Technically, this topology is a departure from Regulation However, as illustrated earlier, the connection with Earth may not be required, such as for a generator onboard a mobile unit or a generator supplying a site office via a short length of protected cable.
It is a topology also used in installations deploying simple separation, such as for supplies to mobile units depicted in Figure Figure It can also be safe for temporary systems in construction and similar, but with provisos. The main one is the use of a residual current device RCD on the output of the generator to provide protection against accidental earthing of the system for example, the frame of the generator sitting in wet mud or failure of cable insulation.
The RCD must be set at no more than mA with a time delay of no more than 0. The other requirement of this floating mode is that it is for a short duration.
If possible, such systems should have an earth electrode; the protection will then be much more reliable, especially in detecting cable faults. It is also important to think of the temporary distribution connected to the generator when considering the RCD rating.
A generator supplying power tools or other final circuits directly would need to have a 30 mA RCD fitted on the output. If the generator is supplying a distribution unit that has 30 mA RCDs protecting final circuits such as those fitted in a consumer unit in a portable building , then the supply from the generator is a distribution circuit, not a final circuit, and can be treated as such when considering Regulation The third topology shown in Figure 5 is common with but not limited to smaller generating sets of 1 or 2 KVA.
A notable feature about this arrangement is that an RCD on the output of the generator will serve no purpose — it is the only generator arrangement where this is so. In addition, equipment requiring a connection with earth for functional reasons for example, for internal filtering or electromagnetic compatibility EMC measures, common on many modern power supplies will not work effectively, as the protective conductor is not connected to the supply.
This can lead to a voltage appearing on the casing of the equipment. It is also important to ensure that the protective conductor is not connected to the mass of Earth such as by connecting it to earthed metalwork , as this would turn the arrangement into an IT system Regulation In practice, IT systems are difficult to implement as there is a requirement for a reliable earth electrode of known resistance to enable IMDs to function, which is often impractical to achieve for most temporary systems deployed for a short duration.
One aspect of the arrangement in Figure 5 is that a first fault will go undetected with Class I equipment. Then in step 1 later on you say to drive an 8 foot rod into the ground. My main question is, can I use the 4 foot grounding rod and be plenty safe? I had a 15kw diesel unit wired for home back up, by a frequently used Master Electrician. He used an 8 ft. Check your local code requirements. It varies. How would you recommend grounding a portable generator when the area that it will be used in has concrete flooring?
My generator quiet box is next to my main power panel. I wonder if I can ground to the ground bar in the panel instead of driving a rod in the ground. I just bought a generator and was surprised about it needing grounding. I will be using it out of the back of pickup as I drive around my propery cutting high dead limbs and branches off of several himlock and doug fir trees using an electric chain saw on an expanding pole.
So basically you are saying every time move my truck I have to pound a copper rod at least four feet into the ground. I worry I may not get them out and will need to purchase a lot of rods. Are all portable generators like this? Wow, what a hassle that is going to be. If you have a metal fence in your property you can ground it to that. The frame of a portable generator is not required to be grounded to the earth if: 1 The generator only supplies equipment or cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and 2 The metal parts of generator and the grounding terminals of the receptacles are bonded to the generator frame.
Thanks for a great write up Matt. I have a question regarding grounding a portable generator as a backup home power supply. My question is, will it hurt anything if I also grounded the generator? This is fine but if the neutral of the generater is not connected to the earth ie the frame and also the earth. In this case, the engine, fuel tank, and generator housing are all bonded to the frame, so that any electricity flowing through the generator outside of the wiring is grounded by the frame.
The manufacturer should provide extremely clear instructions on whether or not your generator needs to be grounded. This means you will need to connect your generator to a separate grounding rod. The copper rod should be hammered into the ground or buried at least 8 feet deep although you can buy a 4 foot rod, but 8 is standard for home installations.
If you are in rocky or difficult terrain, the rod can be hammered in at an angle of up to 45 degrees. Use your wire strippers to strip out about six to 12 inches of insulation off one end of the copper wire.
Then wrap this around the top of the grounding rod, using your pliers to make sure it is wound tightly around the rod. You can connect your generator to the grounding rod using the other end of your copper wire.
Depending on the distance between the existing mains supply and expected generator location, I fit a garage consumer unit to provide overload and RCD facilities. Earth rods installed at both ends of the generator supply cable as if the power goes off, you have to assume the earth protection could well go as well. Flying lead made up to connect the generator to wall inlet which will in turn connect the frame of the portable generator to the earthing rods.
Depending on the configuration of the generator, either normal testing or run lead off existing mains to the input side to check RCD operation. Hope that helps. Have a look at this link which is from the HSE with regards to earthing generators, I have found it really useful in the past. Thanx everybody, I downloaded the PDF document from the hse last night and found it useful Regards Carl. ArthurHall Posts: Joined: 25 July A couple of years ago I was called to a private house.
The guy had a change over switch and a lead to a portable 3kw generator to power the central heating boiler, lights and the kettle during power cuts. Everything worked ok until he changed the central heating boiler, the new boiler would not work off the generator.
After much investigation and head scratching it turned out the boiler did not have a pilot light, instead a high voltage sparked to earth to light the gas when required. The generator was earthed but did not have a neutral earth link. Putting a link in at the output of the generator solved the problem and allowed the boiler to light. Originally posted by: ArthurHall A couple of years ago I was called to a private house. The problem I had was that the boiler and generator frames were earthed ok but the v winding was floating with respect to earth so there was no return path.
For instance, what would happen if the pipework was floating, which would happen if connected with plastic pipe, and the cpc and bonding if present failed for some reason? The services connected to the metal boiler frame metal pipes, taps, any metal parts may have a high voltage present on them when the spark generator operated and the spark was arcing. It seems to be a very strange design to me. Effectively any break in the cpc could have the high voltage present across the break resulting in an arc.
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