PC Case conduct electricity?

[esplin2966]

Hey everyone, someone in my group brought up a serious concern with custom designed cases in general that I don't know the answer to. My guess is there are some other case designers who also don't know the answer to this, so I'm going to put it out here for everyone to discuss:

We are designing cases out of steel, aluminum, etc., which are all electrically conductive materials. If the case is electrically conductive, it can be a potential safety hazard. For example, a novice builder ignores all other builder's advice and gets a crappy PSU for his build. 3 months later, his power supply breaks or something and shorts with his case. Wouldn't touching his case electrocute him?

As case designers, how do we account for this safety hazard? To my understanding, most forms of finishing on aluminum/steel just protects the material from corrosion and/or make the material look better, so that doesn't change the electrical conductivity.

w360, Necere, and dondan, you've worked/are working with Lian Li so I'm sure if there is a safety precaution to be taken they've already briefed you on it. Can one of you comment on this subject?

 

[Aibohphobia]

The housing on the PSU is grounded so a metal case in contact with it would be grounded too.

 

[esplin2966]

The housing on the PSU is grounded so a metal case in contact with it would be grounded too.

So we don't have to worry about the scenario where the PSU breaks/becomes ungrounded, or is just unbelievably crappy?

Not challenging, just asking. I just want to make sure to do what the law requires of me.

 

[Aibohphobia]

That's why people should only buy PSUs that are UL (or equivalent) certified.

I'm not an electrical engineer but I think it'd actually be safer for the case not to be isolated from the PSU so that in the more likely scenario that some of the wiring shorts to the case it would be grounded.

 

[GiGaBiTe]

So we don't have to worry about the scenario where the PSU breaks/becomes ungrounded, or is just unbelievably crappy?

Not challenging, just asking. I just want to make sure to do what the law requires of me.

I've disassembled a pretty significant number of trash IED power supplies. You don't have to worry about them potentially being ungrounded because a large percentage of them are ungrounded or have bad grounds.

I've seen Logisys, Deer, Delta, Coolmax, Diablotek and a number of other Asia-X brands where they didn't bother using decoupling capacitors to ground, nor did they bother to actually connect the mains ground wire to the housing. Basically the whole machine the units were plugged into became a floating ground that lead to all sorts of lovely problems.

 

[AFD]

I would think that a faulty PSU shorting out and electrocuting the consumer via the case would still be a liability on the PSU manufacturer, and not the case manufacturer or designer. Heck, you could take it even one step further.. would a desk manufacturer be held responsible for an incident where the PSU transferred electricity through the PSU housing, into the PC case, into a metal desk, and then into the consumer?

Perhaps it could be a liability for the case manufacturer, if for example, the case included an internal PSU extension (like the M1) and due to some strange oversight in design, a part of the case itself cut into or wore away at the internal extension cable and caused the short.

(Just my thoughts.. I am not a lawyer )

 

[esplin2966]

I would think that a faulty PSU shorting out and electrocuting the consumer via the case would still be a liability on the PSU manufacturer, and not the case manufacturer or designer. Heck, you could take it even one step further.. would a desk manufacturer be held responsible for an incident where the PSU transferred electricity through the PSU housing, into the PC case, into a metal desk, and then into the consumer?

Perhaps it could be a liability for the case manufacturer, if for example, the case included an internal PSU extension (like the M1) and due to some strange oversight in design, a part of the case itself cut into or wore away at the internal extension cable and caused the short.

(Just my thoughts.. I am not a lawyer )

This argument makes a lot of sense. I will wait for w360/Necere/dondan to come in with their professional insight though, since a lot of laws aren't that intuitive

 

[SaperPL]

The CE sign generally requires you to predict possible scenarios of faulty components and misuse of the machine and you're responsible to assuring safety of your product in those conditions except when the user intentionally uses machine in the wrong way. In general you're responsible for the safety of a complete machine using your component(pc case) and possible scenarios connected to its use.

