Rcbo. How often should you test it?

Sleeper12 · 21-05-2014 7:58pm #1

How often should you test the RCBO on the fusebox? I'm guessing at least every 6 months or so but like smoke alarms in our homes does anyone really test them?
Photo below is a Triton T90xr that started to go on fire today in kildare. Rcbo didn't trip at all.
Obviously a fault with the shower but the RCBO failed miserably.

hufpc8w3adnk65 · 21-05-2014 8:24pm

tpmcompany1 wrote: »

How often should you test the RCBO on the fusebox? I'm guessing at least every 6 months or so but like smoke alarms in our homes does anyone really test them?
Photo below is a Triton T90xr that started to go on fire today in kildare. Rcbo didn't trip at all.
Obviously a fault with the shower but the RCBO failed miserably.

What exactly caught on fire?? I can't see any fire damage in that picture?

Sleeper12 · 21-05-2014 8:37pm

MrMac84 wrote: »

What exactly caught on fire?? I can't see any fire damage in that picture?

I'm sort of stumped with that. Home owners wanted to keep the shower so didn't have too long to look. Tco was in pieces, prongs on the element are not rusted, that's heat damage that looks like rust. The cover was partly melted. The worst area was around the pump area. None of the wires were damaged though I had to cut the input cable as the screws it connector block were seized.
There are no tiles in the shower. They use that plastic celuplast stuff. Had to rip shower from the wall as it had fused to the celuplast wall.

21-05-2014 9:07pm

Why is it that you think the RCBO should have tripped?

The RCBO should trip under the following conditions:

1) Over current - Perhaps the fire did not cause the current to exceed the rating of the RCBO

2) If the current flowing to earth exceeds 30mA - Perhaps the current flowing to earth was less than 30mA (I am assuming that IΔn = 30mA as specified in ET101:2008)

tomdempsey200 · 21-05-2014 9:09pm

tpmcompany1 wrote: »

How often should you test the RCBO on the fusebox? I'm guessing at least every 6 months or so but like smoke alarms in our homes does anyone really test them?
Photo below is a Triton T90xr that started to go on fire today in kildare. Rcbo didn't trip at all.
Obviously a fault with the shower but the RCBO failed miserably.

what makes you think the rcbo failed miserably?

did you test it?

21-05-2014 9:18pm

In general there is a lot of confusion about what an RCBO should actually do.
Correctly functioning RCBOs may not prevent a fire even when selected and installed correctly.

This link from ABB sums it up nicely:

"RCBOs combine in a single device the residual current function and the overcurrent protection function typical of MCBs"

Sleeper12 · 21-05-2014 9:30pm

2011 wrote: »

In general there is a lot of confusion about what an RCBO should actually do.
Correctly functioning RCBOs may not prevent a fire even when selected and installed correctly.

This link from ABB sums it up nicely:

"RCBOs combine in a single device the residual current function and the overcurrent protection function typical of MCBs"

Ok so as I'm a plumber & not an electrician please don't laugh but I based my assumption that the rcbo failed on me pressing the test button on the rcbo & it didn't trip. I know that only proves that the test function is faulty but between that and the damage done to the shower. I'm putting my money on the rcbo.
As I say what has me stumped is the main damage to the cover was the pump are (not an area you'd expect) but on the shower itself most of the damage was around the element & Tco. But no melted cables.
Again I ask please don't laugh.
:-)

21-05-2014 9:35pm

tpmcompany1 wrote: »

I based my assumption that the rcbo failed on me pressing the test button on the rcbo & it didn't trip.

Based on this new information the clearly RCBO is faulty.
The test button performs an electrical (not a mechanical) test on the unit, so you are correct.
This information was omitted from your earlier post.

I know that only proves that the test function is faulty but between that and the damage done to the shower. I'm putting my money on the rcbo.

Although it is possible that the RCBO failure contributed to the failure of the shower I would think it unlikely.

Sleeper12 · 21-05-2014 9:37pm

Here is a better of the element / tco area

Robbie.G · 21-05-2014 9:51pm

tpmcompany1 wrote: »

Here is a better of the element / tco area

Looks more like water / moisture damage than heat damage

Sleeper12 · 21-05-2014 9:55pm

Ok so that didn't sound as foolish as I thought it might. :-)
I've seen a lot of damaged showers over the years but usually the fault is pretty obvious. If seen plenty of showers that went on fire but I'd expect to see badly melted cables as the cause.
Anyway just curious, should I recommend my clients should be testing the rcbo? If how often?
Also I'm sorry about the size of the photos, I'm working on that problem.

hufpc8w3adnk65 · 21-05-2014 9:55pm

Robbie.G wrote: »

Looks more like water / moisture damage than heat damage

And the unit didn't catch fire. Thats a huge over exertion. The black inside is the brushes off the motor. 99% of those models look like that when opened. (Bar the rust)

Sleeper12 · 21-05-2014 10:00pm

Robbie.G wrote: »

Looks more like water / moisture damage than heat damage

Yes I see the copper greening & the white down the front could be limescale from a leaking element. I got there about 3 hours after it happened. There were no leaks by then. None at all. Not a drop. It's one I'd love to have brought home. I'd still be mucking about with it now!

