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In Reply to: ? about a Cheater plug to eliminate hum---might this configuration cause "death"? posted by jjk12 on April 6, 2007 at 15:19:26:
Isn't it interesting how everyone has an expert opinion. It's like this. Residential power supplies in North America are with a 3-wire 120/240 VAC system. That is, with two "hot" wires and a neutral. The voltage is measured between the two hot wires at 240 volts, and between each hot wire and neutral (or ground if the neutral is grounded) at 120 volts. The 240 volt supply is used for your stove, clothes dryer and air conditioner, the 120 volt supply for everything else. The only reason that the 240 volt supply is used is because power consumption, or Watts, is a multiplication of volts and amps. By doubling the voltage to 240 for the big loads, the size of the supply wires and the breakers can be cut in half.As the power supply is AC, at 60 Hz, that essentially means that the generator from the utility has the job of moving electrons back and forth 60 times per second.
By code, the neutral is called the "grounded" conductor, the ground wire is the "grounding" conductor. In most jurisdictions, the neutral must be grounded, but at one point only to prevent ground loops. This is generally done at the distribution panel, where it can be easily inspected.
With a stereo system, every power cord will obviously have a hot and neutral wire to provide 120 VAC to the component. Some will have a two-wire connection cord, some will have three. Those with three will have a ground wire connected to the frame or chassis ground of the device.
That being said, the ground path through that device may be at a different potential from the ground of the duplex receptacle that is supplying the power. With a difference in potential, and a resultant voltage rise, this can cause a current through a ground loop that can cause an audible hum.
Lifting the ground of the amplifier by either breaking off the ground pin or using an adapter plug with the ground removed is a well recognized means of preventing or reducing problems with ground loop hum through the speakers.
If this was truly a death defying situation, then why do they sell appliances and devices with only two-pin plugs as opposed to three-pin?
In fact, my Bryston 4B amplifier has a switch on the back labelled "Normal" and "Separ" for separate which lifts the ground pin if there is a ground loop hum problem.
Any risk or danger of electrocution is only possible if the hot wire becomes connected through a major fault to the metal frame or chassis of a component. If that were to occur, with no ground wire, and the grounded neutral wire was through a high resistance, there is a chance of getting a shock. With a separate ground wire connected, the hot wire would have a low resistance path to ground that would trip the supply breaker or blow a fuse.
With stereo equipment, however, the supply power being connected through an isolation transformer or a step-down transformer will introduce a high impedance path that will cause a trip on the primary side only. That is, if your cat chews through the supply wire to your amplifier, the breaker will trip. If something happens internal to the component on the step-down side of the transformer, separate protection is required.
If anyone has concerns about whether a two-pin Hot/Neutral wire is safe or not, just have a look around your house at your floor/table lamps, kettle, toaster, etc.
A ground wire is most definitely a personnel and equipment saving means, but remember, if your electrical supply system was properly installed, the neutral wire is grounded.
Follow Ups:
Two wire appliances, such as hand-held drills and other power tools, are "double-insulated", meaning they have no metal parts that can readily become energized, even if an internal hot wire becomes completely detached.Three wire plugs have a ground wire that is used on appliances with metal enclosures that CAN become energized in the event of a short circuit (i.e. frayed hot wire, hot wire come loose, component failure, etc.).
In normal operation of a three wire branch circuit, when an enclosure becomes energized, the ground wire (via the ground PIN) provides a path for the fault current to return to source. Since the breaker is on the 120V (hot), the breaker "sees" the fault current and trips very quickly. This is because the fault current magnitude is high, because typically the impedance of a short circuit is quite low. (This is why it is called a "short" - it's an abnormal path where the source voltage goes directly to ground, instead of driving the loads in the device it is intended to drive.)
If you cut the ground pin off, you do NOT have the same appliance as a typical two-prong appliance. You have an appliance that was DESIGNED to RELY upon that ground pin in the even of a short that has it's main safety feature completely disabled! When a short to the case occurs when the ground pin is removed, the enclosure remains energized, but no fault current can flow (except for a small current due to capacitive coupling which is insufficient to trip the breaker).
