Sparks wrote:
You are quite correct, I thought it went into the head, but after removing a
load of insulation tape, it appears to be connected to a clamp round the
main cable (and it's loose!)
It is clamped around a solid part (looks like a pipe) - Can I just use a
normal earth clamp used on pipes on it?
Yes, but remember that it's a soft lead pipe with old wires inside, so
don't overtighten the clamp!
What size should the generator's earth be - currently it is mainly 2.5mm in
the 6mm T&E)
I pondered on that, and wondered whether to recommend that the earth
should be the same size as the phase and neutral. It should be really,
but since there's an RCD in-line it's not really that important. But I
did say upgrade that 6 mm^2 to 10 or 16. The best job really would be
to use 10 or 16 mm^2 2-core SWA all the way from the genny shed to the
transfer switch.
Both the head to the Henley block, and the Henley block to the split load
has always been 6mm since it was installed (By a "proper sparkie") was this
ever acceptable? (Installed, probably 20 years ago)
Yes 6 was used in the 14th Edition days when the standard meter tail
size was 16 mm^2. The change would have been around 1981.
- have you consulted with the local mains supply DNO?
Errm, nope! (What does DNO stand for! and how do I find them!)
Distribution network operator, i.e. the company which has taken over
running the LV network from the old electricity board. If you don't
know the name, your electricity supplier (the one wot sends you bills)
should be able to tell you who to contact.
- the earth from the genny frame to the electrode should be 16 mm^2
(unless protected in conduit);
do you mean from the frame to the earth rod, or the earthing terminal in the
house?
Genny frame to earth rod, including the section buried in the ground.
Assuming an insulated wire with no other protection this needs to be 16
mm^2 in order to have adequate mechanical strength.
- the bond between the genny's neutral and earth should be made in the
generator, not at the junction box on the house wall (TN-S system).
I have a wooden box with forced air flow though it that genny lives in - In
there I also have a "Power Conditioner" - not sure of it's model - it
weighs, probably 50-60KG
It has "Watford Control" on the side
Picture of it here (The amp meter is broken, as you will see!)
http://www.altphuk.co.uk/images/power_conditioner.jpg
Are you wiring that in-line with the genny's output? If it contains an
isolating transformer then you'd have to move the N-E bonding point to
the secondary side.
Your arrangement has a combined N & E conductor between the genny and the
junction box, which isn't allowed. To be clear you should be bonding one
end of the genny winding and its frame to earth at the genny. This
defines the neutral point for your independent TN-S system. It may require
some modification of the genny's internal wiring as portable gennies (like
the picture) often have floating or centre-tapped-to-earth outputs;
Sounds right, if I measure the voltage on the generator, across the L & N I
get 230
but if I measure from L to E or N to E I get 115v but with the bonding of N
to E, I get 230 from L to E and N to L
So it sounds as if the output (when unbonded) is floating. If there was
a centre-tap already connected to earth then something would go bang
when you also earthed the neutral. To be absolutely sure temporarily
connect N to E through an ordinary 100 W lamp and make sure that the
lamp doesn't light at all and you still have 230 V L-N and L-E and 0 V N-E.
So, inside the generator, so I just connect the L and the E together and
break this connection in the box on the side of the house?
Assuming you meant N and E, then yes.
- you should make your genny installation permanent by fixing the
genset
to a floor slab (or whatever) and get rid of the 32 A plug and socket
arrangement.
The reason I wanted this plug and socket, is I have another much smaller
generator (2KW) so if the main one blows up, I can plug this in - Overkill
or what :-) (This spare one was given to me!)
Could I clamp the generator to the box it is in, and screw the box down, but
still keep the plug/socket?
I was giving you chapter and verse on the regs (BS 7671). It's open to
interpretation though. As you seem to have a dedicated genny shed then
we can probably say that the installation is permanent, so the
regulation is satisfied, even with the plug & socket.
Failing that the 100 mA RCD in the transfer switch will need to be changed
for a 30 mA type (see reg. 551-04-06, re. gensets that are "not
permanently fixed");
The transfer switch did originally have a 30mA RCD, but it kept tripping
(but the other RCD's downstream of it didn't)
So I changed it presuming it was faulty, I though 100mA would be ok as it is
TT (This one behaves)
I agree that a 100 mA RCD is a much more sensible choice, and is legit
now that we've decided that the genny installation is permanent. Your
system is not TT though, it's TN-S, because you have a metallic earth
path back to the "earthed point of the supply source" - i.e. the N-E
bonding point on the genny output. A TT system relies on conduction
through the soil for earth protection and that's not the case here.
- the 6 mm^2 cabling between genny and house is too small. You have a
long run (26 m) and voltage drop would be excessive on 6 mm^2. I'd
recommend 10 mm^2 minimum and preferably 16 mm^2 for this;
Okay, the bit in the house is reasonably easy to change, (when I say easy,
it does result in the front room & hall carpet and floorboards coming up,
and the kitchen kick plates being removed!) but the 5m SWA between the
generator and the house is going to be a right pain in the arse (most of it
is under the {new} patio!) would just upgrading the main T&E Run be ok?
OIC, it's all in place already. You now have to decide whether it's
worth changing. Certainly do the T&E section when you can and take that
up to 16 mm^2. I'd leave the SWA section.
- is the 7.5 kVA genny capacity adequate to supply all your load? If not
you are supposed to have automatic load shedding arrangements (see reg.
551-02-03);
No, but as the generator is not automatic, can I just have some instructions
to turn X Y and Z off on the consumer units?
Again BS 7671 does say automatic - but I think what you propose is quite
adequate. Unless you've got extensive electric space heating or
electric showers then 7.5 kVA is unlikely to be exceeded anyway.
Yes, that's OK, the earths are in parallel but if the mains cable is
completely severed your independent system still has its own earth.
Great - how can I test this rod is providing an acceptable earth?
If you have a loop tester then you can do a direct measurement between
the mains phase and the electrode. If not then see
http://groups.google.com/groups?as_umsgid=01bd6c2d%240cd8b9e0%24LocalHost@d og40
for my DIY method.
--
Andy