why not 3-pronge

leftwinger57

Hi guys,
While rewirering my rack into a dedicated Samson power strip, I noticed that most all of the devices use just 2-pronge polarity type plugs. Why is this, aren't all electical devices rquired to be at least grounded through the plug at the very least. Most houses built after the 50s use 14g Romex high voltage
grounded wire. The green conductor gets tied into every box and outlet in the house. I just think it's a strange that 3pronge plugs are not used and the power wires are not a heavier gauge.....lw

aboroth00

The equipment has 2 prong plugs because the casing isn't metal so there's no risk of an electrified casing, or there is an internal ground within the amp to prevent it from being electrified. Adding thicker wire doesn't necessarily make a difference. It's not audio equipment we're talking about here . Adding thicker wire can actual increase the resistance.

Typically if the casing isn't metal it uses a 2 prong plug.

ben62670

Wrong and wrong.

aboroth00

All plugs are technically grounded through the 2 prong polarity plug. You'll notice usually that 1 side is positive and 1 side is negatve, left and right side. The negative side also carries the ground which grounds your equipment. However the 3rd prong is added for safety in case any wires come loose.

Here's a link to the 2 vs 3 prong issue: http://electronics.howstuffworks.com/question110.htm

"If you look around your house, what you will find is that just about every appliance with a metal case has a three-prong outlet. This may also include some things, like your computer, that have a metal-encased power supply inside even if the device itself comes in a plastic case. The idea behind grounding is to protect the people who use metal-encased appliances from electric shock. The casing is connected directly to the ground prong.

Let's say that a wire comes loose inside an ungrounded metal case, and the loose wire touches the metal case. If the loose wire is hot, then the metal case is now hot, and anyone who touches it will get a potentially fatal shock. With the case grounded, the electricity from the hot wire flows straight to ground, and this trips the fuse in the fuse box. Now the appliance won't work, but it won't kill you either."

This usually applies to most metal cased audio equipment. However if you do come across an Emotiva amp you'll notice they use a 2 prong even though it has a metal casing. This is due to the chasis being double shielding and having its own internal ground.

The advantages of this is to avoid ground loop hums.

Theheadsn

ben62670 wrote: »

Wrong and wrong.

:biggrin:

ben62670

Sorry I am kinda dry. I have/had many pieces of audio gear with metal chassis and no ground.

BlueFox

I have sometimes wondered why some gear has 3 prongs, and some have 2. As Ben mentioned, the 2 prong gear has metal cases. I always thought it was the law that now everything has to have 3 prongs, but obviously that is not the case.

ben62670

Some manufactures probably choose not to have a ground for ground loop reasons.

bobman1235

ben62670 wrote: »

Sorry I am kinda dry. I have/had many pieces of audio gear with metal chassis and no ground.

You can have a metal chassis and no third prong, BUT the reason FOR the third prong IS in fact chassis ground, generally. aboroth00 never said ALL metal chasses had a third prong, just that any equipment without a metal case would not necessitate it. Not really wrong....

ben62670

I know what the ground is for. I have been in a lot of equipment

aboroth00

ben62670 wrote: »

Some manufactures probably choose not to have a ground for ground loop reasons.

Everything has a ground it's just where it grounds is the question.

leftwinger57

I'm caught inthe middle of this one.TheYamaha all metal,even the feet, Deon cdp all plastic,Klipsch set plastic and the sub is wood, The Adcom heavy duty steel
.SO it'sa hogbog of materials and it doesn't seem to matter as long as your house it grounded and your plugs are polarity correct....lw

Tour2ma

aboroth00 wrote: »

Everything has a ground it's just where it grounds is the question.

Agree, but then why did you say this earlier about eliminating the third prong???

aboroth00 wrote: »

The advantages of this is to avoid ground loop hums.

The third prong and the ground prong of a two-prong plug end up in exactly the same point in your breaker box.

If ground loops are less common in two-prong land, this is the first I've heard of it...

And sorry if I seem to be picking on you... not my intent.

On3s&Z3r0s

Tour2ma wrote: »

The third prong and the ground prong of a two-prong plug end up in exactly the same point in your breaker box.

I think you're propagating shoddy intel here. This is definitely not true in all cases. From every outlet the neutrals will always go back to the neutral bus bar, and the neutral bus is ultimately grounded. But the ground wire does not necessarily connect to the neutral bus bar. In many cases it does, but not necessarily. You could have a separate equipment ground bar, sub-panels, etc. Plus, the ground on the cable carrying your cable/satellite signal is likely to be different from the ground for the electrical service panel. It's in the the cases where you're wrong that a ground loop is most likely to occur. The wikipedia article on ground loop is a pretty good explanation.

Tour2ma wrote: »

If ground loops are less common in two-prong land, this is the first I've heard of it.

Ground loop hum is definitely less common in equipment that uses two-prong plugs.

Fongolio

I just switched my Eico ST70 from two prong to three with the ground wire going to chassis. At the same time I was upgrading resistors (I have a thread going just for the mods on the Eico). I still had a fairly significant hum situation with the unit that has seriously been depleted. Only at very high volume is it noticeable now. I don't know if that's due to the AC plug mod or the resistor upgrades but I just feel better knowing the unit is chassis grounded properly.

ben62670

aboroth00 wrote: »

Everything has a ground it's just where it grounds is the question.

Wrong again. The neutral is not tied to the chassis. The ground if it had one would be. The difference between the neutral and the ground is the neutral has potential. Another words currant flows through it. The ground nothing flows through it unless there is a fault.