Touching this enclosure can result in a deadly amount of current flow in the human body - just enough to send the heart into fibrilation. This is the deadliest type of shock. Shocks less severe only cause small contact burns or discomfort. Shocks more severe will completely stop the heart, but in this case the heart can be restarted.
When a heart is in fibrillation, it spasms uselessly and cannot provide life-sustaining blood pressure.
The bad news is that only a defribulator can stop fibrilation. This is (oddly enough) a controlled shock which is actually used to stop the heart (not start it like on TV). Sometimes the heart re-starts by itself after a shock from a defibrilator, but failing that, adrenaline is administered to the heart muscle directly, or the chest is opened and the heart is massaged manually.
If you have humming equipment, you have defective equipment, branch circuits, or improper or faulty interconnects. Fix these problems - but do not remove that ground pin.
And avoid listening to misinformed laypersons that believe it's "not a big deal" to do.
Cheers,
Presto
the chances of a metal cabinet powering up, and your body's resistance to ground being low enough to cause fibrillation, are remote, but why take a chance?A personal experience highlighted this danger to me. A carpenter on a job I was on was using a skilsaw (the old metal-bodied style) while standing on a scaffold. His saw shorted out, and because his arm and hand muscles contracted from the current, he could not let go of the saw. Finally, in desperation, he jumped off the scaffold, the cord hooked on the way down, and the saw came unplugged. There was no one around at the time-if he had not been able to stop the current, his heart would have fibrillated, with potentially dire results. For me, lesson learned.
Powermatic:Did you know that falls as a result of electric shock is very common? Electricians have this addage "If the shock doesn't kill you - the fall just might!"
This guy may have made a life saving decision. When you're being shocked and you cannot let go, if you cannot throw yourself with sufficient force to either remove yourself from the device or unplug it... you're done for! Not too many people even have the presence of mind to take such action during a sudden violent shock. Others may face falling to their deaths if they attempt to jump or leap away from the source of the shock. Not a desireable situation at all.
Questions to ask:
1) Was that "old tool" a two-wire double insulated tool? With metal parts - not likely.
2) How much is a new double insulated or properly grounded skil saw?
3) Why did the carpenter wait until he was almost killed to buy the new skil saw, or at least inspect the tool to ensure it was safe?
A very sobering story. Thanks for sharing that.
Cheers,
Presto
The saw of choice for pros, and least on the western side of the country (easterners seem to prefer the sidewinders).This model has remained unchanged for a long, long time (sorry, don't know exact time lines, but well over 50 yrs). This is the latest iteration, but the only real difference between this and much older models is the resin pistol grip, trigger, and top handle, which were previously all metal, like many tools of the period (drills, etc) and the grounded cord. The older, all metal, no-ground type was the kind Rob was using at the time, and it definitely was not double-insulated. The change to the resin parts was done at least 20 yrs. ago. The newest models are 2-wire/w ground, with the ground presumably attached to the magnesium body.
The good/bad with the worm drive skilsaws is that they will, almost literally, last forever. The gear box is oil filled, and I've never heard of a gear failure (new parts are available, though). The brushes are user-replaceable. Armatures eventually wear out, but those are easily rebuilt. The only part that tends to need replacement is the 'foot' (base) that tends to get bent when it's dropped.
The 'bad' aspect of this equation is that there are still lots of the all-metal ones around, and who wants to give up a tool that his granddad gave to him, and still works great?. However, these can be used safely by (a) always plugging into a gfic receptacle (b)attach a 2 wire/w grnd. cord with a solid connection to the metal body (c)wrap handles with tape.
As far as safety on a job site, well, I'll just say that you would not believe some of the shit I've seen. Just skilsaw-wise, some carpenters wire the blade guard up (makes it easier to start a cut)-while many (most?) wood shake and shingle roofers remove the guard completely! It doesn't take much imagination to think about what that spinning blade would do if you accidentally hit the front of your leg as you drop the saw to your side.
