ZING! Bad ground

[jjstafford]

Chomegacontrol power source - I put my hand on the back and got a good shock, or at least a steady Ziiiing. Good grief, I wonder how long it's been without a ground.

It looks pay-back from my cave-man electrical system (ancient post-n-cable). It's an isolated circuit originally for the cistern pump near where the darkroom is now.

All the darkroom goes to the one circuit through a power strip. Doesn't appear to be too much of a load for the 20amp fuse. Never blew. Can I just add a ground? Maybe a wire to the main water line coming in?

Or is this another case where Johnnie (that's moi) is being stupid? Thought I'd better ask before they punch my frequent-fryer card at the emergency room again.

 

[titrisol]

IIRC the proper way to do it is to stick a cooper rod in you lawn.
However, a wire to the water line may work... if it is not PVC

A google search:
HOW TO GROUND AN UNGROUNDED RECEPTACLE:
http://www.electrician.com/articles/grndrec.htm

PROPER TECHNIQUES:
http://www.leminstruments.com/grounding_tutorial/html/start.shtml

DO-IT-ZYOURSELF.com

Grounding of Electrical Systems Differ with Older and Newer Homes
By: Barry Stone

Dear Barry,

As a handyman, I've noticed a makeshift type of electrical ground on many older homes – a steel pipe driven into the earth, with a copper wire running from to the pipe to the electric meter. On newer homes, I've never seen this and am wondering if this is an ok way to ground an electrical system. -- Chris


Dear Chris,

The grounding of electrical systems in older homes was originally done by connecting a heavy gauge copper ground wire, known as a bond wire, to the main water supply pipe. In those days, a main water line was comprised of galvanized steel, an excellent electrical conductor. And since this pipe extended a considerable distance below ground, it served as an adequate basis for grounding the entire electrical system. Problems occurred, however, as these old waterlines became rusted and finally needed replacement. Some of the plumbers who replaced these deteriorated lines were focused primarily on plumbing concerns, with lesser attention to the status of the electrical system. Thus, many of these water lines were replaced with PVC plastic pipe. And since plastic has no capacity for conducting electricity, grounding for those homes was effectively eliminated.

There were, however, some plumbers who realized the necessity of maintaining an electrical ground when installing a PVC water main. And since copper grounding rods were not standard equipment on a plumber's truck, the most handy substitute was a length of galvanized steel pipe, such as the ones you've noticed at older homes.

On newer homes, grounding is provided either by an eight foot length of half inch diameter copper rod, driven deep into the ground, or by connecting a bond wire to the steel bars which reinforce the concrete foundation of the building.

Some of the galvanized grounding pipes you've seen may be functionally adequate, but the lengths of some of these pipes may be insufficient. When you see the exposed pipe stub next to a home, there's no way to determine if it measures the required eight feet, or merely three feet? Furthermore, gradual rusting of the buried pipe diminishes its effectiveness as an electrical ground. For these reasons, replacement with an approved copper grounding rod is recommended wherever a ground pipe of this kind is found.

 

[Monophoto]

Be careful - - be very careful!

First, the prreferred form of grounding is a "metal underground water pipe in direct contact with the earth for 10 ft (3.05 m) or more (including any metal well casing effectively bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joings or sections or insulating pipe)" (Ref National Electrical Code, article 250, section C, paragraph a).

Driven rods ("made electrodes") are acceptable if the available water pipe does not meet the specifications stated in NEC 250C, paragraph a.

The description of the event sounds like there is a voltage difference between the case of the power supply and (probably) the floor you were standing on. But it's not clear to me (an electrical engineer) what was causing that voltage difference.

The electrical service to your home should be grounded at the panel. The (white wire) neutrals of the feeders should be attached to a neutral bus at that panel, and that neutral bus should be attached to the supply ground. The power supply should have a three-prong plug that goes into a three-prong receptacle with a separate ground wire back to the ground bus in the service panel..

The fact that the case of the power supply appears to elevated above ground potential suggests that something is wrong, either inside the power supply itself or in the house wiring. But the bottom line is that the situation is dangerous and whatever is wrong needs to be diagnosed and corrected.

 

[GeorgesGiralt]

Hi !
I advise you not to use the metal pipe (water) as a ground.
It may look as a good idea, until you've got an equipment leaking (which you seems to have) and try to get a shower.
My 2 cents that YOU will become the grounding conductor while wet in the shower...
If your darkroom is near your lawn or garden, dig a hole in the lawn and burry a washing machine stainless steel drum onto which you've bolted a high gauge ground wire. If you bury the drum in a wet part of the lawn, you'll get an inexpensive and very good ground conductor.
Last but not least place a highly sensitive ground fault interrupter at the mains panel, just before or after the fuse protecting your darkroom lines. (rated at 30 mA or less) this may save your life .....
Bear in mind that the device that gave you the shock will trip this device until repaired....
Do not play with your life. If unsure get to a licensed professional. What is the cost of a new wiring compared to the cost of your life ?

