Mira play shower (electrics fried)

ifconfig

I posted this a short while ago to the Plumbing/Heating forum but realise it is probably more an electrical issue .... here goes :

My plumber sent 2 of his lads over to fix a faulty safety valve in the cold water tank earlier today.
While I had both of them here I gave them a look at the one and only electric shower which we have installed in an annex room on the ground floor of the house.
They opened it up and found that 2 of the mains supply wires were fried and shorting.. *dangerous!!**
The model is a Mira play.
Obviously we won't be using this shower until it is fixed and replaced.

Approx 2 yrs ago we had a problem after an ESB outage (brownout) which caused a number of high load appliances to become unsafe.
For example, our geothermal heat pump soft start module was fried.
We installed a surge protector module in the fuseboard in the garage to protect that in future.
I suspect that the same incident may have caused the electric shower assembly to become unsafe.

OK. Main question is .. in ballpark terms how much would I expect to pay to get a Mira play shower replaced and fitted these days ?

Also.. I wonder if my hunch as to the root cause may be correct.
I shiver to think how unsafe that shower has been for such a long time.
We don't use it a lot but ...

-ifc

meercat

cant quote on the shower replacement costs

however i would say that loose connections were most likely the cause of the burnt out connections
i have frequently come across such problems(the connection needs to be tightened with a big screwdriver not a phase tester)

Davy

Loose connections or supplied with undersized cables cause the problem more so than an external issue.

Is the problem at the termination block inside the shower housing? Do you have a picture?

Bruthal

Loose connections are the likely cause. If its just the terminal block and a small part of the cables burnt, its probably repairable fairly easily by a competent person.

Photos of it would help a lot. for posters here to offer advice.

ifconfig

I meant to post this some weeks ago but only had someone over yesterday to open up that shower housing.
See attached file in this post !!

I have subsequently found out that our ESB supply (single phase/enhanced 16kVA) may have been subjective to relatively frequent events of low voltage supply (based on a report of a neighbour adjacent to us on the supply line).
The report shows numerous dips to 195V or as low as 188V ! at various times of day over a 2 week monitoring period.

Someone on a different forum wondered why the breakers hadn't tripped with this shower while operating.
Look at the burn damage here !!!
I'm going to get an Electrician to look at it to determine if this was caused by loose wiring or potentially by the voltage brownouts / and current spikes.

I've just replaced a microcontroller , relay switch and other components in the Heatpump which were definitely caused by lack of regulation in the ESB networks supply (damage == 400Euros materials + labour)

meercat

Still looks like a loose connection fault though

meercat

Double post
Sorry

ifconfig

Sure Meercat.
Looking at that picture would you say the overall shower kit can be salvaged and only the power block section could be replaced to restore it to being safe and functional ? (assuming pumps, etc haven't had collateral damage).

-ifc

meercat

robbie7730 wrote: »

Loose connections are the likely cause. If its just the terminal block and a small part of the cables burnt, its probably repairable fairly easily by a competent person.

Photos of it would help a lot. for posters here to offer advice.

Robbie posted this earlier
I would agree
New connector block and strip back burnt cables and remake should do the trick

ifconfig

Ok.
and going back to another part of my question ....
Why would this have happened and not tripped the breaker switches ?

—ifc

meercat wrote: »

Robbie posted this earlier
I would agree
New connector block and strip back burnt cables and remake should do the trick

meercat

ifconfig wrote: »

Ok.
and going back to another part of my question ....
Why would this have happened and not tripped the breaker switches ?

—ifc


There would be no direct short or overload which would cause the tripswitch to activate
Just also check that your shower is rcd protected
The rcd would only activate if there is a fault to earth(this is not your case though)
Pic of board would help

Bruthal

ifconfig wrote: »

Ok.
and going back to another part of my question ....
Why would this have happened and not tripped the breaker switches ?

—ifc

Simply because the shower will operate at a lower kw with lower voltage.

Some will claim the shower kw remains the same, and so a lower voltage = higher current, and this seems to cause some confusion at times. A shower is only working at its design rating at its design voltage because its resistance/impedance remains constant. So a lower voltage = lower amps = lower wattage.

Take for example a 9kw shower at 230v will draw 39 amps. So its resistance/impedance is 230v/39 amps = 5.9 ohms.

If the voltage drops to 188v, the shower impedance/resistance is still 5.9 ohms or so.

188v/5.9 = 31.9 amps the shower now draws. So it now takes 31 amps instead of 39 amps, therefore no tripped breaker.

The shower now operates at 6kw instead of 9kw (188v x 31 amps)

If there is no short circuit or earth fault, no tripping will happen.

Edit:
Maybe they meant why did it not trip with the burn damage, i was thinking they were asking with reference to the lower voltage.

