Wiring load question
 

Just looking at my house ring main and a bit bothered with my kitchen
sockets.

The socket ring is one loop from a 30 amp fuse using 2.5 T&E.

In the corner of the kitchen the ring goes down from the ceiling into
an above worktop double socket and then down under the worktop into
another double socket.

I always assumed the ring would go into the top socket with one wire
unbroken and on to the bottom one and the other wire into and out of
the socket. ie both sockets on the full ring.

I have just found the ring stops at the above worktop socket and the
bottom one is a spur.

Fine, except the bottom one has a washing machine and a dishwasher
plugged in. If both machines are on and the heaters go on, it seems
to me that the load on the spur wire is near maximum.

To do what I thought would be the accepted thing would have involved
only an extra meter of cable and avoided three sets of wires in the
top socket terminals.

Any comments please?

Wiring load question
 

"EricP" wrote in message
...
Just looking at my house ring main and a bit bothered with my kitchen
sockets.

The socket ring is one loop from a 30 amp fuse using 2.5 T&E.

In the corner of the kitchen the ring goes down from the ceiling into
an above worktop double socket and then down under the worktop into
another double socket.

I always assumed the ring would go into the top socket with one wire
unbroken and on to the bottom one and the other wire into and out of
the socket. ie both sockets on the full ring.

I have just found the ring stops at the above worktop socket and the
bottom one is a spur.

Fine, except the bottom one has a washing machine and a dishwasher
plugged in. If both machines are on and the heaters go on, it seems
to me that the load on the spur wire is near maximum.

To do what I thought would be the accepted thing would have involved
only an extra meter of cable and avoided three sets of wires in the
top socket terminals.

Any comments please?

2.5mm flat tw/e has a current carrying capacity of 20A. The IEE regs do
allow a spur to be wired in 2.5 despite the potential 26A loading. It's not
a situation I would design for though and if you can incorporate it into
your ring I would do it.

Wiring load question
 

On Tue, 8 Nov 2005 19:13:45 -0000, "Bob Watkinson"
wrote:

Any comments please?

2.5mm flat tw/e has a current carrying capacity of 20A. The IEE regs do
allow a spur to be wired in 2.5 despite the potential 26A loading. It's not
a situation I would design for though and if you can incorporate it into
your ring I would do it.

Thanks for the figures, exactly what I want. As the appliances are the
type where the maximum loading could be prolonged, I will extend the
ring. The installer put conduit in and everything, why not the extra
little bit of cheap cable? He must have spent longer twisting the
three pairs of wires and fitting them in the back of the socket.

I may be able to pull through the conduit, but if not, it's only 2m of
bolster work through decent plaster. Could have done without it
though.

Again many thanks :))

Wiring load question
 

EricP wrote:
On Tue, 8 Nov 2005 19:13:45 -0000, "Bob Watkinson"
wrote:

Any comments please?

2.5mm flat tw/e has a current carrying capacity of 20A.

No, it is rated to carry 20A continuous. That means it has higher
current carrying capacity, but more significantly will happily carry
much more intermittently.


The IEE regs do
allow a spur to be wired in 2.5 despite the potential 26A loading. It's not
a situation I would design for though and if you can incorporate it into
your ring I would do it.

because its fine.


Thanks for the figures, exactly what I want. As the appliances are the
type where the maximum loading could be prolonged,

no theyre not.

I will extend the
ring. The installer put conduit in and everything, why not the extra
little bit of cheap cable? He must have spent longer twisting the
three pairs of wires and fitting them in the back of the socket.

I may be able to pull through the conduit, but if not, it's only 2m of
bolster work through decent plaster. Could have done without it
though.

If you switch both machines on and monitor the cable temp, you'll find
all is well. PVC is rated to operate at upto 70C. 60C is hot enough to
hurt.


NT

Wiring load question
 

wrote in message
ups.com...
EricP wrote:
On Tue, 8 Nov 2005 19:13:45 -0000, "Bob Watkinson"
wrote:

Any comments please?

2.5mm flat tw/e has a current carrying capacity of 20A.

No, it is rated to carry 20A continuous. That means it has higher
current carrying capacity, but more significantly will happily carry
much more intermittently.

That may be so but when designing circuits we have to follow the regulations
irrespective of our assumptions of whether or not full load current is to
be carried intermittently or not. The regs allow diversity in some
situations but not in others and when they do then specific calculations are
made to determine an assumed load. As an electrical engineer it would have
been irresponsible to recommend anything other than what I did.

Wiring load question
 

Bob Watkinson wrote:
wrote in message
ups.com...
EricP wrote:
On Tue, 8 Nov 2005 19:13:45 -0000, "Bob Watkinson"
wrote:

Any comments please?

2.5mm flat tw/e has a current carrying capacity of 20A.

No, it is rated to carry 20A continuous. That means it has higher
current carrying capacity, but more significantly will happily carry
much more intermittently.

That may be so but when designing circuits we have to follow the regulations
irrespective of our assumptions of whether or not full load current is to
be carried intermittently or not. The regs allow diversity in some
situations but not in others and when they do then specific calculations are
made to determine an assumed load. As an electrical engineer it would have
been irresponsible to recommend anything other than what I did.

even though the socket on 2.5 is both safe and within regs?

NT

Wiring load question
 

wrote in message
ups.com...
Bob Watkinson wrote:
wrote in message
ups.com...
EricP wrote:
On Tue, 8 Nov 2005 19:13:45 -0000, "Bob Watkinson"
wrote:

Any comments please?

2.5mm flat tw/e has a current carrying capacity of 20A.

No, it is rated to carry 20A continuous. That means it has higher
current carrying capacity, but more significantly will happily carry
much more intermittently.

