| Subject: Grounding question |
Author:
JD
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Date Posted: 7:41pm
The Question:
"Grounding Question"
Regarding a modern AC household appliance (i.e., a stereo receiver) that has a two-pronged electrical plug: Is that appliance typically grounded -- assuming it's plugged into an up-to-code receptacle?
Note: The unit in question has a "Signal GND" terminal, but I don't see how it can be grounded without a three-pronged plug.
Answer:
Not really...well sort of"
In response to message #0
LAST EDITED ON Feb-20-04 AT 06:40 PM (PST)
Go outside and look at your pole. If you have a standard service you'll probably see three wires coming into your house.
The voltage of these wires is:
110v
110v
and neutral
In your panel these three wires come in and connect to different areas.
One 110 to power bus A (a physical bar on the right)
One 110 to power bus B ( a physical bar on the left)
The neutral to a neutral grounding bar.
Bus bar A and B are your power. The create a series of lugs your breakers connect to. Stick a breaker into the lug hook a wire up and turn the breaker on and you've got 110 power in the wire.
The neutral or ground is just a bar with a lot of connections on it. no breakers, but three four or maybe five differen't kinds wires connect to it.
The neutral to the pole. (Big lug)
Circuit neutrals (white wires, small lugs)
in some cases
Case ground connected to a buried electrode (Cooper wire, medim lug)
UF Circuit grounds (copper wires, small lugs)
Sub Panel neutrals (Black wire tagged white medium lug)
Here's the deal in order to get power to do something it has to go somewhere.
In this case the hot wire 110 has to go to neutral.
Basically a 110 circuit is just two wires the black power and the white neutral. The black takes the power from the breaker to the appliance the white returns it to the neutral bar.
Neutral acts as a ground in the power circuit.
Look at your outlet. The black power wire connects to the small slot white neutral wire to the longer one.
What about that third hole?
Well the third is a case ground. Remember the old days when tools were made of metal
Well used to be that there was a third wire that connected the metal case of the appliance to that third prong on the plug. That third hole in turn was then connected to the case or box around your outlet so when the appliance was plugged in it's case was grounded to the oultet case. Not a power circuit ground but a case ground.
Systems used to be all conduit or flex, so the wires where protected by a metal sheath, and all outlet boxes interconnected by the metal tubes. Ground to one box your grounded to the whole system.
The idea with the third wire is if something went wrong in the appliance, say a wire got loose and shorted out to the metal cover it would travel through the case ground to the system ground and blow the circuit. Simply put it's better that a short blow the breaker then energise the case and electricute you.
In UF or Romex systems there are no tubes so theres a third plain copper wire in the system that links all the boxes and all the outlet grounds back to the neutral bus bar.
So is your stereo grounded?
Well the power circuit certainly is or it wouldn't work. One side of the cord goes to power, one to neutral, but that's not grounded in the classic sense.
Is it's case grounded?
Probably not: with the onset of circuit boards most sytems went low voltage, so they no longer need a case ground.
The power goes in the back immediately to a transformer that kicks it down to 24volts. Since the whole thing then runs on low voltage there's no danger of a short killing the user. The 24v system also has internal fusing to kill it in case of a short (fire protection) so there is no need for a case ground. Stereo, Tv's, Vcr's, no case grounds in this case
So is your Stereo grounded in the classic sense I.E. case grounded?
No.
It is grounded in an electrical circuit sense, but then again so is every electrical appliance known to man. That friggin power has to go somewhere in order to work
Tight lines, Jim
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