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Old 31st August 2003, 07:56 PM   #1
sobazz is offline sobazz  Denmark
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Default Alternative safety ground

Well, a month ago I finished some low wattage P3A mono blocks. I plan to use them in a building, where I have no access to a safety ground.

You can find some pictures here. The space is very tight and I certainly don't like the idea of using the amps without the safety ground.

Could I construct an alternative safety ground by connecting the earth pin from the amp inlets to some kind of relay that connects to earth (not the electrical term "earth")? If yes, how?

I hope you understand me... :-)


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Old 31st August 2003, 08:37 PM   #2
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Hello -

You don't need to use the safety ground if you pay attention to certain details. Please remember that all Japanese receivers use only a 2 wire AC mains cord, and there is no problem. The technique to use is called "double insulation".

This sounds like you need to enclose everything in a second plastic enclosure, but this is not true. Instead, everything from the AC mains up to the transformer primary must have a redundant back-up system.

In the case of insulation, the standard is 1500 V, so things must be instead insulated to 3000 V. This is typically done by adding a second layer of insulation ("double insulated"). So for instance the wires that go from the IEC power inlet to the transformer should be sheathed in a second PVC sleeve. That way if there is a transient on the AC mains that could penetrate the first layer of insulation, then the second layer of insulation should contain things.

There are some other things to watch for as well. All connections on the primary side of the transformer need a redundant back up. If you are using "Fast-On" mechanical connectors, they need to have an insulating sleeve. This way, if they come loose and flop against the chassis, they will not apply AC mains voltage to the chassis. If you use soldered joints, you must also wrap the wire before soldering. That way if the solder fails, the mechanical joint will not let the wire flop against the chassis.

Finally, there needs to be sufficient insulation between the primary winding of the transformer and the core. The standard is one layer of insulation that is good to 1500 V. You can either use two layers or a single, thicker layer rated at 3000 V. In the case of the home constructer where the transformer has already been made, simply mount the transformer with electrical isolation mounts. You have probably already done this, as the normal way to mount a toroid is with rubber washers.

The bottom line is that if you build your amps with reasonable care, there is no need for an AC safety ground.

Hope this helps,
Charles Hansen
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Old 3rd September 2003, 07:32 PM   #3
PRR is offline PRR  United States
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> a building, where I have no access to a safety ground.

> Could I construct an alternative safety ground by connecting the earth pin from the amp inlets to some kind of relay that connects to earth (not the electrical term "earth")?

No.

Not under US electrical code, and probably not where you are.

Connecting to dirt or water pipes can be much more dangerous than no safety ground at all.

The only legal and safe ground is AT the fuse-box. If that ground was not wired into your rooms, do not try to get clever.

If you do not have ANY approved grounding wires in your apartment, I would worry more about your stove/hotplate and other basic electrical appliances than about something you lovingly wired with your own hands (looks like beautiful work).

As Charles says, it would be best to insulate everything inside from the case. However with Audio, our jacks are at circuit-ground potential (unlike a Power Drill where the metal parts can have plastic insulators between the motor and the metal you touch).

If you are worried about electric shock, get a "GFI", "GFIC", "RCB", or "Shock Proof". The exact name (and specs) vary by country, but it is a box that will disconnect its electrical outlet if it does not see *exactly* the same current on both wires. These boxes are often required on outdoor outlets, construction sites, bathrooms, etc. There are units to go inside the fusebox, units that go in the wall, and also units that look like a heavy electrical extension cord with a large box on the end.

I would just leave it alone and enjoy.
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Old 3rd September 2003, 08:13 PM   #4
AuroraB is offline AuroraB  Norway
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In Scandinavia, and Norway- where I live,- the regulations say that there should be an "potential equalization" connection between real ground, -either by ground wires,spikes etc, and your water line, to avoid any potential between your tap or sink, and the ground connection used for your house. The power company's ground shall be referred to real ground anyway. Most power companies distributes a power ground, but usually only via buried cables, not by open air lines, and it is a well known fact that the powerco's ground can be rather lousy, as it is solely dependant on the local earth resistance, which can vary a lot!! Very long cable runs also degrades the performance of a safety ground..

In installations where proper safety ground is mandatory, large copper plates are buried either in the sea or in constant wet soil , or copper poles are sulphur welded into solid rock.