Of course the CE sign isn't required (in the EU) if you're making a case and not selling whole machine but its rules are something that can give you the general idea of what are you responsible for as a machine designer.

As for the desk - if someone builds a conductive metal desk then perhaps its also his obligation to allow/enforce grounding of the whole desk somehow.

 

[cyclone3d]

If the power supply shorts, there is absolutely no way that you are going to get shocked from the case being electrically conductive.. unless of course you are also in a bathtub full of water with the case.

Or unless you are running some ungodly gauge of wire with no circuit breaker or a super high rated circuit breaker.

If it shorts hot to neutral, it will blow the breaker. If it shorts hot to ground, it should also blow a the breaker.

If you are not on the main breaker box, you will have a neutral ground if wired properly so it will still pop a breaker if a short happens.

Most of the time however, if a power supply shorts out, it is just going to die and not pop a breaker. Even super crappy ones are going to fry the power supply itself.. but maybe take some other components out with it.

And even if it doesn't blow a breaker, and you touched the case, you would have to be touching ground or both hot and neutral for it to shock you. And that is very, very, very unlikely to happen unless you mean to do it.

Just touching a single live wire without a path to ground will not do anything. This is coming from somebody who has worked on live circuits a fair number of times. And yes, I have shocked myself a lot of times with 120v A/C.

Cases have been made of metal for what... 25+ years.. or basically ever since a computer was invented?

And the same goes for most everything that was ever made that uses A/C power. A lot of the newer stuff has crappy plastic cases, but that is because of cost cutting measures, not because of safety issues.

You short hot to neutral or ground and it is going to blow out the weakest link in the circuit and then be dead.

 

[hoggy]

I think the OP was thinking more along the lines of if the ground wasn't connected at all, then yes the case would pull up to mains voltage if the psu failed in such a way that the incoming supply came into contact with the chassis.

PC PSU's and Cases essentially fall under PELV (Protected Extra Low Voltage) whereby they should be protected in such a way that no SINGLE fault might cause an electric shock.

They would also fall under ADS (Automatic disconnection of Supply) such as MCB's, RCD's Fuses etc.

I've tried to find a "plain English" document to explain:
http://electrical.theiet.org/wiring-matters/26/electric-shock.cfm?type=pdf

If your going plastic then depending on your design you may be able to go down the route of Double Insulated (Square Within a Square symbol.) This does allow you to use a 2 prong power cable such as that of the PS3 or PS4 which is great to save space; however the rules on this are a lot more complicated so i won't go into it here.

For piece of mind i'd make sure the PSU was physically screwed to the chassis.

It would also be wise to include with your case documentation the standard "Electrical Hazard Warning"


To actually answer your question:
Yes someone can and probably will, buy a crap PSU and put it in your case.
Yes someone can and probably will, buy a crap PSU and put it in anyones case.
Yes the case could technically become live under the worst circumstances in your case (earth / ground not connected & fault on the AC side.)
Yes the case could technically become live under the worst circumstances in anyone elses case (earth / ground not connected & fault on the AC side.)

Likelihood of the above is pretty slim though.

 

[Rav3n]

Hey everyone, someone in my group brought up a serious concern with custom designed cases in general that I don't know the answer to. My guess is there are some other case designers who also don't know the answer to this, so I'm going to put it out here for everyone to discuss:

We are designing cases out of steel, aluminum, etc., which are all electrically conductive materials. If the case is electrically conductive, it can be a potential safety hazard. For example, a novice builder ignores all other builder's advice and gets a crappy PSU for his build. 3 months later, his power supply breaks or something and shorts with his case. Wouldn't touching his case electrocute him?

The PSU is grounded, and anything attached to it is grounded. If electrocution was a serious risk, cases would be made from non conductive material.

 

[JoanTheSpark]

modern powerboards should have not just MCBs installed, but also RCDs or even more 'modern' RCBOs.. those are available for over 10 years now and no magic.
With those installed you actually can touch the hot wire and earth and you're protected as the max current that will flow is 30mA and then they should switch OFF.

