Grancuda
Well-known member
When using a small portable generator, they all seem to have a threaded stud for an earth ground. Is this to be used every time you use it or just when you use grounded plug devices?
Grounding portable generator - do you ground every time?
- Thread starter Grancuda
- Start date
doorfx
Well-known member
I've never used it.
vettex2
Banned
never have
slip knot
Well-known member
I've used my welding machine as a generator for years and have never grounded it.
When I use my personal generator at our Lions Club cookouts I always drive a single ground rod if we are on grass. My theory is it can't hurt. I too would like to know some expert opinions on this such as how can a GFI work properly if the genny is not grounded.
Is your compressor equiped with a GFI? The portable ones I've seen have a simple resetable breaker.
Ideally you would want as low a loop impedance as possible by grounding it. This will ensure that the breaker goes out in case your equipment connected to the generator develops a fault to ground.
If the loop impedance is too high because of the high resistance of the surface the generator is standing on + the paint of the frame; then even a direct short to ground in an appliance won't trip the breaker, leaving dangerous potentials.
Ideally you would want as low a loop impedance as possible by grounding it. This will ensure that the breaker goes out in case your equipment connected to the generator develops a fault to ground.
If the loop impedance is too high because of the high resistance of the surface the generator is standing on + the paint of the frame; then even a direct short to ground in an appliance won't trip the breaker, leaving dangerous potentials.
DTE
Well-known member
mine has a place to attach a ground wire so I always do. I have a piece of solid copper wire clamped to a 18 inch stake and drive it in the ground.
cavalry
Well-known member
I only use a generator backfed into my shop. I am sure some protection is offered through the ground in the shop back to the generator but a driven ground at the generator would offer more protection against lightning strikes or something...then again my generator is probably a little different than the ones most use.
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trainer
Well-known member
Wouldnt a generator with a bonded neutral be safer if it was not tied to a ground rod?
Imagine standing in a puddle, operating a power tool with a 3 prong grounded plug
Scenerio 1 has a ground rod at the edge of the puddle. Something in the tool fails and you complete the circuit back to the generatior through your body and the puddle.
scenerio 2: No ground rod , generator is not electrically connected to earth. Tool fails and results in an open circuit or current returns through the "ground" connector in the cable.
Imagine standing in a puddle, operating a power tool with a 3 prong grounded plug
Scenerio 1 has a ground rod at the edge of the puddle. Something in the tool fails and you complete the circuit back to the generatior through your body and the puddle.
scenerio 2: No ground rod , generator is not electrically connected to earth. Tool fails and results in an open circuit or current returns through the "ground" connector in the cable.
kd3pc
Well-known member
osha has recently released a statement on this exact thing...
no rods in 90% of cases....is the short message...
read it at your leisure.
no rods in 90% of cases....is the short message...
read it at your leisure.
Alchymist
Well-known member
A GFCI doesn't depend on a ground to work. It senses the difference in current between the hot and the neutral, and trips if it exceeds a few milliamps.
southalabama
Well-known member
Never have I ever.
555
Well-known member
Yes I do. I operated generators in the Army and got in the habit of grounding.
Regards,
John
Regards,
John
How can you have a bonded neutral without a ground rod?
The reason for an earth ground is to keep the voltages from floating wrt local earth. Without it you can get weird transient common mode voltages—the two sides will always be 120v apart, but they could be 0v and 120v or 1000v and 1120v away from local ground.
That said, outside a building wiring situation, it's probably a non-issue. Building wiring can have transient voltages induced by lightning, and bonding neutral to ground will drain those off. For a generator being used for a single piece of equipment it's unlikely to matter.
Sent from my Nexus 6 using Tapatalk
The reason for an earth ground is to keep the voltages from floating wrt local earth. Without it you can get weird transient common mode voltages—the two sides will always be 120v apart, but they could be 0v and 120v or 1000v and 1120v away from local ground.
That said, outside a building wiring situation, it's probably a non-issue. Building wiring can have transient voltages induced by lightning, and bonding neutral to ground will drain those off. For a generator being used for a single piece of equipment it's unlikely to matter.
Sent from my Nexus 6 using Tapatalk
It does need some kind of ground to operate. In a fault situation, if the generator is isolated from the ground, too little current will flow (from the live, through your body, through ground, back to the generator frale) for the GFCI to detect an imbalance in current and trip.
Technically you could be holding on to the live wire (or faulty shorted equipment attached to it) without getting a shock until you also touch the generator; sort of like an isolation transformer.
But I agree, highly unlikely scenario. Do portable generators in the US have a GFCI, because here they just have a breaker. These would benefit from a better ground, but I don't think anyone bothers.
sberry
Banned
GFCI doesn't require a ground and is one of the legal ways to use 3 wire appliances on 2 wire circuits. Again, the earth doesn't have anything in this case to do with faults, there is a wire for it or it is gfci protected.
You do need a path back to the generator to trip the gfci: through the earth!
Imagine the generator being isolated completely from the earth ground: then you could short the live wire coming from the generator directly to an earth ground without the gfci ever noticing a thing since there's no current flow.
