Earthing for Hot Water Unit

[jackspratt]

I have a 3500 watt Panasonic wall mounted unit which has just gone kaput - it is about 3 1/2 years old. It replaced a previous unit of exactly the same model, which lasted about 5 years.

The unit is about 15 metres from the main power box, and has its own 32A breaker. It is a further 5 metres (approx) to where the main earth wire connects to the 1 meter ground pole.

The wiring for the house was done by a qualified sparky, to near western standards. Everything is 2.5 wiring.

The guy who takes care of our electrical issues now (different to the above guy), has suggested we install a separate ground pole to earth just the heater, on the outside of the wall where it is located ie a lot closer.

Does this sound like a good idea?

[dunroaming]

Sorry but that sounds scary, earthing on a shower or water unit should be a minimum of 6mm cable not 2.5

[jackspratt]

My apologies - I have re-checked, and the wiring for the HW is 4, and the main earth wire from the box is 6.

[dunroaming]

That sounds right and yes it's preferable to ground the unit desperately

[andymu]

For a 3500 watt heater with supply voltage 220v your using about 16amp. A 2.5mm twin and earth supply cable is easily enough on a 20 amp breaker. If you have 4mm on a 32 amp ok. If the water heater already has an earth in the supply cable (twin and earth) you dont need another. If your installation has been installed to near UK standards you will have a 100mA rcd on your incoming supply to your property. So no you dont need to do anything. Over 30 years as a sparks in England, not a google search.

[Barney]

Jacksprat
Be careful what you change.
Does your heater unit have a RCD type test button.
I’ll assume it does.
If it works and shuts the power when depressed then it’s ok.

Generally with earth all wires they should be installed back to the earth bar in your switchboard. Meaning all appliances should have a separate earth wire either internal to the cable or if a 2 wire cable then a separate earth should be run to the grounding point n the unit.
Is your 32A supply breaker have RCD or similar? Or maybe you have a main breaker with this trip feature.

I’m not sure on the exact regs in Thailand but what I have advised regarding all grounds going back to the main switch box should be the rule.
In saying all this we are in Thailand. So others may differ in opinion.
In electrical college the first item you are taught is that the most important wire always is the earth.


Sent from my iPhone using Tapatalk

[jackspratt]

Thanks Barney (and dunroaming and andy).

Heater has a test button. After it stopped working, pressing the button tripped the entire house supply - not just the HW circuit.

Looking at the power board, the (green) earth wire from the HW has many other green wires on the same bar. And a larger green wire which goes to the ground bar.

It seems strange that 2 HW units from a seemingly reputable manufacturer (Panasonic) have stopped working over an 8 year period. That's why I am curious about the earthing.

To complicate matters, I have ordered the same unit again. Mainly because it means I can almost "plug and play" with the same screw settings into the wall, and not having to worry about the way the tiles were cut to fit the original unit.

[dunroaming]

Have you contacted the Panasonic service centre they might be interested to check there units for cause of failure as it doesn't look good on them either. I would at least try to make contact and explain what's happened you might be surprised!

[jackspratt]

Hadn't thought about that, dun.

I did check out the warranty documents, and didn't see much hope there.

But I will look into approaching Panasonic directly tomorrow.

Thanks

[bluejets]

Never ceases to amaze me how many seem to think that a rod driven in to the ground is going to achieve anything.
As Barney says, the final sub-circuit earth should run back to the earth link in the main or sub-board, whichever applies.
What happens to it there in many instances is another mis-information.
2.5sq mm earth is fine for a 4sq mm main conductor protection up to around 20m run.
What is more important is the size of the circuit breaker in relation to the fault current and the earth loop impedance.
Often this is overlooked.

With a main switchboard only installation, the MEN system which should apply as it is the major system in Thailand (but should be checked as who knows what has been connected to what), the commoned earths should be connected to one and one only main earth electrode AND an earth link to the main neutral bar.
In the MEN system, the main earth electrode is in place primarily to keep the mains supply from floating above ground and not to carry fault current through extremely high impedance earth back to the transformer.

