HWS trips 20A CB after a few minutes

[thierryx96]

Hi there,

I have a Vulcan (2009) Hot Water System (HWS) which is now tripping the 20A CB on my switchboard. The switchboard has been replaced one month ago (no problems since today, though).

The tripping happens 1-2 minutes after I switch the CB back on. Does it means I can rule out any short circuit / earth connection problem? I would assume that should trip the CB instantly?

I have set the thermostat to the lowest temp (60, was 80 before) and examined the wires (nothing suspicious). The thermostat is labelled: "240V – resistive load 30A", does it means the HWS might draw up to 30A? thus the CB being too low?

Thanks a lot for you help!

Thierry

 

[loz2754]

No. That just means the thermostat is capable of carrying 30 amps.
It would be helpful to know the rating of the actual heating element if possible.

 

[thierryx96]

HWS specs (was hard to read as behind please see attached screenshot)

HEATING UNIT LOWER 3600
HEATING UNIT UPPER N/A (none)
RATED POWER INPUT 3600
240V

Thermostat specs: 240V 30A ST1204113 - I could find the manual here: https://www.stokesap.com.au/documents/productpdf/STOKES_THERMOSTATS_CONTROLS.pdf.


Hope this helps!

 

[Pete999]

Hi there,

I have a Vulcan (2009) Hot Water System (HWS) which is now tripping the 20A CB on my switchboard. The switchboard has been replaced one month ago (no problems since today, though).

The tripping happens 1-2 minutes after I switch the CB back on. Does it means I can rule out any short circuit / earth connection problem? I would assume that should trip the CB instantly?

I have set the thermostat to the lowest temp (60, was 80 before) and examined the wires (nothing suspicious). The thermostat is labelled: "240V – resistive load 30A", does it means the HWS might draw up to 30A? thus the CB being too low?

Thanks a lot for you help!

Thierry

What size in KW is the heater?

 

[thierryx96]

3600W - single heating unit (lower)

 

[James]

1st thing I would be doing is sticking a clamp meter on it and seeing what load is being drawn.

 

[loz2754]

3600 Watts is around 15 amps, so should not trip a 20 amp breaker. Sounds like it's a faulty element. Insulation resistance test will prove it.

 

[James]

3600 Watts is around 15 amps, so should not trip a 30 amp breaker. Sounds like it's a faulty element. Insulation resistance test will prove it.

It’s a 20A breaker.

if I had To give it odds,
80% chance of faulty heating element
19% chance of faulty breaker
1% something else.

 

[loz2754]

It’s a 20A breaker.

if I had To give it odds,
80% chance of faulty heating element
19% chance of faulty breaker
1% something else.

Sorry yes I meant to say 20 amp. Duh!

Edited my post...

 

[thierryx96]

Thanks for hints, really helpful.

It seems the problem solved itself: after I reset the CB to ON again a few time, it just stop tripping and remained ON since then.

I guess if it happens again I would go with a clamp meter (didn't knew these existed), if it draws more than 20A, I could assume faulty heating element, right?

With a broken thermostat, I would assume it would not draw more than 20A, but might just over-consume power over time?

 

[Wilko]

Hi - pic of your board with the 20A mcb that trips please .

 

[thierryx96]

here you go @Wilko, CB has been redone recently by a qualified sparky.

 

[newfutile]

It appears to be an RCBO not just a MCB, this could be tripping from earth fault currents , this is much more likely than over current especially on a C rated breaker.

 

[Wilko]

Agree with @newfutile thought, the RCBO used here will trip with earth leakage current of 30mA. This could happen with a dodgy element and is readily confirmed with an insulation resistance check.