I recently purchase a generator (we have massive thunderstorms and PEPCO keeps dying!). Following the instructions, I drove a copper tube (they said 'pipe') several feet into the earth. I then connected 12g wire to it from the generators ground lug.

I tested the line with a testing device that shows 'open ground'. I would like to know how to remedy this situation. The tester is 'known good' in that it does show 'correct wiring' on the house wiring when the power came back on.

Thanks!

Joe Wilk
Gaithersburg, MD USA

 

This tester is attached to the ground lug on one end and the earth on the other and still shows open ground?

 

Several problems with your situation. First, it takes a special meter http://www.goodmart.com/products/83386.htm to determine the adequacy of a ground rod and its resistance relative to ground. The only thing you can test with an ohm meter would be from the ground lug on the gen to the end of the pipe.
Oh yeah the pipe. The electric code requires the rod to be 8' long (with all in contact with the earth, if using conduit or tubing then 3/4" size minimum, and it must have corrosion protection.

 

That is a minor concern, the grounding to earth and as Ron said, just do it like the instructions call for. Here is some more about generators and installs and grounding. Depending on the hookup it may be grounded thru the regular electric system. That will depend on the type of generator that is to be installed. If the generator is to be permanently installed then the answer is governed by the bonding of the neutral at the generator.

If the neutral is bonded at the generator then you transfer the neutral in the transfer switch. This is done to avoid having two connections to ground on the neutral at both the service equipment and the frame of the generator.

If the neutral is not bonded to the frame of the generator then you do not transfer the neutral so that the generator's neutral will be grounded by the main bonding jumper in the home's service disconnecting means.

A power inlet for a portable generator is done the same way in that a four wire with ground inlet, such as the L14-XX 120/240, is wired to a two pole transfer mechanism. A three wire without ground inlet, such as a L11-XX is wired to a three pole transfer device. In general three pole transfer devices are only available as switches.

 

Thanks for the info folks! I had been using a simple three-pronged tester that I plugged into the output of the generator, not an ohm meter. I am on my way to the hardware store for an 8' rod that is corrosion-protected.

Thanks again!

By the way, the generator is a small 1850 watt device that is not connected to the main wiring, just so I can keep the refridgerator and freezer running when PEPCO drops the ball.

 

No ground rod is required for that generator if you are only suplying cord and plug connected loads from receptacle outlets located on the generator. The ground lug on the generator frame is provided for bonding the generator to the frame of a motor vehicle if it is run while mounted on the vehicle or for attaching to a ground rod if it is used to supply fixed wiring systems.
--
Tom Horne
An electrician in Takoma Park.
I'm in the residential white pages.

 

I agree too, if it is not connected to the house wiring (cord and plug conenctions directly to generator, then you do not need a ground rod, as mentioned.

 

Thank you one and all.

I went out and got an 8' grounding rod. I sunk it and secured the 12g wire to it. I then used my cheap Radio Shack circuit teter (showed open ground yesterday), and found a 'hot/neutral reverse'. The manufacturer tel sme it is kosher, as the proximity of the hot & neutral to each other in the generator.

That sound right?

thank you once again!

Num

Tom, I see you in Takoma Park.

 

Does it show hot & neutral reversed when the generator on? It shouldn't.

 

Yeah Ron. It does show hot/netral reversed with generator on.

I called Coleman (manufacturer~its a Briggs & Stratton motor). they told me that the way the wires are so close in the machine, and considering I was using a cheapo tester, the hot/neutral reverse was not uncommon or unsafe.

Joe

 

Colemans full of it then!!!
The goon that wired it has got the wires reversed.

With a meter you should get around 0v from the equipment ground to the neutral (wide slot on the receptacle) and around 120v from the narrow slot to the equipment ground.

 

I switched the white & black leads (the white had been wired to the wide blade) and got an 'Open Ground'.

I then re-wired it to the way it came (white to the wide blade):

• tested and got the 'Hot/Neutral' reversed
• tested voltage/continuity with voltage tested that says -DC voltage @ 120 V (no matter how I put the leads into the white/black slots)~Not AC, but DC
• I am getting approximately 50 volts on EITHER blade to ground.

