Generator harmonics

[glcaines]

Final note.. I spoke with a generator supplier. He told me they connect the ground to the generator frame because of lightning. A direct strike to the service has taken out many a generator sold that did not have the generator grounded to the frame. I personally did the no code thing and put the ground strap back on my 803. I can't see how a ground loop can happen to shock hazzard if you are bonded at both ends and both ends have double grounding rods. The green wire carries any possible short. Just like a power tool shorting to it's case. If the ground point of the plug is connected and you are holding the shorted tool you don't get a shock. The ground rod only protects against lightning. And a short to ground strong enough to hurt you should trip the breaker.

That is what I don't understand. I only have ground rods at the house end, none at the trailer. I have a permanently attached separate ground cable that runs from the trailer/genset frames to the ground rods at the house. The jumper is in place, which connects the neutral on the generator to the trailer/genset frame. If anything shorts to the trailer or genset frames the electricity would follow the permanently attached ground cable to the grounding rod at the house. How would it be possible for the genset or trailer frame to become energized and the electricity short through personnel to ground. I'm not trying to be argumentative, I'm just trying to understand this.

 

[Scoobyshep]

Circuit breaker 101 they typically go off from 1 of 2 things thermal (overload) or magnetic (short circuit) alot of times they will be rferred to thermalmag breakers, (there are variations but not going too indepth in that) . The textbook definition of grounding is Providing a low impedance path to the source to facilitate the operation of the overcurrent protective device. IE a ground fault will run the breaker to overload and cause the breaker to trip instead of making some metal casing live until someone becomes a ground jumper.

Now the bond no bond thing. Not having the generator bonded at all causes the generator neutral to float (the neutral has no ground reference ) line to line will still be 208 or 240 (depends what its configured for) but the line to ground will imbalance depending on the loads.
Double bonds (generator is bonded and the house (or load )is bonded). this is bad because it now parallels neutral and ground. Why? because the neutrals job is to carry the unbalanced load back to the source example you are pulling 10 amps on l1 and 20 amps on l3 10 amps are being directed back to the source via the neutral. if the system is double bonded neutral will carry 5 and ground will carry 5 the danger is now the ground is carrying a load and can cause an electric shock in the right conditions. properly bonded the ground will only have a load during a ground fault event. The whole idea is to keep the chassis at 0 potential.


Where does most of your ground reference come from? Utility . ground rod(s) don't do as much as you think they do (way too many factors here to go into) but utility is also neutral bonded and that ground surface is much larger than your rods).


Can you add a rod at the generator? yes. BUT you have to think about what that does to your grounding field. A lightning strike or surge or ground fault will now seek that rod as well as utility and the service rod(s). Some municipalities require that ground wire to be sized large enough for the largest possible fault current, so a #10 or #8 ground for a 30 to 50 amp generator would have to be closer to a #4 or #6 because its now an active service ground (it belongs to the service grounding network and now has to protect to 200 amps (or whatever your service is rated at)


The long story short is ground the Chassis, Bond once, Be safe, and don't let me hear about you on the news as homeowner electrocuted by generator.

 

[glcaines]

Thanks. What about replacing the jumper with a switch to make it easy to use the genset remotely without having to add the jumper each time?

 

[Scoobyshep]

Thanks. What about replacing the jumper with a switch to make it easy to use the genset remotely without having to add the jumper each time?

As long as it is rated for the current it should be fine.

 

[Daybreak]

Final note.. I spoke with a generator supplier. He told me they connect the ground to the generator frame because of lightning. A direct strike to the service has taken out many a generator sold that did not have the generator grounded to the frame. I personally did the no code thing and put the ground strap back on my 803. I can't see how a ground loop can happen to shock hazzard if you are bonded at both ends and both ends have double grounding rods. The green wire carries any possible short. Just like a power tool shorting to it's case. If the ground point of the plug is connected and you are holding the shorted tool you don't get a shock. The ground rod only protects against lightning. And a short to ground strong enough to hurt you should trip the breaker.

