Electrical question......

[fried1765]

I just ordered a new 8500W DuroMax dual fuel generator.
This unit has a 30Amp/240 volt 4 pole twist lok output.
I want to be able to use it with a nearby three prong dryer receptacle.
The internet seems to say that I must use a 4 prong receptacle.
If I must use a 4 prong receptacle, I do not see how there could be any benefit.

There are only three wires inbound to that receptacle, the current supply is buried, and is 600ft long underground (2 hots +neutral)....... (I ain"t diggin 600' to add a ground wire!
Should I just take that (4th wire) ground from the new 4 prong receptacle, and hook it to a ground rod ?
I thought this was a no-no.
Seems like all that would be grounded would be the 15' distance from the generator to the new 4 prong receptacle.
I should do....What?

 

[sagor]

Residential electrical must have one and only one "ground" in the entire system (in most jurisdictions). So the answer also depends if the generator has an isolated ground (and floating neutral), or if the ground/neutral are tied together in the generator.
Most "portable" generators have the ground/neutral tied together inside, meaning you must use that as the "ground" (with ground rod) and never tie it to the house ground. Doing so would create a ground loop. If the generator has an isolated neutral (like many home standby generators with automatic transfer switches), then you could use the house ground, as it is grounded only at one point, usually at the service entrance.
All these "rules" can vary a bit by region or area. The only real answer is to get a qualified electrician to inspect and/or install your wiring so it meets electrical code. Never assume....be safe rather than sorry later.

 

[fried1765]

Residential electrical must have one and only one "ground" in the entire system (in most jurisdictions). So the answer also depends if the generator has an isolated ground (and floating neutral), or if the ground/neutral are tied together in the generator.
Most "portable" generators have the ground/neutral tied together inside, meaning you must use that as the "ground" (with ground rod) and never tie it to the house ground. Doing so would create a ground loop. If the generator has an isolated neutral (like many home standby generators with automatic transfer switches), then you could use the house ground, as it is grounded only at one point, usually at the service entrance.
All these "rules" can vary a bit by region or area. The only real answer is to get a qualified electrician to inspect and/or install your wiring so it meets electrical code. Never assume....be safe rather than sorry later.

Thanks, but clear as mud to me!
If ground and neutral were "tied together inside" the generator, why would the generator supply outlet have 4 prongs?
Seems like 3 would be enough.
Should I take the 4th pin on the 4 prong receptacle, and connect it to a ground rod?
The circuit at the existing receptacle is 3 wire (2 hots and neutral) there is no ground.
That cannot be changed!
I suspect that 3 "electricians" might offer 3 differing opinions.

 

[sagor]

I see something about GFCI breakers on that generator, that would need that 4th wire to work. True about 3 different opinions. But an electrician that installs home generators and transfer switches should know which is which. You could maybe ask the manufacturer if the neutral is floating or bonded at the generator. That might give a clue. Sorry, can’t help more than that.

 

[fried1765]

I see something about GFCI breakers on that generator, that would need that 4th wire to work. True about 3 different opinions. But an electrician that installs home generators and transfer switches should know which is which. You could maybe ask the manufacturer if the neutral is floating or bonded at the generator. That might give a clue. Sorry, can’t help more than that.

Thanks!
The generator has a 4 pin outlet (two hots, a neutral, and a ground)
I will run 4 wires from the generator outlet to a 4 pin wall receptacle.
The existing long underground installation is 3 wire (no ground).
At the wall receptacle, I will wire the 4th pin/lug (ground) to a grounding rod.

 

[GreensvilleJay]

re:
The internet seems to say that I must use a 4 prong receptacle.
If I must use a 4 prong receptacle, I do not see how there could be any benefit.

4 prongs recepts cost more ,have higher profit margin ?

re: I suspect that 3 "electricians" might offer 3 differing opinions.

5 really , and only ONE is applicable......

Whether you tie neutral to ground depends on HOW the genny is being used.

one use....powering a 2 prong drill in the woods....really no ground is needed

another .. powering an RV..no ground is needed,as RV is on 4 rubber tires...

backfeeding a house...THAT could be 'complicated',as the 'must have only ONE ground' is kinda dubious

 

[fried1765]

re:
The internet seems to say that I must use a 4 prong receptacle.
If I must use a 4 prong receptacle, I do not see how there could be any benefit.