 

[Bob F.]

... and... replace your fuse with a suitable breaker - not sure what they are called in your part of the world, but "Earth Leakage Circuit Breaker" or "Residual Current Circuit Breaker" in the UK. This will trip as soon as it detects any leakage to earth; it won't wait until 30Amps or so has flowed through you for several seconds leaving you a twitching, but very dead, heap on the floor as a fuse will...

Bob.

 

[Calamity Jane]

On behalf of the electrical company, I suggest you run a single green wire (the heavier the better) back to your main electrical entrance panel to provide a proper ground to the electrical outlets in your darkroom. The green wire should terminate on the electrical box your power strip is plugged into and on the ground bar in the electrical panel. If you aren't comfortable working in the electrical panel, find a friend who is and who knows something about household wiring.

When you bond your darkroom to the electrical panel, it WILL be properly grounded. If you have any trouble after that, contact your electrical utility and THEY will fix it.

Using a GFI breaker wherever you are mixing electricity and water is a good idea and is actually required by the electrical code in most areas.

 

[Monophoto]

Bob's suggestion for a ground fault circuit interruptor on a darkroom circuit is an excellent idea. Today it is possible to purchase ground fault interruptors that install in a receptacle box, and that can also be arranged to protect any receptacles downstream of the point of installation.

I don't want to start a flame war, but this is a serious issue of personal safety. The prevailing electrical code in the US is the National Electrical Code, and in most US jurisdictions it has the force of law. While compliance with the NEC is not mandatory outside the US, it is viewed throughout the worlds as an authoritative respository of recommended practices with respect to electrical safety.

The passage I quoted above explicitly states that the preferred form of grounding is to an underground metal water pipe. The code is also explicit about the requirements for a "made" electrode in those instances in which there is no suitable water pipe, or when a supplemental electrode is desired - it specifies the minimum length and diameter of driven ground rods, the minimum surface area of plate electrodes, the minimum size of the conductor that must be used to connect the ground to the panel, and the required form of electrical connection.

There is a lot of carefully considered reasoning behind the provisions of the NEC - this is a concensus standard that was developed by a panel of technical experts and is subject to a mandatory three-year review and revision cycle to assure that any new knowlege is incorporated as soon as it becomes available.

If there is any doubt about what is the right thing to do, hire a qualified electrical contractor, and make sure that the installation is inspected by the local building authority.

 

[Jim Chinn]

To sum it up, if you are not absolutely sure of what you are doing, call an electrician it will cost something, but you have peace of mind that the job is done correctly and to code.

One consideration, I don't know if you may ever sell your house or not, but if you were to list it and an inspector finds something not up to code, you will have to fix it anyway. So better to make sure it is done right the first time.

 

[jjstafford]

Thanks to each of you for your help. I am adequately frightened by the potential danger. As is, I cannot hire an electrician. At least not soon. So I will carefully check out the ground that serves the rest of the house. I've a lot of #2 cable that I can use to bring the ground into the darkroom, and I can make a simple box for those few recepticles.

It does bother me that the Chromeacontrol is 'leaking' electricity, but I'm not competent to fix that. I don't think.

I owe you all for your help.

jjs

 

[Calamity Jane]

With no ground to your darkroom equipment, it may not be the Chromeacontrol that is leaking.

You see, since ALL the "grounds" are hooked together but not connected to Mother Earth, all the leakages will add together and the resultant voltage will appear on all equipment with a 3-prong plug.

You need not be overly concerned since most all equipment leaks a tiny amount and, if standing on a concrete floor, the human body can detect voltages down to about 1 volt. Voltages about about 30 volts become VERY uncomfortable very quickly. Voltages about 50 volts become dangerous if there is 0.030 or more Miliamperes of current available.

(One of my duties with the power company is grounding and the electrical safety of equipment.)

 

[Monophoto]

Jane is right - we dont' know where the problem is, only what the symptoms are.

Jane also noted that voltage itself is not hazardous - it's current that induces cardiac fibrillation and leads to death. And the thresholds of sensibility and danger vary between people. Charles F. Dalziel proved that in his experiments on students at the University of California at Berkley back in the early 60's. Many of us have inadvertantly been exposed to the voltage in a 120v residential circuit with no apparent harm, and yet the incident in New York last year in which a pedestrial was electrocuted after coming in contact with an electrified manhole cover involved on about 50 volts. I have personally experienced shocks at voltage at the several thousand volt level and I'm still walking around (though some would suspect there was permanent brain damage).

I think the most important point in this thread is that electricity can be dangerous. And its a really good idea to have a ground fault circuit interruptor on the receptacle circuit to a darkroom.