Sparks ( email@example.com) wrote:
: > : Okay, but with the transfer switch, there shouldn't be a problem!
: > I wouldn't trust a switch to switch an earth unless specially designed
: > to do so and recommended for that purpose by the manufacturer. There
: > are too many risks if the earth contact doesn't! You will also have
: > an extra link in the bonding between the CU and your earth (I assume
: > that if the generator earth is switch then the mains earth must also
: > be).
: The earth from the generator goes into the trasnfer switch *box* not
: through the actual switch - it is just a thru connection, and has a link to
: the generator's nuteral (Well, the load side of the power conditioner)
As I noted before, I would make this link from the neutral on the power
conditioner output to the earth at the main earthing terminal. I would
avoid having links in boxes because 1) they are less robust, you end up
with a link from neutral to terminal and then from terminal to main
earthing terminal and 2) they are not immediately obvious which doesn't
help someone understand the wiring when they look at it.
The operation of the transfer switch doesn't solve the interface issues
with your electricity supplier. If:
- you connect the neutral on the generator to your earth rod (which is
- you connect the live on the generator to the suppliers earth (which
would occur in the case of a fault in an appliance)
- there is no link between the suppliers earth and your earth rod due
to a wiring problem (unlikely but possible)
- your RCD on the generator is faulty (possible)
then you apply 230V to the supplier's earth connection.
If your supplier has a man busily working away in a hole half full of
water in the road trying to restore your supply and he grabs the earth /
neutral wire (depending on your supply type) then he may die.
Yes, the above is a very contrived and hopefully highly unlikely
sequence of events and this is NOT a recommendation to include any
kind of switching of the earth. The point is that the safety of the
public supply tends to be taken very seriously and in order to avoid
your supplier deciding to cut you off because it thinks your
arrangement is unsafe it is best to have the discussion before rather
than after it becomes an issue.
: > : L&N from meter into DP isolator
: > :
: > : L&N from isolator to transfer switch (Double Pole, Three position switch
: > : (Mains, off & Generator))
: > :
: > : L,N&E from generator into transfer switch (Transfer switch has a 30mA
: > : for the generator)
: > What is the earth connection for? Is it to bond the switch or is it
: > actually switched?
: It is just a thru connection, and provides earth to nutral bonding for the
: generator supply (via the poer conditioner)
As noted elsewhere, through connections for earths are bad. Wire earths
in a star arrangement unless there is a very good reason to do otherwise.
: > For best integrity, I would make sure that all the earth connections
: > come together at a single main earthing terminal. This would include:
: > 1. Earth rod.
: > 2. Mains supply earth (see my previous post regarding confirming
: > this with the supplier - if you can't link the two earths you can't use
: > this arrangement)!
: > 3. Connection to consumer unit(s).
: > 4. Equipotential bonding of gas, water, etc.
: > 5. Neutral connection (to generator terminal).
: > 6. Earth connection for generator chassis.
: > I would also connect anything else that needs bonding to this terminal.
: > Make sure you get something designed for this purpose (its a relatively
: > common part but you will have more connections than normal).
: OK, makes sence here - All the earths currently connect to the earth
: block in the CU - Therefor, is there any point in having another box?
A lot depends on the design of the installation. Some installations
will have a separate terminal block of some sort for the earth with a
wire going from there to the consumer unit (this is what is shown in
the IEE on-site guide for example). It is possible to use the
earthing bar in the consumer unit but you are going to end up with
a number of bonding connections leading to it and I suspect it will
be neater to have a separate main earthing terminal rather than cram
eveything into the consumer unit. It should also be possible to get
easy access to the earth connections for testing purposes and this
might be difficult in the CU.
Note that whatever you decide to use for your main earthing terminal,
all the main bonding wires that connect to it shouldn't have any joins
in them (there shouldn't be any need, they should run straight from the
terminal to the pipe, rod, generator chassis or whatever it is they run
: > : The earth rod is situated next to the generator, and is connected to the
: > : chassis of the generator (via the supplied earthing bolt)
: > There isn't a problem in keeping this arrangement (providing its
: > existance is clearly noted near the main earthing terminal!) but I would
: > ensure that I used the "star" arrangement with a single main earthing
: > terminal as well.
: As in a notice there is a rod, stuck on the CU? or have I missed the point
My concern is that someone will carry out work on the installation in
future and not be aware that in addition to the "star" earth arrangement
with separate wires going from the main earthing terminal to the
generator chassis and to the earth rod there is another separate earth
bond between the generator chassis and the earth rod. This won't be a
problem in 99.9% of cases but it avoids confusion which is always a good
thing. If you have the opportunity, a sketch of the circuit arrangement
fixed to the wall next to the CU is never a bad idea (unless its wrong!).
: > : There is also a power conditioner in between the generator and the
: > : switch (Bloody heavy!)