4 prongs recepts cost more ,have higher profit margin ?

re: I suspect that 3 "electricians" might offer 3 differing opinions.

5 really , and only ONE is applicable......

Whether you tie neutral to ground depends on HOW the genny is being used.

one use....powering a 2 prong drill in the woods....really no ground is needed

another .. powering an RV..no ground is needed,as RV is on 4 rubber tires...

backfeeding a house...THAT could be 'complicated',as the 'must have only ONE ground' is kinda dubious

By grounding only the 4 prong receptacle (adjacent to the remote generator) ONLY the generator itself will be grounded.
The other three prongs of that 4 prong receptacle consist of 2 hots and a neutral
There is only one ground for that 3 wire feed/back feed, and that ground is in the main service entrance box, 600 feet away.

 

[GreensvilleJay]

unless someone has strapped the genny neutral and grounds together......

 

[fried1765]

unless someone has strapped the genny neutral and grounds together......

Would only need a three pin female receptacle at the generator end, if they were bonded internally.
Seems like all new generators have 4 pin female receptacles.

 

[GreensvilleJay]

options..... gives them / you choices. Also cheaper for them as 4 pin is 'universal' to the World.
Same as every electrical panel sold here in Canada has ground- neutral connected though installer can disconnect them if required.

 

[sagor]

They probably use the 4 pin socket because the 240V outlet is a split phase, 120V on each side of neutral, neutral, and a ground. Things like a dryer 3 pin plug is 240V only, there is no neutral, just the 2 hot phases for 240V and a ground.
I did a quick look around at that generator and a manual clearly showed the ground and neutral bonded inside the generator. That is ok if all the loads are isolated from the entrance neutral/ground. Most electrical services, at the entry point, have the ground and neutral bonded at the entrance point. For a house backup generator, one can have one and only one place in the entire circuit where the neutral and ground are bonded together. This is true for just about all electrical codes. Thus for this generator, you have to make sure the house neutral is not connected to two grounding points at the same time, as that can create ground loops.
Transfer switches for portable generators (bonded) will switch the neutral from house to generator (disconnecting neutral from ground at service entrance). Home standby generators with floating neutral will have transfer switches that just switch the 2 hot phases, as the neutral is only bonded at the service entrance, not at the generator, and no need to switch it around (generator neutral tied to house neutral permanently).
There are always a few people that "know better" and do what they want, ignoring grounding regulations. A rare few of them earn the Darwin award....

 

[fried1765]

They probably use the 4 pin socket because the 240V outlet is a split phase, 120V on each side of neutral, neutral, and a ground. Things like a dryer 3 pin plug is 240V only, there is no neutral, just the 2 hot phases for 240V and a ground.
I did a quick look around at that generator and a manual clearly showed the ground and neutral bonded inside the generator. That is ok if all the loads are isolated from the entrance neutral/ground. Most electrical services, at the entry point, have the ground and neutral bonded at the entrance point. For a house backup generator, one can have one and only one place in the entire circuit where the neutral and ground are bonded together. This is true for just about all electrical codes. Thus for this generator, you have to make sure the house neutral is not connected to two grounding points at the same time, as that can create ground loops.
Transfer switches for portable generators (bonded) will switch the neutral from house to generator (disconnecting neutral from ground at service entrance). Home standby generators with floating neutral will have transfer switches that just switch the 2 hot phases, as the neutral is only bonded at the service entrance, not at the generator, and no need to switch it around (generator neutral tied to house neutral permanently).
There are always a few people that "know better" and do what they want, ignoring grounding regulations. A rare few of them earn the Darwin award....

So I could use some more 'splanin.......
A neutral and two hots run from the house to this outbuilding....600 feet away.
No ground.
The house service entrance box (600"away) has the neutral and ground bonded.
The generator will live in the outbuilding.
The generator receptacle has 4 prongs, and one is apparently a ground.
Should THAT ground at the generator output (600' away from the house) now be connected to a purpose added grounding rod?
If not.......what should be done?

