and 5A fuses as, IME,
3A fuses - especially on portable equipments - seem to have
mechanical problems. Drop the plug and the fuse fails
mechanically, but 2A and 5A don't.
3A and 13A fuses are perfectly suitable standard fuses for all new
equipment. An appliance takes one or the other depending upon it's power
And you do know that you should not put a 1A fuse into a plug don't you?
Yes, I am an engineer by education and experience and we used to design
product for the UK and EU countries. We're NA. I'm retired now for health
reasons, but I remember being surprised the first time I came across the
plug fuses. I was also surprised to discover that most equipment was sold
sans power cords; it was up to the user to get those.
This experience was gained as manager for a telecom compliance testing
laboratory. We served NA, Europe, UK and the Pac Rim down to Australia.
Every country would be similar "except" and it used to be "interesting"
keeping them straight<g>.
It's the same here in NA in some places, especially w/r to the earth. Hot
and neutral have to be right though or you won't pass inspection. That
doesn't stop the do it yourselfers from doing their own work, though,
without regard to polairty.
Here only generators would be often miswired, even often use
multi-branches with a common neutral to make wiring easier. Some bands love
the miswires because they're sure their amps are working when they hear that
Ah, we'd call that whole-house protection over here. I never thought about
what their trips might be current-wise. They're fairly new over the last few
years. Then we also have arc-fault-interruptors; should an arc occur
anywhere, even without being able to ever pop the breakers, they'll open. I
haven't installed any yet but plan to - arcs are what start fires.
That's news to me. I didn't know the individual ring ckts were fused or
switched. It sort of makes me shudder to think about trying to locate a ring
ckt's fuse or switch.
Thanks for the response; we seldom got near the actual bldg wiring in my
business unless we had to figure out an earth or neutral problem that
screwed up a PBX. We had a plant for R&D and Repair in Wales and I always
loved having to make a trip over there. Well, except for that long, boring
trip across the pond, that is! I never got anywhere other than Wales for
sightseeing and a couple trips into London some evenings, but I loved it.
A question about US installations from an interested UK reader.
If you have 3 phase power installed into a property in the US, do you
get three lots of 220/110 v split phase supplies eg 110v 3phase as well
as 220v 3 phase?
Or how does it installed if not?
How do US power consumption meters work for 110v and 220 v split phase?
or do you have two meters in the home?
Oof! That's a tricky one because there are several different kinds of wye
and delta arrangements for 3-phase power. You can get 120, 208, 220, 240,
360 and 480 and sometimes higher voltages for specialized industries. You'll
never find any of these wye or delta arrangements in the home though.
Probably the easiest way to answer is to provide a link or two. Also,
these would never be found in a residence. Residential is always
single-phase, split-phases into the home with 110Vac per leg,or 220Vac
between the split (xfmr is center tapped for neutral and that's bonded to
earth with an electrode driven into the ground).
lol, that depends too! Yes every home or apartment has its own electric
meter. I said it depends because the old analog meters are presently being
switched out in favor of newer digital meters which can provide a lot more
information. To read the digital meters, they only need to drive by in
their vehicles and which then transmits the address and power usage details
to them. The transmissions are even encrypted.
I'm sure they probably all work as in the UK, measuring kilowatt-hours. With
a residence, there is no accounting for power factor of course; you take
what it measures<g>. In reality it gets explained iike it would make little
difference, but from some of the electric motor (furnace, fans, etc) power
factors that run for long periods of time that I see in my own house, I'm
not so sure it's negligible!
Power from the grid, high voltage, is connected to the grid's transformer.
This is a center-tapped transformer, which converts the single-phase input
voltate into split-phase ( two 120Vac outputs w/r to the centertap (which is
neutral/earth and bonded at the pole)).
So coming TO the house from the transformer are three wires: The two out
of phase hots, and neutral. Once in the meter, there is no ground nameing
any longer since earth ground for the house is derived from a separate
electrode driven into the ground.
From the meter, the two hots go into the Mains panel Mains Breakers or
Fuses along with the third wire, which connects to the Earth bar within the
panel and which all internal ckts return their earth grounds to. Earth and
Neutral are only allowed to be tied together within the Mains panel and
nowhere else unless a special exception is claimed.
Where the breakers hang, there are two busbars giving every other breaker
the opposite phase of 120Vac. So to get 240Vac, you use a "ganged" double
breaker where two adjacent buses are connected. Thus, the difference between
the output side of breaker to breaker then will measure 240Vac since they
are out of phase.
A LOT of people like to mislabel this as 2-phase power, but that's wrong:
It's called split-phase. One phase is split via the centertapped transformer
providing the power from the grid. In most cases people don't care, but
don't call it two phase when you're talking to anyone in the business or who
is a little egotistical<G>.
Thus, residences are only equipped with 120 or 240 @ 60 Hz in the US and
Canada. The 240Vac only gets used for major appliances such as our well
pump, clothes drier, water heaters, things that otherwise would require very
large, heavy cabling. Lights and all normal receptacle in the living areas
are almost exclusively 120Vac.
In 240Vac install, the Neutral isn't used though there are exceptions.
Earth is always connected to anything that's not class II design.
In the event I haven't put you to sleep, which I know my verbosity has a
habit of doing to people, you might check out Mike Holt's site if you'd like
some good, down to earth definitions and descriptions of the many different
variables that are possible. I highly recommend him and it's a "safe" site,
pushing nothing nefarious or covertly.
Hmm, looks like he's made the forums major, too;
It's been a long time since I visited his site.
And here's a popular product here in the US; don't know if they make other
localized product. "Kill-a-watt meter".
I bet that's all clear as mud, huh? I tried!
120 ----------- ---------Mains Sw ---------Breakers Buss 120Vac to
meter 240Vac Hot to
120 ----------- ----------Mains Sw----------Breakers Buss 120Vac to
Neutral -----------------------------------------Bonded to Mains breaker
I'm with you so far and i understand the difference between 2 phase and
split phase. Returning to my questions though....
How does one meter measure the power pulled from both legs of the split
THREE phase question.
If a property has THREE phase power installed do they get all three 110v
phases with respect to neutral as well as all three 220v phases?
Hmm, I think the wikipedia link touched on that; it's just measuring the VA
(kWH) of both hot leads. More power makes the meter click faster, basically.
The site "How Stuff Works" might have something for you in more detail. I
don't pretend to know the cktry inside a meter but it seems to be rather
simple. It's not meter design, which I don't seem to be able to find
quickly, but it may help too:
No. IME anyway, the phases are all 120 Vac but each is slightly out of phase
(but not 180 degrees) from each other. A 208V ac system is shown here,
comprised of the three 120Vac phases:
As for 220, remember, our systems are different than yours. 240 (here) is
"built" from two 120V lines from a center-tapped xfmr, being called 'split
phase' since the phase shifting is done via the xfmr on the pole. There are
several WYE and DELTA situations which, again, are easy to look up on Google
or your favorite search engine.
This is an advertisement, but with good information, all based on 220Vac
sourced from 120V:
In industrial buildings, you'll often find humongous wires coming from the
xfmr to a quick disconnect and then splitting off to several panels, each
panel meant for a separate part of the plant, and within those, heavier
panels for the hi-curent equipment. Somewhere in the mix will be large
capacitor banks used to correct for power factor and the meters are usually
in that same vicinity IME. That's a generality of course, and things vary,
but ... that's the gist of it.
I trust that helps a little. It's hard to explain some parts of these
things without writing a book that duplicates what's already been written,
which is why I use the links for references. You might want to look a tad
further into some of the original links I provided you too; occasionally the
meat of the info isn't onscreen when you open the page.
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