Core Electronics Forum

Mains power construction regulations/guidelines


I have a mains-powered (240V AC) bathroom ceiling heater light / extractor fan. (This kind of thing: At the moment the extractor fan and the heating lights are connected to separate switches so they can be turned on independently of each other. I am going to put a Draft Stoppa ( on the heater/fan unit. However, when a Draft Stoppa is installed on a combined heating-light/fan unit the fan is required to be wired so that it runs whenever the heating lights are turned on (to avoid overheating or worse).

What I want is that everything is set up so that if the heating is on then the fan is also turned on, but I can also turn on the fan without the heating turned on. I had an electrician look at this but was advised that it wasn’t possible without pulling extra cables through the wall (which is not really possible in this case). All the electrician could do with the existing wiring was to reconnect the wire from the fan switch to the heater switch, so that the heater switch controlled the heater and the fan simultaneously (both on or both off).

Having thought about it, I am positive I can do what I want by installing a box in the ceiling between the current wires and the heater/fan unit. I think that the simplest and most reliable approach would be to use a relay that is driven by the wire to the heater to switch a line from the heater input across to the fan input. This would require a relay with a 240V coil driving contacts rated at 240V and a much higher current than the fan needs. It only relies on basic physics. The coil only draws an extra ~0.5W (~2mA current). If the contacts ever fail permanently open or permanently closed there’s no safety problem. As far as I can tell, the worst that could happen would be if the coil insulation broke down and caused a short between the windings. I could put in the lowest power fuse I could find to guard against short circuits. So I think I could easily build this, that it should be very reliable and safe to leave unattended in the sealing (appropriately boxed to keep out rats or whatever).

Ms question is: Is there a readily available guide to laying out and enclosing mains power circuits so that I can be confident that I haven’t done anything dumb from a safety point of view. Basically I want to be confident that if I handed it to an electrician to connect the wires they wouldn’t refuse to do it.

The simple answer to you question is that you can’t do this. While you could use a relay to control the device you still need a switch to isolate the circuit.

The electrician is legally required to comply withe the wiring rules and to determin the appropiate way to wire the circuit. Even if you come up with a way you think you can do it they’re going to ignore everything you tell them.

I’m also a licensed electrician.

Shaun Price

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Is an access panel required to get at the box?

Talk to the electrician. They need to design, build and install it. Everything has to be built with equipment approved for use in Australia.


Thanks, @Shaun21504.

you still need a switch to isolate the circuit.

The wall switches will still be there and used. Is that not as capable of being isolated as would be the case if the switches were wired directly to the heater lights and fan? If not, there could be isolating switches on the Active lines between the control box and heater/fan unit.

The electrician is legally required to comply with the wiring rules
and to determine the appropriate way to wire the circuit.

So as long as the electrician independently determines
that the circuit is compliant
it’s OK for them to build/install it?

Talk to the electrician.

Yes, I will. I want it to be compliant.
But before talking to the licensed professional
I want to have my own well-founded views
on what’s possible and reasonable.

How do “smart home” hobbyists deal with this issue?
Using off the shelf remote controlled power switches with a microcontroller
to OR the fan and heater control signals
seems like technical overkill and inherently less reliable
than using a relay.


Hi there Rgayler, Shaun is giving you good advice. You should also consider your Insurance. If by chance you start a fire at your IXL and they discover your work-around I wouldn’t like your chance. Although I am not sure why the additional wiring is not possible unless your existing cables are rendered into thew wall.
You may be able to design a wireless or Bluetooth solution. Build a PCB with a relay, a wireless/Bluetooth receiver and ATtiny85 and place a wireless transmitter and switch beside your IXL switches. You could also add a temperature sensor to trigger the fan if the heater comes on as a backup safeguard.
There are also some Smart-home solutions you might discuss with your electrician where multiple devices can be operated on a single wire by using different frequencies.
This would mean you would not be interfering with the AC wiring but again you may still invalidate your insurance if something were to go wrong.

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Hey rgayler,

I’m afraid that getting a quote from an electrician is your only safe option here as working with 240VAC can be extremely dangerous, both due to the risk of electrocution and the risk of heating causing a fire. Unless you have a licence to perform this kind of work it’s always the safest option to contact a local professional and get their recommendations and complete the work. I apologize I couldn’t provide much assistance but the most important consideration here is your safety. To answer your question

Generally, these hobbyists will either be electricians, have an electricians licence or after designing a system have an electrician install it.


Thanks @Adrian30968.

Ross, it’s not just hobbyists have this issue. As a hobbyist you have some lewleeway when it comes to regulation. Your house is connected to the electricity grid and is not something you can practice your hobby on.