 

[GreensvilleJay]

Do NOT connect it's ground to a grounding rod....
instead...
Place generator on 4 rubber pads.
It's case( green wire, 'ground' ) is connected to neutral(white wire) internally which then goes 600' to the 'service entrance' ground at your breaker box.
Curious, I downloaded the manual, nice they supplied the schematic and yes, neutral and ground ARE connected internally.

 

[sagor]

Either way is dangerous. By putting in a ground rod, your neutral will be grounded at two places 600ft apart. That can create ground loops that actually conduct electricity, and it may be possible that one end of the "ground" will be hotter than the other. Earth ground is not a perfect ground, so there will be potential between the two points. Not putting in a ground rod, you might still get "loops", but this time via neutral trying to find a way back to "ground" at the house, which is not connected (only ground is generator chassis). Thus, your 600ft will provide some wire resistance and thus create a voltage potential as well.
Either way, your GFCIs in the house may not trip properly, or always trip due to ground loops. You can't get around this without a ground wire running between the generator and the house (and isolated from service entrance ground). An electrical fault in an appliance or wiring that causes a short to ground may not trip a breaker because the path back to the grounding point on generator is high resistance (via the earth only). All of these are dangerous.
I can't explain any better than that, just based on my experience installing a home standby generator and following electrical codes. It mystifies me as well, but "grounding" has to be done right. If you had a generator with an isolated neutral, you would not have this problem in the first place, your 3 wires would be good enough with existing neutral/ground tie point at the house. In other words, you bought the "wrong type" of backup generator based on the existing wiring you have. Your basic choice is to get a home standby generator with isolated neutral, or re-wire the 600ft run of cable with a 4 conductor cable for a portable generator. In both cases, you need a proper transfer switch (or proper interlock device), which are designed differently for portable generators (neutral grounded) vs home standby generators (floating neutral).
Bottom line is that the neutral/ground tie point must exist at one and only one place in a home system according to most electrical codes. You can move it, connect somewhere else, but must disconnect others so there is still only one neutral/ground tie point active for the whole house at any point in time.
I'm going to resign from this thread now, I've recommended the best I can for the sake of safety. Others may have differing views, let them voice their opinions as well.

 

[fried1765]

Either way is dangerous. By putting in a ground rod, your neutral will be grounded at two places 600ft apart. That can create ground loops that actually conduct electricity, and it may be possible that one end of the "ground" will be hotter than the other. Earth ground is not a perfect ground, so there will be potential between the two points. Not putting in a ground rod, you might still get "loops", but this time via neutral trying to find a way back to "ground" at the house, which is not connected (only ground is generator chassis). Thus, your 600ft will provide some wire resistance and thus create a voltage potential as well.
Either way, your GFCIs in the house may not trip properly, or always trip due to ground loops. You can't get around this without a ground wire running between the generator and the house (and isolated from service entrance ground). An electrical fault in an appliance or wiring that causes a short to ground may not trip a breaker because the path back to the grounding point on generator is high resistance (via the earth only). All of these are dangerous.
I can't explain any better than that, just based on my experience installing a home standby generator and following electrical codes. It mystifies me as well, but "grounding" has to be done right. If you had a generator with an isolated neutral, you would not have this problem in the first place, your 3 wires would be good enough with existing neutral/ground tie point at the house. In other words, you bought the "wrong type" of backup generator based on the existing wiring you have. Your basic choice is to get a home standby generator with isolated neutral, or re-wire the 600ft run of cable with a 4 conductor cable for a portable generator. In both cases, you need a proper transfer switch (or proper interlock device), which are designed differently for portable generators (neutral grounded) vs home standby generators (floating neutral).
Bottom line is that the neutral/ground tie point must exist at one and only one place in a home system according to most electrical codes. You can move it, connect somewhere else, but must disconnect others so there is still only one neutral/ground tie point active for the whole house at any point in time.
I'm going to resign from this thread now, I've recommended the best I can for the sake of safety. Others may have differing views, let them voice their opinions as well.
/QUOTE]

Thank you for your attempt/advice.
I am not at all concerned with GFCI's tripping.
The house was built in 1730, and electricity came in 1947.
There never have been, nor will there ever be, any GFCI's, or Arc Fault breakers.
Much wiring is old style Romex with no ground.
There is some "BX" cable which uses the steel shell as ground.
All receptacles in the house are two prong, non grounded.
Running 600' of new 4 conductor #2 or #4 underground cable is not an option.
I will not be using an interlocking switch ( see my original post)

I will take the advice offered in post #13, as it appears to be the only practical option.