Another matter is EMI protection for those custom cases.. if you look at your standard DELL or HP case there are all kinds of springs that connect the whole housing and create a faraday cage for the components inside. I know that my construction doesn't do this..

 

[hoggy]

and you certainly don't want EMF getting into your system do you???

www.youtube.com/watch?v=EyHgVEbQ_nY

link related...(sort of)

 

[Zap]

As for the desk - if someone builds a conductive metal desk then perhaps its also his obligation to allow/enforce grounding of the whole desk somehow.

You can lead a horse to water...

I can totally envision a metal desk with a grounding strap, and someone NOT bothering to use it.

If the power supply shorts, there is absolutely no way that you are going to get shocked from the case being electrically conductive..

The issue is where that electricity is going. This is why a mechanical power switch works. One side can be connected to live power, but if there isn't anywhere for the power to go, then it doesn't do anything. This is why batteries have anodes and cathodes (- and +) and why all power cords have at least two separate paths for power.

I believe UL certification covers product safety. Nothing to do with quality, but that it probably won't kill you or your other equipment. Of course plenty of PSU companies at the, ahem, lower end of the spectrum that just sticks the UL Certification Mark on their product without actually having had it tested or certified.

Another matter is EMI protection for those custom cases.. if you look at your standard DELL or HP case there are all kinds of springs that connect the whole housing and create a faraday cage for the components inside.

Yup. In the USA at least, this is for FCC Class A and B certification. This is for how much EMI a computer can radiate.

 

[esplin2966]

Ok, I just checked. Both my Silverstone ML07 and my Minibox M350 do not conduct electricity.

This is certainly not proof, but it's some evidence that we may have to design cases that are non-conductive. I will try to get in contact with Silverstone OEM in the next few days. In the meantime, can some of you check if your case is conductive?

 

[hoggy]

Is it painted by any chance? Or Anodized?

Favorite trick in the electrical world was to connect an earth up without scratching the paint off. Therefore no earth...

 

[hoggy]

Or just plastic....

Model No.
SST-ML07B (black)
--
--
--
Material
Reinforced plastic outer shell, steel body

 

[Spotswood]

Heh? Lian Li has been making bare/anodized aluminum cases forever.

 

[esplin2966]

Or just plastic....

I checked the metal part. It looks to be just painted, but for those who want the premium finished aluminum look (like me), this might be an issue.

Heh? Lian Li has been making bare/anodized aluminum cases forever.

Do you own a Lian Li case? If so, it would be cool if you could check if the inner wall conducts with the outer wall. Even if the exterior is just aluminum, if it's painted inside then it's not really dangerous in the way I have described in the OP.

 

[JoanTheSpark]

Is it painted by any chance? Or Anodized?

Favorite trick in the electrical world was to connect an earth up without scratching the paint off. Therefore no earth...

I wouldn't consider that a 'trick'

Anyhow, if the case is made from metal and the 230VAC is coming in through the PSU and earth isn't properly connected to the PSUs housing, there isn't much you can do about the whole situation of the whole case being able to go hot, besides running a 2nd power cable to your box and properly connecting earth to your case.
The only thing that will safe you then & you are having a big control over is getting an RCD or RCBO into the circuitry that feeds the 230VAC to your PSU.

In Europe - Germany I think - they are required by law for bathroom installations.
In my house over here in Oz we got them in every circuit and from some teardowns of RCBOs we found these ones to be the nicest (cost does matter, but this is a play with death issue, so making sure they're good might pay off):

I just don't know if they're available for 120Vac as well..

 

[esplin2966]

Ok, I think I finally figured out why Lian Li can do bare-bone looking aluminum chassis without worrying about electrocution safety. Basically all aluminum chassis have to go through the anodizing finish, which helps the aluminum surface bond with paint, prevent corrosion, increase surface hardness, and makes the surface non-conductive.

