Shower Keeps tripping the RCD

We had an electric shower installed about a year ago, which has always worked fine.
It is an 8.5KW electric shower. At the time, there was not a free fuse in our fuse box for the new circuit, so a new box was added containing an RCD (80A) and an MCB(40A). The shower runs from this, alone.
Suddenly this week, the shower started as normal, then there was a bang, and the water was cold. The RCD had tripped. The MCB was fine.
I reset the RCD, pulled the cord again for the shower, and the light flicks straight on and then off again. The dial on the shower at this point is in the off position.
I took the cover off the shower unit, and it looked ok, although a little damp inside. I also took the cover off the switch, and that looked ok, not damp. Looking in the loft, there is some damp around where the wires enter and leave, presumably steam through the hole.
The shower unit itsself is still under warranty, but does it sound as though this is what is the problem? From what I understand of an RCD it detects a current leakage?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

From what I understand of an RCD it detects an imbalance of current between live and neutral. The difference is going somewhere - presumably to earth via ? So maybe looks like an earth fault?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Sean wrote:

The "bang" sounds ominous! Where did it come from? RCDs usually at best give you a "click" when they trip.

So the fault lies after the switch then. Most likely in the shower itself.

The shower should not be damp inside. That alone could trip the RCD. However in this case I would expect that something has gone wrong with the shower (judging by the noise)

Contact the manufacturers support line. Many of them are quite good at sorting problems like this.
> From what I understand of an RCD

It detects current imbalance - i.e. the current in the live must match that in the neutral +/- 30mA typically. If it does not then it trips. So usually you can infer that if there is an imbalance that you are leaking power either from the protected circuit, or even possibly into it from another circuit.
--
Cheers,

John.

/=================================================================\
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Unfortunately the person in the shower can not explain where the noise came from, although a faint bang was heard elsewhere in the house, which could have just been the click on the RCD.

So the shower is still drawing a current when the dial is off? This was the only reason I didnt go straight to the manufacturer, because I thought if the dial is off, it wouldn't be this at fault.

The RCD has 0.01A written on it. I presume this is 10mA Thanks for your answer and the explanation at the end. I will contact Kohler Mira and see what they have to say.
Thanks again.
Sean.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Sean wrote:

Since you have a 10mA RCD it will take very little to trip it. The dampness alone inside the shower may do it. You could try drying it off with a hairdrier for a bit and then see if it runs.
--
Cheers,

John.

/=================================================================\
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Sean wrote on 27/05/2006 :

They detect an imbalance between the current flowing in neutral and live. Such an imbalance usually, though not always, indicates that some of the current in the live is leaking to ground through a fault of some sort. Damp inside the heater or switch would certainly be enough to trip the RCD. You could try carefully drying both out and seeing if it trips after that. If it does, suspect a more serious fault in the shower.
--

Regards,
Harry (M1BYT) (L)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.