The link shows current prices for skilsaws. The black-handled worm drives are the same as the red-handled, just heavier (and cheaper).
- http://www.amazon.com/s/ref=nb_ss_gw/102-2292484-5623340?url=search-alias=aps&field-keywords=skilsaw&Go.x=11&Go.y=8&Go=Go (Open in New Window)
I have not had to wield a saw all day every day but you are absolutely correct about the east vs. west difference regarding the preference of worm drives and sidewinders!My 5150 consumer grade sidewinder is at least 20 years old, well used in a DIY/handyman sort of way (including cutting concrete and cast pipe with abrasive blades).
Are they all made in China now?
--
Al G
Born To Tinker!
the company is now owned by Bosch. They'd be idiots to do anything to undermine the reputation for durability that this saw has.The sidewinders have certain advantages (lighter, startup torque doesn't twist the saw), but also disadvantages (the 'line of sight' on the 77 is on the left which is perfect for right-handers, the linear motor makes it easier to cut straight lines(at least for me (-:), and the gearing gives it a bit more torque). In the end, you pick your poison, get out on the deck, and start cutting up some damn studs!
...that even the best made tools are not immune from electrical failure.Perhaps moving to a moulded handle was for electrical isolation reasons...
Cheers,
Presto
If the manufacturer has designed the component properly and is using the chassis as a "Faraday shield", lifting the third pin ( ground ) defeats their engineering skills and could potentially lower performance potentials of the system. As always, it is best to track down the offending piece of gear / problem within the installation and fix it rather than lift the ground and band-aid it.Obviously, this takes for granted that the average AC installation has a low resistance path to ground, which may be assuming all too much. Most AC installations aren't worth shit, hence the major benefits that most achieve when installing heavy gauge dedicated lines and cleaning / weather-proofing their grounding system. Sean
>
Yes, I thought it was really odd that all the neutrals and grounds got connected to the same strip in the panel. What's the ground for if it's the same as a neutral?I only use cheater plugs when they work, but it's the best tweak in the kit. No worries, I'm still alive.
-Rod
Your use of cheater plugs is dangerous.Let me provide a more simple explanation than the correct ones given so far.
Take a typical appliance or audio component with a metal case. The AC goes in to a power transformer or other device, with both the hot and neutral wires insulated from the case.
If something goes wrong inside and connects the hot wire to the case, the neutral will not be affected because it is insulated from the case. However, the case will be at the hot wire potential. If you touch the case while also touching something connected to earth, you will be killed.
The AC "ground" is a separate conductor that goes back to the entrance panel and is tied to the neutral there. If the ground is present and the case is connected to it, the fault that connects the case to the hot wire will cause large fault current to flow through the ground conductor, which will trip the circuit breaker. This will happen before the case can reach the hot wire potential and harm anybody.
Some appliances and audio components are designed with what is called "double-insulation" and do not need the "ground" wire. Ayre is one maker that uses this approach. The insulation is such that a fault that would connect the case to the hot wire is considered unlikely by the Underwriters Laboratories.
Cheater plugs defeat the AC "ground" connection and create the possibility of lethal voltage appearing on the case. Hum from ground loops is a problem in pro audio as well as home audio systems. There is a safe solution sold to the pro audio market: the Hum X from ebtechaudio.com. See the link.
Thanks to Tuckers for finding this device and calling it to my attention. It contains a pair of rectifier diodes wired anti-parallel, and shunted by a 1000-ohm resistor. Diodes have the property of not conducting much below their "forward" voltage of about 0.5 volts, so the pair presents high impedance to small ground loop hum voltage, but low impedance to fault current. The 1000-ohm resistor is there so that devices such as battery backup UPS that look for a ground will see a ground and continue to operate. Audio components don't need the resistor.
