9.5kw shower on a 6mm cable in new build

[JohnW2]

As long as the stated power is at 240V... I've been finding in recent times that 230V is being used and sometime even the hangover from 220V.

Maybe it's changed 'recently' but, if so, I hadn't noticed.

It seems that most energy-hungry products (showers, heaters, cookers, kettles etc. etc.) have almost always quoted the 'power' at 240V - I can but presume down to the marketing people, who want their products to sound 'as powerful as possible'!

Kind Regards, John

 

[jj4091]

Surely the fact that the buzzing stops when the shower is on a lower setting suggests that the mcb is being overloaded or faulty. Either way on a new build it should be rectified to the customers satisfaction no matter what the calculations suggest.

 

[sparkwright]

What make is the consumer unit?

Perhaps a 45amp MCB exists?

May be worth checking to see if there are other loose connections within the cu.

 

[JohnW2]

Surely the fact that the buzzing stops when the shower is on a lower setting suggests that the mcb is being overloaded or faulty.

Not necessarily. If it were due to, say, a loose connection, it might only occur when the shower was drawing high currents.

Either way on a new build it should be rectified to the customers satisfaction no matter what the calculations suggest.

Quite so. I suppose that they have been "trying".

Kind Regards, John

 

[SUNRAY]

Maybe it's changed 'recently' but, if so, I hadn't noticed.

It seems that most energy-hungry products (showers, heaters, cookers, kettles etc. etc.) have almost always quoted the 'power' at 240V - I can but presume down to the marketing people, who want their products to sound 'as powerful as possible'!

Kind Regards, John

Yes I Agree, however historically I've experienced electrical goods manufactured in other European countries for 220V so we are going back a while simply being fitted with a 13A plug and sold here and I found a good number of 3KW washing machines running >15A and overheated plug/socket.
More recently I've been testing and finding a rating at 230V:

As an example a replacement 3KW drinks water boiler kept overheating a 13A plup/socket.
The plate shew 230V, 3KW, 13A however my clamp measured >15A and calculating resistance from actual voltage indicated 3KW @ 220V and 13.7A
An original adjacent machine shew 220-240V, 2500-3000W, 13A and measured <13A
Measuring resistance of the machines with a cheap multimeter gave 17 & 20Ω (probes shorted tends to be around 0.8 to 1Ω so more like 16 - 16.2 & 19 - 19.2Ω) I concluded the machines were actually rated at 220V and 240V.

 

[ShaunShep]

I different contractor attended yesterday. Tried yet another MCB, the buzzing was still there. They said it's a 10mm cable (not 6mm), and that the MCB was probably getting close to it's limit (40amp MCB, shower pulling between 37-39amp) and causing some kind of vibration. The vibrating stopped if you lifted the MCB slightly so it's fixing hook was tight against the bracket it attaches to.

They installed 50amp MCB and the buzzing has gone.

 

[bernardgreen]

The overload detection in the MCB includes a coil through which the current passes. This coil is part of an electro-magnet pulling against a spring, If there is a large fault current then the electro-magnet will overcome the spring and operate the trip mechanism and the MCB will cut the power.

This coil and/or magnetic items close to the coil can vibrate due to the alternating magnetic field created by a current that is not enough to operate the trip mechanism.

 

[ShaunShep]

The overload detection in the MCB includes a coil through which the current passes. This coil is part of an electro-magnet pulling against a spring, If there is a large fault current then the electro-magnet will overcome the spring and operate the trip mechanism and the MCB will cut the power.

This coil and/or magnetic items close to the coil can vibrate due to the alternating magnetic field created by a current that is not enough to operate the trip mechanism.

ah ok, that makes sense. Like a tug of war between the spring and magnet With neither one being strong enough to overpower the other.

 

[charliegolf]

Surely the fact that the buzzing stops when the shower is on a lower setting suggests that the mcb is being overloaded or faulty. Either way on a new build it should be rectified to the customers satisfaction no matter what the calculations suggest.

Don't elec showers run at full power all the time, and just put more volume of water through when asked for lower temps?

 

[flameport]

Most have a half power setting, which makes a mediocre shower into a useless one.

 

[skenk]

What brand is the distribution board/MCB's? you wouldn't expect a 40A mcb to chatter even if it was drawing a little more than 40A

 

[ShaunShep]

The brand is BG

 

[flameport]

BG MCBs can be installed incorrectly so that the connection to the busbar isn't clamped under the terminal.
Should be in position 2 in the image, but can be installed with it in position 1 which will result in a poor connection, overheating, arcing, buzzing and whatever else.

The installation of another 50A MCB may just have coincidentally connected to the busbar properly and the previous ones were not.

Better quality devices have an additional metal tab on the moving cage contact so that incorrect installation is impossible.

 

[JohnW2]

ah ok, that makes sense. Like a tug of war between the spring and magnet With neither one being strong enough to overpower the other.

As a 'last resort' thought, has anyone suggested that you might ask the electrician to try altering the position of the shower MCB within the CU - so I suppose it's not impossible that the buzzing is related to the filed of its coil interacting with something in the vicinity?

Kind Regards, John

 

[Agile]

I am surprised that a slight buzzing from an MCB is causing any significant disturbance to the occupiers and particularly when one of them is having a shower some way away from the MCB.

I am also a little surprised that no one has commented on the lowered protection which the 50A MCB will give.

The calculated currents are likely to be rather higher that the actual currents which will be slightly reduced due to the connection cable resistances. The heater element will probably also increase its resistance a fair bit from cold to heated temperatures.