Electricians Advice Needed - Shower Installation

[Nomisf]

Hi All,

I am hoping we have some resident electricians here who can guide me,

My estate agent commissioned the replacement of the electric shower in my rented accommodation, however the new shower trips the MCB if used for more than 6-7 minutes.

I have done my own prodding and found out that the shower installed is 9.5kw (Triton Enrich) but is installed behind a 32A MCB (Wylex NSB32) on what "appears" to be 6mm2 core cable. Our incoming voltage is around 230v on the dot.

Looking at the datasheet for the NSB32, a trip time of around 10 minutes at 130% load (41A, I calculated) seems to be about right.

The agency are refusing to accept that the installation is incorrect, so I was wondering if anyone could point me at the part of the electrical code that covers this ?

Thanks!

 

[Nomisf]

6mm is within spec but should really be a 40amp MCB, as long as the cable is clipped not buried in anything.

I always though it best practice to just fit 10mm for showers.

In all fairness, I do need to find the offcut of the cable they left and check with with my calipers - as I can't tell 6vs10mm by eye.

A 9.5kW shower should be installed with 10mm2 cable with a fuse rating of 40-45A, NOT 6mm2 !
It should also be RCD or RCBO protected.

A >9kW shower supplied by 6mm2 cable on a 32A MCB (normally used for 5mm (2x2.5)) screams cowboy installer who doesn't know what he is doing.

We have a split box, with the MCB for the shower and plugs running through an RCD - so we are at least safe in that respect.

The issue is, the contractor refuses to admit that the shower is wrong - and is trying to force the landlord to have the wiring in the walls checked.

 

[Nomisf]

DO NOT replace the 32A MCB with a 40A one without upgrading the 6mm cable to 10mm, this is getting into an area of danger as 40A is slightly too high to sufficiently protect 6mm cable from current overload and poses a potential fire risk in certain situations and installs!!

Page 276, BS 7671, reference method B


For a 9.5kW load 10mm2 cable and a 45A fuse rating should have been used, anything lower is just too close to current carrying capacity's and ratings, although possible it would require lots of calculations with variables being taken into account before being deemed safe and electrically sound.

With electrics it's always best to go with the belt & braces approach, an over engineered and spec'd installation is the best option imho.

Thank you


Also thanks

I have nothing to add other than that this thread is a great example of why I love these forums.

Agreed


I have taken the face plate off the shower, and can confirm the CPC is a single solid core - as per below picture.



Sorry its taken so long to reply - its turned into an all out war between the landlord and the letting agency, culminating in us changing agency mid term

 

[Nomisf]

I thought I ought to put a final nail in this thread.

After the landlord trying his hardest to blame anyone but the contractor, I wrote directly to the contractor - laying out my own calculations and the regulations above.

His response was "oh well I am just a handman/plumber I don't understand any of this and don't care - i just put showers on the wall". Although he agreed to replace the shower with one I specified "if i am the expert".

Cue a few weeks wait, and he showed up with a 8.5kw shower rather than the 7.5kw I recommended and fitted it with my landlords supervision - who had no idea what he was looking at either.

The good news is at least, the 36.2A this draws is sufficiently low to scrape under the tolerance of the 35A breaker.

At this point, the shower works - and I give up. In my opinion there shouldn't be anyone out there wiring up showers who can't do basic bloody maths. It won't be my problem in 2 months anyway, the amount of drawn out maintience issues I have had in this place spell the end of my tenancy!

In 8 months,

- Plaster broke away from half the walls
- Shower problem
- Backfiring boiler
- Shed fell down due to disrepair
- Fences attached also fell down
- Leaking toilet waste pipe
- 3 months of blocked radiators