No grounding on electrical installation... sugestions!

[riscado]

On a garage where I usually fix/build/test amps/rehearse I currently have no grounding on the electrical installation, which is common practice where I live on garage electrical installations among contractors, don't ask me why (the building flats have ground but not the garage).

Since this is a potentially dangerous situation and given the fact that most tube amps used under these conditions become really noisy unless we are touching the guitar and thus serving as ground, I'd like to try and remedy, unfortunately the garage isn't mine so I can't go one breaking tiles and installing a proper rod to ground, is there any other suggestion that could wor out given the conditions? thanks

[nickt]

Have you got a water pipe handy? (guess: no!) Best I can come up with.

[riscado]

sorry nickt, didn't quite get that one...

[nickt]

sorry nickt, didn't quite get that one...

Ok if you have a metal water pipe it's already in the ground. Hence you attach your earth wire/cable to the pipe. It's pretty standard practice in Australia (well it was last time I looked).

Obviously it won't work if you have plastic water pipes like a lot of modern buildings. I'd suggest getting a qualified electrician to look at your problem what ever you do - you only live once so it may as well be as long as possible!

[VacuumVoodoo]

You can connect protective earth ("ground") to the garaghe water pipe if there is one. It MUST be connected through a ground fault circuit breaker.

[riscado]

thanks for the help guys... I now some of the pipes I have are pvc, but maybe the smaller ones are metal...

Could you explain the "ground fault circuit breaker", I didn't quite get that either!

Thanks again

[VacuumVoodoo]

It's a small box connected between mains feed line and your mains outlet. It measures current in the earth/ground wire and if it exceeds regulatory safety limit cuts out the power to outlet(s). It's a life saver.

[mhuss]

I'd suggest getting an electrical junction box and a GFI outlet (they sell mains sockets with GFIs built in).

Connect a non-grounded plug and wire to it, to plug into the unsafe mains outlet.

Also connect a ground wire to it, and run that to a good earth ground. If there are no suitable grounded water pipes in the garage, you can get a copper coated grounding rod (or even a length of copper pipe) -- these are normally 2/3 meter long or so -- and drive that into the earth just leaving the top exposed. Connect the ground wire to that rod.

Except (potentially) for the rod in the ground, you'll be doing nothing to the rental garage to upset the owner or make it in any way less safe.

--mark

[Ears]

I currently have no grounding on the electrical installation, which is common practice where I live on garage electrical installations among contractors, don't ask me why (the building flats have ground but not the garage).

Forgive my curiousity, but what part of the world are you in that allows this and what is your domestic mains voltage value? Am I correct in thinking that the US at 110 - 120V did not in the past ground domestic plugs but now does so (or is at least moving toward the universal use of safe practise)? Do the US regulations vary State by State?

[jjman]

One of the purposes of the ground terminal, in the USA at least, is to provide an alternate path for the current to return if a hot lead touches a “chassis” thus tripping the breaker at the panel. Without the ground terminal, the chassis could be hot here.

In the USA, the neutral buss is often connected to the ground buss in the breaker box. I wonder if it would be a good idea to connect the neutral to the ground terminal/buss in the garage? This way a hot wire touching a chassis will trip the breaker on a 3 prong amp.

[nickt]

In the USA, the neutral buss is often connected to the ground buss in the breaker box. I wonder if it would be a good idea to connect the neutral to the ground terminal/buss in the garage? This way a hot wire touching a chassis will trip the breaker on a 3 prong amp.

Not sure about the US because there are/were a whole lot of issues around polarity because power was "floating". US amps used to have a polarity switch which grounded one or other of the mains leads direct to the chassis!!! You used to always be hearing about guitarists frying because the PA and their guitar were different potentials.

These days the neutral wire is always at ground potential HOWEVER there may be an imbalance that causes it to be a bit above ground. What happens is electricity is usually supplied in 3 phases 120 degrees apart if you add them up you get zero hence the return wire can be common and smaller (which is why you usually see four wires where you have above ground power - city not cross country). If one of the 3 phases is loaded less than the others then neutral will have some voltage on it.

The neutral is tied to ground all over the place (distribution trannies, meter boxes, etc) and you have a separate local ground (say to a water pipe) in your house to ensure chassis etc are at properground potential.

Not sure if this helps (or if it's correct for the US!) but its the way I was taught 30 years ago for Oz.

[skyboltone]

You can connect protective earth ("ground") to the garaghe water pipe if there is one. It MUST be connected through a ground fault circuit breaker.

Alexander, you are almost always correct so I tread lightly here. But; as a retired electrician and electrical inspector with extensive experience writing safety procedures, may I ask why and how you would install GFCI protection on a system where the neutral (presuming it's in the USA and has a grounded circuit conductor) may or may not be bonded to the system ground?

For those who may be puzzled, Alex is referring to a device that measures the current flow entering a circuit via the "hot" wire and compares it to the current that returns via the "neutral" or grounded conductor. If the difference between the two currents is greater than 10ma for personnel ground fault protection or 30ma for equipment ground fault protection the device will trip the circuit. In most of Europe, domestic power systems are not referenced to ground at all. You could connect one of the "hot" wires directly to a ground rod and nothing will happen. There are advantages to that. It's tough to get a shock unless you get across both wires. Very unlikely without real effort. In the US where systems are required by code to be referenced to ground at some point, the imbalance detected by the GFCI means current is getting back to the "source" via some other path than the neutral. Presumably you.