That may be so but when designing circuits we have to follow the
regulations
irrespective of our assumptions of whether or not full load current is
to
be carried intermittently or not. The regs allow diversity in some
situations but not in others and when they do then specific calculations
are
made to determine an assumed load. As an electrical engineer it would
have
been irresponsible to recommend anything other than what I did.

even though the socket on 2.5 is both safe and within regs?

Yes. If you read again my post to th OP you'll find I said the regs covered
it but I don't like to design it that way personally. It's not good practice
to under-rate a cable given a potential load. Far better to do the job
properly. There are many thing that are technically within the regs but you
wouldn't do it. Would you wire a whole house in 16mm and protect it with a
single 60A fuse. Course you wouldn't it would be silly but the regs allow
it.

NT

Wiring load question
 

Fine, except the bottom one has a washing machine and a dishwasher
plugged in. If both machines are on and the heaters go on, it seems
to me that the load on the spur wire is near maximum.

There's no problem with the spur per-se. It will handle the current. You do
have a problem with a designed in point loading on the ring, which would not
be considered a good idea these days. This point load would be the same even
if the socket is on the ring proper and would not be solved by a circuit
reconfiguration.

The correct solution these days is to have a dedicated circuit to the
laundry appliances, leaving the ring for portable appliances. This is how I
wired mine up. I've got a 32A ring and a separate 32A radial for the
dishwasher, washing machine and tumble dryer, run in 6mm cable. I can run
all the appliances simultaneously in complete confidence. The main kitchen
ring ends up quite underloaded, with only intermittent loads, like kettles
and microwaves, which is the best way to run them.

Christian.

Wiring load question
 

On Wed, 9 Nov 2005 10:09:26 -0000, "Christian McArdle"
wrote:

Fine, except the bottom one has a washing machine and a dishwasher
plugged in. If both machines are on and the heaters go on, it seems
to me that the load on the spur wire is near maximum.

There's no problem with the spur per-se. It will handle the current. You do
have a problem with a designed in point loading on the ring, which would not
be considered a good idea these days. This point load would be the same even
if the socket is on the ring proper and would not be solved by a circuit
reconfiguration.

The correct solution these days is to have a dedicated circuit to the
laundry appliances, leaving the ring for portable appliances. This is how I
wired mine up. I've got a 32A ring and a separate 32A radial for the
dishwasher, washing machine and tumble dryer, run in 6mm cable. I can run
all the appliances simultaneously in complete confidence. The main kitchen
ring ends up quite underloaded, with only intermittent loads, like kettles
and microwaves, which is the best way to run them.

Christian.

No fear of you having problems then. :))

Thanks for the input.

Wiring load question
 

"Christian McArdle" wrote in message
...
Fine, except the bottom one has a washing machine and a dishwasher
plugged in. If both machines are on and the heaters go on, it seems
to me that the load on the spur wire is near maximum.

There's no problem with the spur per-se. It will handle the current. You
do
have a problem with a designed in point loading on the ring, which would
not
be considered a good idea these days. This point load would be the same
even
if the socket is on the ring proper and would not be solved by a circuit
reconfiguration.

Well it would actually. With a ring you have two current paths instead of
one so the current effectively is halved in the conductors.

The correct solution these days is to have a dedicated circuit to the
laundry appliances, leaving the ring for portable appliances.

Nothing wrong with your solution, though it depends on having sufficient
ways in the CU and is only really achievable in a rewire. When you say this
is the correct solution, how is it more correct than the OP wiring his
appliances into the ring (which is what I would do using FCU's as they are
fixed appliances)

This is how I
wired mine up. I've got a 32A ring and a separate 32A radial for the
dishwasher, washing machine and tumble dryer, run in 6mm cable. I can run
all the appliances simultaneously in complete confidence.

IMHO I would say a little overkill. If you really wanted to keep these items
off the main ring they would have all have sat quite happily on a 32A
dedicated ring wired in 2.5mm. A much easier task than wrestling with 6mm
and even with all three on I doubt you would get tripping.

The main kitchen
ring ends up quite underloaded, with only intermittent loads, like kettles
and microwaves, which is the best way to run them.

Christian.

Wiring load question
 

Nothing wrong with your solution, though it depends on having sufficient
ways in the CU and is only really achievable in a rewire. When you say
this
is the correct solution, how is it more correct than the OP wiring his
appliances into the ring (which is what I would do using FCU's as they are
fixed appliances)

The current wiring regulations require you to consider the ring balance. In
particular, it is not permitted to "design in" substantial and foreseeable
point loads. Personally, I think running all the laundry off one double
socket is a substantial and foreseeable point load and is poor practice when
designing the circuits. That is not to say that an existing system should be
regarded as dangerous or requiring rectification, it is just good practice
when designing a modern installation.

Christian.

Wiring load question
 

"Christian McArdle" wrote in message
...
Nothing wrong with your solution, though it depends on having sufficient
ways in the CU and is only really achievable in a rewire. When you say
this
is the correct solution, how is it more correct than the OP wiring his
appliances into the ring (which is what I would do using FCU's as they
are
fixed appliances)

The current wiring regulations require you to consider the ring balance.
In
particular, it is not permitted to "design in" substantial and foreseeable
point loads. Personally, I think running all the laundry off one double
socket is a substantial and foreseeable point load and is poor practice
when
designing the circuits. That is not to say that an existing system should
be
regarded as dangerous or requiring rectification, it is just good practice
when designing a modern installation.

Christian.

Which regulation are you referring to? I believe you're mistaken, I've never
seen such a requirement in the regs or any revisions. In current
distribution the current is distributed evenly along parallel paths
irrespective of where the load is.