Steve, I'm a UK guy but live in China at present. I agree with your posting and also don't recommend rg12 to add a safety ground, based on what he's told us about his kit so far. I didn't know US had 240V power domestically, so I appreciate the education here.
Clarification - the neutral in a center-tap 240VAC-supplied system carries current back from the two "phases". When the loads connected to these 180 degree out-of-phase connection are not balanced (practically always) the return currents do not cancel. There is resistance in the neutral conductor and similar resistance in the safety grounding conductor. This produces a voltage on the neutral conductor relative to the building entrance ground connection and a different voltage relative to the safety ground conductor at every point of these away from the entrance panel connection.
My comments were from the perspective of a more optimized situation where all the cans around the big circuits are tied to the same ground. Although if there's a big radiated noise source in the area or long signal line it might be better if the chassis were floating with the signal lines. In a residential situation the biggest source of noise in an audio system could easily be a floating chassis, especially with video electronics, which is probably why video equipment is usually shielded with a a ground connection, even if the cabinet is plastic.
There seems to be a little misconception on the actual purpose and functon of grounding.
Grounding and bonding. The following is based on a solidly grounded conventional wiring system. For simplicity's sake, I will not discuss corner grounding, impedance grounding, or ungrounded systems in this post.
The terms are defined in Article 100 and 250.2 of the NEC. Section 250.4 provides the performance requirements of Article 250. Grounding is a connection to earth, and bonding is the connection of items to each other.
Bonding is crucial inside a structure, because without it, if something goes wrong and an ungrounded conductor comes in contact with a piece of metal that someone can touch, that someone will receive a shock and potentially be electrocuted due to the uncleared fault. A quick and dirty definition for bonding is connecting electrical devices together in the attempt to trip a breaker, if an ungrounded conductor touches surface metal associated with the system.
What does the earth have to do with this? Nothing.
Then why is it called an “Equipment Grounding Conductor (EGC)” in the NEC if it’s primary purpose is to “bond” things together? Simple answer: tradition. It’s always been called that, and the terms in the NEC have served to confuse people for a long time. Proposals have been made to change the term, and progress has been made, but the EGC continues to hold it’s misnomer.
Electricity does not seek the path of least resistance to the earth. It seeks all available paths back to it’s source, in proportion to their resistance. The reason that a person gets shocked when touching an ungrounded conductor and the earth is because the neutral of the system is repeatedly connected to earth in a grounded electrical system. The earth becomes part of a return path to the transformer – it’s part of one route back to the source; the earth is not the destination for the electricity.
Driving a ground rod to ‘ground’ any electrical equipment does not provide the low-resistance path required to trip breakers. Driving a ground rod, or using a Ufer, or a metal water pipe is not a substitute for an EGC. A ground rod with 25 ohms to earth will allow almost five amps to escape the system into the earth when directly energized from a 120V source. Five amps will never trip a 15A or 20A breaker, and in the meantime everything bonded to this ground rod will be energized to 120V.
Grounding and bonding. The following is based on a solidly grounded conventional wiring system. For simplicity's sake, I will not discuss corner grounding, impedance grounding, or ungrounded systems in this post.
The terms are defined in Article 100 and 250.2 of the NEC. Section 250.4 provides the performance requirements of Article 250. Grounding is a connection to earth, and bonding is the connection of items to each other.
Bonding is crucial inside a structure, because without it, if something goes wrong and an ungrounded conductor comes in contact with a piece of metal that someone can touch, that someone will receive a shock and potentially be electrocuted due to the uncleared fault. A quick and dirty definition for bonding is connecting electrical devices together in the attempt to trip a breaker, if an ungrounded conductor touches surface metal associated with the system.
What does the earth have to do with this? Nothing.
Then why is it called an “Equipment Grounding Conductor (EGC)” in the NEC if it’s primary purpose is to “bond” things together? Simple answer: tradition. It’s always been called that, and the terms in the NEC have served to confuse people for a long time. Proposals have been made to change the term, and progress has been made, but the EGC continues to hold it’s misnomer.
Electricity does not seek the path of least resistance to the earth. It seeks all available paths back to it’s source, in proportion to their resistance. The reason that a person gets shocked when touching an ungrounded conductor and the earth is because the neutral of the system is repeatedly connected to earth in a grounded electrical system. The earth becomes part of a return path to the transformer – it’s part of one route back to the source; the earth is not the destination for the electricity.
Driving a ground rod to ‘ground’ any electrical equipment does not provide the low-resistance path required to trip breakers. Driving a ground rod, or using a Ufer, or a metal water pipe is not a substitute for an EGC. A ground rod with 25 ohms to earth will allow almost five amps to escape the system into the earth when directly energized from a 120V source. Five amps will never trip a 15A or 20A breaker, and in the meantime everything bonded to this ground rod will be energized to 120V.
No. Double insulation decouples the case (if metal) from the safety ground. A metal case does not need to be grounded for safety purposes if double insulation is used, but it must be grounded if single insulation is used. DIY and kit-built equipment usually has single insulation; commercial equipment is often double-insulated. (By 'case' I also include any metal parts which can be touched, such as screw heads)
As the original mains lead had no ground, then the equipment either had a non-conducting case with no metal parts exposed or it was double-insulated. In the first case there is nothing to connect to the safety ground. In the second case a metal case could be grounded but this might introduce a ground loop, depending on how the signal grounds and safety grounds are currently connected, if at all.
My advice is to cut off the ground lead at both ends of the cable i.e. pretend it isn't there. One possible exception: if the signal ground is currently floating then connecting it to the safety ground at one and only one place might reduce noise, or it might not.
Video electronics frequently are connected to cable program source, a sattelite disc, or an outside antenna. All are lightning attractors. The ground rod attached to the safety ground of the house wiring dumps lightning to the earth, which is where it was headed before interrupted by your house and equipment. Audio equipment is not frequently connected to cable TV or antennas, and can best be allowed to not be connected to earth except at one point for safety purposes. Lawyers for each audio component manufacturer will argue that THEIR equipment must be safety grounded (if not double insulated). For complete safety against lawsuits, they are correct. For actually listening to music without hum, a single earth tree ground system works better, unless expensive DI units or isolation transformers are purchased to isolate each safety grounded component. My mixer has a terminal for the ground of the headshell of the turntable, which is necessary to shield the mag cartridge against hum. The mixer has 2 wire power, since it was a kit and not inspected by UL etc. It has a metal case containing line power, so it should actually be safety grounded. None of my Dynaco equipment power amps has third pins, as all was built before 1966. I have connected a 16 ga wire to the safety ground from the metal case of the mixer, same terminal as the phono shell ground. This makes what I think is the ideal tree grounding system, except for the needs of lawyers. Dynaco is bankrupt, so they don't have a lawyer.
We run on 240vish to everything in a standard private property. That step down from 55kv(I think) at the local substation. The neutral is then referenced to ground I believe.
This why observing live and neutral is important. If you've got the two confused the fuse will blow on the neutral side and still have a live ac voltage flowing.
some people will have up to 3 phase which are 120 degrees out of phase but this is not really of importance.
In a double insulated product its designed in such way that no fault condition could cause the case to become live, but i think we've already established that.
YouTube - Ground Loops
I think this a good example.
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