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In Reply to: RE: Star Ground Question posted by em on June 17, 2009 at 14:48:19
Good safety question.
In using a cheater plug, you are eliminating the Protective Earth connection.
This means that if there's ever is a short circuit on the chassis, or if for some odd reason the chassis of the equipment becomes 'hot', you touch the chassis, the short circuit will pass through you and not through the 3rd wire. Not a good feeling...
If your use a cheater plug, and eliminate a hum problem, then somehow your equipment is finding a path from the Neutral wire to the Protective Earth wire or some other ground loop problem.
The safe answer is NO, don't use cheater plugs, they bypass the safety ground.
If you need a cheater plug to eliminate hum, there's a problem in the receptacle wiring or a ground configuration issue inside of one of your components.
Maybe, inside one of your components, there is a connection between the DC star ground and the 3rd Green wire.
This can happen either at the IEC socket, direct DC ground to chassis at one or multiple locations, via a 0.01uF/1000V Ceramic cap or via a small 10 Ohm resistor between the safety ground and the DC ground.
It's common to find 2 wire vintage gear using the chassis as the DC ground plane. These components can wreak havoc when connected to 3 wire equipment.
Modern DVD, CD, etc. components can only have a 2 wire plug, but it's polarized. And the chassis is completely isolated from the internal circuitry. The internal power supply DC ground is totaly insulated and isolated from the chassis.
A bit of troubleshooting is needed if you are having hum issues, if not, then be assured that if a component has a 3 wire plug, the 3rd wire is there for a very important reason.
If the same branch circuit that feeds your gear is not sharing a light dimmer, these are also notorious noise offenders for our HiFi systems.
Follow Ups:
Thank you for your very informative response.Two very knowledgeable Audio Dealers told me to use Cheater Plugs.They said they are SAFE.Now I wonder.
Many thanks
"very knowledgable audio dealers"
That is pretty much an oxymoron.
You need to look at signal returns/grounds in your equipment, not at the safety/ground wiring. I have just about all of my equipment AC grounded with 3 prong connectors. These include diy preamps, diy and factory amps, dacs, and numerous diy power suppllies. My tuners and turntables are not.
I have zero hum in my system.
Yes... "Cheaters" are not safe, but you can also examine why this is so in practical terms and a broader context.
The reason for the existence of "Cheaters" is that back when Electrical Home wiring standards adopted a 3 wire safety ground male plug and 3 wire receptacle with an extra wire connected to the PE ground bus and the home Ground rod, users needed a "Cheater" in order to connect their 3 prong appliances into the existing 2 wire legacy receptacles. Most legacy systems used metal conduit as the safety ground and these were not actually "Bonded' together but were all connected to the ground rod at the main service entrance panel metal chassis. But... these metal conduits eventually oxidized and lost continuity, thus they created a safety and fire hazard. Today Grounding and Bonding are two terms that need to be understood in order to create hazard free electrical installations.
When a component has a 3 prong cord, it doesn't necessarily imply that the 3rd safety ground wire is actually connected internally when the component has an IEC male connector. I have opened up some current manufacture tube amps and have found the 3rd solder post bone-dry and not connected to anything. The existence of the IEC socket is today a fe-facto "business" enabler for the Power Cord swapping market. Having this feature allows users to spend more money on exotic power cords which sometimes only use 2 of the 3 wires anyway. So much for being "Grounded" I say. Do exotic Power Cords make a measurable and audible difference, I sure hope they do. I have played around with some power cords and swear that I do hear a difference, subtle as it may be.
Usually, I have found that on equipment with a fixed 3 prong power cable exiting via strain relief and grommet, this is where you are not able to change power cords, almost always, the 3rd wire is really connected to the chassis via a solder, a lug and some lock washers. Here you do need a cheater plug to troubleshoot ground loop issues.
This is mostly due to manufacturing cost as it's cheaper to use fixed power cord than to install an extra IEC power socket and punch the required hole in the metal. Each extra hole on a chassis makes the manufacture more expensive, and a simple round hole is far less expensive.
Cheater plugs will make a difference when troubleshooting for an offending component that is causing or enabling a ground loop. This may be due to the fact that somehow, somewhere the DC ground is being electrically connected to the chassis at one or various points in the system. If at the same time, the 3rd wire is also connected to the chassis somewhere, you can have hum.
The cheater plug will lift the 3rd wire and isolate the mains transformer Neutral wire from causing a ground loop when this wire meets the PE bus at the service entrance. If also connected to the power supply DC ground in the component, if that DC ground is referenced to the chassis, or PE ground somehow.
Some electric guitar amps and a few hi-end Hi Fi amps employ a ground lift switch. This is a simple way to "emulate" a cheater plug without actually having one. Almost always the manufacturer is responsible and careful to completely isolate the DC ground from the chassis.
Some manufacturers install a 0.01 uF/1000VAC ceramic disk cap in parallel with a SPST 250VAC rated switch. In the closed position the 3rd wire is connected to the chassis via the switch. In the open position the only thing left is the capacitor in series with the green wire to the chassis. The open position eliminates DC continuity and AC couples the ground wire to the chassis. Thusly called a Ground Lift. Should actually be called a "Safety Ground Lift."
When you have a Bar full of drunk bikers waiting to hear Freebyrd... it's much easier as the Guitarist, Bassist, etc. to throw a switch and kill the hum than to ask "is there a cheater plug in the house."
Yes there are safety issues here as well, but recently there have not been any Electric Guitar related electrocutions as in the 60'-70's when electrical systems lacked a safety ground standard.
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