So we need more information:
1) How does the power get to the garage? Overhead? Via an underground pipe? Via a piece of romex hidden in a wall (attached garage)?

2) Outbuildings and garages where power is distributed from a building service have been REQUIRED to have a ground wire from the building service that accompanies the hot and neutral for a minimum of 60 years. Probably more like 100. Thus, if no third wire (117VAC) or fourth wire (117/230) is with the feed wires then what we have here is an illegal installation. Not to mention unsafe. In fact, if more than one circuit feeds the building (117VAC) then a ground rod MUST be driven and the ground conductor from the main service must be connected at the outbuilding.

3) Prior to about 1955 it was common to use the ground buss and the neutral buss interchangeably at the main service ONLY!!!!Old habits die hard and the practice continued in some areas for many more years. It's fine. Safe. It is not however safe to use the neutral as a ground wire (on anything other than a three wire range service) once you've gotten past the main service. If you do, you run the risk of having ground loops where current will travel on grounded surfaces at any point from the second, (illegal) bond back to the main service. It is seriously not OK to just use the white for a ground in the garage. OK?

4) So, what to do? Once again I need more information. What size and how many wires are feeding the power to the garage and how do they get there? The solution is to get an additional wire (sized like the feed conductors) from the garage back to the main house and tie in there to the grounding conductor. By law green or bare copper. As others have mentioned a continuous metallic pipeing system (other than gas) that is bonded at the building service can make an effective ground in your case but not a legal one. The only place the code allows that is in the case of a well service. But I would certainly look the other way because it's safe and effective; provided that you check continuity between the point where you make your connection to the water pipe back to the green or bare copper wire at the building service. In the case that I've just described you'll be safe and you won't get any circulating currents. I remind you however do NOT connect the white wire to that new found ground connection. You may end up killing a plumber some day. Not always a bad thing but inconvinient at the least.........just kidding!!! Lighten up for heaven's sake!

Let me know which parts of the preceeding diatribe are incomprehensible.

Dan H

Second edit. It was very very common prior to 1960 or so in the US to use metal boxes and run a separate copper wire, snakeing throughout the house, all the way from the main service ground point and attach it at each metalic box. Then, the receptacle strap, screwed with a metal screw to the steel box would ground that little screw that holds the plate on. are you sure you don't have that situation? If you do this is how you tell. Take the plate off, get your volt meter out, set it for AC voltage and test between the shorter of the two virtical slots in the plug and the strap holding the outlet to the box. If you get 117VAC then you're in business. It's a grounded system. Just go to the hardware store and get some grounding pigtails, (pieces of green wire with a 10/32 green colored screw attached). There will be a threaded hole in the back of the box that you screw the pigtail to, then attach that pigtail to the green screw on a new "U" ground (three prong) outlet. Finished business.

[skyboltone]

Riscado, you're in Argentina right? Maybe all this stuff really doesn't apply.

Here's another very safe and quick fix. How many circuits do you use? 15 or 20 amp? What? Anyway, you can set up what's called a separately derived system. Then it doesn't matter if you ground it or not from a safety standpoint. Remember those crazy Europeans and their ungrounded systems?

Anyway, install an isolation transformer. 117 in 117 out. On which ever wire coming out that you decide to call the white or neutral, attach that to the green or grounded conductor at the same time, but only on the downstream side. You've isolated your garage system completely from the house system. You won't get shocked from water pipes, or any other grounded metal surface. Maybe simplest of all.

I'm going to set up something similar. My workshop is in an ocean freight container in a big parking lot. I don't have an electrical service. I have to run a generator. Anyway, the generator is producing 117VAC at 30 amps but there is 54 volts from neutral to ground!!!!! I put a 300ohm/10watt resistor between neutral and ground and it sucked it down to about a volt but the resistor gets hot! The generator says the neutral is bonded at the set but clearly it is not. And I need 220 to run my compressor anyway. So I'm going to a surplus place tomorrow to find a 3KVA 2:1 transformer of some sort and make myself a separately derived system. Then I don't give a hoot if it's grounded or not.

Dan

[VacuumVoodoo]

You can connect protective earth ("ground") to the garaghe water pipe if there is one. It MUST be connected through a ground fault circuit breaker.

Alexander, you are almost always correct so I tread lightly here. But; as a retired electrician and electrical inspector with extensive experience writing safety procedures, may I ask why and how you would install GFCI protection on a system where the neutral (presuming it's in the USA and has a grounded circuit conductor) may or may not be bonded to the system ground?

For those who may be puzzled, Alex is referring to a device that measures the current flow entering a circuit via the "hot" wire and compares it to the current that returns via the "neutral" or grounded conductor. If the difference between the two currents is greater than 10ma for personnel ground fault protection or 30ma for equipment ground fault protection the device will trip the circuit. In most of Europe, domestic power systems are not referenced to ground at all.

Yes, that's how it works in EU. I don't know how this is done in other areas. I live in an apartment building and there's a GFI in every apartment as standard in each individual distributor box.

[riscado]

Hi thanks for all the replies, still reading them through and digesting ideas...

By the way I'm in portugal - europe, and the power suply is 230V - 50hz (although I get readings closer to 238V)