Sleeper12 · 21-05-2014 10:07pm

MrMac84 wrote: »

And the unit didn't catch fire. Thats a huge over exertion. The black inside is the brushes off the motor. 99% of those models look like that when opened. (Bar the rust)

The cover was on fire. Home owner said this repeatedly. They insisted small flames came out of the hole in the cover around the pump area. If you smelt it you'd know. Picture melted cables at the connection block, now multiple the smell by 100.
I stress the Cooper terminals on the element are not rusted.

Sir Arthur Daley · 22-05-2014 9:06am

Robbie.G wrote: »

Looks more like water / moisture damage than heat damage

tpmcompany1 wrote: »

They insisted small flames came out of the hole in the cover around the pump area.

Could the hole in the cover have been the cause of this damage?

Sleeper12 · 22-05-2014 9:13am

Sir Arthur Daley wrote: »

Could the hole in the cover have been the cause of this damage?

No. The hole in the cover happened as plastic melted from inside. Cover damage was about pump (not an area you'd expect to cause trouble) the heat seems to have come from element. The Tco was in several pieces. It had turned VERY brittle & yet very little damage to the cables attached to the element.
It's a strange one.

Sir Arthur Daley · 22-05-2014 9:17am

Can you put a pic up of cover?

Sleeper12 · 22-05-2014 9:25am

Sorry I didn't get a pic of the cover & client asked to hold on to everything.

Sir Arthur Daley · 22-05-2014 9:28am

No problem, is that bathroom a damp and cold one like you would have in an old extension?

Sleeper12 · 22-05-2014 9:44am

Its an on-suite & has a window. shower is backing on to two interior walls. Everything seem clean & bright.
The inside of the shower looks a mess as you can see but the black is not carbon deposit (well there would be some carbon under the mess). The brushes are only worn a few mill.
If you look at the element terminals you'll see they look rusted but they are copper & copper doesn't rust. Then the screws going into the terminals are not rusted looking so clearly this is heat damage & not water damage.
Everything I see seems to contradict something else.

Sir Arthur Daley · 22-05-2014 9:54am

The element terminals are not made of copper i thought?

Sleeper12 · 22-05-2014 10:14am

Now that I look at the photo I see what you mean.The part that the cable screws into are a metal ( copper is too soft to screw into, the screws would pull out) but these are attached to copper uprights going into the copper top of the can. The metal part that the cable screws into should be a shiny metal colour, almost stainless steel but again that isn't rust. The heat has stripped the chrome off them. And yet the green on the copper top suggests water as does the white staining further down the heating can.
Am I right in saying:
. No cables melted at terminals anywhere in the shower suggests it was not an electrical fault?

tomdempsey200 · 22-05-2014 10:59am

have you seen this type of thing before?

can you not identify the source of the fire damage?

Sleeper12 · 22-05-2014 11:15am

I work on between 3 to 6 showers per day. I've seen plenty of fires in showers over the years but you'd usually see a melted connector block where someone had not tightened the connection enough.
I'm thinking, no melted cables so its not electrical. Next I think, if the top of the heating can springs a leak & it sprays the terminals then it explains the damage to the element. But I get there a few hours after it happens & there is no leak.
That leaves 2 options in my mind. First & not too likely, there was a leak but the heat sealed it up (I know how it sounds)
Second & slightly more likely, there is a leak but it needs the pump running to increase the pressure enough to make it leak.
The only leak like that would be the pump but Ive never seen a leaky pump spray water so far in the shower.

I don't think I'll get to the bottom of it but would love to hear from any electricians on how often a homeowner should test their rcbo?

tomdempsey200 · 22-05-2014 11:40am

the wiring rules states that a notice must be placed at the rcd stating that the rcd must be tested "regularly"

I think the recommended interval is 3 months

Sleeper12 · 22-05-2014 11:42am

I,ve never seen one of those at any fusebox but thanks for the info. I can now recommend this to my clients.

tomdempsey200 · 22-05-2014 11:47am

tpmcompany1 wrote: »

I,ve never seen one of those at any fusebox but thanks for the info. I can now recommend this to my clients.

you should be using them on your shower installs to comply with wiring rules!

22-05-2014 1:01pm

My guess:

1) This is due to an electrical fault. What else could generate that much heat?

2) The heating is due to a high resistance joint.

As we all know heat generated = I^2 x R.
As I is in the region of 40 amps the resistance does not have to be very high.
The high resistance joint is the one that failed, the element terminals.

frankmul · 22-05-2014 1:21pm

tomdempsey200 wrote: »

the wiring rules states that a notice must be placed at the rcd stating that the rcd must be tested "regularly"

I think the recommended interval is 3 months

I thought it was 3 months also, with the change in the season or something to that effect was said. I can only see a recommendation that it's tested every 3-6 months

Sleeper12 · 22-05-2014 1:34pm

tomdempsey200 wrote: »

you should be using them on your shower installs to comply with wiring rules!

Obviously we install rcbo with full instructions but I know my electrician has not been leaving instructions to test the rcbo every 3 months.
That will change from today.

frankmul · 22-05-2014 1:41pm

tpmcompany1 wrote: »

Obviously we install rcbo with full instructions but I know my electrician has not been leaving instructions to test the rcbo every 3 months.
That will change from today.

http://www.reci.ie/Portals/0/Documents/18766aRECI_News.pdf

See page 2, rule 531.2.2.2

Rcbo. How often should you test it?

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