I think you can safely use your water pipe as safety ground, provided it is a metal pipe. Otherwise you can buy purpose made copper rod, to hammer into the ground ( "jordspyd" ), but you must reach wet soil, in order to have "something better than good faith".....

I wonder if PRRs comment is valid, because AFAIK, even by US regulations, ground and neutral shall be connected at your local transformer station...that's at least what our customers order when we rig diesel generators, converters or transformer for our US customers...
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Old 3rd September 2003, 08:21 PM   #5
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i have a random ignorant question (dammit jim, i'm an architect, not an electrician) :

is there a way to measure whether or not you've got a good ground connection? like if i stuck a rod in the back yard, how would i know when/if i had reached 'ground' and how good that connection was?

thanks

/andrew - with his head in the clouds
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Old 3rd September 2003, 08:25 PM   #6
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Problem with using a copper water pipe is that it can be uncertain whether there exists continuity (very low impendence) on the pipe all the way to earth. Its not to uncommon these days that somewhere down the road some PVC or PEX plumbing got thrown into the mix and that water pipe isnít as earthy as you might want it to be.

And any current sunk to it can cause electrolysis and early failure of hot water heaters and other appliances.

And current on the ground can cause an electrocution hazard to if the pipe does not have low impendence to ground.

All in all, IMHO, err to the side of caution and watch out for this.

Quote:
is there a way to measure whether or not you've got a good ground connection? like if i stuck a rod in the back yard, how would i know when/if i had reached 'ground' and how good that connection was?
Long time ago I used to run generators for outdoor music shows (lucky I'm Still alive). I was a fan of using more than one GND rod and if the ground (the dirt the copper was pounded into) was dry I would always pore a pitcher of beer on the ground around the GND rod. I would get the beer from the drain spillage at the concession stands, a handy electrolyte.

I think the tool for making proper ground measurements is known as a "Megger" or Mega-ohm meter. These things typically use a hand-cranked dynamo to generate enough potential between surfaces to measure very high resistances... or something to that effect. Like I said, lucky I'm still alive.
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Old 3rd September 2003, 08:31 PM   #7
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Quote:
Originally posted by faustian bargin
i have a random ignorant question (dammit jim, i'm an architect, not an electrician) :

is there a way to measure whether or not you've got a good ground connection? like if i stuck a rod in the back yard, how would i know when/if i had reached 'ground' and how good that connection was?
You're at ground when you reach ground.

But why bother? I don't see that a literal earth ground has any relevance to audio equipment.

se
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Old 3rd September 2003, 10:13 PM   #8
AuroraB is offline AuroraB  Norway
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Most equipment will be just fine without the ground connection....and most of our household items don't need them either, as they are mostly built with non conducting materials anyway..thus for most of Europe, TVs, videos, DVDs etc. does not have ground wire,- only the tiny 0.5-0.75 sq.mm. twowire power cord...

In many countries, Norway included, ground was not mandatory, and thus not installed in normal living rooms, bedrooms etc.
Ground was only used with "technical" household items, like electric stoves, water heaters, washing machines etc..as they are/were mostly made out of metal....
It is just two or three years since our regulations was changed to include ground everywhere, but only for new installations and reworks....

Under normal conditions ground does not mean anything, except where you need it for reference for e.g. interference filters, like in PCs. Safety ground of course, is just a safety precaution, but most commercial equipment is built roughly according to the "double insulated" standard, just as described.....
Any DIYers in doubt about their own skills in building the PSU part, should seriosly get some "recipe" or "how to do it" booklet.....
BTW- in Norway the mains connection of a PSU should really be made by a certified electrician, if we play it by strict regulations..

YES- mandatory safety ground systems, like in areas used for handling of explosives, should be checked out once a year, (by us at least.) This is done by precision low ohm meters, and reference ground prongs inserted for the measurement purpose only. "Meggers" are high voltage ( often 1000V or more), high resistance instruments, used for checking insulation quality or electrical ground leaks.
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Old 3rd September 2003, 10:23 PM   #9
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Thanks for the Megger clarification.

I suppose (facetiously) that wearing one of these doesnít help the sound at all:

http://www.thinkgeek.com/gadgets/watches/62f7/
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Old 4th September 2003, 01:40 AM   #10
EC8010 is offline EC8010  United Kingdom
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The original Megger was a substantial hand-cranked job that produced 500V. Twiddly electronic versions produce the same (or more) voltage in a smaller lighter case, but whistle and need batteries.

Da5id4Vz, what's with the zone chart?
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