On 31/01/2018 00:55, Roger Hayter wrote:
jim k wrote:

I have two immersions, & what I didn't find out til I went to fit
the boost timers is that one of the exstg two immersion
switches, A, also feeds the spur? to switch B of the other
immersion....

Net result is so far I can't fit both "feed" cables into the
terminals on the rear of the boost timer that I want to
replace
switch A..

Any workarounds please?

I'll check the ratings of the immersion heaters tomorrow but I
believe they are 3kw. The cables are thick multi stranded & I
can't fit two in the terminals of the new boost switch at A.


I suppose the radial cable from the CU (supplying both immersions)
should be ?4mm? It's protected by a 32amp rcbo...

But the feed from switch A to switch B needn't be in 4mm too if
immersion B is 3kw? I'm thinking that could be 2.5mm2? which
might be more doable...

TIA

If you've got a spare way in the CU it might be simpler all round to run
another 2.5mm^2 cable in parallel and use two 20A MCBs.


A 16A MCB is more often used than a 20A MCB for 3kW immersion heaters,
however that makes little or no difference in most cases.

The one that gets me are garage CU's that come with a RCD main switch
and 16A MCB and a 6A MCB. Why not a 20A MCB and a 6A MCB? You would
normally run a 20A radial for the sockets from such a CU.

--
Adam