Again, the generator frame will almost always provide a good enough ground by itself, even a resistance of 7kohm between generator frame and the earth will allow enough current to flow to trip a 30mA GFCI on 230V.
Imagine the generator being isolated completely from the earth ground: then you could short the live wire coming from the generator directly to an earth ground without the gfci ever noticing a thing since there's no current flow.
Again, the generator frame will almost always provide a good enough ground by itself, even a resistance of 7kohm between generator frame and the earth will allow enough current to flow to trip a 30mA GFCI on 230V.
Alchymist
Well-known member
The "bonded neutral" refers to the neutral in the generator being connected to the generator frame. Has nothing to do with "ground" In addition. if the generator is tied into a building where the transfer switch does not switch the neutral, the generator neutral must NOT be connected to the frame of the generator.
Not true. Any imbalance in hot to neutral in a GCFI will trip it. Since there is no current flow, there is no danger. If someone were to contact either the hot or the neutral in an ungrounded generator, while standing on a grounded surface, nothing will happen, as there is no current path. It is true that if the generator is grounded AND the generator ground (frame) is connected to neutral, current will flow in this situation and the GFCI will trip.
Running a generator without a ground (earth) reference is like running an isolation transformer from POCO lines. Unless something is directly between hot and neutral, no current will flow.
Well, that's what I was saying, right?; no current path, so the gfci won't trip. I mentioned it was similar to an isolation transformer or even an IT earthed net.
I was replying to sberry; a gfci becomes kind of useless without any ground connection of the generator.
It won't detect a phase wire becoming shorted to ground since there's no current flowing= no current imbalance. This would effectively turn the IT system into a TN system though.
If someone were to touch the other (neutral) wire coming from the generator; at that point current will flow from the phase wire (which has some kind of fault to ground) into the ground, through your body, back to the generator via the neutral wire. Again no current imbalance and nothing to stop the generator from burning you up inside.
That's why IT systems are very safe until there's a single insulation fault; they should have an isolation monitoring device. A single fault won't hurt you, but a second fault becomes very very dangerous.
Even worse with 3 phase systems.
That's the reason why the utilities provide us with earth referenced power. They could have provided everyone from isolation transformers which would be great and safe. Only problem is that they can't guarantee that there will nowhere in the whole system be a fault to ground on any of the wires effectively turning it into an earth referenced system. Safer to just earth reference everything from the getgo and use gfci's.
I was replying to sberry; a gfci becomes kind of useless without any ground connection of the generator.
It won't detect a phase wire becoming shorted to ground since there's no current flowing= no current imbalance. This would effectively turn the IT system into a TN system though.
If someone were to touch the other (neutral) wire coming from the generator; at that point current will flow from the phase wire (which has some kind of fault to ground) into the ground, through your body, back to the generator via the neutral wire. Again no current imbalance and nothing to stop the generator from burning you up inside.
That's why IT systems are very safe until there's a single insulation fault; they should have an isolation monitoring device. A single fault won't hurt you, but a second fault becomes very very dangerous.
Even worse with 3 phase systems.
That's the reason why the utilities provide us with earth referenced power. They could have provided everyone from isolation transformers which would be great and safe. Only problem is that they can't guarantee that there will nowhere in the whole system be a fault to ground on any of the wires effectively turning it into an earth referenced system. Safer to just earth reference everything from the getgo and use gfci's.
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sberry
Banned
You are going to get there but gfci doesn't need a ground. Its what makes it so valuable, even if there is an interruption along the way, improper bond etc it works. It should be called ground fault circuit sensing interrupter for lack of better wording.
It monitors current, if its not going back on neutral it must be going somewhere else, shuts it off.
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Banjorear
Well-known member
sberry
Banned
It should be grounded but it doesn't need it to work.
NOZZLEMAN
Well-known member
Had a PTO driven 40K on a specialty piece of fire apparatus, it had a cable reel on it with a clamp to ground the generator - usually to a fire hydrant...
The reason ground references become important is that even without a ground connection, lightning and the electric fields that produce it can induce large voltage differentials in the electric grid.
There's two things happening there: one is large static charges, which create the electric field, and then the lightning itself, which discharges the static charge, but in doing so creates a magnetic field that induces voltages in nearby conductors.
You can fit this info the usual framework of current loops by treating it as capacitances between earth and the layers of the atmosphere, but eh.
You don't want multiple connections between protective earth and neutral because then your protective earth connections will start carrying current and float away from ground potential due to voltage drop. That one connection is the bonding point, and generally speaking is also where neutral is connected to actual earth.
Sent from my Nexus 6 using Tapatalk
There's two things happening there: one is large static charges, which create the electric field, and then the lightning itself, which discharges the static charge, but in doing so creates a magnetic field that induces voltages in nearby conductors.
You can fit this info the usual framework of current loops by treating it as capacitances between earth and the layers of the atmosphere, but eh.
You don't want multiple connections between protective earth and neutral because then your protective earth connections will start carrying current and float away from ground potential due to voltage drop. That one connection is the bonding point, and generally speaking is also where neutral is connected to actual earth.
Sent from my Nexus 6 using Tapatalk