Any earth fault current in an earthed piece of equipment will then flow down the earth wire to the main earth link in the switchboard and from there to the neutral conductor and back to the main pole transformer star point, completing the low resistance path.
If all calculations correct, breaker should trip under a pre-determined fault current.
6ka breakers for domestic these days is a must as should be the use of combination breaker/safety switch (combo's)for each and every circuit.

[jackspratt]

To complete the picture here, the (new) sparky fitted the new water heater today.

He has formal qualifications from the Ban Dung Technical School, and is the electrician (plus other duties) at the BD hospital.

Given Barney's and bluejet's advice above, I was a bit concerned about the separate earth pole solution. However without my saying anything, he just connected the new earth wire to the existing one inside the heater, and Bob's ya uncle.

Are two earths better than one?

[Khun Paul]

I have had installed over the years, Safety T Cut a completely sperate box that detect minoir movements in the electrical circuit and cuts everything if it is not happy .
Plus also installed is a seperate Earth wire to the showers, just as an added precaution . AND a large earth wire connecting the existing Fuse Board to a earth spike ( deep some two metres ) designated by the same electrician that installed the Safe T Cut box to ensure zero problems re earthing. It may sound as overkill, but updating an existing installation in a lot cheaper than re-installing it with earth wires throughout , quotes cost of re-installing , ( redecoration not included ) some 30k . Updating only 10 K

[kopkei]

so if the home does not has any grounding /earth , using a single rod driven into the ground to ground only the hwh will not do the job???..

[minimiglia]

will do the job just fine

[bluejets]

Sorry but that sounds scary, earthing on a shower or water unit should be a minimum of 6mm cable not 2.5

Fortunately, electrical calculations on sizes follow a predetermined precalculated law of physics and are displayed for all and sundry in the SAA wiring rules.

The OP quoted 4sq mm as the final sub-circuit size and 32A circuit breaker which is what I used for reference.
My apologies - I have re-checked, and the wiring for the HW is 4, and the main earth wire from the box is 6.

2.5sq mm earth is for 4 sq mm final sub-circuit, with 6 sq mm final sub-circuit 2.5sq mm earth is required.

It is not as quoted some gut feeling on what should be.

6sq mm earthing conductor is for circuit cable sizing up to 16sq mm as in mains conductors.

Final sizing is, as previously mentioned, a factor of the either calculated or measured, earth loop impedance.

FYI I have been an electrical contractor in domestic, industrial and commercial for some 45 years now in case anyone is wondering.

[dunroaming]

My reply wasn't purely gut feeling! Which country are you from as 6mm is the minimum standard in the UK for a shower? I thought but maybe you can correct me it's determined by the KW of the shower or hot water unit being installed and could infact require 12 mm earthing cable! Happy to be educated. I expect your from Australia as quoting only their regulations which were actually updated in 2018 and include revised procedures for electrical works including showers and hot water heaters.

[bluejets]

Already told you , SAA wiring rules.
And NO, it hasn't been updated in the manner you quote.

[andymu]

I would be intrested in knowing what test results were filled out on the installation cert. The earth fault loop impedance to be exact. If he didnt test anything maybe it would be wise to get your installation checked by an electrian.

[dunroaming]

So other countries have their own standards of safety regulations and don't actually follow the SAA requirements, always been told it's better to be safe than sorry and the difference in price between 4mm and 6 mm is minimal. Sorry forgot to mention I'm an electrical procurement professional with 35 years experience and have never seen 4 mm used for water heaters or showers but you live and learn.

[AlexO]

Need to put this one to bed. To be really safe no one should depend on an earth wire for their personal safety. The human body can suffer heart fibrillations and perhaps even death when subjected to currents greater than 50mA. The best way to protect yourself is by fitting a 30ma RCD in the circuit which will effectively trip before fault currents reach a potentially fatal level. Some people put the RCD on the main incoming supply but this means the whole supply is cut off for a small fault on an appliance. The best way is too fit these RCD's on power circuits but some existing dist boards do not have the internal space for them. If this is the case bring the feed from the MCB and the correct neutral wire out of the MCB board and route through an external RCD in its own box. No more worries after that. Speaking as someone with more than 45 years experience of working with IEE Regulations and British Standard Regulations.