Hey all,


Just wanna check if the behaviour is normal as I'm getting mixed response for it. The switch you turn on before you shower to get hot water - I usually turn off after shower but one night I've forgotten about it...in the morning I found the fuse actually tripped. When I turn the fuse back up, hot waters are back as normal.

I also tested the machine's ELCB and it's all working fine, all lights are green on the water heater display.

What I wanna check is it normal to trip? Or it really depends on the electrical setup of the building? What is normal as I'm getting mixed response.

Possible scenario for the fuse to trip:
1. Even without water coming out from the machine, the machine is active and when there's a sudden power surge, it'll trip.
2. The configuration of the electrical system in the particular building is designed as such, to trip if certain fuses (like hot water) are turned on for an extended period of time. 3. Or the fuse gets too hot because even without showering, the machine is still drawing power/electricity.


please advise.

No..

Yes..

Depends if there is a pump and your wiring insulation is bad..

No..

No.. the thyristor or the RCD (fuse) should not get hot and yes there is a small current passing through for the LED to light up but not enough to energise the thyristor to switch on the pump..

Edit * Also it requires water to flow to move the built in magnet in the heater piping to switch on the reed switch before the element heater will operate..

This post has been edited by Richard: Jan 8 2017, 06:23 PM

Hey, thanks for your speedy response.
My water heater is the one with pump but don't think it makes a difference because it's not being used at the time of trip.

Spoke to 2 electricians, 1 said is normal and the other one is saying it's a faulty fuse.

May I know your recommendation?

I don't understand "faulty fuse"..

Strictly the only fuse in a residential unit at before the kWH meter meaning the 40A/60A HRC fuse beside the TNB kWH meter..

Does your electrician mean the main RCD (100mA trip) or the water heater RCD (30mA trip)?

If this is an isolated case I would recommend no further action ..

If it happens on a regular basis then I would replace the component that is tripping..

Understand that all electrical components with pressure contacts will wear and tear..

All electrical contacts especially high current contacts will arc thus develop pits (holes on the surface) cause smaller contact area and heat up..

You need to replace those devices..

Sorry don't really understand you as it was quite technical on the HRC/RCD part.

I'll try to explain with a bit more detail, what was involved:

#1. the switch to turn on the hot water (30A written on the switch, with red light once it's on)
#2. the fuse that in the main electrical box

So I left switch #1 on overnight which caused fuse #2 tripped in the main electrical box.
Yes it is the only fuse that tripped in the electrical box.

Turn the fuse back to "on" which then the #1 switch became functional again, with the red light showing on the switch and hot water coming out from the water heater

It happened only once because it was the only one time I forgot turn off the switch after showering.

As for the water heater, I've tested the ELCB button after putting the fuse back on in which it cuts off the hot water / electricity the moment I pressed on the test button. The indicators on the water heater reports a healthy wiring without any leakage (all greens).

40A/60A HRC (high rupture capacity) also known as a cut-out fuse where TNB will remove if you don't pay your bills..

Technically this is the only fuse in the whole house.. A fuse blows open meaning the fuse wire overheats and melts .. you cannot reset..

Inside your house is a Distribution Board (DB) which is a whole set of mcb (miniature circuit breakers) which has 2 ways to trip a bimetallic strip (thermal) and a electro magnet (magnetic).. You can reset..

Inside DB is also a device (what you call fuse) has a test button is the RCD (residual current device).. It trips when detects faulty wiring..

My guess ..

Somewhere between #1 switch and your water heater is a fault which trips your #2..

It can be an insect on the wire, loose connection or even humid dust ..

As bathroom is a wet environment damp surface dust will conduct electricity leak from Live or Neutral wire .. Or your water heater is old, loose wiring, poor insulation or bad components..

An electrician can check the connections for you..

If it happens just that one time it could be nuisance tripping (like when lightning hits overhead cable and high voltage surge trips your #2)

I can only guess.. Good luck..

Well, it only happened once, so it could be insect, loose connection or humid dust like what you said.

I think the voltage surge is quite likely. But like you mentioned before, is the power consumption enough to cause a surge? Or it doesn't matter because electricity keeps flowing regardless.

There's never been any issue until the trip, so I really wanna check the potential cause / danger. As you are aware that electricity leak can be really dangerous during showers ... so I want to be absolutely sure lol. Definitely won't be the water heater because it is only about 15 months old. I had it changed when I moved in.

My 0.02:

As long as the water heater ELCB / RCD can trip if you press the test button, you should be fine.

Many reason why your common RCD can trip, you shouldn't be too worried if it happens once.

You can try to switch on the water heater overnight again, if it trips again, most probably the wiring from the switch to the water heater is defective. ( insulator is damaged along the wiring, or water heater power inlet is stripped and is too near to each other. )

yes it happened only that once when I forgot to turn it off overnight

I've been showering hot water for a few days already.
Tested the machine again and yes it does cut off when I press the button. Also, indication the lights are showing green (means ok) on the water heater display.

Would just like to know for future reference - "insulator is damaged along the wiring, or water heater power inlet is stripped and is too near to each other" <-- do you know roughly how much to fix and will it be a big job?

if wiring insulation is damaged - you'll need to re-wire only from your switch to your water heater, probably RM100 can be done. But main problem will be finding an electrician willing to take up this small job; and if you want the wiring to be concealed inside the wall; it will be messy and you might need to retile your wall.

2nd problem - just open up your water heater, cut the copper shorter so it fits into the terminal block nicely without exposing any copper wires and screw it back in.