Question: I have a circuit that will be placed in somewhat close proximity to 220 VAC mains power. The mains power lines are bundled together of around 20 pairs (live and neutral) those 20 pairs should total up to around 50A max. My circuit will be reading the current consumption of those lines using a non-invasive current transformers which will then be read by my circuit. The circuit uses precision components which can be sensitive to voltage induced by those power lines.

How do you recommend to protect my circuit from those noise?

My first idea is to shield it with a Faraday cage, but making my own Faraday cage seems to be inelegant, I was thinking to somehow hide it. I thought if I place it in one of those small metal control boxes such as these:

[![enter image description here](https://i.stack.imgur.com/mAlL4.jpg)](https://i.stack.imgur.com/mAlL4.jpg) 

Do these control boxes protect from outside noise? Most Faraday cages I see are in mesh form factor but it should work the same way as these boxes, right?

Answer: 
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Are the circuits the same as the ones that use the ADS1115 (as per your earlier question)? 

```

> 
> *@Andyaka yes they are the one, alongside other complimentary circuits
>  – Jake quin*
> 
> 
> 

First, the input protection circuits
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Given that your input circuits look like this: -

[![enter image description here](https://i.stack.imgur.com/oGj79.png)](https://i.stack.imgur.com/oGj79.png)

And the TI data sheet says: -

> 
> These filter resistors produce a voltage drop because of the input
>  currents flowing into and out of the ADC. This voltage drop could
>  contribute to an additional gain error. Limit the filter resistor
>  values to below 1 kΩ.
> 
> 
> 

I would go for something higher than 100 ohm for R62 to R63 - possibly 470 ohm or 680 ohm.

The TI data sheet also tells us that the absolute maximum current into these pins is 10 mA (absolute maximum ratings) and so this allows the real external inputs to be 4.7 volts to 6.8 volts either side of the supply rails used for the device. In other words, with only 100 ohm resistors you get a headroom of only 1 volt and I would want to ensure this was maximized without compromising performance so, 470 ohm or 680 ohm would seem sensible.

Because you have now given yourself this headroom, you can put TVS diodes on those external inputs to dirty digital ground with no risk of attenuating or clipping the signals you wish to monitor. You could use 6 to 10 volt TVS diodes and further protect those inputs. This is something I would consider anyway.

The main question:
------------------

> 
> *My first idea is to shield it with a Faraday cage, but making my own
>  Faraday cage seems to be inelegant, i was thinking to somehow hide it.
>  I thought if I place it in one of those small metal control boxes*
> 
> 
> 

Yes, they actually do a good job of protecting against electric fields and, if they are made of steel/iron will also do a good job of reducing low frequency magnetic field interference that a non ferrous metal cabinet wouldn't cope with at all well.
If these control boxes are conductive, then you can use them as a faraday cage. Because the mains power lines are very low frequency (50Hz/60Hz), you do not have to consider the skin-effect, which reduces shielding quality for high frequency signals. A conductive box of any kind will work perfectly. You could even use some aluminium foil to wrap your circuit into.