What's written on your contract? Quotation?

For single phase house appliance the neutral must be the same size as phase.

In industry 3phase machines like motors then can have half sized neutral

In data centers with high harmonics the neutral is double the size of phase conductor.
Also important must use sirim certified cables like fajar mega

For water heater remember to install 10ma rcd
Yes must use 2.5mm² for both live and neutral
Earth can be half size

What's written on your contract? Quotation?

For single phase house appliance the neutral must be the same size as phase.

In industry 3phase machines like motors then can have half sized neutral

In data centers with high harmonics the neutral is double the size of phase conductor.
Also important must use sirim certified cables like fajar mega

For water heater remember to install 10ma rcd
Yes must use 2.5mm² for both live and neutral
Earth can be half size

Thanks so much for the quick reply!!

Around RM20k+ for master bedroom toilet and garden renovation. For the water heater single point wiring is RM260.

The house is on 3 phase, this one doesn't matter right?

Yes, the wires they used is Sirim MS 2112-3 certified, not sure what brand though, I can't find the packaging. 2.5mm wire should be good enough for 3kW water heater right?

Yes, after learning from the sifus here, I've installed an EPS 10ma RCCB a few years back.
OK, I will ask them to re-pull the wiring tomorrow or worst case knock down the new wall tiles. Thanks for the advice again!

Good day fellow forumers!

I've hired a contractor to do renovation for my parents' 2 storeys old house.
I've asked them to totally knock down everything inside the master bedroom toilet.
And I've asked them to change new wiring for the (instant) water heater shower unit too.

So, just now I went to check the progress and I found that the contractor used 2.5mm for the live wire,
but only 1.5mm for the neutral and ground wires. And they tiled it up already. Is it dangerous?
Should I ask them to knock down the new tiles and redo the neutral/ground wires with 2.5mm ones?

My parents' house is on 3 phase power. And there is a sub DB upstairs powering 3 bedrooms.
The said downsized wires are upstairs in the master bedroom toilet.

Thank you experienced sifus for your inputs!!

Good day fellow forumers!

I've hired a contractor to do renovation for my parents' 2 storeys old house.
I've asked them to totally knock down everything inside the master bedroom toilet.
And I've asked them to change new wiring for the (instant) water heater shower unit too.

So, just now I went to check the progress and I found that the contractor used 2.5mm for the live wire,
but only 1.5mm for the neutral and ground wires. And they tiled it up already. Is it dangerous?
Should I ask them to knock down the new tiles and redo the neutral/ground wires with 2.5mm ones?

My parents' house is on 3 phase power. And there is a sub DB upstairs powering 3 bedrooms.
The said downsized wires are upstairs in the master bedroom toilet.

Thank you experienced sifus for your inputs!!

usually no need to brake tiles. just pull the wires through the pvc hose
should use 4mm2 cables. (my mistake. should not be 2.5)

https://www.st.gov.my/en/contents/publicati...r%20Systems.pdf

you may read the guide cover to cover.
some points
- use double pole 20A water heater switch
- as much as possible, the LN wires should not have joints.
- earth cable should not have joints.
- do not use 3pin plug to connect water heater
- leave a loop of wire before entering water heater (so water wont go inside)

usually no need to brake tiles. just pull the wires through the pvc hose
should use 4mm2 cables. (my mistake. should not be 2.5)

https://www.st.gov.my/en/contents/publicati...r%20Systems.pdf

you may read the guide cover to cover.
some points
- use double pole 20A water heater switch
- as much as possible, the LN wires should not have joints.
- earth cable should not have joints.
- do not use 3pin plug to connect water heater
- leave a loop of wire before entering water heater (so water wont go inside)

Damn, my electrician put 3 pin plug for the water heater when we did whole house reno.

Yeah usage of 3-pin socket + plug connection to power up water heater is a BIG NO for water heater, according to Suruhanjaya Tenaga guideline.
U can either

a. get the contractor to remove the 3-pin socket and its junction box and connect the electrical cable directly to the water heater, which u might need to hack some walls to hide the cable and to fill / cover the hole left from the removal of the junction box, or

b. a cheaper and faster option is just to replace the 3-pin socket with a water heater connector (shown below) while reusing the 3-pin socket's junction box, so no hacking or filling holes required. U can easily purchase the water heater connector online - Shopee / Lazada

usually no need to brake tiles. just pull the wires through the pvc hose
should use 4mm2 cables. (my mistake. should not be 2.5)

https://www.st.gov.my/en/contents/publicati...r%20Systems.pdf

you may read the guide cover to cover.
some points
- use double pole 20A water heater switch
- as much as possible, the LN wires should not have joints.
- earth cable should not have joints.
- do not use 3pin plug to connect water heater
- leave a loop of wire before entering water heater (so water wont go inside)

Must be same size as phase (live) conductor.

That contractor is really endangering your parents' life by fixing underspec power cable. Water heaters with power rating below 5.711kW have to use 4mm2 cables, based on Suruhanjaya Tenaga's guidelines.



And the rest just follow lj0000's good advice.

Understood, thanks lj0000, ceo684 and Selene Yeo for the advice!! Sorry for late reply, was busy juggling work and renovation.
The contractor basically just pushed the blame on his staff. Excuse is 2.5mm finished, so his staff used 1.5mm. Quite BS la.
I warned him to be more careful and professional.
By the way, I've also decided to change completely new wiring for the common bathroom's water heater from DB too.

I bought Mega 4mm wire for the contractor to use this time.
The (instant) water heater I bought is Deka 4.5kW high power version.
For the RCBO, I bought Schneider Easy9 25A, 1P+N, 6kA, C Curve 10mA.
Schneider RCBO somehow doesn't have 20A version.

1) Should I buy EPS 20A 2P 10mA 6kA RCBO Type AC instead?

25a is ok
4500/230=20amps already


2) Why EPS RCBO has 2 poles, while Schneider RCBO only has 1 pole?

Rcbo need to compare live and neutral
Mcb only measure the live.

3) Is RCBO only good enough? Or should I use MCB + RCCB setup?

Rcbo save space. It's only 1din size. so ya it's good idea to use rcbo. Drawback is, if fail then harder to buy and more expensive compare to separate mcb+rcd.
There are debates that voltage based rcbo should be used. When tnb voltage is low then the current sensing won't work, that should not happen for domestic lah



Thank you all again!!

Understood, thanks lj0000, ceo684 and Selene Yeo for the advice!! Sorry for late reply, was busy juggling work and renovation.
The contractor basically just pushed the blame on his staff. Excuse is 2.5mm finished, so his staff used 1.5mm. Quite BS la.
I warned him to be more careful and professional.
By the way, I've also decided to change completely new wiring for the common bathroom's water heater from DB too.

I bought Mega 4mm wire for the contractor to use this time.
The (instant) water heater I bought is Deka 4.5kW high power version.
For the RCBO, I bought Schneider Easy9 25A, 1P+N, 6kA, C Curve 10mA.
Schneider RCBO somehow doesn't have 20A version.

1) Should I buy EPS 20A 2P 10mA 6kA RCBO Type AC instead?
2) Why EPS RCBO has 2 poles, while Schneider RCBO only has 1 pole?
3) Is RCBO only good enough? Or should I use MCB + RCCB setup?

Thank you all again!!

With 4mm cable the RCBO you have is sufficient.

Just to show what happens when 1.2mmsq (40x0076) is used on a WH:

my house using 2.5mm wires with 10ma RCD, not connecting to MCB. it means no protection on the overloading ?

RCD only does NOT give overload protection. There should be a MCB in tandem with the RCD 10mA.