Ground (heading way off topic)
I am no expert for other parts of the world (and not that much of one here...) but in the US our 120v wall outlets have 3 terminals, hot, neutral and ground. Neutral is tied to ground at the fuse box/circuit breaker panel in the house. Ground is typically tied to the chassis of the component internally. The shield for cable TV is also tied to ground. So, if you have an A/V system with the cable TV hooked up and/or a component with a three prong electrical cord, the shields of your interconnect cables and probably the (-) terminals of your amps outputs are all at ground/neutral. I checked a Parasound HCA-1500A amp I had lying around last night and it's (-) speaker terminals were at ground. Below is a warning from my Sunfire subs manual. So, using the amp in stereo would be no problem. But, if I were to bridge the amp (BTL) which ignores the (-) terminals for both channels and uses one of the (+) terminals as the speakers (-), and try to use the speaker level inputs of the sub, I would burn up the amp.
Note: this is also the source of 60Hz buzzing in a system, the grounds and neutrals are not all equal, there is often a resistance/voltage difference between them. You can check for AC voltage between the chassis of different pieces of equipment. Especially equipment without polarized plugs. My old 60's EICO tube amp's manual had a troubleshooting section that included looking for a spark while plugging in the preamp leads and reversing one or the other AC plugs orientation!
--David
I am no expert for other parts of the world (and not that much of one here...) but in the US our 120v wall outlets have 3 terminals, hot, neutral and ground. Neutral is tied to ground at the fuse box/circuit breaker panel in the house. Ground is typically tied to the chassis of the component internally. The shield for cable TV is also tied to ground. So, if you have an A/V system with the cable TV hooked up and/or a component with a three prong electrical cord, the shields of your interconnect cables and probably the (-) terminals of your amps outputs are all at ground/neutral. I checked a Parasound HCA-1500A amp I had lying around last night and it's (-) speaker terminals were at ground. Below is a warning from my Sunfire subs manual. So, using the amp in stereo would be no problem. But, if I were to bridge the amp (BTL) which ignores the (-) terminals for both channels and uses one of the (+) terminals as the speakers (-), and try to use the speaker level inputs of the sub, I would burn up the amp.
Note: this is also the source of 60Hz buzzing in a system, the grounds and neutrals are not all equal, there is often a resistance/voltage difference between them. You can check for AC voltage between the chassis of different pieces of equipment. Especially equipment without polarized plugs. My old 60's EICO tube amp's manual had a troubleshooting section that included looking for a spark while plugging in the preamp leads and reversing one or the other AC plugs orientation!
--David
Attachments
kelticwizard said:
I may be wrong, but I think even hospital grade isolation transformers are required by code to connect the ground of the "isolated" outlet back to the ground of the wall outlet. "Safety Ground?"
Isolated ground outlets simply break the ground connection with the wiring conduit, they are still grounded back at the main ground for the wiring system.
--David (way off topic, poor Rob just wanted some Bass!)
So its pretty much the same as the 3 wire UK.
But your making one fatal mis-assumption.
The majority of consumer goods do not have a 3 wire lead, they have two.
To do this they must meet stringent insulation standards.
In newer equipment there is no ground to tie to.
For hi-fi systems the amplifier is tied to ground for minimum noise.
All other components use two mains connections and are referenced
to ground via the amplifier.
I wouldn't be surprised that RA's system has no ground connection at all.
Regarding ND's rather graphic warning - entirely irrelevant
for consumer goods - only hi-fi kit, and still irrelevant for
reasons that are too tedious to explain here.
🙂 (agree ND WOT, totally useless to RA)
But your making one fatal mis-assumption.
The majority of consumer goods do not have a 3 wire lead, they have two.
To do this they must meet stringent insulation standards.
In newer equipment there is no ground to tie to.
For hi-fi systems the amplifier is tied to ground for minimum noise.
All other components use two mains connections and are referenced
to ground via the amplifier.
I wouldn't be surprised that RA's system has no ground connection at all.
Regarding ND's rather graphic warning - entirely irrelevant
for consumer goods - only hi-fi kit, and still irrelevant for
reasons that are too tedious to explain here.
🙂 (agree ND WOT, totally useless to RA)
If you have a two terminal in, three terminal out power transformer, is net-david saying that the ground of the output should be connected to the ground of the wall AC?
kelticwizard said:
No, I was talking about an AC isolation transformer, you plug it into the wall and then plug a standard AC operated device into it. I have looked and tried to see if the ground on the output is isolated also, but I think to meet code the ground has to be connected to an "earth" ground, not a ground similated by the transformer. I may be wrong.😕
Although, I do believe that some equipment that has a 3 pin AC connector and a 2 wire primary/3 wire secondary center tapped transformer do tie the AC ground to the circuit ground.
--David
First, RobAche feel free to ask more questions at any time, we are just meandering here. 🙂
Second, okay, but I think that code goes for an isolation transformer.
Let's take an amp.
Suppose I have a two terminal in, three terminal out step down transformer-say, output ±25 Volts. The output ground will have no connection to the ground from the wall, will it? Therefore, the ground of the circuit will be isolated?
Second, okay, but I think that code goes for an isolation transformer.
Let's take an amp.
Suppose I have a two terminal in, three terminal out step down transformer-say, output ±25 Volts. The output ground will have no connection to the ground from the wall, will it? Therefore, the ground of the circuit will be isolated?
KC,
If an amplifier has a steel case and is not constructed to the
relevant isulation standards required for two wire mains use
then it must be grounded with a third wire to the mains plug,
internally the secondary centre tap will connected to this
ground.
I'll repeat : in hi-fi systems (not consumer boxes) nearly always
the amplifier is grounded. All the other components, CD player,
cassette deck etc are constructed to the insulation standard that
allows two wire mains connection.
When connected to the amplifier they are referenced to ground
by the amplifier via the negative lead of the connection.
This approach prevents the formation of 'ground loops'.
An amplifier does not have to be grounded.
If the ground is omitted relevant insulation practices should be used in its construction.
Usually they are not so most amplifiers are grounded.
Most consumer boxes are double insulated and not connected to ground, my TV for example.
If you know what you are doing adding a single ground connection at the correct point to a
connected system can reduce noise.
🙂
If an amplifier has a steel case and is not constructed to the
relevant isulation standards required for two wire mains use
then it must be grounded with a third wire to the mains plug,
internally the secondary centre tap will connected to this
ground.
I'll repeat : in hi-fi systems (not consumer boxes) nearly always
the amplifier is grounded. All the other components, CD player,
cassette deck etc are constructed to the insulation standard that
allows two wire mains connection.
When connected to the amplifier they are referenced to ground
by the amplifier via the negative lead of the connection.
This approach prevents the formation of 'ground loops'.
An amplifier does not have to be grounded.
If the ground is omitted relevant insulation practices should be used in its construction.
Usually they are not so most amplifiers are grounded.
Most consumer boxes are double insulated and not connected to ground, my TV for example.
If you know what you are doing adding a single ground connection at the correct point to a
connected system can reduce noise.
🙂
- Status
- Not open for further replies.