I will be installing a standby generator located about 50 ft. from the grounding rod for my house. If I ground the generator only in main panel, then there is a possibility that the generator frame will be at a slightly different potential than the adjacent earth on which someone touching the generator may be standing. If I install a ground rod at the generator location, then I will be introducing a ground loop with its associated problems.
How, according to the NEC, should the generator be grounded? Please provide a code reference (or quote) if you can.
There should be grounding requirements in the installation instructions. Generally there is an external ground lug on the frame or housing of the generator. This would get connected to your grounding electrode conductor for lightning protection. There should also be an equipment grounding conductor that is run with generator conductors to the transfer switch or panel that you will be supplying the generator power to.
Actually up to a record 200,000 amps has been measured, however it lasts for only about a millisecond so the wire will not heat appreciably during that short time.
Most commonly, the lightning current ceases in about a millisecond for a given stroke, but sometimes there is a continuing current on the order of
100 amps following one or more of the strokes. This is called "hot lightning" and it is the cause of lightning fires. The continuing current only lasts for only 0.2 seconds and so a typical ground wire is sufficient.
The gen only needs small wire attached to even a long nail driven into the ground, a lightning rod is overkill
LOL. You guys are making me laugh tonight. Thanks. This reminds of the person a few years back who posted about sticking a wire from her computer out the window to a coat hanger in the ground because her house was not a grounded system.
Maybe on the next job I'll connect a ground wire good for 7000 amps to a long nail and show the inspector this thread. LOL
I really do appreciate all you folks who took the time to reply. However, the subject began "code question" amd so far none of the replies have tried to answer the question based on code. Also the question asked was "How, according to the NEC, should the generator be grounded?" Does anyone have an answer based upon their knowledge of the NEC?
As to the long nail suggestion you may be very certain that the nail will not be connected well to the ground when it is new and much less so after it begins to rust. That is why long ground rods are used and why two are sometimes required. That is also why they are made of copper. Yes the outside of the copper will corrode but the copper oxide, unlike rust, is conductive.
Grounding and bonding depend on whether or not is a seperatley derived system or not. I assume you are permanantly mounting the generator and it is not a portable unit. I also assume you are installing a transfer switch. Is this correct? NEC 2005 Article 250 is where to look.
OK short code answer. You connect the frame of the generator to the grounding system of the house always If the transfer switch also switched the white (neutral) you bond the neutral in the generator to the frame. (that is a separately derived system) If the transfer switch only switches the hots do not bond the neutral, it gets bonded via the bonding jumper in your service disconnect for the utility feed. That is not a separately derived system..
I wrestled with this about a decade ago and at that time couldn't find a clear reference in the NEC. The intent of the NEC seemed to too establish a good single point ground at the entrance panel/meter base. I did this with two ground rods (10 ft as I recall) at the mater base. The run to the entrance panel is about 15 ft further inside my basement. I have six subpanels, and none of these are grounded...all neutrals tie back to the entrance panel.
My generator is located at the other end of my house, about 150 ft away. I have a 10 ft ground rod at the generator to which the generator is connected and a single #4 stranded copper wire, perhaps 200 ft long, buried along the perimeter of the basement that bonds this ground rod to the two ground rods at the meter base. At the time I did this I felt that I was in compliance with the NEC (although today I can't cite a specific reference.)
It is a permanent installation. I will not be using a transfer switch. I will be backfeeding the panel through one of the breakers. That breaker has a mechanical interlock which prevents both it and the main breaker being on at the same time. (It is impossible to turn on the backfeed breaker on unless the main is off, and impossible to turn the main breaker on unless the backfeed breaker is off.)
OK that is what we needed to know. That is not a separaate;y derived system, you want to remove the jumper between the ground and the neutral in the generator. You still run a green wire ground between the generator and your house grounding system. A rod is not needed
They differ by panel model within manufacturer and are all hideously expensive. Here's what I did on a Square D panel.
The connection to the generator goes to a double circuit breaker located in the upper right column. For normal, non-emergency, operation, this breaker is OFF.
It's possible to fashion a metal or plexiglass plate that nudges against both the main circuit switch and this odd circuit breaker. This plate is bolted to the panel cover via elongated holes in the plate that allow the plate to slide, making contact with the two switch handles. The trick is to match the sliding with the positions of the main switch and the odd breaker. The breaker can't be turned ON unless the main switch is OFF. The main switch can't be turned ON unless the breaker is OFF.
On a Square D, main switch ON is to the right and circuit breaker OFF is to the right. If you have a block plate between the levers, it's obvious the circuit breaker can't be moved to the left (ON) unless the main is first moved to the left (OFF) and the blocking plate moved likewise. Similarily, the main can't be moved right (ON) unless the circuit breaker is first moved right (OFF) and the blocking plate scooted over with it.
Get the model and make of your panel and do a search on "{make} {model} interlock" The results will give you an idea of how the manufacturer of your panel wants the thing to work. You can then either find the best price on the "approved" device or, as I did, fashion your own.
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