• The forum software that supports hummy.tv has been upgraded to XenForo 2.3!

    Please bear with us as we continue to tweak things, and feel free to post any questions, issues or suggestions in the upgrade thread.

Frozen on last channel

Black Hole said:
Needing to be earthed is a fallacy. What you need is to be at the same potential as what you are working on.
Click to expand...
And for that to be earthed. Do you know another way of ensuring you are at the same potential, Grumpy?
 
'Scuse me, but I was involved in this kind of thing professionally. You can have a bench mat and your work pieces on the bench mat and your wrist strap connected to the bench mat, but there is no need to connect the whole lot to earth. All the official instructions say you do, but that is an extra level of safety and not strictly necessary purely from the static control point of view.

For working on equipment when there are no other static control measures: if you are yourself insulated from earth (and with modern fabrics, rubber soled shoes, etc you probably are), then touching the equipment chassis will be sufficient to bring yourself to the same potential as the equipment without needing to worry whether there is an earth connection. Do not however move much without re-grounding yourself, because man-made materials have a habit of generating static when rubbed.
 
In this case you would be unable to use any mains driven (Earthed) test equipment or have the item under test connected to anything else that is earthed i.e. an A/V amp etc.
 
Of course, but I was not discussing a "powered up" situation - that's a whole different ball park. Home-brew anti-static setups with metal foil and direct connections to earth or the plumbing are absolutely NOT SAFE when equipment is powered up (proper mats, leads, wristbands etc contain current-limiting resistances which can dissipate static but limit shock currents to safe values - if you are going to do this DO NOT SKIMP).

In case anybody is confused by the comments of the back-biters: the subject was the safe replacement of a HDD with precautions against possible electrostatic damage.
  1. Disconnect anything you are working on from the mains and anything else (HDMI, Ethernet, whatever), it is not necessary to worry about maintaining an earth connection (and double-insulated equipment is frequently not earthed through the mains plug anyway). Unpower anything that is battery powered, and if in doubt remove the batteries.
  2. Hopefully the equipment in question has a metal structure, even better if the structure is connected to some kind of 0V reference for screening purposes. Either way the metal represents the best chance you have of eliminating any voltage differences between you and the equipment - it's the voltage difference which does the harm, not the actual voltage. Touch some bare metal for a few seconds, preferably before you even open the box, and repeat at frequent intervals during surgery.
  3. Do not remove the replacement HDD from its protective bag until you need it. Note that the bag itself is only conductive on the inside, so touching the outside does not achieve equlibrium. If possible, remove the HDD from the bag non-connector end first, and ensure you touch the metal case not the connector pins.
  4. While holding the HDD, touch the metal of the equipment again before plugging cables into the HDD.
  5. Presuming you are not chucking out the old HDD, insert it into the protective bag using the same precautions.
 
BH : Needing to be earthed is a fallacy. What you need is to be at the same potential as what you are working on. .
Click to expand...
Having both the equipment and yourself at some potential many thousands of volts above earth is not a safe as having everything at earth potential
 
Black Hole said:
  1. Disconnect anything you are working on from the mains and anything else (HDMI, Ethernet, whatever), it is not necessary to worry about maintaining an earth connection (and double-insulated equipment is frequently not earthed through the mains plug anyway).
  2. Hopefully the equipment in question has a metal structure, even better if the structure is connected to some kind of 0V reference for screening purposes. Either way the metal represents the best chance you have of eliminating any voltage differences between you and the equipment - it's the voltage difference which does the harm, not the actual voltage. Touch some bare metal for a few seconds, preferably before you even open the box, and repeat at frequent intervals during surgery.
  3. While holding the HDD, touch the metal of the equipment again before plugging cables into the HDD.
Click to expand...
Each time you touch the metal, you will discharge any static on your body (caused by rubbing your shoes on the carpet, etc) into the equipment. That is why it is better to have both yourself and the equipment earthed, so the static charge at thousands of volts goes to earth.
What is the point of discharging the static from your body into whatever you are working on? It defeats the object of all the precautions. If there was a convenient sink at 10v in the house, you could use that instead, but lacking that, earthing is the best policy.
I agree about the possibility of the earth on the socket not being connected to the chassis, though, but thought it overcomplicated things to mention it, and I am not even sure it is applicable to the Foxsat HDR.
Of course, not everyone has earthed their radiators either.
 
You must log in or register to reply here.
Back
Top