Following on from the "Terminal blocks" posting yesterday, I've now removed
the terminal blocks and soldered the wire joins.

I thought I'd better test everything so decided to turn on/plug in
everything I owned. Thus the dishwasher, washing machine, kettle, oven
(yup - into the ring main, courtesy of the kitchen fitters), fan heater,
halogen heater and everything else was operating at the same time. The
electricity meter was spinning around pretty quick.

Well, I'm still here, so I guess it all worked fine.

One slight problem I thought I'd raise... Because some of the ring main
cable is exposed, I thought I would feel this to see if it was getting warm.
I also felt my new joints (which are safely wrapped in electrical tape).

One of the cables felt warm (the solder joint part seemed fine). Only very
slightly warm, to the extent that I could be imagining it, but it was
certainly warmer than the other ring main cable next to it. BUT! The
warm-ish cable came from the socket that the fan heater was plugged into. I
ought to point out that the mains cable leading out of the back of the fan
heater gets warm too. I don't know what its rating is - 2KW?

I THINK I'm right in saying that there's nothing to be worried about here.
But I thought I'd better check the experts of this group who have been so
helpful so far.

Brian wrote:
Following on from the "Terminal blocks" posting yesterday, I've now
removed
the terminal blocks and soldered the wire joins.

I thought I'd better test everything so decided to turn on/plug in
everything I owned. Thus the dishwasher, washing machine, kettle,
oven
(yup - into the ring main, courtesy of the kitchen fitters), fan
heater,
halogen heater and everything else was operating at the same time.
The
electricity meter was spinning around pretty quick.

Well, I'm still here, so I guess it all worked fine.

One slight problem I thought I'd raise... Because some of the ring
main
cable is exposed, I thought I would feel this to see if it was
getting warm.
I also felt my new joints (which are safely wrapped in electrical
tape).

One of the cables felt warm (the solder joint part seemed fine). Only
very
slightly warm, to the extent that I could be imagining it, but it was
certainly warmer than the other ring main cable next to it. BUT! The
warm-ish cable came from the socket that the fan heater was plugged
into. I
ought to point out that the mains cable leading out of the back of
the fan
heater gets warm too. I don't know what its rating is - 2KW?

I THINK I'm right in saying that there's nothing to be worried about
here.
But I thought I'd better check the experts of this group who have
been so
helpful so far.


cable will get warm if you put enough currents through it. PVC cable is
rated to 60 or 70C (?), so if it burnt you its too hot.


NT

Brian wrote:

I THINK I'm right in saying that there's nothing to be worried about here.
But I thought I'd better check the experts of this group who have been so
helpful so far.

Nothing to worry about. You could in some cases have a cable sitting
there at 60 degrees C and it still be considered safe and within
designed limits.

Circuit design is based on the concept of a temperature "budget". The
top limit is set by what the cable insulation will stand (70 deg C for
PVC, 90 for XLPE and some LSOH cables).

Things like anticipated ambient temperatures (general and local to the
cable), its length (i.e. its resistance), proximity to other cables and
to thermal insulation etc, all eat into that budget. What remains
dictates the maximum amount of current the circuit can carry (and hence
the power it can dissipate as heat generated by the current flowing
through the cable resistance).

An allowance is also made for "diversity" i.e. the assumption that the
situation you have artificially created with all appliances on at once
is very unlikely to happen in reality - so a certain amount of
theoretical overloading is permitted.

--
Cheers,

John.

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On Sun, 15 May 2005 20:37:24 +0000 (UTC), Brian wrote:

it was certainly warmer than the other ring main cable next to it.

Was that "other ring main cable" part of the same ring with the warm
cable or part of another ring? Both sides of the same ring getting
marginally warm under fairly hefty loads like you applied I wouldn't
be too concerned about. A noticeable difference in temp I'd be a bit
more worried about and start looking for a break in the ring, though
it depends a bit on where the load is applied to the ring. In the
middle the load will be evenly distributed on the two halves, right at
one end the short leg will supply more of the current and thus have
more I^2R losses related to the resistance difference between the long
and short paths.

--
Cheers
Dave. pam is missing e-mail