Most gear does not "float" the chassis ( because of poor design and cost cutting measures ), but instead, ties the chassis and board to neutral / ground. This is commonly referred to as "star grounding". While many manufacturers actually advertise such a design as being beneficial, it only works effectively in high impedance i.e. tubed circuitry. It is completely useless and actually detrimental for use with most Solid State designs.If the "hot" wire were to come into contact with the chassis of a "star grounded" piece of gear using a "cheater" ( ground lift ) plug, the path to ground would still remain conductive. That is, the current would flow through the interconnects tied to other gear in the system, which hopefully is grounded. This would in turn pop the fuse of the component, IF the component was properly fused.
The exception to this would be if the safety ground of all of the components had been lifted simultaneously and / or one was using interconnects with a very small gauge ground conductor. With nothing in the system grounded, the path to Earth ground is broken, negating the fusible link. With very small ground conductors on interconnects, the conductor itself would break connection, acting much like a fuse itself. Once that connection was broken, the path to ground would also be broken, leaving the voltage on the chassis of the component to seek ground elsewhere.
Other than that, i agree with everything that Al has to say. Start by fixing your AC / grounding system and most all of your problems will be taken care of. If something should come up after the AC / grounding system has been dealt with, it shouldn't be too hard to find the problem or offending piece of junk gear. The most common problem after "fixing" the AC system would be gear that uses old school non-polarized two pronged plugs. In that case, here's a link that may help some of you solve such a problem. Sean
>
I appreciate your always posting in order to try to educate. Convoluted EE theorizing to explain away the necessity of the ground pin does a disservice.BTW, thanks for the link.
Ground does not equal neutral.Neutrals are grounded at the panelboard (aka in ONE place). That's the only "common" thing about them - that one single connection point. Everywhere else, they are different, isolated from one another, and have TOTALLY DIFFERENT purposes.
Netrals: are connected to the tail end of CIRCUITS and carry current back to the source in NORMAL conditions.
Grounds: are connected to metallic components that are NOT INTENDED to be energized, and carry fault current back to the source in ABNORMAL (short-circuit or fault) conditions.
Still think they're the same?
Cheers,
Presto
The neutral wire is the grounded conductor, that means that if there is any fault that connects the supply wire to the neutral that it will cause the supply power fuse or breaker to trip.The ground wire, or grounding conductor is intended to provide protection in the event that the hot or supply wire becomes connected through an insulation or component fault directly to ground.
While at first glance it may seem that they provide the same function, that is not the case. The neutral is the return path for the AC supply system, and is part of the two-wire supply scheme. The ground wire, under normal circumstances, will only conduct electricity if there is a fault.
Grrrrr.Picky, picky. Don't mix your grounds.
Of course, code requires the grounds to all be tied together in a box. How's that GFI know the ground wasn't right?
I've got a 4 gang switch box for some lights with one switch for a plug on the common landscape lighting circuit on a GFI from another panel. It took way too long to figure out why the GFI kept tripping.
-Rod
the difference (amperage) coming and going. Any leak, no matter how small, will trip it.
"Man is the only animal that blushes - or needs to" Mark Twain
> > Isn't it interesting how everyone has an expert opinion. < <Indeed. And those opinions are often wrong. Quite wrong. To wit:
> > Lifting the ground of the amplifier by either breaking off the ground pin or using an adapter plug with the ground removed is a well recognized means of preventing or reducing problems with ground loop hum through the speakers. < <
Yes, it is. It's also well-recognized as being the foolish, lazy, dangerous way to deal with ground loops.
> > If this was truly a death defying situation, then why do they sell appliances and devices with only two-pin plugs as opposed to three-pin? < <
Some equipment uses a type of chassis called, "double insulated." There is a significant difference between a grounded chassis and a double insulated chassis. Not understanding this difference, and then treating the two types as the same, is a great way to get an electrical shock.
