9.5kw shower on a 6mm cable in new build

[sparkwright]

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.

It was remarked by the last electrician that the cable wasn't 6mm2, but in fact 10mm2.

Clearly, the 40A MCB wasn't coping.

One would like to think the cable is clear of thermal insulation - and if not, I hope this is rectified.

 

[Agile]

I would take the view that the 40A MCB was coping perfectly and a small amount of buzzing is only to be expected as a biproduct of their use.

I am still wondering how one should view an MCB rated at 20% above the normal expected current.

 

[sparkwright]

I would take the view that the 40A MCB was coping perfectly and a small amount of buzzing is only to be expected as a biproduct of their use.

I am still wondering how one should view an MCB rated at 20% above the normal expected current.

The MCB protects the cable, and the cable is currently believed to be 10mm2

45A MCBs and RCBOs are not made by all manufacturers, but I believe it would be better if they were.

 

[Agile]

Well a normally fitted 10mm cable would be well able to carry 50 amps.

But I would prefer to see the current protection on the shower unit at rather lower than plus 20%. But that is probably rather a personal choice.

From my experience electric shower units rarely fail in an overcurrent mode and most from internal connections overheating and going open circuit.

 

[Adam_151]

I am still wondering how one should view an MCB rated at 20% above the normal expected current.

As a sensible design pratice? and one that is required by the electrical standards in some nations.

Its not considered desirable to have the MCB running right on its nominal rating for any resonable length of time, it'll increase the heat generated in the enclosure for a start, especially if you do it on all the circuits. As long the nominal rating does not exceed the capacity of the cable as installed after deratings have been considered* then its not a problem. Standard advice is that 32A electric vehicle supply point are supplied on 40A protection

*If overload protection is actually needed - because someone will be sure to pull me up on that if I don't say it

 

[Agile]

Whilst I am not yet familiar with most EV charging circuits, I would expect that the many variables of largely discharged batteries, age, temperature, etc. may well result in less good regulation of the charging current than might be ideal and consequently could sometimes exceed the expected maximum power required.

 

[JohnW2]

Its not considered desirable to have the MCB running right on its nominal rating for any resonable length of time,

I agree, but we're talking about a shower, and I wouldn't think (unless, perhaps, one has teenage daughters like the ones I once had ) that it would generally be drawing its high current for long enough to be a cause for significant concern,

*If overload protection is actually needed - because someone will be sure to pull me up on that if I don't say it

I'm not one for "pulling people up" over such an issue, but I do acknowledge that it's not difficult to argue that it is exceptionally unlikely (even if Sunray has some contrary anecdotes!) that a shower ever would result in an 'overload' current.

Kind Regards, John

 

[robinbanks]

may well result in less good regulation of the charging current

Doubt it; the car is the driver for it, not the charger, and the car has quite a sophisticated charge management system

 

[Agile]

That may well depend a lot on the actual car.

Some are fed with 230v mains and have the charger in the car.

Others are fed directly with the DC charging voltage from the home based charger.

 

[Adam_151]

Some are fed with 230v mains and have the charger in the car.

That is pretty much standard, now the charger in the car can vary between models in, for instance whether or not it can make use of three phases or just one, but as far as I know, its present in all normal EVs (we will exclude things like milk floats and road sweepers here! - normal EVs, like you can go to a showroom and buy to carry your family around in)

The charger on board (or BCB - Battery charging bock as its sometimes termed), will only pull what the supply equipment tells it that it is allowed to (theres a PWM waveform that varies in duty cycle), how much it can charge the batteries with that does depend on state of charge, temperature, etc, and it might decide to pull less than the maximum its allowed, no problem with that, it just won't pull more and I wouldn't be supprised if presented with a car that disobeyed the rules, the EVSE would cut it off

Others are fed directly with the DC charging voltage from the home based charger.

Many vehicles have the ability to accept DC charging as well, but this generally will not be from a home charger, thats mode 4 charging and generally found on the service station chargers and they start from about 40kw go upto the hundreds of kws, by which time the charger itself is in a cubicle about the size of a package sub...

You can have one of the smaller mode 4 DC chargers at home if you have a three phase supply and the spare capacity, however it'll not be cheap https://www.voltaev.co.uk/collections/commercial-ev-chargers/products/evd40s-p-tethered-40kw-32a-dc

 

[Agile]

If I had forked out for a new all electric car then I would be dead scared of charging it with any of the high output chargers just because of the likely reduction in the life of the battery.

Careful use of length of charge would be my solution.

But my transport needs are so variable that I would still be very wary of an all electric car for the time being.

 

[JohnW2]

You can have one of the smaller mode 4 DC chargers at home if you have a three phase supply and the spare capacity, however it'll not be cheap https://www.voltaev.co.uk/collections/commercial-ev-chargers/products/evd40s-p-tethered-40kw-32a-dc

40 kW and 32A seems to imply 1,250 V - is that standard?

Also, I'm not sure that (m)any domestic 3-phase installations would have 40 kW of 'spare capacity', would they?

Kind Regards, John

 

[robinbanks]

just because of the likely reduction in the life of the battery

Honestly, it's a problem you can hand over to the charge management system of the car. These aren't just some simple lead acid cells being banged with 15v from a cheap Chinese toroidal transformer til they boil dry

Careful use of length of charge would be my solution.

How do you *know* it's a problem you have to solve ?

I'm not saying you should buy an EV, but I do think you should avoid inventing problems and turning them into reasons not to do something

 

[ShaunShep]

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.

The consumer unit is in a hallway, and you could hear the buzzing noise throughout the whole of downstairs. So not only was it annoying to anyone else in the house, it was also a concern to us because as afar as I’m aware, a buzzing from a consumer unit that is clearly audible from some distance away is a concern and shouldn’t just be ignored?

 

[BigBarney]

Its the main switch that will be buzzing