So basically, all chassis manufactured do not have conductive surfaces. If the material is aluminum, they anodize it. If the material is steel, they paint it or do something else. That's all there is to this issue.

 

[Aibohphobia]

What about OEMs (Dell, HP, etc.) with their unpainted galvanized steel cases?

 

[mtrupi]

Browse the pictures of power supply reviews here and you should see a green wire bonding the chassis to ground. This should be enough to make it safe even though it could still become unsafe.

 

[Tony Ou]

Ok, I think I finally figured out why Lian Li can do bare-bone looking aluminum chassis without worrying about electrocution safety. Basically all aluminum chassis have to go through the anodizing finish, which helps the aluminum surface bond with paint, prevent corrosion, increase surface hardness, and makes the surface non-conductive

Anodizing is usually only applied to the exterior of an aluminum chassis while interior is chromate treated to keep it electrically conductive for EMI shielding purposes and still providing corrosion resistance.

What about OEMs (Dell, HP, etc.) with their unpainted galvanized steel cases?

Big OEMs require that their PCs are EMI shielded, that's why they have unpainted internals too.

 

[EdZ]

The standard for cases is for the case ground to be attached to the PSU ground, generally because they're screwed together. The screws must bass through both the PSU case and the chassis, and the interior of these screwholes will be bare metal.This means that no matter what cosmetic coating is applied to the outside of the case the chassis will still be grounded.

You would have to go enormously out of your way to isolate the chassis from ground, and doing so would end up being more work to ensure you comply with electrical safety regulation. In the UK at least, if an electrical device has a case then that case must be either grounded, or the entire appliance must be double-insulated.

A conductive PC case is a non-issue unless you are doing some truly bizarre things with internal isolation (e.g. floating plastic PSU mount).

 

[esplin2966]

Anodizing is usually only applied to the exterior of an aluminum chassis while interior is chromate treated to keep it electrically conductive for EMI shielding purposes and still providing corrosion resistance.




Big OEMs require that their PCs are EMI shielded, that's why they have unpainted internals too.

I see. Thanks for the input.

The standard for cases is for the case ground to be attached to the PSU ground, generally because they're screwed together. The screws must bass through both the PSU case and the chassis, and the interior of these screwholes will be bare metal.This means that no matter what cosmetic coating is applied to the outside of the case the chassis will still be grounded.

You would have to go enormously out of your way to isolate the chassis from ground, and doing so would end up being more work to ensure you comply with electrical safety regulation. In the UK at least, if an electrical device has a case then that case must be either grounded, or the entire appliance must be double-insulated.

A conductive PC case is a non-issue unless you are doing some truly bizarre things with internal isolation (e.g. floating plastic PSU mount).

I just looked up double insulation. I would guess that safety regulations in the US will be very similar to the UK.

 

[WiSK]

Here's the grounding system on one of my rigs.

The two arched wires connect the case frame, the motherboard tray and the AC filter of the PSU. It routes to the ground pin of the power plug, via the PSU housing. I cut out 2 x 2 notches in the housing and filed them so I could attach spade crimps.



As EdZ says, generally your chassis is automatically grounded by the simple effort of screwing a PSU to it. In my case the PSU is insulated from the chassis, so I had to make the connections myself.

 

[kooki]

Might I add another question to the discussion of this thread? It is related.
Is "using plastic standoffs for your motherboard a bad thing" a consensus among you, experts?
I never thought about it, but this thread kinda makes me wonder...

The mobo should ground itself with the PSU's ground. But having a case with the PSU insulated from the chassis (like WiSK has it) and no direct contact from the mobo to the chassis might generate some unwanted difference on voltage which might lead to a sudden short if they touch each other somehow. Right?

 

[EdZ]

In the case where you have the PSU ground isolated from the case, and the motherboard isolated from the case, then there is the possibility that floating ground could end up at a different potential to the motherboard, resulting in the possibility of a discharge. Leave the switch set to 'more magic'.