John Rumm wrote:
On 11/11/2010 13:56, wrote:

I know this is a slightly odd question, I will try and explain.

[snip]

Finally to the question, space is limited on the boat and there are
very few places where flush mounted sockets are possible so the
neatest solution is to use two and four way 'trailing sockets' (as in,
the sockets of a multi-way extension lead). However these are
supposed to be protected by a 13 amp fuse in the plug, I really want
to wire them permanently and, if I do this, they will be protected by
16 amp MCBs. It feels to me as if this should be OK as 16 amp MCBs
will, in reality, probably trip at or close to the same current levels
as a 13 amp fuse.

Does this seem a reasonable/safe approach? It doesn't have to conform
to any specific wiring regulations (which it almost certainly won't),
no one is ever going to inspect the wiring of the boat at that sort of
level of detail. On the other hand I do want it to be safe for the
usual mix of family and friends as well as for me.

What does the team think?

Short answer, I would use a 10A MCB rather than a 16. That will let you
draw 15A pretty much indefinitely.

There is evidence that some of the lower quality (i.e. probably cheaper)
4 way leads are not adequately protected by their 13A fuse - since this
will usually permit a sustained load of 20A and not all of them are up
to that. Read the report starting page 18:

http://www.esc.org.uk/pdfs/business-...n-Issue-18.pdf

All of the failures noted there seem to have been in the plug which I
am going to remove, thus it would seem that my usage will actually be
safer, I just need to keep an eye on the sockets.


a 16A MCB will be somewhat more tolerant to sustained overload than a
13A fuse. If you compa

http://wiki.diyfaq.org.uk/index.php?...FusingTime.png

with

http://wiki.diyfaq.org.uk/index.php?...e-MCBTypeB.png

It's difficult to compare but if my interpretation of the fuse curves
is right (I'm assuming a 13 amp fuse lies in the *band* between the
two RH curves) then a 13 amp fuse can be distinctly worse than a 16
amp MCB can't it? E.g. at 30 amps a 13 amp fuse could take up to 400
seconds to blow whereas a 16 amp MCB will trip after about 200
seconds. It's not a big difference though.

I do have some 10 amp MCBs so could go with them I guess, the supply
as a whole can only provide 16 amps. Maybe I could put in one set of
full sized sockets where, if/when needed anything that draws close to
the limit can be plugged in.

Thanks for the links and advice.

--
Chris Green