Wiring Ring mains to MCBs in consumer units
 

In my flat I've discovered that each end of the two socket ring mains
go back to separate MCBs. I've tested this by using a multimeter,
turning off an MCB and still getting 240V on the live terminal (i.e
I've got to switch off 2 MCBs to turn off the circuit). To clarify I
have 2 32A MCBs per ring main, (4 in total). I would have thought
that both ends of the ring main should go back to the same MCB (i.e.
two wires into the MCB) The way it's been wired, each individual live
wire goes back to an individual MCB.

Have I got 2 MCBs too many in my fusebox. I think its wired
incorrectly am I right


Thanks.

Jamie

Wiring Ring mains to MCBs in consumer units
 

Yes you are right!

Wiring Ring mains to MCBs in consumer units
 

"jamie T" wrote
| In my flat I've discovered that each end of the two socket ring mains
| go back to separate MCBs. I've tested this by using a multimeter,
| turning off an MCB and still getting 240V on the live terminal (i.e
| I've got to switch off 2 MCBs to turn off the circuit). To clarify I
| have 2 32A MCBs per ring main, (4 in total). I would have thought
| that both ends of the ring main should go back to the same MCB (i.e.
| two wires into the MCB) The way it's been wired, each individual live
| wire goes back to an individual MCB.
| Have I got 2 MCBs too many in my fusebox. I think its wired
| incorrectly am I right

It is wired incorrectly. Each end of the ring should go back into the same
MCB.

Owain

Wiring Ring mains to MCBs in consumer units
 

In my flat I've discovered that each end of the two socket ring mains
go back to separate MCBs.

Yes. The current wiring is extremely dangerous and could easily lead to a
fire. You should fix the problem immediately. I think the whole installation
should be thoroughly tested. With one absolute shocker like that, there
could be many other disturbing irregularities.

Christian.

Wiring Ring mains to MCBs in consumer units
 

"Christian McArdle" wrote in message
. net...
In my flat I've discovered that each end of the two socket ring mains
go back to separate MCBs.

Yes. The current wiring is extremely dangerous and could easily lead to a
fire. You should fix the problem immediately. I think the whole
installation
should be thoroughly tested. With one absolute shocker like that, there
could be many other disturbing irregularities.


does this mean that the circuits are effectively protected at (a chilling)
64A at the moment, or is the effect not quite that simple and liable to be
indeterminate?


--
Richard Sampson

email me at
richard at olifant d-ot co do-t uk

Wiring Ring mains to MCBs in consumer units
 

On Fri, 28 May 2004 14:48:24 UTC, "RichardS" noaccess@invalid wrote:

does this mean that the circuits are effectively protected at (a chilling)
64A at the moment, or is the effect not quite that simple and liable to be
indeterminate?

No, they're protected at 32A. Which is fine, as that is well within the
rating of the ring as a whole.

But, think what happens if ONE of those breakers trips. You are left
with what is effectively a radial circuit, protected at 32A by the
remaining breaker. But with a single cable feeding each outlet, the
cable (if 2.5mmT+E) rated at as little as 20A.

--
Bob Eager
begin a new life...dump Windows!

Wiring Ring mains to MCBs in consumer units
 

does this mean that the circuits are effectively protected at (a chilling)
64A at the moment, or is the effect not quite that simple and liable to be
indeterminate?

It will be dependent on where the point loads are applied. It is protected
at between 32A and 64A. I suspect it would be much closer to 64A on an
average distribution of point loads.

Christian.

Wiring Ring mains to MCBs in consumer units
 

On Fri, 28 May 2004 15:07:51 UTC, "Christian McArdle"
wrote:

does this mean that the circuits are effectively protected at (a chilling)
64A at the moment, or is the effect not quite that simple and liable to be
indeterminate?

It will be dependent on where the point loads are applied. It is protected
at between 32A and 64A. I suspect it would be much closer to 64A on an
average distribution of point loads.

(slaps head). Of course.... I was concentrating too much on the overload
if one MCB tripped. Wther one is tripped or not, it'll still overload!

--
Bob Eager
begin a new life...dump Windows!

Wiring Ring mains to MCBs in consumer units
 

"RichardS" noaccess@invalid wrote in message
.. .

"Christian McArdle" wrote in
message
. net...
In my flat I've discovered that each end of the two socket ring
mains
go back to separate MCBs.

Yes. The current wiring is extremely dangerous and could easily
lead to a
fire. You should fix the problem immediately. I think the whole
installation
should be thoroughly tested. With one absolute shocker like that,
there
could be many other disturbing irregularities.


does this mean that the circuits are effectively protected at (a
chilling)
64A at the moment, or is the effect not quite that simple and
liable to be
indeterminate?

I think that would only be correct if the load on the circuit was
balenced e.g. at the mid point of the ring. If you put the 32A load
within a few mm of one MCB I don't think you could draw much above
32A (at least not for long) before the 32A MCB trips but this is
still above what the cables rated at since most of the current would
be travelling down the shorter (lower resistance) leg. In summary
your protecting the cable at 32A but the circuit between 32&64 A
depending on where the load is.

HTH

Jim

Jim

--
Richard Sampson

email me at
richard at olifant d-ot co do-t uk

Wiring Ring mains to MCBs in consumer units
 

I think that would only be correct if the load on the circuit was
balenced e.g. at the mid point of the ring. If you put the 32A load
within a few mm of one MCB I don't think you could draw much above
32A (at least not for long) before the 32A MCB trips but this is
still above what the cables rated at since most of the current would
be travelling down the shorter (lower resistance) leg. In summary
your protecting the cable at 32A but the circuit between 32&64 A
depending on where the load is.

The overload tripping current will be very close to 64 amps (probably over),
the impedance for an overload current will have negligable difference
anywhere on the ring main cabling - (Kirchov's current law if you want to
look it up and work it out exactly)
If it was a short circuit current then then the difference in the impedance
would have a measurable effect but then the short circuit current would be
only for a very short period of time and into the thousands of amps range.
It is a very serious fire hazard in an overload situation as this could be
applied for a long perion melting the cable. It is also a bad situation for
anyone working on it.

Wiring Ring mains to MCBs in consumer units
 

Wiring Ring mains to MCBs in consumer units
 

On 28 May 2004 10:27:34 -0700, (Matt Beard) strung
together this:

Well, at the best this setup is non-standard and dangerously confusing
(unless very clearly marked).

Nope, just dangerous.

I am not sure it the regs specifically forbid wiring
multiple paths

They do in this way.

at the very least you would need the wiring to
be able to safely carry the 64A that you are effectively protected by
(assuming a single load or fault at the mid-point of this "ring"). In
this 32A+32A case you would need 6mm^2 conductors (rather large for a
ring).

Nope, it's still dangerous and wrong.
--

SJW
A.C.S. Ltd

Wiring Ring mains to MCBs in consumer units
 

"jamie T" wrote in message
om...
In my flat I've discovered that each end of the two socket ring mains
go back to separate MCBs. I've tested this by using a multimeter,
turning off an MCB and still getting 240V on the live terminal (i.e
I've got to switch off 2 MCBs to turn off the circuit).

Well spotted, but you should confirm ring continuity of live, neutral and
earth conductors by checking impedance across the open ends of the cables
you think are the ring. Then they both go to a single MCB. There are other
tests as well. Think there may be guidance on the TLC website.

Alan