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Phil, Mechanical Engineer.
Category: Plumbing
Satisfied Customers: 8678
Experience:  Retired mech. contractor, shop owner, 51 yrs experience.
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We had a Rinnai 330 litre solar water heater system installed

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We had a Rinnai 330 litre solar water heater system installed 3 years ago. The tank model no is MP219144, and has a 2.4kW booster element. When installed it was connected to an existing hot water switch & fuse in the meter box. Last year we had an indoor switch installed & a circuit breaker added to the meter box. Since then it has been almost impossible to use the booster, as it trips the circuit breaker, often when the indoor switch is turned off or on, and quite frequently without any apparent reason. Today I checked the wiring and switch, and ascertained that electricity was getting to the unit. However while testing resistances, I found that there was less than 1 ohm resistance between the neutral terminal of the heating element and earth, despite its apparently being insulated. Is this normal? Is it part of the design? If it were not for the earth cable, the water pipework would be live when the booster operates. To me this appears to be the problem, but I would appreciate your answer.

Bill Francis

Phil :

Welcome. I will stay with you until the situation resolves. I hold questions open after positive ratings to allow for unlimited follow up.

Phil :

This is not an answer so far, I will switch us to Q and A format... our chat server is apparently having problems.

Phil and other Plumbing Specialists are ready to help you
You have what is called a 'grounded neutral' system.

Power coming into a 'load' such as heating element...puts its energy into the heating element (a resistance) .. coming out the other side is the *same amount of electrons, but with virtually no voltage (read same as 'pressure' or 'force') behind them...

Neutral is connected to Ground so that the electrons have a base from which to oscillate back and forth from.

Thats why you have virtually no resistance between neutral and ground.

Thats a 1% summary of the electrical engineering behind your question on the neutral / ground situation. I can provide links to diagrams and engineering data if you need it.


Regarding the issue of the breaker tripping... I need to know two things.

1. What voltage rating is stamped onto the heating element where the wires connect.

2. Do you have Line 1 and Line 2 (230 volts) going to the heating element, or just Line 1 or Line 2, and a neutral wire.

So far it sounds like the electrician had wired a 110 volt rated heating element with 230 volts, or installed too small a circuit breaker.

We can go from there.

Customer: replied 4 years ago.

Hi, Phil,


thanks for the electrical info regarding the 'grounded neutral'. It's not something I have come across before, but it explains a lot. In Australia, mains power is nominally 240V, although in Western Australia, where I live, it is around 250V. Yesterday's test gave a reading of 246V.

The heater is rated at 240V/10A, and the circuit breaker also 240V. The heater has two wires to the element, a red (live) and a black (neutral), which are connected through a temperature limiting cut-out.

My main concern was that the heating element had not developed a fault, and had started grounding out. Your answer suggests that it is operating as designed. Therefore, the culprit would appear to be the circuit breaker, but if you have any other suggestions I would appreciate hearing them.


Bill Francis

Hello again, I had mistakenly assumed you were in the USA. The color codes for wiring in Australia (and other countries) is at this link, about 1/4 of the way down the page CLICK HERE

My statements regarding the white neutral are INCORRECT for Australia.

It does look like the circuit breaker may be too small for the load, the voltage rating on the breaker is not the relevant issue here..... it is the amperage that trips the breaker... In this case your load is called out at 10 amps, so the breaker should be 15 amp rated, and the wire sized accordingly, size 12 AWG minimum. Metric size
2.59 mm to 2.05 mm the smallest permissible size.


It will be best If opt out, and we can see if an electrical expert from Australia is available to assist you.

Customer: replied 4 years ago.

HI, Phil,

thanks once again. I don't know that we can go much further. Apart from the wiring in between, it can only be either the heater electrics or the circuit breaker. If the heating element is working as it is supposed to, that only leaves the circuit breaker. And to that end I have asked the electrician who installed it to replace it with another, to see whether the problem continues. However, this may not be for another day or two (or longer with the weekend upon us). I'll let you know what happens.


Bill Francis

Thats a good plan Francis, I will be looking forward hearing from you. Can you tell me now what the amp rating is on the breaker... it is normal cast into the end of the breaker toggle switch itself... a 10 would indicate a 10 amp breaker for instance.. you need 15 amp rated if the wire is 2.05mm or larger in diameter, copper.

Customer: replied 4 years ago.

Hi, Phil,


the breaker is rated at 16A.


Bill Francis

Hello again, in that case you will need to use a clamp around style amp meter to determine why your 10 amp load is tripping a 15 amp breaker.... thats the big question here.

Your electrician should have one, or you can buy one at any large hardware store or home repair type store electrical department. $60 or so.

Thanks for the positive rating.

Stay in touch as necessary.

Customer: replied 4 years ago.

Hi, Phil,


thanks for the assistance. The problem was the circuit breaker. We bought a new one and installed it, and all is working OK. No further questions.


Once again, many thanks.


Bill Francis