> > In fact, my Bryston 4B amplifier has a switch on the back labelled "Normal" and "Separ" for separate which lifts the ground pin if there is a ground loop hum problem. < <
Indeed it does have such a switch; however, the switch DOES NOT DISCONNECT THE CHASSIS EARTH GROUND. It switches in resistance between the chassis ground and the signal ground to reduce the flow of noise current.
> > If anyone has concerns about whether a two-pin Hot/Neutral wire is safe or not, just have a look around your house at your floor/table lamps, kettle, toaster, etc. < <Indeed. Most household appliances are double-insulated; something you really ought to try to understand before espousing an "expert opinion."
Hey, sorry, didn't mean to cause a fuss. I've been working with electrical power and control systems for quite a while. Double insulated simply means that the electrical supply cord is insulated, and that the device the cord is connected to is assumed to be non-conducting. Sort of like your plastic bodied electric drill. Mind you, take it outside in a rainstorm, things might be different...Cheers
Well, it depends on what type of device you're supplying power to. As I mentioned in my first post, have a look around your house at the type of cords used to connect electrical devices.Anything without an isolation or step-down transformer inside it will not have a separate ground wire, because it doesn't need it. Should your floor lamp have a three-prong plug with a ground wire for the metal shell of the lampholder? If it's such a good idea, why don't they do it? If the hot and neutral wire to the lamp become shorted, the supply power breaker or fuse will trip off.
Anything with an isolation transformer inside will likely have a ground wire connected to the chassis or frame ground.
Stereo systems and electronic data paths are highly susceptible to electrical noise caused by ground loops that create noise along the signal path. Lifting the chassic ground can break the ground loop path and interrupt the ground loop current.
If you look back on electrical systems installed in residential buildings, the earlier systems consisted of a parallel blade plug with a hot and neutral only. Over the years, this was considerably improved to the modern three-prong plug with a hot, neutral and ground.
This was introduced as a safety measure, so that even with an ungrounded neutral or with an isolation transformer the ground wire would provide a low resistance path for an insulation or component fault.
Safer is always better, and electrical systems continue to improve with ground fault circuit breakers/receptacles and now with arc-flash circuit breakers.
But, remember that the original question was, to paraphrase, "If I lift the ground wire on my preamp to eliminate hum, did I create a hazard?"
The question could be re-stated as "Is it possible for me to be electrocuted if my preamp develops a fault between the hot wire and the chassis?"
Moving along, the next question would be "what could cause a breaker or fuse not to trip if the hot wire did become connected to the chassis of the component?"
The only way that can happen is if the hot wire is isolated from the neutral or the ground wire of the supply cord, as seen by the input power protection device through either isolation or a high resistance connection.
And, if that were the case, the power supply could now be isolated from the supply ground or grounded neutral, so that if you did come in contact with it you would be isolated as well.
It's like the old razor transformers that used to be installed in bathrooms. It was a 1:1 isolation transformer with an ungrounded secondary to the two-pin razor plug.
If you did come in contact between an outside ground path and the isolated hot wire, there would not be a shock because the hot wire was isolated from the supply power ground, so there was no current flow.
Mind you, if you went across the isolated hot and neutral, you would be in parallel....
"And, if that were the case, the power supply could now be isolated from the supply ground or grounded neutral, so that if you did come in contact with it you would be isolated as well."How is that so? The chasis is not connected to neutral - of course. The chasis is also no longer connected to ground (thanks to our pin clipping DIYer).
The chasis is isolated from neutral AND ground (no ground pin anymore), so no ground fault current of SUFFICIENT MAGNITUDE to trip the breaker can flow.
But this does not mean anyone unfortunate enough to touch the energized chasis is "isolated" as well. Having no proper path for ground current does not change the fact the chasis has been unintentionally energized, and the safeguard that was designed to isolate the power source (by fault current via the ground path) has been intentionally broken by removal of the ground pin. No fault current, no breaker operation, no isolation. Chasis remains energized.
Your logic here is faulty - and dangerous.
Cheers,
Presto
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