Grounding aluminium casing

Hi guys,

I am planning to use an aluminium casing for my project, but just want to check that it is safe to do so. I am using a 12V 3A AC to DC power supply (https://cpc.farnell.com/pro-elec/pel00854/ac-dc-psu-12v-3a-2-5mm-dc-plug/dp/PW04270?st=power%20supply%20ac%20dc%203a) to power a TB6600 stepper motor driver. Can I assume that it is safe to do this with the aluminium casing because the power supply converts AC UK mains 230V to 12V DC? The power supply will plug into a DC socket connector through a hole cut out of the aluminium casing. Please see below photo showing this:

Thanks very much for any advice!

Why wouldn't it be safe to do so when the power supply is only 12V

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What do you mean by "grounding the casing"?

Sorry, I'd forgotten I'd named the post that. I was supposed to ask if it would be necessary to ground the casing

So that's an external power supply - it takes car of all the high voltage stuff, and just gives you a nice low voltage output.

A key reason people use these things is exactly so that they don't have to worry about mains stuff & safety in their equipment.

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No.

Safety grounding is for stuff with mains in it - you've kept the mains out of it, so you're fine.

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Yes, it's safe and grounding the box may help to keep electrical noise (EMI) from the stepper motor from interfering with other devices. It doesn't have to be earth-grounded. The local/Arduino ground can be isolated.

When there is AC power going into a metal box, the box should usually be earth grounded to make sure that when something "goes wrong" there can never be AC voltage on the box and it will always be safe to touch.

In your case, the 12VDC is isolated from the AC power and it's safe to touch the low voltages. (1) (Anything over 50V is considered dangerous by most regulatory organizations, and it needs to be protected/isolated so nobody can touch it. Anything less the 50V is usually considered safe.)

(1) You can gen a high-voltage inductive "kick" and a shock from a (low voltage) motor but it's short duration and it usually won't hurt you.

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Thanks very much for the helpful info awneil and doug. This is the first Arduino project I have done, so I just thought I would double check to be better safe than sorry!

It's not necessary, besides how would you "ground" the case

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Pretty obvious I'd have thought.
Most associate "grounding" with such equipment on low voltage to mean connecting the case to negative supply for shielding purposes.

From the responses here it would seem to be far from obvious. With mains powered projects there is a danger of confusing the project power supply GND and what in the UK we know as mains Earth

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The post is not too clear and I always worry when people ask questions about mains stuff .

Using the wall wart outside of the box , no earth is needed , He may want to connect the 0v of the 12v supply to the case for shielding or whatever if he wants.

IF he has an aluminium case with a 12v power supply powered off the mains inside it :
If there is then mains electricity within the casing , it should always have an earth bond to the aluminium case .
A loose connection or frayed cable, or if got wet , could make the casing live .

He should use a competent person to deal with mains connections ( earthing , fusing, cable sizing cable clamps and how a mains cable passes into the box are all important ).

.

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No, not obvious at all and @alfie_148 clarified what he meant.
Connecting a meal enclosure to a power supply negative is far from being grounded, in fact it could present a possible shock hazard.
"Most" have no idea what they are doing in regards to grounding.
Shielding: There will be no shielding if the induced currents have no where to go!

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and if the case is earthed that should then trip the earth leak switch as well (if there is one)

There is no mains supply [mod edit: redacted]

Yes, there is - but it is external to the unit:

image

Yes but the supply to the project is low voltage. [Mod edit: redacted]

There is clearly a valid discussion about when and how it is appropriate to connect a metal case to the circuit ground and / or mains safety earth, however, sadly, that discussion has decended into rudeness. By all means continue the discussion but please remember to do so in reply to the OP's question and please be polite and respectful of other contributors with whom you might not agree.

I've removed comments that I thought rude, and possibly some valid points. By all means make any valid points again, but make sure they are polite.

Thank you

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