Grounds

[MarkTheShark]

Why do some components have a 2 wire (no ground) and others have a 3 prong with ground? Shouldn't the whole system be bonded to one ground source?

 

[j_garcia]

IMO, simply because some of these devices don't explicitly need it. Low power units like a disc player, cable box, etc... generally do not need a separate ground as part of their design. Receiver, amp, sub, etc.. do.

 

[slipperybidness]

Why do some components have a 2 wire (no ground) and others have a 3 prong with ground? Shouldn't the whole system be bonded to one ground source?

If it is only a 2-prong cord, then the device "should" be double-insulated.

The 3-prong cords--that extra prong is the "safety ground".

Even the 2-prong cords--the neutral is indeed tied to ground, but it is at the power supply box where neutral is tied to ground.

 

[MarkTheShark]

Thanks j, My Marantz 5011 AV has a lot of inputs and outs, I am surprised it does not have a dedicated ground. Maybe to prevent a ground loop?

 

[MarkTheShark]

Thanks Slipperybidness. The safety ground should be for a lightning strike or surge. I could see a surge coming into an AV receiver from the cable line in, even though it's grounded at the service entrance.

 

[j_garcia]

I have seen some AVRs that don't have it and I could not tell you why they would or would not use it for a particular design. Not sure how it relates to cost of production, but I wouldn't expect a big difference.

 

[slipperybidness]

Thanks j, My Marantz 5011 AV has a lot of inputs and outs, I am surprised it does not have a dedicated ground. Maybe to prevent a ground loop?

Most AVRs tend to be 2-prong only.

 

[slipperybidness]

Thanks Slipperybidness. The safety ground should be for a lightning strike or surge. I could see a surge coming into an AV receiver from the cable line in, even though it's grounded at the service entrance.

Nope!

The safety ground is for YOUR safety! It provides a very low resistance path directly to ground. So, if a live wire comes loose and hits the metal chassis, then the current should take the path of least resistance to ground (through the safety ground) and NOT through you and your heart! Furthermore, that large instantaneous current should blow fuses and/or trip breakers at the panel!

In general, if your house gets struck by lightning, you're hosed!

My neighbors house took a direct hit! Then lost EVERYTHING that was plugged into an outlet! It got my computer, and I was dang lucky that was all that I lost!

And, in general, cable companies are notorious for terrible grounds on their systems.

If you look at very old houses, they don't even have 3-prong receptacles! There was a time when there was no such thing as a safety ground!

 

[MarkTheShark]

Slippery, Thanks for the info. I wonder if switching all my AV gear off with a wall switch would prevent lightning damage.

 

[slipperybidness]

Slippery, Thanks for the info. I wonder if switching all my AV gear off with a wall switch would prevent lightning damage.

During a lightning storm, I will unplug all of my gear. I would not risk it with a switched outlet.

Be aware--You should also disconnect the coax cable if you are trying to protect your gear, that is another place for lightning to enter and fry your electronics.

Either unplug everything, or invest in a whole-house lightning protection system (pricey and not 100% foolproof)

 

[TLS Guy]

Slippery, Thanks for the info. I wonder if switching all my AV gear off with a wall switch would prevent lightning damage.

A lightning strike will jump switch contacts without breaking a sweat.

The reasons for double insulated gear, two prong, is ground loop prevention. It takes a minute potential between grounds to cause a nasty hum. Even the grounds in most power cords are too small with too high a resistance and can cause hum.

Ideally a system should have just one ground. If you have a complex system the best way of avoiding hum is with a star cluster grounding system built from Gauge 5 solid copper. That is what I have done.

 

[Speedskater]

The

Thanks Slipperybidness. The safety ground should be for a lightning strike or surge. I could see a surge coming into an AV receiver from the cable line in, even though it's grounded at the service entrance.

The green Safety Ground (EGC) wire main purpose is to trip the circuit breaker if there is a ground fault (short-circuit), it has nothing to do with lightning strikes or surges. The (GEC) ground circuit connects to Planet Earth through the ground rods. The power company Neutral, the EGC and the GEC all connect together in the main breaker box (with some exceptions).

Yes the cable line can be a problem, but it should also have it's own surge protector connected to the main breaker box.

