Immersion heater continuously blowing fuses

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kai

breezer said:
i bet the 15 A fuse goes before the 13A fuse does because the 13A fuse is for a plug top and the 15 a i will bet is a hrc, they tend to be slightly quicker

Perhaps this may be an example of incorrect discrimination in a circuit, where the minor device does not operate before the major device???
 
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on the other hand they are both protecting the same thing anyway so it doesn't really matter

i'll start to belive that descrimination of overcurrent devices really matters when i see rcd layouts that even try to achive it.

im starting to feel that rcd sockets are the only proper way to do rcd protection.

why do we accept a single rcd covering every socket in the house?
or worse everything electrical in the house?
or only slightly better and rare a RCBO covering a whole floor?
 
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plugwash said:
on the other hand they are both protecting the same thing anyway so it doesn't really matter

i'll start to belive that descrimination of overcurrent devices really matters when i see rcd layouts that even try to achive it.
Cost is an issue..

why do we accept a single rcd covering every socket in the house?
Cost. Inertia. Infrequent trips so it's not much of a problem?

or worse everything electrical in the house?
Old installations (apart from TT, does anybody install RCD incomers these days?)

or only slightly better and rare a RCBO covering a whole floor?
Cost. Inertia. The problem it solves is not important?

314-01-01 requires that every installation be divided into circuits as necessary to (i) avoid danger and minimise inconvenience in the event of a fault.

Given that "minimise" means to reduce to the smallest possible amount, (not practical, or feasible) the only truly compliant solution is an RCBO per socket.

Wouldn't that be fun.
 
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ban-all-sheds said:
Given that "minimise" means to reduce to the smallest possible amount, (not practical, or feasible) the only truly compliant solution is an RCBO per socket.

Wouldn't that be fun.

to go to the extreme, all sockets should then be single (if double needed then have 2 singles next to each other), just incase there is a fault on 1 appliance connected to a double the other appliance (if connected) will also switch off
 
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so then why if we don't bother with discrimination at all on rcd protection do we get worked up over it on overcurrent/short cuircut protection?
 
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That still doesn't address the fact that a L-N or L-E fault will take out all of the other sockets - the only way to minimise inconvenience is 1 socket per circuit.

Here's another one - what's the cost, including installation of a new CH boiler, particularly next year when condensing ones will be compulsory?

What's the relative cost of a small UPS to keep the ignition, pump and valves going in the event of a power cut?

You could argue that not putting a boiler on a UPS does not minimise inconvenience, and so does not conform to the regs, and therefore after Jan 01 will be illegal.
 
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This problem may arise from the sloppy modern tendency to use "minimise" not as a superlative but as a comparative - to mean "reduce" or "lessen".
Alternatively, what was intended could have been a sensible engineering compromise between cost, practicality and the ideal?
Either way, ambiguity.
 

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