Howdy,
NOT all generator are alike.
This is a Military MEP generator.
A commercial permanent generator supplier is going by what he sells. Most do not have a simple N-G bonding strap like a MEP. Why? Those are meant to be permanently mounted, and the generator frame is meant to be grounded. But, I do not think there is a bonding strap to make the N-G electrical side of generation.

 

[LEOK]

Many things can load the neutral, poor connections, switching power supplies, poor grounding. So by bonding to the neutral can make the case hot. Most conventional ground rods don't meet the standard of 25 ohms or less. The two main reasons the screw clamp at the ground rod and dry soil. If you lose electronics during near bye lightning strikes check your ground. The spec's for communication closets is 5 ohms. Cadweld oneshot kits are cheap and weld the ground wire to the rod, also if you can use a ground rod joiner and drive 20 feet down, I put them near a gutter run off. Also the use aluminum wire and connection points in the panels are not coated with noalox which causes resistance increase. Whenever I'm wiring in new circuits in the panel I brush on noalox, if for no other reason it keeps the lugs from freezing from corrosion.

 

[technoid]

Circuit breaker 101 they typically go off from 1 of 2 things thermal (overload) or magnetic (short circuit) alot of times they will be rferred to thermalmag breakers, (there are variations but not going too indepth in that) . The textbook definition of grounding is Providing a low impedance path to the source to facilitate the operation of the overcurrent protective device. IE a ground fault will run the breaker to overload and cause the breaker to trip instead of making some metal casing live until someone becomes a ground jumper.

Now the bond no bond thing. Not having the generator bonded at all causes the generator neutral to float (the neutral has no ground reference ) line to line will still be 208 or 240 (depends what its configured for) but the line to ground will imbalance depending on the loads.
Double bonds (generator is bonded and the house (or load )is bonded). this is bad because it now parallels neutral and ground. Why? because the neutrals job is to carry the unbalanced load back to the source example you are pulling 10 amps on l1 and 20 amps on l3 10 amps are being directed back to the source via the neutral. if the system is double bonded neutral will carry 5 and ground will carry 5 the danger is now the ground is carrying a load and can cause an electric shock in the right conditions. properly bonded the ground will only have a load during a ground fault event. The whole idea is to keep the chassis at 0 potential.


Where does most of your ground reference come from? Utility . ground rod(s) don't do as much as you think they do (way too many factors here to go into) but utility is also neutral bonded and that ground surface is much larger than your rods).


Can you add a rod at the generator? yes. BUT you have to think about what that does to your grounding field. A lightning strike or surge or ground fault will now seek that rod as well as utility and the service rod(s). Some municipalities require that ground wire to be sized large enough for the largest possible fault current, so a #10 or #8 ground for a 30 to 50 amp generator would have to be closer to a #4 or #6 because its now an active service ground (it belongs to the service grounding network and now has to protect to 200 amps (or whatever your service is rated at)


The long story short is ground the Chassis, Bond once, Be safe, and don't let me hear about you on the news as homeowner electrocuted by generator.

Good answer. So it seems the idea is that if the utilities ground is poor than you can become the better ground and shock hazzard is potential. This I understand. So then I guess the best way to protect the poor genset from a lightning strike is to keep it unplugged during non use. I also keep my genset load balanced. Not only is it more efficient in power factor but in fuel usage as well. Good discussion here.

 

[glcaines]

I read that virtually all small portable commercial generators have the neutral permanently bonded to the frame. I assume this is because a lot of them are used remotely. I would also assume that virtually no one ever drives a ground rod in the ground when using these remotely, such as camping, etc. Amazing that more people aren't hurt using generators.

 

[Scoobyshep]

I read that virtually all portable commercial generators have the neutral permanently bonded to the frame. I assume this is because a lot of them are used remotely. I would also assume that virtually no one ever drives a ground rod in the ground when using these remotely, such as camping, etc.

Its because they are not ment to be used to power a house. The neutral is bonded to the chassis to provide a ground reference.

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