Kitchen Wiring

[ScottInnesx]

That was exactly @telectrix suggestion.

Sorry I’m confused. not sure where I said I am using a FCU at?
[automerge]1593890258[/automerge]

Hence my question.

mate, I’m just gonna run in the cables. need to know what I need. Thats all, not claiming to be an expert

 

[pc1966]

Sorry I’m confused. not sure where I said I am using a FCU at?

You didn't, but Dustydazzler's example had them.

 

[ScottInnesx]

You didn't, but Dustydazzler's example had them.

Thats make sense, I was getting confused. Thanks for clearing that up

 

[nicebutdim]

20A D/P switch (with or without neon) above w/top. single socket for appliance below. that way you don't have 2 x 13A fuses in series. as Punch used to say (before he was declared a non-PC wife-beating sexist)That's the way to do it.

edit: to the pc brigade... i should have said "genderist".

Some more learning for me here.

House is under 3 years old and all appliances in kitchen & utility are controlled by a switched FCU (not cooker obviously) above single unswitched sockets.

What problems could this cause where both fuses are of equal rating or is this just bad practise?

 

[pc1966]

What problems could this cause where both fuses are of equal rating or is this just bad practise?

It is bad practice as in the event of a fault you might have one, the other, or both fuses blow. And if one survives it is probably so weakened that it might blow on small overloads / switch-on surges in the near future.

When cascading protective devices you want to have selectivity - so the one closest to the fault goes and those upstream survive intact. For fuses of the same general family then you typically get that for a 1:2 ratio (and in some cases with a 1:1.6 ratio).

So if you have a 13A fused outlet then really the downstream fuse ought to be 5A or less, so you get reliable disconnection of the closest OCPD.

For MCB in cascade it is hard to be much selectivity when you hit the instantaneous magnetic trip region, hence for an out building the preference for a fused-switch feeding the garage CU sort of thing. Similarly for fuse/MCB/fuse combinations it is complicated as to quite what will happen as the trip curves typically intersect at two fault currents. Whole books have been written on it!

 

[nicebutdim]

It's not something I'd encountered before (other than in extension leads), nor thought much about. It hadn't even occured to me that the situation existed in my kitchen until reading this thread.

Will have to learn more on the subject, but I'm a bit surprised that a practicing electrician would have fitted these. Must have been the only in-stock option at the cheapest of cheap accessory supplier on that day

 

[James]

It's not something I'd encountered before (other than in extension leads), nor thought much about. It hadn't even occured to me that the situation existed in my kitchen until reading this thread.

Will have to learn more on the subject, but I'm a bit surprised that a practicing electrician would have fitted these. Must have been the only in-stock option at the cheapest of cheap accessory supplier on that day

To be fair, it is a fairly common practice.
And let’s face it, if the washing machine blows a fuse, it has to be pulled out to investigate the fault.
At that time, change both fuses when it is repaired or replaced.

More often than not, a 32A B type breaker will trip before a 13A fuse anyway.

 

[nicebutdim]

At that time, change both fuses when it is repaired or replaced.

This is exactly the thought that occured to me, should a fuse ever blow.

I like information and learn a lot from this forum, but this was one of those occasions were the information had immediate relevance.

Back to reading again...

 

[richy3333]

Jesus, are we now teaching DIY-Dave’s For free ?