Anything you put in the installation in Australia needs to be RMC certified, comply with the AS3000 Wiring Rules, comply with any rules the local grid operator requires and many more. Check out the ACMA site for other requirements like EMC. Ever after all this you need the electrician to approve it all and install it. I personally don’t know any that would including myself on my own house and I’m a licenced electrician.

To get all these approvals will take you months and cost tens of thousands of dollars. Unless you have a spare $50k-100k (possibly more) laying around you don’t need I would look at alternatives that don’t need to be wired into the mains.

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Hi @Adrian309681,

You should also consider your Insurance

Yes. I am very conservative about insurance. That’s why I posted the question. If the electrician won’t do it then it won’t happen. I would be willing to build the control box as a project, but only if the electrician was happy to install it without bending the rules.

I am not sure why the additional wiring is not possible unless your existing cables are rendered into the wall.

The wiring is inside the door frame and a very tight fit. It was put there a few years back when the wall was stripped back to the wooden frame during renovation. The adjacent wall tiles are half behind a cabinet fixed to the wall, so anything with the possibility of breaking a tile would lead to too much grief.

You may be able to design a wireless or Bluetooth solution.

I could, but I won’t. I spend a lot of my professional life dealing with systems that have stopped working for obscure reasons. For something that I want to shove in the ceiling and then ignore for the rest of my life I prefer a device that only relies on physics continuing to work the same way.

There are also some Smart-home solutions …

I raised the smart-home issue because it appears to be a legal way to achieve the same result. So what is it about a smart-home approach that makes it legal? If I could understand that then I might be able to modify the control box with relays approach so that it is obviously legal. For example, if the legal magic for smart home approaches is that everything is connected via plug and socket rather than connecting directly to the house AC wiring, then maybe the modification for me is to have each of the switches in the bathroom wired to a socket in the ceiling (by an electrician) and have the control box and fan/heater unit plug into those sockets.

Smart-home … may still invalidate your insurance if something were to go wrong.

Yes. That is a separate issue that I have not seen discussed anywhere. I would be interested to see some informed commentary on that. Given that it is now easy to get smart-home power control devices and that insurance companies will try to avoid paying out if at all possible I would have thought some test cases would have already arisen.

As I said earlier in this thread, I am not intending to be a cowboy and shove a power control device in my ceiling just because I can. What I am doing by asking the question is trying to understand the possibilities and constraints on possible solutions before having the conversation with the electrician. In my experience, people tend to believe that what they’ve always done is the only way that works and is compatible with the rules, but that belief is not always true. So I like to have my own well-founded views about what’s possible before getting into the discussion with the electrician.

What makes all devices legal for connection to the power grid (fixed wiring in your house) is that they are designed to the rules and have been tested and certified by an approved test lab. It’s the testing that costs all the money and it’s rare to pass first time. You’ll also need to have an ABN and register as a supplier and hold issurance.

An electrician can only construct a control box for you if all the components are RMC certified and the design meets the standards. If you construct it yourself the electrician will basically have to pull it apart to inspect your work.

You can connect a device to a socket outlet you built youself as long as it complies with the rules but not in the way you mentioned. If it’s basically a permenant installation and the plug is to get around the rules then unfortunately the rules include this so it’s legally the same as being wired directly so you’ll need an electrician regardless.

The main electrical standard is the AS3000. Any home control system in Australia has to be certified and meet these standards. There are many more rules that you need to comply to for building your own appliances and these rules are costly. Check the Standards Australia website and search for any that may be relevant.

This isn’t like Uber testing the rules on taxis. The rules are there for safety reasons and fairly consistent across the world. If you were to get caught breaking them you’re looking at very high fines and possible imprisonment. No electrician I know would risk that.

You can get off the shelf home automation systems that do this. Make sure you buy one from an Australian distributor and that it has a valid RMC mark.

Check the ACMA site for RMC requirements which will explain why it has to be an Australian distributor. I’ve had plenty of customers buy light fittings from outside of Australia and no electrician will install them.

My experience with insurers (I’ve worked for them and made claims) is that if you follow all the rules and the policy covers what your claiming they will pay out. They obviously make very sure you have followed the rules and you’re covered under the policy.

Hopefully this helps you in your understanding of why it’s virtually impossible to build your own home automation systems. If you still have questions please feel free to ask. I’m sure your not the only person wondering.

This is all my personal opinion based on my experience. Please consult with the relevant regulatory authorities and certified compliance testing facilities.

Thanks for your comprehensive reply, Shaun.

@rgayler, I think this can be done, without needing any additional cables installed other than at the switch, @Shaun21504 can probably confirm it. As @Shaun21504 has said, this will require a licensed electrician.

I’m assuming that you have two way switch mechanisms installed. Instead of the active going to the common terminal, it should go to either the 1 or 2 terminal. The common terminal should now be for the supply to the fan. A bridge wire just needs to be installed between the remaining terminal on the fan switch to the load side of the heater switch.