: > I would check whether this provides isolation (i.e. contains a 1:1
: > transformer), you may need additional bonding and neutral referencing if
: > it does.
: My nutral bonding is the load side of the conditioner,
: So I guess that would be OK?
So far as the house supply is concerned yes. If the power conditioner
did provide isolation, I would also be tempted to reference the
generator output to earth as well.
: > I'm confused about your RCD arrangements. It sounds like you have two
: > separate RCD protected sub-supplies in your consumer unit which is
: > strange. Normal practise with TN-S or TN-C-S is to 30mA RCD protect
: > circuits where there is significant risk of shock (e.g. sockets) either
: > with a single RCD or individual RCBOs for each circuit and to leave
: > circuits which are a low shock risk (e.g. lighting) unprotected by RCD.
: > Usually this means that there is a single main switch in the consumer
: > unit which feeds lighting circuits via MCBs and feeds rings via a 30mA
: > RCD and MCBs or feeds rings via 30mA RCBOs.
: You are correct - two seperate curcuits, one for lighting, and the other for
: both protected by a 30mA RCD each - no main isolator in the CU.
: I added an isolator in a seperate box when the elec co. came and
: disconnected me while
: I was connecting the transfer switch (Now I dont have to call them out
I don't particularly like this - see the bottom of this post.
: > Since when running on the generator supply you will be operating a TT
: > system, you need to protect all circuits with a minimum of a 100mA
: > time delayed RCD.
: > : The generator has a 30A thermal fuse on it's control panel
: > :
: > : Do I actually need the RCD in the transfer switch (on the generator
: > : as all circuits are protected via the RCD's in the CU? Will this cause
: > : problems having RCD's connected to RCD's? (I was thinking of swapping
: > : RCD in the transfer switch for an isolator)
: > You don't actually need an additional RCD if all your circuits are
: > currently RCD protected in the consumer unit.
: OK, will remove the RCD in the Transfer switch and replace it with a
: (I am sure I will find a use for the spare RCD at some point!)
I didn't note it before and a lot depends on your installation but if at
all possible, I would keep the amount of wiring from the generator which
is NOT protected by an RCD to an absolute minimum (i.e. have the RCD as
close to the generator as possible). This minimises the amount of
wiring which is unprotected and where an earth fault could exist without
any of your protective devices operating. For example if you keep your
present consumer unit arrangmement and the generator is only 2m from the
CU then I wouldn't be worried. If there is a 20m underground cable run
from the generator to the CU I would want an RCD at the generator (if
this is the case then I would also need to think again about your
earthing arrangements - my suggestions have been based on the generator
being located within a couple of metres of the house).
: > Since your current arrangement is a little strange I would be tempted
: > to sort out the consumer unit however so that it is more normal in its
: > arrangement with a split between non-RCD and RCD protected sides. I
: > would then put a 100mA time delayed RCD either on the input to the
: > consumer unit or, for extra reliability and since its only required
: > during operation from the generator, put it between the generator and
: > the transfer switch. As I noted in my previous email, the generator
: > supply must be connected to earth on the incoming side of the RCD
: > (you are doing this already but I will reiterate it because its
: > important!).
: I cant see the value in changing this!
: If someone was to get a shock off the lighting circuit,
: they will be protected to 30mA with my setup.
: I really dont get why people dont do this in a "normal" installation.
: The idea of changing it to a lesser protection is in my mind ludecrus!
: Any risk is a risk affter all!
: I do of course stand to be corrected here,
: maybe there is a good reason not to do it my way!
If your house catches fire, your lighting will stop working a lot
sooner if you have a 30mA RCD fitted. If your house is on fire and you
can't see where you're going you might die. The risks assocaited with
changing bulbs are very small unless you have really dodgy light
fittings - the risks associated with house fires are a little greater.
(There is a similar argument for whole house RCDs which doesn't apply
in your case which goes along the lines of person using hand held tool
when tool becomes defective and RCD trips plunging the whole house into
darkness. Person falls off ladder with power tool, impaling themselves
on it as they land.)
There are also boring practical arguments like having freezers on RCDs
is a bad idea because you can come back from holiday to a freezer full
of rotting food because an RCD has tripped due to something unrelated
to the freezer.
: Unlike some electritions, who when challenged "Why is that done that way"
: I can't reply "Cos that's the rules gov." - I want to know why somthing is
: "Thoes are the rules" is not good enough fo me!
I wouldn't say that the application of RCDs I have described is the rules
but it is recommended. If you believe that the risks from your lighting
arrangements are greater than I have suggested then please keep the RCD
(I'd be looking to fix the lighting though!).
Of course, when running on the generator, you have to have at least a
100mA RCD in the supply to ensure that the supply trips should there be
an earth fault. A 100mA RCD should be a lot more resistant to tripping
in most of the cases I have described than a 30mA one.
Hope this all makes sense,