FTGV

The 3rd prong is strictly a safety ground.Products that forgo using the 3rd prong need to be double insulated .ie built so that there is no potential of a lethal voltage being encountered.

Tour2ma

On3s&Z3r0s wrote: »

I think you're propagating shoddy intel here. This is definitely not true in all cases. From every outlet the neutrals will always go back to the neutral bus bar, and the neutral bus is ultimately grounded. But the ground wire does not necessarily connect to the neutral bus bar. In many cases it does, but not necessarily. You could have a separate equipment ground bar, sub-panels, etc. Plus, the ground on the cable carrying your cable/satellite signal is likely to be different from the ground for the electrical service panel. It's in the the cases where you're wrong that a ground loop is most likely to occur. The wikipedia article on ground loop is a pretty good explanation.

It wouldn't be the first time... but never intentionally.

I looked at wiki... It says...
"The first solution is to ensure that all metal chassis are interconnected, then connected to the electrical distribution system at one point (often referred to as a "single-point ground")."

Are you saying that you've seen (or do) installs with two separate grounding rods? One for the neutral bar and one for the ground wires? The way I read the quoted wiki bit is that you want one...

I may have over generalized, but what I said has been correct for my previous three homes. While in one home the neutral bus did not collect the grounds, they used the same ground rod, i.e., same difference.

Not sure about my current home as breaker box is inside and on an interior wall. Certainly easy enough to check with a VOM... if I can find the little effer...

Cable, the two times I had it, was grounded by cable company at their j-box. Current satellite rig was installed near my power line's entry point specifically so it could use the existing ground rod.

On3s&Z3r0s wrote: »

Ground loop hum is definitely less common in equipment that uses two-prong plugs.

Old audiobugs (pre-third prongers) would beg to differ... (no offense Fongolio... ). That said, it might not be fair to compare different eras.

I can barely remember the last time I had a ground loop issue. It was in my college dorm and a flourescent ballast (that went bad) was to blame.

On3s&Z3r0s

Actually, the single-point ground is exactly what I was referring to. Even though your entire household electrical system may ultimately tie in to the same network of ground rods, I'm pretty sure (based on direct experience) you can still get different ground potentials depending on where and how the ground wires are connected (meaning if they're not all connected the same, you don't have a single-point ground even if they do all end up in the same place). I also think you'd have to have more sensitive test equipment than the average DMM to measure ground potential. I agree that if you only have everything plugged into the same outlet (or at least the same circuit) it's pretty difficult to get a ground loop hum regardless of whether the equipment (or circuit for that matter) is using two or three conductors. But it's pretty easy to get it if you're got grounded equipment on different circuits (like a remodel that added circuits off a sub-panel for example) or if your equipment has multiple different grounds (like for cable/antenna) if they take different paths to the same grounding network. In those cases, "lifting" the ground on some of the otherwise grounded equipment usually helps but may not be a very good long term solution.

As a more concrete example, my cable system has always been bonded to my house's grounding system (no separate rod or anything), but I did have some hum that I solved with a cheater plug until in a remodel I added a whole-house surge arrestor off the service panel. (Older, ungrounded equipment didn't hum... at least not nearly as much, which is how I decided to use the cheater.)

All of the house's telecommunications wiring goes through that arrestor now so the "first" ground that all the wiring (high and low voltage) sees is that arrestor, basically making it a single-point ground. Before, the mains grounds was in the panel and the cable ground being connected externally to the grounding system with external grounding clamps. Anyway, no more cheater necessary.

aboroth00

ben62670 wrote: »

Wrong again. The neutral is not tied to the chassis. The ground if it had one would be. The difference between the neutral and the ground is the neutral has potential. Another words currant flows through it. The ground nothing flows through it unless there is a fault.

You really like to say the word wrong for some reason. :biggrin:

I never said the neutral was tied to the chassis or did I? I don't quite recall. But the neutral does connect to a ground and thus is the ground in the case of a 2 prong. The neutral and the ground are the same wire in the sense that it connects it to the ground in your fuse box.

A ground does however have a potential. This is why we hear a ground loop hum because different pieceas of equipment have different reference points for grounds and causes a voltage difference. The earth we arbitrate as a ground and has a certain potential. However what is important is that a ground is an infinite sink for electricity to absorb it all for your equipment not to harm you.

ben62670

Wrong:biggrin: A ground only has potential if the hot or neutral comes in contact with the chassis(failure). The neutral is used in the circuit where a ground isn't.

aboroth00

ben62670 wrote: »

Wrong:biggrin: A ground only has potential if the hot or neutral comes in contact with the chassis(failure). The neutral is used in the circuit where a ground isn't.

The conductor for the ground and neutral are usually one in the same and are sometimes used to mention the other. But yes a ground is not integral in a circuit, there's a hot and neutral end. I just didn't mention it as I thought it was obvious. However in practical households, the ground wire is used in conjunction as the neutral wire which meets at points such as the breaker.

However a ground does have a potential in physics and ground voltages are usually relative numbers to the earth. Every ground has a potential, otherwise we would never have ground loop hums. The ground again in physics ideally absorbs all charge without changing its potential. Basically when the hot wire comes into contact with the chassis, the current is directed into the earth by the ground or wherever it is grounded.

But yes, the ground WIRE does complete the circuit and carries current.

ben62670

OK remove the ground and the device still works. The ground is used for safety and no the circuit.

bmor

Here are some basic diagrams that may help explain the situation.

http://www.allaboutcircuits.com/vol_1/chpt_3/8.html

Grounding and bonding situations can be complicated even to those who do it for a living.