# Ungrounded Receiver



## z80analog (Oct 29, 2013)

New a/v receiver SC-68. Power cord does not have a ground terminal, so ... the receiver itself is not grounded. I assume it is built like a power tool which might be advertised as "double insulated." But, well, I guess I am a little worried about electrical shock and stuff. Without a grounded chassis I assume there would not be electrostatic discharge when touching the receiver. And if I did ground the receiver, that there could be ES discharge but it would be harmless to the internals. Are there sonic or "ground noise" issues I would need to worry about if I were to ground this thing? Should I absolutely not ground it? Thanks!


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## RBTO (Jan 27, 2010)

Usually the equipment designers know what they are doing, and grounding the case most likely wouldn't improve on anything sonic-wise, and may in fact create problems with ground loops. If you're worried about electrical shock problems, place your gear on a GFI breaker (or outlet) and all should be well. Static discharge will still take place with an isolated case, and the discharge will find its way to earth ground one way or another. Usually a path exists that won't cause harm to the electronics but if you have a major static problem, get a can of "Static Guard" and spray the offending fabrics (a good practice even with moderate static issues).


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## z80analog (Oct 29, 2013)

I didn't think about a GFI. Perfect. Thank you!


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## RBTO (Jan 27, 2010)

I've also seen a GFI adapter at Home Depot that plugs into an existing outlet and provides GFI protection to equipment plugged into the adapter. That might save you replacing an outlet or installing a GFI breaker.


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## lcaillo (May 2, 2006)

It is almost unheard of for a modern receiver to have a safety problem. Everything made for the US that does not have a ground on the a.c. input MUST be dual isolated. Additionally, the chassis finds ground through the connected sources. I have seen high leakage current due to defects in cabel boxes and satellite receivers, never in an audio receiver.


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## z80analog (Oct 29, 2013)

I was making two assumptoins: 1) all components ground their chassis to earth ground coming from the power cord to protect the consumer from internal shorts to the chassis; 2) all small-signal interconnects floated their grounds to ensure isolation from gound noise.


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## lcaillo (May 2, 2006)

z80analog said:


> I was making two assumptoins: 1) all components ground their chassis to earth ground coming from the power cord to protect the consumer from internal shorts to the chassis; 2) all small-signal interconnects floated their grounds to ensure isolation from gound noise.


Neither are correct, in general. The chassis is isolated from both hot and neutral in all double isolated devices, i.e. those with two prong a.c. cords. Now what should happen is that the potential of the chassis and the neutral are the same, since back at the electrical service neutral should be at ground potential. The purpose of a grounded a.c. line is to provide for safety if something should go wrong that causes a difference in potential between earth ground and neutral, or something shorts to the chassis. Double isolated devices are safe because the chassis can never (except under extreme failure scenarios) gather a high potential relative to earth ground because both sides are completely isolated. The chassis can be at earth ground, or near it by connection to outside sources that are grounded. The chassis floats relative to hot and neutral in the primary side of the power supply but ground is usually at chassis ground on unbalanced signals.


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## z80analog (Oct 29, 2013)

lcaillo said:


> Now what should happen is that the potential of the chassis and the neutral are the same, since back at the electrical service neutral should be at ground potential.


Thank you for your reply lcaillo. I believe the chassis is floating with respect to ground potential, because the chassis is not connected to the neutral; it is "isolated" from neutral via double-insulated design. So the chassis can be any potential w.r.t. ground. If the neutral wire coming into the chassis became unhinged and touched the chassis internally, then I agree the chassis would be at ground. The device would not work, but since the hot wire did not touch the chassis, everyone is safe. If the hot wire became unhinged and touched, then the device would not work but we would have a big problem, because the chassis would be at hot potential and possibly kill a consumer who touched it and ground somewhere else (like the TV backpanel, which is grounded). So a choice by the manufacturer to double-insulate instead of ground to house via a third wire in the power cord, to me indicates that grounding the chassis introduces noise that is more undesirable than the very slight possibily of electrical death. That's what I'm trying to get to: is that the reason? Does grounding introduce unwanted electrical noise? If it does, then I won't ground the chassis on my own.


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## lcaillo (May 2, 2006)

Grounded systems cost more to build by a very small margin, and are on average no more safe. Perhaps less so when people lift the grounds to relieve noise issues. You are correct, the extra ground path is a source of potential noise.

I should have been more clear. Ground and neutral in either system should be at the same potential. This is never totally true because of impedance in the lines. Being at the same potential does not mean that they are connected at the device, however. Things can be isolated and be at the same potential. Ideally, but never really true.


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## RBTO (Jan 27, 2010)

Your description of circuit failure and subsequent problems is quite correct, but as has been mentioned, the probability of a hot short to the case happening is _extremely_ low. When you ground the case, what would you ground it too??? It takes on the potential of whatever ground you choose, and that _may_ carry noise since it's not the same as a signal ground (a signal ground being a poor choice for electrical protection). 

Again, if you're really worried about getting shocked, plug your unit into a GFI. A GFI measures the net current being delivered to your two pronged device and if it's not zero (meaning some of it is going to ground through you),_ both_ hot and cold lines are broken in very short order. End of story! No fatal shocks. No ground issues. Don't bother grounding the chassis!!!!


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## z80analog (Oct 29, 2013)

RBTO said:


> Don't bother grounding the chassis!!!!


Right-o. I will use a GFI outlet as that solves electrical shock problem and does not introduce home ground noise. Thanks!


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