 

[fried1765]

Do NOT connect it's ground to a grounding rod....
instead...
Place generator on 4 rubber pads.
It's case( green wire, 'ground' ) is connected to neutral(white wire) internally which then goes 600' to the 'service entrance' ground at your breaker box.
Curious, I downloaded the manual, nice they supplied the schematic and yes, neutral and ground ARE connected internally.

Thank you!
Generator has two large rubber wheels, so will simply get two additional rubber pads.

 

[Flintknapper]

Either way is dangerous. By putting in a ground rod, your neutral will be grounded at two places 600ft apart. That can create ground loops that actually conduct electricity, and it may be possible that one end of the "ground" will be hotter than the other. Earth ground is not a perfect ground, so there will be potential between the two points. Not putting in a ground rod, you might still get "loops", but this time via neutral trying to find a way back to "ground" at the house, which is not connected (only ground is generator chassis). Thus, your 600ft will provide some wire resistance and thus create a voltage potential as well.
Either way, your GFCIs in the house may not trip properly, or always trip due to ground loops. You can't get around this without a ground wire running between the generator and the house (and isolated from service entrance ground). An electrical fault in an appliance or wiring that causes a short to ground may not trip a breaker because the path back to the grounding point on generator is high resistance (via the earth only). All of these are dangerous.
I can't explain any better than that, just based on my experience installing a home standby generator and following electrical codes. It mystifies me as well, but "grounding" has to be done right. If you had a generator with an isolated neutral, you would not have this problem in the first place, your 3 wires would be good enough with existing neutral/ground tie point at the house. In other words, you bought the "wrong type" of backup generator based on the existing wiring you have. Your basic choice is to get a home standby generator with isolated neutral, or re-wire the 600ft run of cable with a 4 conductor cable for a portable generator. In both cases, you need a proper transfer switch (or proper interlock device), which are designed differently for portable generators (neutral grounded) vs home standby generators (floating neutral).
Bottom line is that the neutral/ground tie point must exist at one and only one place in a home system according to most electrical codes. You can move it, connect somewhere else, but must disconnect others so there is still only one neutral/ground tie point active for the whole house at any point in time.
I'm going to resign from this thread now, I've recommended the best I can for the sake of safety. Others may have differing views, let them voice their opinions as well.

^^^^^^



Well stated and I agree on every point. I was thinking that most/all of the open frame generators (of the OP's manufacturer) were a Floating Neutral not Bonded...but this needs to be established.

And VERY important to have only one ground point.

 

[Flintknapper]

Thank you!
Generator has two large rubber wheels, so will simply get two additional rubber pads.

This would help prevent creating a second ground (ground loop), but I think you still need to verify whether you have a floating neutral (best for your situation) or a bonded neutral. I would also have an qualified electrician assess your set up.

If you have a bonded neutral gen-set, in some cases it can be un-bonded but this would leave the metal frame capable of shocking you if there were a fault somewhere, so like @sagor said earlier, it could be dangerous either way (under certain conditions).

 

[fried1765]

This would help prevent creating a second ground (ground loop), but I think you still need to verify whether you have a floating neutral (best for your situation) or a bonded neutral. I would also have an qualified electrician assess your set up.

If you have a bonded neutral gen-set, in some cases it can be un-bonded but this would leave the metal frame capable of shocking you if there were a fault somewhere, so like @sagor said earlier, it could be dangerous either way (under certain conditions).

After all these opinions, I rather suspect that three a "qualified electricians" may also have 3 different opinions?

 

[Flintknapper]

After all these opinions, I rather suspect that three a "qualified electricians" may also have 3 different opinions?

Or they may not.

But soliciting opinions on the internet from admittedly non-professionals is less likely to provide you the safe solution you seek (if one is to be had).

I applaud you for recognizing the need to wire the system correctly and your concerns for safety.

A good electrician should be able to size up your installation and explain what (or what not) should be done.

Also explain any safety concerns and the reasons for them.