Upgrading Power Cables and Fuses

dalemurray wrote:I will admit I may be an idiot but, I question the need for grounded cord; though my situation may be unique to most of America.

All circuits are in electrical metallic tubing (EMT) conduit.
All conduit is grounded by virtue of connection to breaker panel.
All outlet boxes are metallic.
The outlets earth ground is provided via its attachment to the metallic outlet box (metal tabs, metal screws, etc).
Positive and neutral leads run in conduit back to breaker box where neutral is attached to ground.

So, neutral runs to ground in breaker box.
Conduit provides earth ground by connection to the very same breaker box.

If the neutral lead is attached to the amps chassis, and this lead run to ground, what benefit would I get by attaching another wire to the amps chassis and it running to ground, too?

At first I was concerned about not having a three prong cable but in reality it appears of no benefit to me anyway. Am I, in fact, and idiot?

You are correct regarding US wiring standards. The neutral (white wire) and the ground (green, uninsulated, or armored cable) are connected to the exact same point in the circuit breaker box (which is grounded to earth). However, these conductors must never be connected anywhere else in the circuit. That is the code. If there is ever *any* flow of current in the ground wire that is intended to indicate a problem. GFCI's are designed specifically to detect this and trip.

So although the neutral and ground do connect to the same point eventually, it is very dangerous to attempt to ground an appliance by connecting the neutral to the chassis for at least a couple reasons: (1) The hot and neutral could easily be reversed in a miss wired outlet or if a non polarized cord were used which would run hot directly to the chassis. (2) if the neutral wire is open circuited for some reason, the chassis would rise to hot level through the amp transformer primary.

Bay far, the safest option is to run a dedicated ground to the chassis, but in any case never connect neutral to chassis. It would be better to leave it float.

Basically, I'm alright because my electrical is correct. If I were to move to a new home with wiring I have not personally validated, I could very well get fried for lack of dedicated ground to chassis; correct?

Are you saying you already connected your neutral to chassis?

Or are you referring to some old equipment? Back in the 70's or so, it was common to see neutral (or hot) connected to chassis in cases where it was impossible to touch the chassis because it was inside a box, but this should never be the case today.

I do not have my amp in front of me; ST-120.

Before I run my mouth any further I need to open it up and take a look.

I plan to rebuild it in a new chassis and intend to use 3 prong plug when I do.

On the ST-120 the power comes in and goes through a transformer and the chassis
is floating. It's possible to introduce a ground loop and hum by tying it to ground.

Is it safer to tie the chassis to ground, most likely yes.

Just something to be aware of.

I built my VTA120 in a custom chassis with custom layout and tried it without grounding the chassis. Unfortunately, I got a ton of hum and grounding the chassis killed it.