Thats definitely a loose connection at that terminal. I often seen connections into showers barely tightened.

cast_iron

Is it me, or does the supply cable look a bit under-sized?

ifconfig

Robbie.. thanks for the information regarding the electric shower not being a constant power device, therefore - low voltage supply (which we know is an issue in the locality) would not have given rise to increased current flow through the electric shower (in fact the opposite).

So, is it arcing due to a faulty internal connection within the shower supply block which looks like the most likely cause here ?
I really have no idea if that shower is RCD protected.
It has its own dedicated breaker at the fuse board - that's all I know.

I saw something on some UK forum about some kind of current limiting breaker unit called an MCD (?).
I'm careful to raise that as it may be a red herring.

Ok.. accepting that the shower problem was probably due to internal wiring.
Is it still a reasonable statement that our electrical failures in the geothermal heat pump might have been due to low supply voltage/high currents during brownouts ?
Are heat pumps different to elec showers in terms of power/load characteristics ? Are they using switched power supplies ?

The soft start module fried and died 2 yrs ago, the main microcontroller and a special capillary relay switch died a week ago or so and the technician saw excessive arcing on a timer relay as well.

—ifc

Bruthal

ifconfig wrote: »

Robbie.. thanks for the information regarding the electric shower not being a constant power device, therefore - low voltage supply (which we know is an issue in the locality) would not have given rise to increased current flow through the electric shower (in fact the opposite).

Yes, if the voltage reduces, the shower kw output reduces also. A 10% drop in voltage would be a 19% drop in shower output.

So, is it arcing due to a faulty internal connection within the shower supply block which looks like the most likely cause here ?

probably not actually arcing, just the terminal overheating from being loose, which means there is a small resistance in the connection causing heat, and as it gets hotter, the connection gets worse, escalating the problem. Sometimes arcing can start if the connection fails but the gap of the open connection is tiny, and this then really destroys the terminal.

I really have no idea if that shower is RCD protected.
It has its own dedicated breaker at the fuse board - that's all I know.

RCDs have a test button, the sockets should have one, and in times past shower`s may have been connected through that. See is there a second RCD with test button, they are double the width of MCBs. If there is no second one, switch the socket one off and see if the shower goes off.

Unless you have an old board with fuses.

I saw something on some UK forum about some kind of current limiting breaker unit called an MCD (?).
I'm careful to raise that as it may be a red herring.

MCB maybe? They are current limiting breakers. Miniature Circuit Breakers.

Ok.. accepting that the shower problem was probably due to internal wiring.
Is it still a reasonable statement that our electrical failures in the geothermal heat pump might have been due to low supply voltage/high currents during brownouts ?
Are heat pumps different to elec showers in terms of power/load characteristics ? Are they using switched power supplies ?

The soft start module fried and died 2 yrs ago, the main microcontroller and a special capillary relay switch died a week ago or so and the technician saw excessive arcing on a timer relay as well.

—ifc

Motors can suffer over-current from low voltage if they have a load on them alright, because the rotor speed decreases compared to synchronous speed (for induction motors) or the back emf in universal ones decreases resulting in increased currents, and can be burnt out in fact, or their controllers as it looks like happened there with yours.

Bruthal

cast_iron wrote: »

Is it me, or does the supply cable look a bit under-sized?

It looks like a 6sq anyway.

ifconfig

Is a 6sq cable adequate ?

I realise someone mentioned the most likely failure was undersized supply cable and/or loose terminal connection.
We are surmising the latter — is this 6q cable dimension ok for this sort of assembly (I've no idea — I'm not an electrician...)

-ifc

Bruthal

ifconfig wrote: »

Is a 6sq cable adequate ?

I realise someone mentioned the most likely failure was undersized supply cable and/or loose terminal connection.
We are surmising the latter — is this 6q cable dimension ok for this sort of assembly (I've no idea — I'm not an electrician...)

-ifc

Its usually 10 sq for a shower now, but having 6 sq would`t cause the problem here if the connections were sound.

ifconfig

Showed the photo to a neighbour , who has the same electric shower.

He reckons that water must be getting into the enclosure.

Could this be the case at all ?
I'm still with you guys that the root cause was loose terminal connection, exacerbated by sparking, heat.. vicious cycle, etc...

The only other factor in our house is that the water delivered from local water scheme is extremely scaly and hard with lime.

—ifc

meercat

That burning does not look as if it was caused by moisture ingress to me

Perhaps there are water marks in the enclosure elsewhere ?

Bruthal

For water to cause that burning, the water would have to bridge from live to neutral or earth, and so the burning would not be confined to one connector.

Earth being the nearest connection would mean the RCD tripping before any burning like that could ever happen, if there was an RCD fitted.

It was almost certainly a loose connection, nothing more complex than that.

Bruthal

meercat wrote: »

That burning does not look as if it was caused by moisture ingress to me

Perhaps there are water marks in the enclosure elsewhere ?

Definitely not water.

ifconfig

Thanks for this info.
I will have my electrician look at it and will get it sorted very soon.
In the meantime that shower is off bounds.

-ifc