Grounding appliances in a 2-prong apartment?

January 5, 2006 8:35 PM

Grounding my old Marantz stereo amp in a two-prong outlet? (We're talking American 110v.)

Right. So. I've moved into my new, old apartment. How old is it? It's so old that I was greeted with warnings of lead-based paint. Also troubling are the rooms' uniform, two-prong outlets.

I've got an old Marantz stereo amp/receiver through which I run my digital audio (model escapes me; probably has a "3000" in it? Not extremely valuable, but still.). It features a grounding post, to which I've formerly attached a regular three-prong extension cord (with the hot and common wires taped up). Plugged into a three-prong outlet, this connects the stereo's ground to the building's own wiring, and stops the speaker buzz.

Obviously, that solution doesn't work now. I've got a few of the common type of adaptor seen below, which have a little a little metal ground tab and a sternly embossed admonition to connect this to the building's ground. More explicit instructions, I assume, were excised for reasons of space. Such considerations mean nothing here, AskMeFi, so please go to it!

posted by electric_counterpoint to technology (8 comments total)

Ooh, forgot to mention this amusing/harmful anecdote: since I've been using the stereo ungrounded, I've found that hitting the power button does nothing to actually turn off the unit. Now I've got to release the power switch as well as shorting it by touching the metal knobs. Part of my thinks "yikes"; part of me thinks "sweet!" Whatever this is doing to my poor $50 amp, I'd like to prevent it doing the same to my $250 connected iPod.

Oh, also, I've got some other electronics (guitar amp, pedal board, etc.) that I imagine would benefit from a good ground, so bonus points if your solution is fungible.
posted by electric_counterpoint at 8:39 PM on January 5, 2006

Well, the simple answer is this: you need to get one strand of wire from the breaker box to each outlet in the house. Those common grounds will all be hooked up to a grounding rod, or maybe a cold water pipe, outside your house. ;-P Install three prong outlets, hooking the new ground wire up to the ground screw (and the hot and neutral lines where they used to be).

That's a royal pain in the ass. What we did in our 50 year old house was hire an electrician to replace the ancient breaker panel, and while he was at it he installed two, brand new and properly grounded outlets for our computers. I didn't envy him the insulation he inhaled while he was up in our attic.

Other than that, you could see if you can get a ground wire from the outlet you use the amp at to a cold water pipe, IF your pipes are all metal (which they probably are, in a house that old). If a cold water pipe happens to be nearby (as is the case for our disposal, and the one grounded outlet we wanted to install downstairs), that is not so bad. Fishing wires can be a *real* pain in the ass, but it ain't rocket science. However, this DIY solution may very well violate electrical codes. I dunno on that -- my electrician father told me it was OK from a safety point of view, but he does not do the code thing (he works his electrical magic in cranes).
posted by teece at 9:04 PM on January 5, 2006

The idea with the adapter is that you remove the screw from the outlet's faceplate, plug-in the adapter, and then re-fasten the faceplate so that the screw has contact with the adapter. That isn't always effective as the outlet box isn't necessarily grounded.

Have you asked your landlord about upgrading the outlets? Depending on when and how your building was built, it could be a relatively simple fix. Alternately, you can run a lead from the Marantz's ground screw to a water or radiator pipe.
posted by nathan_teske at 9:10 PM on January 5, 2006

That ground screw is actually to "ground" a turntable to the amp, not ground the amp to, er, ground. Leave it disconnected.
posted by zsazsa at 9:18 PM on January 5, 2006

Hm. Well, since it seems like your system works better grounded, go ahead and do it.
posted by zsazsa at 9:27 PM on January 5, 2006

That little tab with the hole in it has a hole for a reason. there's a good chance that even though your outlets don't have the third prong, because of the nature of ancient wiring methods (metal armored flexible conduit or rigid black iron) all of your outlets actually are grounded. That tab should be long enough to line up with the central screw that holds the faceplate on to the outlet. My suggestion, stop by your local hardware store / Mega-Home-Mart and pickup an outlet tester. usually $10 or less and has 3 or so LEDs/neon lamps that will tell you the status of your outlets (ground good, polarity reversed or not, etc...). remove the screw from the outlet plate but don't remove the the plate itself. plug in your adapter doohicky and replace the screw through the hole in the little metal tab. plug your newly acquired tester into the adapter and look at the lights to see if you have a good ground.
Of course there are ways of testing for ground outside of this but i'll assume you don't have a multimeter or continuity tester handy... :)
best of luck.
posted by skatz at 11:51 PM on January 5, 2006

zsazsa is correct, the only thing that should get connected to that grounding tab is the turntable ground.

Does the amp have a two or three prong cord? Most older amps were designed with two prong cords and should be fine plugged into a two prong outlet. Even with three prong cords one trick to stop buzzing from ground loops is to use a cheater plug like you show above to specifically not ground the amp, but rather to let its ground float. Actual earth grounding is for safety, not sound. Grounding between components can be an issue and hence your ground screw for grounding the turntable. Why the power button won't work is a mystery to me, but it could be a sign that the wiring is reversed (hot and neutral) and that your amp is sensitive to this difference. The tester skatz mentioned should tell you, or a multimeter if you know what you are doing. If the wiring is reversed get the landlord in pronto - he may or may not be obligated to install three pronged grounded outlets, but reversed outlets are definitely a code violation and a safety hazard.
posted by caddis at 7:18 AM on January 6, 2006

Grounding is beneficial only if you have a short in the appliance and could get a shock. Lack of grounding doesn't harm the sound, except for the wire from the turntable to the amplifier, which needs to be either connected or disconnected according to which way eliminates loud hum.

However, plug orientation makes a small but cumulatively audible difference in background hum. Based on a tip in one of the audio magazines, I spent about an hour sitting on the floor behind my system with everything except the amp unplugged and disconnected. I began with the amp, turning the volume all the way up, and reversing the plug to find which way was quieter. Then I plugged in the other items (CD player, turntable, cassette, reel-to-reel, DBX processor). Yes, reel-to-reel. That's how old I am. ;-)
posted by KRS at 2:02 PM on January 6, 2006