On 26/09/2020 00:27, Fredxx wrote:
On 24/09/2020 12:18:05, wrote:
On Monday, 21 September 2020 04:07:20 UTC+1, FredxxÂ* wrote:
On 21/09/2020 04:02:32, ARW wrote:
On 21/09/2020 00:08, Fredxx wrote:
On 20/09/2020 09:11:41, Jeff Layman wrote:
Fortunately not mine!

A friend just told me "I have just replaced a single electric socket
in our lounge with a switched double. In order to stop the supply, I
had to switch off two trip switches at the same time." That didn't
sound right, or safe.

DIYWiki notes: at
(http://wiki.diyfaq.org.uk/index.php/Ring_circuit):
"The ring circuit cable starts at the consumer unit (fusebox]),
visits
each socket in turn, and then returns to the consumer unit. The 2
cable
ends at the CU are connected together in all modern rings, and
supplied
by one fuse or MCB."

That confirms there should be one MCB, but I note the use of "...in
all modern rings...". Does that mean there might have been two fuses
or MCBs in early rings? I think his house was built around 1980.

I can see the logic, where the two MCBs are each rated for 2.5mm cable
which will allow more current be safely pulled along the ring.

I wonder if it will catch on?






Obviously you would need a common RCD.

Actually you do not as there will be no imbalance between live and
neutral.

Any imbalance (leakage to earth) would be shared between the two RCDs,
assuming they are identical. So the residual current would be close to
twice the expected value before one tripped. The other would follow
immediately.

Any slightly high R joint would result in imbalance & trip the RCDs.

I have to say was my thought. Worst case scenario would be live fed
through RCD and neutral fed through the other RCD.

Both would see an imbalance equal to the current drawn by the load.

Thanks to John's input I can now find the diagram I drew.

http://i428.photobucket.com/albums/q...o2020/ring.jpg

The argument was about if the RCDs would trip in a normally functioning
circuit.

Add a high resistance on one of the lines and there will be a trip.

--
Adam

On 26/09/2020 13:39, ARW wrote:
On 26/09/2020 00:27, Fredxx wrote:
On 24/09/2020 12:18:05, wrote:
On Monday, 21 September 2020 04:07:20 UTC+1, FredxxÂ* wrote:
On 21/09/2020 04:02:32, ARW wrote:
On 21/09/2020 00:08, Fredxx wrote:
On 20/09/2020 09:11:41, Jeff Layman wrote:
Fortunately not mine!

A friend just told me "I have just replaced a single electric socket
in our lounge with a switched double. In order to stop the supply, I
had to switch off two trip switches at the same time." That didn't
sound right, or safe.

DIYWiki notes: at
(http://wiki.diyfaq.org.uk/index.php/Ring_circuit):
"The ring circuit cable starts at the consumer unit (fusebox]),
visits
each socket in turn, and then returns to the consumer unit. The 2
cable
ends at the CU are connected together in all modern rings, and
supplied
by one fuse or MCB."

That confirms there should be one MCB, but I note the use of "...in
all modern rings...". Does that mean there might have been two fuses
or MCBs in early rings? I think his house was built around 1980.

I can see the logic, where the two MCBs are each rated for 2.5mm
cable
which will allow more current be safely pulled along the ring.

I wonder if it will catch on?






Obviously you would need a common RCD.

Actually you do not as there will be no imbalance between live and
neutral.

Any imbalance (leakage to earth) would be shared between the two RCDs,
assuming they are identical. So the residual current would be close to
twice the expected value before one tripped. The other would follow
immediately.

Any slightly high R joint would result in imbalance & trip the RCDs.

I have to say was my thought. Worst case scenario would be live fed
through RCD and neutral fed through the other RCD.

Both would see an imbalance equal to the current drawn by the load.

Thanks to John's input I can now find the diagram I drew.

http://i428.photobucket.com/albums/q...o2020/ring.jpg

The argument was about if the RCDs would trip in a normally functioning
circuit.

Add a high resistance on one of the lines and there will be a trip.

I did a circuit simulation model at the time:

http://wiki.diyfaq.org.uk/index.php?...Crosswired.gif

That took into account the likely circuit lengths and some estimated
loads, so that one could probe the current imbalances. Even with a 1m of
extra cable and a 12.5A of load spread over the circuits, the setup just
about stays sufficiently balanced to not trip:

http://wiki.diyfaq.org.uk/index.php?...ntBalanc.g if

(Note I inverted one curve so it does not obscure the other)




--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Friday, 25 September 2020 15:24:49 UTC+1, Max Demian wrote:
On 24/09/2020 21:48, tabbypurr wrote:
On Thursday, 24 September 2020 17:24:20 UTC+1, Max Demian wrote:
On 24/09/2020 12:15, tabbypurr wrote:
On Sunday, 20 September 2020 10:54:40 UTC+1, wrote:
On Sunday, 20 September 2020 10:48:07 UTC+1, Chris Green wrote:

Our house (as in the house I grew up in, back in the 1950s) had a very
early ring circuit as it was built in 1949 or thereabouts. It
definitely had fuses at each end of the ring. Whether that was as it
should have been or just how the electrician (my father I think)
thought it should be I don't know.

When rings were first introduced, people used to make them from 2 15A radial circuits joined together.

I don't know how officially-sanctioned that was or for how long.

It was part of the original rationale for the design.

Was each circuit fused for the whole ring, or half?

