Whats the biggest shower I can fit please?

[ColJack]

I read on another post here that the DNO only alows something daft like 16A per house when planning a housing estate network..

 

[John_D]

Diversity can be applied to cookers because there is an oven heater, and separate ring heaters, you probably won't be using all of them at the same time. In a shower you can only choose stage 1 or stage 2heating. A 9k5 shower on stage 1 heating will probably not trip a 32A breaker on a 6mm cable

 

[ricicle]

I read on another post here that the DNO only alows something daft like 16A per house when planning a housing estate network..

AFAIK it's 2Kw (8A approx)

 

[John_D]

oops sorry folks decimal pointer slipped

 

[Softus]

A 9k5 shower on stage 1 heating will probably not trip a 32A breaker on a 6mm cable

Eh? A non-faulty 9.5kW shower, even on full chat, will definitely trip a 32A breaker, even on 1mm² cable.

 

[scotster]

Been busy since I popped away!

I have followed the cable all the way back to the CU and it is in hollow spaces (clipped against joist or stud).

Stud walls are currently empty although I was intending to inustlate the new shower stud walling where the cabling obvioulsy runs for a short way.


Actually just noticed a mistake. The shower has its own mini single CU connected before the main CU (in parallel off a big junction box) and after the meter.

The shower CU has a swicth breaker of 45A but the fuse in the unit is only rated at 40A. Could I swap that out to 45A if needed?

 

[big-all]

and why do we not apply diversity to showers like we do cookers.?

you only use it for 10-30 mins a day so even if it does get a little warm in use then it has plenty of time to cool down.. it's not like it's constantly overloaded for hours at a time...

normally I would recomend 10mm² for anything over 9kW anyway, i'm just curious..

surely diversity is to allow for the fact that only part the avalable load will be in use at any one time thus within safe margins

where as possibly overloading for 30 mins and cooling down is not safe or good practice

 

[Softus]

I have followed the cable all the way back to the CU and it is in hollow spaces (clipped against joist or stud).

In that case the cable could carry up to 46A, which isn't enough for a 10.8kW load.

Stud walls are currently empty although I was intending to inustlate the new shower stud walling where the cabling obvioulsy runs for a short way.

...which would de-rate the rable.

The shower CU has a swicth breaker of 45A but the fuse in the unit is only rated at 40A. Could I swap that out to 45A if needed?

No, because the non-fusing/non-tripping current of the MCB is required to be 13% greater than the design current (i.e. > 1.13 x 45A). In any case, running an MCB at or near its limit for long periods will cause it to overheat, and eventually weaken.

 

[ricicle]

No, because the non-fusing/non-tripping current of the MCB is required to be 13% greater than the design current (i.e. > 1.13 x 45A). In any case, running an MCB at or near its limit for long periods will cause it to overheat, and eventually weaken.

Where is that written?

 

[Softus]

In the Wiki.

 

[ricicle]

In the Wiki.

I would like to know where that factor of 1.13 was taken from.It must have been a particular manufacturers data sheet as I have never seen it.
I've used the 1.45 factor but never seen the 1.13

 

[Softus]

One certain error on my part - one of omission: I shoudl have said Type B MCB.

I'll see what I can look up on the 1.13 factor and get back to you.

 

[Softus]

I would like to know where that factor of 1.13 was taken from.
.
.
.
I've used the 1.45 factor but never seen the 1.13

I believe that both parameters are given in BS EN 60898-1:2003, but I don't have access to a copy.

 

[Spark123]

For a protective device with a fusing factor of 1.45 there is no need to apply a correction factor as these have already been calculated into the tables of current carrying capacities of the cables. These include devices such as MCBs, BS1361, BS88 fuse links. The other one, BS3036 semi enclosed rewirable fuses have a fusing factor of 2. To compensate for this, the ratio between the two is applied to the current carrying capacity of the cable i.e. 1.45/2=0.725.
At the end of the day, all standard circuits should be designed so the current carrying capacity of the cable (after correction factors) is greater than the nominal setting of the overcurrent protective device which is greater than the design current.

 

[Softus]

I understood of all those words, but have no idea what conclusion you've reached.