Egon
Epic Contributor
After we go thru all the personnel installation procedures perhaps a reference to what is officially required may be in order.
Bonded or Floating Neutral for generator?
- Thread starter stumblinhorse
- Start date
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stumblinhorse
Platinum Member
Not installing personnel it is just me and myself.
Not sure how to reference something official…. As in all things what is required depends on what works and is safe. Once my install is “in order” I will say what worked and what was safe.
GeneV
Elite Member
Coby, I dunno how common or uncommon, but I believe your sep. derived system illustrates it (if I'm reading it right). Alls it is is an isolated neutral bus bar in the transfer switch, flipping the switch connects it to either your main panel or the generator. But in any case, I found the whole thing including a transfer switch itself too convoluted, when it's so easy just to do an interlock on the main panel and convert the generator to floating neutral, so that's what I went with.
GSVette
Gold Member
What I really wish I’d somebody selling a generator with a switchable ( from bonded to floating ) neutral. I have the breaker interlock type install with a inlet plug so that I can hookup my cheapie Predator 8500w generator ( which is a bonded neutral generator)-I really don’t want to pull the generator cap and disconnect the bonded neutral when I’m wanting to power the house as the generator is dual duty-I use it around the ranch to power tools and such.
CobyRupert
Super Member
Shhh, keep this a secret…but:
The point of “unbonding” the generator’s N + G when connected to and supplying your house’s panel (where N + G are already bonded) is so neutral current returning to the generator’s winding, from the panel, is not using the ground (G) conductor as a parallel path with the neutral conductor.
It is only in this ‘generator to panel’ patch cord that you would have this “objectionable current” in the ground conductor.
So what’s the problem with having about 1/2 the neutral current in the ground conductor?
Answer: Voltage drop in the conductor….or technically voltage rise..because it’s rising from 0 volts at the grounded (to earth) main panel’s N + G bars.
That is: Ohms law says the voltage (rise) = current (amps) x resistance (ohms). So if you have 30 amps of current traveling through .1 ohms of ground wire to the generator, the generator’s “ground” terminal and FRAME will now be (30A x .1 ohms =) 3 volts above the actual ground (earth).
Now imagine if it’s 50amps neutral current and 2 ohms of wire. The frame could be 100 volts relative to someone standing on earth ground and touching it. Especially if the frame is somehow isolated from the earth that your feet are standing on.
…but also note that a (say) #6 awg conductor’s resistance is only about .491 ohms per 1000 FEET (that’s about .025 ohms for 50’), so the reality of energizing the generator frame (and anything else “grounded”) to a dangerous level by this “objectionable current” is low.
…but still not something you want to do.
The point of “unbonding” the generator’s N + G when connected to and supplying your house’s panel (where N + G are already bonded) is so neutral current returning to the generator’s winding, from the panel, is not using the ground (G) conductor as a parallel path with the neutral conductor.
It is only in this ‘generator to panel’ patch cord that you would have this “objectionable current” in the ground conductor.
So what’s the problem with having about 1/2 the neutral current in the ground conductor?
Answer: Voltage drop in the conductor….or technically voltage rise..because it’s rising from 0 volts at the grounded (to earth) main panel’s N + G bars.
That is: Ohms law says the voltage (rise) = current (amps) x resistance (ohms). So if you have 30 amps of current traveling through .1 ohms of ground wire to the generator, the generator’s “ground” terminal and FRAME will now be (30A x .1 ohms =) 3 volts above the actual ground (earth).
Now imagine if it’s 50amps neutral current and 2 ohms of wire. The frame could be 100 volts relative to someone standing on earth ground and touching it. Especially if the frame is somehow isolated from the earth that your feet are standing on.
…but also note that a (say) #6 awg conductor’s resistance is only about .491 ohms per 1000 FEET (that’s about .025 ohms for 50’), so the reality of energizing the generator frame (and anything else “grounded”) to a dangerous level by this “objectionable current” is low.
…but still not something you want to do.
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GeneV
Elite Member
GS, the simplest thing here is to disconnect the wire on the generator, and then when not using it to power your panel, plug this into it:
The only thing left to do is to remember (and/or label it as such) to always have it plugged in at all other times, other than when you're backfeeding the panel.
GeneV
Elite Member
Oh wow man, you know WAY more about this than I do, this all greek to me lol!
GSVette
Gold Member
Thanks, I was aware of that as a solution. I still would prefer the option of a ‘switchable generator’ neutral as it eliminates altering the ‘as delivered’ generator wiring and would not occupy one of my 110v generator outlets.
I have a ‘bonding’ plug that I bought after the main power panel (and associated interlock and generator infeed’ were installed and inspected. I just haven’t had to use the interlock and generator yet so I’ve not gone to the trouble of unbonding the generator, yet.
CobyRupert
Super Member
Stayed tuned for next week’s “What happens when there’s not a neutral and ground bond and one is needed?”
…things get really wacky!
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stumblinhorse
Platinum Member
Depending on the generator is would be a simple thing to add a switch on the panel. I bet they will do that soon. But for now I might make one myself with a 30amp Switch I put in a j-box on the side of the generator.