Arcam AVR300 - earthed or not earthed?

Discussion in 'AV Receivers & Amplifiers' started by Chris Saunders, Mar 29, 2006.

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  1. Chris Saunders

    Chris Saunders
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    Dear everybody,

    I'm a new Arcam AVR 300 owner, and this is my first visit here. To think there's an Arcam enthusiasts' website, brilliant!

    Anyway, down to business. After living more or less contentedly with a Denon stereo amplifier (PMA S10) for 7-8 years, I found a second-hand Arcam AVR 300 on the market. I looked up a few reviews on the web, and the glowing review in International Audio Review (http://www.iar-80.com/page130.html) did it - I bought the receiver unlistened to.

    There are lots of things I don't understand, but I think I'll try and deal with them one by one (in separate threads).

    I live in Norway, and houses here have earthed sockets in kitchens and bathrooms, but not generally anywhere else. My living room's got a solitary earthed socket, but there are none in any of the bedrooms for instance.

    The problem is that the grounded socket in the living room is miles away from where the kit is - four metres along a short wall, and another six metres along a long wall.

    Is earthing absolutely necessary (for kit safety reasons) and if it is, is it a good idea to lay an extension of about ten metres or so? Or would it be best to get an electrician to convert a convenient non-earthed socket to an earthed one, if that's possible?

    Glad for any advice. Question no 2 coming up in a bit.

    Chris Saunders
     
  2. tvh3ad

    tvh3ad
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    Apologies in advance for me being stateside if your teminology or hardware is slightly different, but the electrical principles are the same...

    The extra "earth" in AC wiring is a safety ground. AC current always requires a ground path and this is designed into every two-wire circuit: one wire contains the current, the other wire provides a ground path. If you were to disassemble your electrical panel, you would see that the circuit breakers (or fuses or whatever's in there in Norway) are connected on one side to the "hot" lead which carries the current (usually black wire in the states) and to the grounding buss on the other side (usually white wire in the states) which leads to a grounding rod, a cold-water pipe, or other suitable earth device.

    The safety ground (usually bare copper or green wire here in the states) was introduced to provide a redundant ground path so that if a fault develops in the primary ground, there will still be a safe, low-resistance path for the current to return to earth. If the safety ground is not connected (or does not exist) *and* the regular ground also fails, the current will find the next most convenient path, which could be, um, you. :suicide: (Stateside, there is even a special type of outlet called a GFCI, or "ground fault circuit interruptor" which is now mandated by code for wet areas like kitchen counters and bathrooms. These outlets shut off the current if they detect that the ground path has faulted, meaning that it has diverted from the regular circuit/safety ground to some other path -- your child with wet hands and no shoes touching the toaster, for instance.)

    Scare tactics aside, it's really not any more dangerous to run the AVR300 without the safety ground than it is to use an ordinary lamp or any other device with a two-prong plug that does not include a safety ground. And hey, it's totally safe if you're only using the remote! ;) If you don't have a safety ground available on your circuit, note that there's even a switch on the back of the AVR300 labeled "ground lift" which is supposed to have the same effect as physically disconnecting the unit from the safety ground.

    All that said, a good safety ground (especially a dedicated ground but I'm not going to get into that in this post) provides one other important function: it can help reduce your system noise floor. All your AV gear should be grounded to the same potential or current hum may invade at one point or another where the ground potential provides the best path (the dreaded and misnamed "ground loop").

    I found that my AVR300 was particularly susceptible to current noise/RFI and I had to do quite a bit of troubleshooting to get things quieted down, but if all your gear is non-safety-grounded, you're probably going to be groovy.

    Hope this helps and doesn't confuse.
     
  3. Chris Saunders

    Chris Saunders
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    Thanks tvh3ad, it was absolutely to the point. Not confusing at all. I didn't know the second wire in a two-wire circuit led to ground - I always assumed it was a bit like breathing - one wire in and the other wire out - what happened before, after or in between was anybody's guess.

    That may explain the Norwegian system (which apparently is the same as the one in Albania - or was, Norway's having to catch up with the rest of the EU and only three-pin sockets are allowed in new homes). I spoke to an electrician just now, and he couldn't understand the necessity of grounding hifi kit, but if there's a ground already built in to the two-wire system, then an extra safety ground (third wire) is good but not absolutely necessary.

    I think I'll try and get hold of a long three-wire extension lead, anyway, and feed everything from that.

    Thanks again,
    Chris Saunders
     
  4. davehk

    davehk
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    The ground lift switch on the AVR300 disconnects the SIGNAL ground from the safety ground, in order to break hum loops (it's in the manual!). The safety ground is still connected. Disconnecting the safety ground on an appliance that is not Class II (double) insulated is a potentially lethal action. Advice to do this is ALWAYS wrong.

    The reason for grounding hi-fi kit is the same as with any other other piece of equipment that has only a single insulating barrier between the internal live conductors and exposed conducting parts (e.g. the metal case!). An electrician who does not understand this is not much of an electrician IMO.

    If a live to chassis fault develops and there is no safety ground, then the case of the unit can be directly connected to the live side of the supply. If the circuit feeding the unit is not protected by an RCD, then you have a potentially lethal situation. The ARCAM manual specifically warns against doing this.

    This is NOT AT ALL the same as having a lamp connected with no earth - any CE compliant lamp that has only a two core flex (cord) will not have exposed conducting parts that could become live in the event of a fault.

    Note that normal circuit breakers (non-RCD) used as Circuit Protective Devices are single pole and only have the live conductor passing through them - the neutral circuit conductor goes directly to the neutral busbar. RCDs have both conductors passing through them, as they have to be able to compare the flow and return current.
     
  5. tvh3ad

    tvh3ad
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    Except for the bit about the function of the ground lift switch -- which I see is in the manual as you say -- it appears that we are in agreement about the function of the safety ground. I wrote that the safety ground is a redundant path and that keeping it connected is the safe thing to do as it can save your life if a fault develops. You wrote exactly the same thing.

    FWIW, I had assumed that the end-user would connect the unit's safety ground to the neutral return. (There are "cheater" plugs sold in the states for this specific purpose.) The only way to completely kill off the safety would be to damage the mains cord.

    Perhaps I minimized the risk unfairly, but you have maximized it equally so.

    No need to get huffy.
     
  6. davehk

    davehk
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    No one's getting huffy - but the advice to "disconnect the earth wire from the plug" or otherwise remove the safety ground to fix problems such as hum loops etc.(I'm not suggesting that you were advocating this) is given in too many places, far too often by people who clearly don't know what they are talkkng about (again - this is not aimed at you, since you didn't suggest it).

    I would argue that it is not a redundant path - it is an essential path that has quite a different purpose to the neutral circuit conductor.

    IMO it is worth being pedantic about this - Dead is Dead - you don't get to go around again.
     
  7. tvh3ad

    tvh3ad
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    Very true! ;)
     

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