2x 15A fuses running a 30A ring. The point was one could add unlimited extra sockets by joining 2x existing 15A socket circuits into a ring. It was an ingenious solution combining cost cutting with safety improvement.

What if you plugged two 3kW fires into sockets near one of the fuses?

Firstly that's unlikely in practice, and very unlikely for them to run for long.

wouldn't it blow, or at least overheat the nearest fuse? A proper ring
main would cope easily with a single 32A fuse.

The cable would run hot, but not hot enough to be a hazard.
15A BS1361 fuses trip in around 20 seconds at 30A, so it probably would. The user wouldn't notice until the other fuse tripped another 20s or so later.
Some users might then fit 30A fuse wire or a suitable nail, enabling the thing to run indefinitely. It would.


NT

On 26/09/2020 20:10, wrote:
On Friday, 25 September 2020 15:24:49 UTC+1, Max Demian wrote:
On 24/09/2020 21:48, tabbypurr wrote:
On Thursday, 24 September 2020 17:24:20 UTC+1, Max Demian
wrote:
On 24/09/2020 12:15, tabbypurr wrote:
On Sunday, 20 September 2020 10:54:40 UTC+1,
wrote:
On Sunday, 20 September 2020 10:48:07 UTC+1, Chris Green
wrote:

Our house (as in the house I grew up in, back in the
1950s) had a very early ring circuit as it was built in
1949 or thereabouts. It definitely had fuses at each end
of the ring. Whether that was as it should have been or
just how the electrician (my father I think) thought it
should be I don't know.

When rings were first introduced, people used to make them
from 2 15A radial circuits joined together.

I don't know how officially-sanctioned that was or for how
long.

It was part of the original rationale for the design.

Was each circuit fused for the whole ring, or half?

2x 15A fuses running a 30A ring. The point was one could add
unlimited extra sockets by joining 2x existing 15A socket
circuits into a ring. It was an ingenious solution combining cost
cutting with safety improvement.

What if you plugged two 3kW fires into sockets near one of the
fuses?

Firstly that's unlikely in practice, and very unlikely for them to
run for long.

wouldn't it blow, or at least overheat the nearest fuse? A proper
ring main would cope easily with a single 32A fuse.

The cable would run hot, but not hot enough to be a hazard. 15A
BS1361 fuses trip in around 20 seconds at 30A,

They might - but that is a bit optimistic - 5 mins sound more likely.

(and in a CU of that era a BS3036 rewireable would be more likely than a
cartridge fuse I would have thought)

so it probably would.
The user wouldn't notice until the other fuse tripped another 20s or
so later. Some users might then fit 30A fuse wire or a suitable nail,
enabling the thing to run indefinitely. It would.


NT



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Saturday, 26 September 2020 22:08:06 UTC+1, John Rumm wrote:
On 26/09/2020 20:10, tabbypurr wrote:
On Friday, 25 September 2020 15:24:49 UTC+1, Max Demian wrote:
On 24/09/2020 21:48, tabbypurr wrote:
On Thursday, 24 September 2020 17:24:20 UTC+1, Max Demian
wrote:
On 24/09/2020 12:15, tabbypurr wrote:
On Sunday, 20 September 2020 10:54:40 UTC+1,
wrote:
On Sunday, 20 September 2020 10:48:07 UTC+1, Chris Green
wrote:

Our house (as in the house I grew up in, back in the
1950s) had a very early ring circuit as it was built in
1949 or thereabouts. It definitely had fuses at each end
of the ring. Whether that was as it should have been or
just how the electrician (my father I think) thought it
should be I don't know.

When rings were first introduced, people used to make them
from 2 15A radial circuits joined together.

I don't know how officially-sanctioned that was or for how
long.

It was part of the original rationale for the design.

Was each circuit fused for the whole ring, or half?

2x 15A fuses running a 30A ring. The point was one could add
unlimited extra sockets by joining 2x existing 15A socket
circuits into a ring. It was an ingenious solution combining cost
cutting with safety improvement.

What if you plugged two 3kW fires into sockets near one of the
fuses?

Firstly that's unlikely in practice, and very unlikely for them to
run for long.

wouldn't it blow, or at least overheat the nearest fuse? A proper
ring main would cope easily with a single 32A fuse.

The cable would run hot, but not hot enough to be a hazard. 15A
BS1361 fuses trip in around 20 seconds at 30A,

They might - but that is a bit optimistic - 5 mins sound more likely.

(and in a CU of that era a BS3036 rewireable would be more likely than a
cartridge fuse I would have thought)


Yes. The open wire fuse links used in 1930s fuseboxes would have been the most common in the 40s - were they BS3036 compliant?

Ah - if BS 1361/2 came about in '47, 3036 was presumably much later.

Anyway, yes it would blow eventually, but the scenario would not be common & was still safe.


NT

Our House is late 40s Semi (ex local authority) and probably rewired 60s / 70s. We have a lot of circuits compared with most, and most sockets only have one T&E. Most crcuits cover a some or more sockets upstairs and downstairs. I decided as I wasn't sure of the topology of most of the circuits to have them fitted with 20A MCBs rather than 30A when we had a new CU. We've only tripped once tripped a circuit by pulling too much consecutively, and we just moved the cement mixer onto a different circuit for the day. I did do a continuity test in the CU on one of the suspect circuits the other day and it does appear to be some some sort of ring (at least in parts (but I realise this is simple test is no guarantee of anything). I found out the hard (amd painful) way that the circuit previously labelled upstairs Power wasn't! I now also test to make sure things are dead before I stick my screwdriver in!