Here’s a brain tickler for trainees

[MFS Electrical]

You have been asked by a customer to install 2 new 10kW Electric Showers in a large house.
The maximum demand has been calculated and it is fine to install one of these showers but not the other.
There is absolutely no other way to install these showers i.e fed from a combi boiler as there is no gas in the property. The showers both have to be Electric.
The customer insists on two showers no matter the cost. What is the most cost effective way of doing this?

 

[MFS Electrical]

Some more info:
There is a split load board with 3 spare ways
Showers 2 at 10kW,
TNCS supply
The customer prefers wall mounted isolators to pull cords
Shower 1 first floor will be run through a stud partition wall the Cu is almost directly below the shower and the length of run is 3m.
Shower 2 in the loft is run through the same stud partition then through the eaves space in the loft clipped to a plank that is away from the insulation of the loft the run for the loft shower is 18metres.

 

[MFS Electrical]

You need to work out the cable size for each of these showers and come up with soloutions to make sure the installation is not overloaded.

 

[SparkyChick]

I've just removed a post by @Spoon because this is a brain teaser for the trainees and I felt it gave a little too much useful information *evil grin*

 

[Spoon]

I've just removed a post by @Spoon because this is a brain teaser for the trainees and I felt it gave a little too much useful information *evil grin*

Sorry @SparkyChick ... I didn't notice it was in the Trainee section... ... I'm still half asleep..

 

[telectrix]

it's OK spoon, i almost posted then saw SC's post.

 

[Richard Burns]

Has the stud partition wall that will be taking both shower cables got insulation in it?

 

[MFS Electrical]

Has the stud partition wall that will be taking both shower cables got insulation in it?

The stud partition doesn’t have insulation in it at all

 

[telectrix]

and if the studding is metal, make sure you have a visa for a country with no extradition treaty.

 

[MFS Electrical]

and if the studding is metal, make sure you have a visa for a country with no extradition treaty.

It’s a traditional stud partition constructed of timber and gyproc

 

[Humour_me]

Ok first post on here so be gentle. Cable calcs would be as follows;

Ib - 10000/230 = 43.5 amps so a 45 amp mcb in one of the spare ways

It - 45/1.03 = 46.35 amps made some assumptions that the ambient temperature would be 20C and the cables would be by them selves not grouped together. Using reference method c this would size the cable at 10mm.

Checking volt drop on the cable would be 4.4 x 43.5 x 3 / 1000 = 0.57v and 4.4 x 43.5 x 18 / 1000 = 3.4v these both come within the allowed 6%.

Might as well check Zs by calculation while I'm at it which would be R1+R2 per meter for 10mm is 6.44 milli ohms so 6.44 x 18 / 1000 = 0.11 ohms. Ze for tncs would be a maximum of 0.35 ohms so worst case would be 0.46 ohms. On a 45 amp mcb the max Zs would be 0.78 so again all good.

Isolators could be vertical 2 gang 50 amp double pole switches mounted out side the bathroom door.

As for making sure about not going over the max demand I can think of two ways of doing it. The simplest and cheapest way would be a subtable rated change over switch mounted some where accessible by the CU so only one shower can be used at a time. The other way that I can think of but maybe wrong (educate me) would be the use of two suitably rated contactors wired as you would for forward reverse motors (few less wires as not swapping two phases just switching the line from one contractor to another). Each contractor would then power one shower. Momentary switches could then be wired by each bathroom to turn on each shower, but not the other.

 

[Spoon]

@marconi didnt know you were a trainee

I'm waiting for @SparkyChick to remove the post, like she did with mine...

 

[SparkyChick]

I just have

 

[MFS Electrical]

I like the editing of the title spot on SC

 

[Sintra]

I like the editing of the title spot on SINTRA