What the hey?

Thanks again for any and all help folks!

Joe Wilk

 

Yup. :doh!:

I called Coleman back and the advise me that it is a 'floating neutral', and that it should read about 50 V from black or white to ground and about 127 from white to black.

I measured, and there is, in fact 127 V betwixt the two.

Is this Kosher?

Can anyone recommend a website that explains grounding/floating neutral?

Regards,

Joe Wilk

[man I wish I could spell right the first time ]

 

I'm so curious that I will come out to Germantown to check this puppy out.

Please advise model number of your generator. I will need to do some research first. My imediate reaction to the idea of a 120 volt generator having an ungrounded & unbonded neutral is that I hope that the outlets on the generator are Ground Fault Circuit Interupter protected.
--
Tom

 

This just means that the neutral and ground arent bonded together at the centertap from the generator.

The ground is just there. Right now the only thing giving you those voltage readings is capacitance. If you were to use a low impedance meter those readings to ground would likely dissappear.

This isnt really a bad thing though. Many services are left ungrounded because if you develop a fault then the breaker wont trip, then equipment can be orderly shut down. If a second fault occurs then the breaker will trip. It also lessens shock hazards because if you were to touch either of the wires then you really have no circuit present other than capacitive coupling. This is used in many hospitals.

Even with a GFCI present and you were to accidently ground either conductor the GFCI will probably not trip because there probably wouldnt be enough unbalanced current present.

 

It only takes six milliamps of leakage to trip a GFCI.
--
Tom

 

First off, my last post originally said 'floating ground' when I meant 'floating neutral'. I went back and fixed it, but hronetd had probably already read it.

Second, I did a search for 'floating neutral' and read some specs in Alberta Canada (eh?) that suggest I am safe with an 8' ground and floating neutral, as has been the general consensus here (I think).

Thank you one and all!!

Joe Wilk

 

Im fully aware that a GFCI's trip threshold is between 4-6ma. I still dont think with a GFCI that you would create enough of an unbalance through capacitance to trip it.

 

I don't mean to be quarrelsome but I have received a nasty shock from cord and plug connected equipment that was supplied by a two wire cord from a portable generator that was not grounded. The equipment was an older circle D light with a two wire inlet. The generator was a world war two civil defense unit that was over two hundred feet away sitting on an ungrounded rescue truck. There was no Equipment Grounding Conductor in the supply cord. Since the threshold of sensation is well above the trip point of a GFCI I would think that you can draw enough current to trip one without a ground path being present.
--
Tom

 

I didnt take your reply to be quarrelsome and didnt intend my reply to be taken that way either. I have taken a few Meyers-Brigss personality type indicators and they all have said that I lack "warmth" in some of my conversations. Im usually straight to the point and dont think a thing about it so if I give a quick reply like that I dont mean it in a bad way. So with that please accept my apologies if I came across harshly, I did not intend to convey those feelings.

With that aside I would say that in your case a GFCI may have helped you out. Its hard to venture why but the generator could have been accidentally grounded by some other means like a frayed cord from another user or other means whether at your end or at the supply. With such a long length of cord and a bigger generator you would surely be making a bigger capacitor so it could have been capacitive. Most times however if its capacitive the voltage will dissappear fairly quick. The hospital systems can have some large run lengths and will only provide a slight tingle. Not really painful but you know its there.

If you did have a GFCI it would depend on where it was located to whether it would have prevented your shock. If it was at the equipment and the accidental ground was along your cord then youd still be shocked. Clearly in this situation the GFCI would have been most benefical directly at you the user.

 

I love the long thread discussion posts, most interesting, but to the original poster of the thread,,, put the thing back like it was, plug the stuff in to it when you need it and leave the damm thing alone. This is a classic case of overthinking. Common sense says that who ever wired it at the factory had some idea what they were doing.

 

No question that I am guilty of overthinking, and not here only. I have infact wired it back to its original condition.

Again, thank you all. Your informed opinions are all appreciated.

Joe Wilk