Advice on wiring up a grow room microcontroller.

FiguringOutLife · Oct 6, 2021

I'm currently building a grow room microcontroller for my startup business and have come to the part where I have to wire up the high voltage side of my system.
Before I make some dodgy wiring and blow myself up I'd like to get some advice from someone with an actual qualification ?
What I've got so far is a microcontroller that switches on and off a series of relays depending on temperature and humidity.
These relays will be wired up to (at this stage) 4 standard wall sockets with a heater, a fan, a dehumidifier, and potentially a humidifier(not sure if I'll need this one).
Only 2 of the 4 appliances should ever be running at one time.

My questions are:
As I'm building this in a metal box should the box itself be grounded?
If so, how would you recommend doing it?
Are there any improvements you would recommend to my wiring?
How can I provide power to my microcontroller without the cowboy style jam it in and screw it tight USB charger setup?

If you can see any concerns that I've overlooked feel free to point them out and suggest fixes.

Photos of my current build with low voltage(microcontroller/sensors) side removed for less cluttered photos:

[ElectriciansForums.net] Advice on wiring up a grow room microcontroller.

Electrics · Oct 6, 2021

A grow room for what..

FiguringOutLife · Oct 6, 2021

CamoElectric said:
A grow room for what..

Microgreens ?. You can look them up on YouTube. They're a superfood/health food thing. Pretty much baby plants ?
It's a bit off topic but I'm always happy to share pictures of my plants if you're curious ?

telectrix · Oct 6, 2021

i thought the set up was a bit undersized for cannabis. ??. and yes i'd earth the box.

FiguringOutLife · Oct 6, 2021

telectrix said:
i thought the set up was a bit undersized for cannabis

telectrix said:
i thought the set up was a bit undersized for cannabis. ??. and yes i'd earth the box.

I'd definitely have to scale up for cannabis production ?? maybe full irrigation and soil monitoring system too ?

I assume when you say you'd earth the box you mean "earth(green/yellow) cable from my input touches the box somehow?
I read somewhere about driving an earth peg and running a separate earth wire to the box but that definitely seems like overkill to me ?

James · Oct 6, 2021

You don’t need to link each earth terminal to the next.
they are commoned together by the din rail and will in turn provide a good connection to the steel backplate.

FiguringOutLife · Oct 6, 2021

James said:
You don’t need to link each earth terminal to the next.
they are commoned together by the din rail and will in turn provide a good connection to the steel backplate.

Right, so if I were to move the earth of my input cable to the closest earth terminal I could completely do away with the rest of my earth wiring?

pc1966 · Oct 6, 2021

FiguringOutLife said:
Right, so if I were to move the earth of my input cable to the closest earth terminal I could completely do away with the rest of my earth wiring?

On the DIN rail, yes.

I would still take a dedicated earth lead from one of the earth terminals to the box, as various mounting screws on to painted plates/boxes are not always reliable means of earthing.

As for USB power supplies, you might use something like this to save on a 13A socket & adaptor arrangement:

MK USB Charging Module White - Euro Data Coms Module - White | MK (K5837WHI)

FiguringOutLife · Oct 6, 2021

pc1966 said:
On the DIN rail, yes.

I would still take a dedicated earth lead from one of the earth terminals to the box, as various mounting screws on to painted plates/boxes are not always reliable means of earthing.

Okay, inputs and outputs earthed to the earth terminals + an earth from the box to an earth terminal.
But all the earth bridges between terminals are redundant as the din rail itseft does that.

Also, that USB Box looks pretty ??
Is my cowboy USB Charger setup safe enough to use until I get your suggested USB box? Or Is it better to just sit on my hands until the proper equipment arrives?

Lucien Nunes · Oct 8, 2021

Make sure you have adequate clearance under the relay PCBs (I can't see clearly). Commercial products built this way often have an insulating rigid plastic sheet underneath to prevent any stray screws etc shorting the PCB pads to earth. Earth both the chassis plate and the box itself with a flylead.

Although there's no particular need to change what you have done here, for future reference, you might like to streamline the supply line connection feeding all the relays by gathering the terminals so that they are alll adjacent and linking them using a jumper bar or plug in link. This avoids the many connections daisy-chained in series. You can also get commoning terminals with many cable entries all connected together inside, and even DIN-rail adaptors for regular Wago lever terminals.

I read somewhere about driving an earth peg and running a separate earth wire to the box but that definitely seems like overkill to me

It's not overkill, it's wrong and potentially dangerous (see what I did there?) With earthing you want everything connected together so it's all at the same potential and you can't get a shock from one part to another. As soon as you bring in a different 'extraneous' potential you can get a shock from one earth connection to another under fault conditions. Everything powered by a Schuko plug should get its earth from the Schuko plug.

GLENNSPARK · Oct 9, 2021

How are you running extraction for the tents...?

FiguringOutLife · Oct 11, 2021

Lucien Nunes said:
Make sure you have adequate clearance under the relay PCBs (I can't see clearly). Commercial products built this way often have an insulating rigid plastic sheet underneath to prevent any stray screws etc shorting the PCB pads to earth. Earth both the chassis plate and the box itself with a flylead.

Although there's no particular need to change what you have done here, for future reference, you might like to streamline the supply line connection feeding all the relays by gathering the terminals so that they are alll adjacent and linking them using a jumper bar or plug in link. This avoids the many connections daisy-chained in series. You can also get commoning terminals with many cable entries all connected together inside, and even DIN-rail adaptors for regular Wago lever terminals.

It's not overkill, it's wrong and potentially dangerous (see what I did there?) With earthing you want everything connected together so it's all at the same potential and you can't get a shock from one part to another. As soon as you bring in a different 'extraneous' potential you can get a shock from one earth connection to another under fault conditions. Everything powered by a Schuko plug should get its earth from the Schuko plug.

That's a lot of information ?
The pcb's are about 1.5cm above the steel backplate. Your concern about shorting them out is very valid. Maybe I put a hdpe plate that I have floating around behind them.
So far I've got a single earth wire fixed between two nuts on one of the studs for the backplate. Is that adequate enough or would you recommend another way of attaching an earth?

So today we learned that unless you want to kill yourself then the earth goes to the same plug that the power comes from ?
I'll remember that.

Would there be a website where I could buy all these fancy things you talk about?
Just reading that list makes me want to start a new project ?

Also, some updated photos of the build:

FiguringOutLife · Oct 11, 2021

GLENNSPARK said:
How are you running extraction for the tents...?

It's actually a full on room as opposed to tents.
At the moment I'm just cracking the window to let fresh air circulate. But eventually I plan to run a fan through one of my spare relay spaces once I have an o2 sensor.

GLENNSPARK · Oct 11, 2021

FiguringOutLife said:
It's actually a full on room as opposed to tents.
At the moment I'm just cracking the window to let fresh air circulate. But eventually I plan to run a fan through one of my spare relay spaces once I have an o2 sensor.

Make sure you use filters or you'll arouse suspicion with the neighbours...???