 

[Bucknekked]

A lightning strike will jump switch contacts without breaking a sweat
Ideally a system should have just one ground. If you have a complex system the best way of avoiding hum is with a star cluster grounding system built from Gauge 5 solid copper. That is what I have done.

TLS Guy speaks the truth on ground. If you want to see what he is referring to , look at the link in his post. As part of the photo library you will see solid copper ground wire running up and down his mounting points for hardware. Each piece of hardware gets a ground to the case.

 

[MarkTheShark]

A lightning strike will jump switch contacts without breaking a sweat.

The reasons for double insulated gear, two prong, is ground loop prevention. It takes a minute potential between grounds to cause a nasty hum. Even the grounds in most power cords are too small with too high a resistance and can cause hum.

Ideally a system should have just one ground. If you have a complex system the best way of avoiding hum is with a star cluster grounding system built from Gauge 5 solid copper. That is what I have done.

Thanks TLS Guy. If there are multiple 20amp circuits in the system and they are grounded, how does the additional grounding of the equipment not cause a ground loop? Is it supposed to drain emf noise to ground?

 

[MarkTheShark]

A lightning strike will jump switch contacts without breaking a sweat.

The reasons for double insulated gear, two prong, is ground loop prevention. It takes a minute potential between grounds to cause a nasty hum. Even the grounds in most power cords are too small with too high a resistance and can cause hum.

Ideally a system should have just one ground. If you have a complex system the best way of avoiding hum is with a star cluster grounding system built from Gauge 5 solid copper. That is what I have done.

TLS guy, that is one impressive studio, do you have a Harmony remote for it?

It's amazing what goes on behind the walls. Nice job.

 

[TLS Guy]

Thanks TLS Guy. If there are multiple 20amp circuits in the system and they are grounded, how does the additional grounding of the equipment not cause a ground loop? Is it supposed to drain emf noise to ground?

Multiple circuits are a big problem, as the ground wire in most houses is not very big.

I solved the issue by having a sub panel in the studio mechanical chase. So the ground lines are short and the star cluster ground ties into it. There are three large 7ft copper rods, with heavy gauge copper wire form the main panel. The grounding rods are very close to the panel. I have the fiber Internet line coming in right by the panel and that is tied in. The satellite dish and FM antenna are also tied in and very close to the panel and house grounding rods.

Proper robust grounding is one of the toughest challenges in all audio systems.

Whenever I visit pro studios, almost invariably there is ground loop hum on the monitors. Engineers make their way here to check mixes not infrequently and also want me to archive and master on occasions. Almost always they comment that this studio is silent. That is not a common occurrence unfortunately.

One thing that would solve all this in a hurry is abandoning metal wire for interconnection and making ALL interconnects fiber.

 

[TLS Guy]

TLS guy, that is one impressive studio, do you have a Harmony remote for it?

It's amazing what goes on behind the walls. Nice job.

No I don't use a harmony remote. A lot of the units predate remotes! I actually don't use remotes much. For the TV I just turn it on and off, either with its remote or the DVR remote. The pre pro I just use the volume control pretty much. I usually change inputs manually and turn it on and off manually, since I have to turn the amps and crossovers on and off manually anyway.

I do use the disc player remotes for navigation. The DAW has a wired keyboard. For he HTPC I use a Logitec RF keyboard.

 

[mtrycrafts]

.... The safety ground should be for a lightning strike or surge. ...

I seriously doubt a lightning strike damage would be avoided by that pin.

 

[Speedskater]

Multiple circuits are a big problem, as the ground wire in most houses is not very big.

For a long time in the US the Safety Ground (EGC) wire has been required to be as large (or larger) than the Hot or Neutral.

I solved the issue by having a sub panel in the studio mechanical chase. So the ground lines are short and the star cluster ground ties into it.

The sub-panel is a good deal. The idea is to reduce the length (and resistance) of the component to component Safety Ground wire.

There are three large 7ft copper rods, with heavy gauge copper wire form the main panel. The grounding rods are very close to the panel. I have the fiber Internet line coming in right by the panel and that is tied in. The satellite dish and FM antenna are also tied in and very close to the panel and house grounding rods.

It's important to note that all the ground rods are connected at the main breaker panel/service entrance.

It's also important to note that the ground rod system (good or bad) has nothing to so with day-to-say AC power quality. (the exceptions being internet, satellite & cable TV)

 

[Diesel57]

How effective is a lighting rod on your house?