Bonded or Floating Neutral for generator?

[Egon]

Another article:

https://www.nspower.ca/docs/default-source/pdf-to-upload/b-28-900(1).pdf?sfvrsn=bd00f2aa_0

 

[cqaigy2]

Switching the neutral or not switching the neutral is just one of two ways that you are allowed to complete and generator installation, it a design choice.
Both ways are code compliant.
A transfer switch is less costly if you don't add the extra pole to switch the neutral.

So when would you want a switched neutral?
On an Industrial Electrical Service with ground fault detection/protection devices. The design requires the generator to be a separately derived system. Switching the neutral off of the utility service and onto the generator makes it a separately derived system.
At Healthcare Facilities with required Life safety systems and required emergency power systems.

The basic reason is if there is a phase to neutral short coming into the service from the utility you prevent possible damage to electrical systems by switching the neutral.
Phase to neutral shorts have happened during severe weather that damages the utilities distribution system.
I have seen the damage of a 6000 amp service blown off it's foundation because of a phase to neutral fault. so switching the neutral is a design consideration engineers usually make on large electrical services.

Thanks for the explanation. Makes sense.

 

[GeneV]

Since my other thread got off the rails I will start a new one about Bonded or Floating neutral generators. I have ordered a generator/inverter for my house. I have a simple sub panel with a manual transfer switch/lockout. So I assume that I have to have a floating neutral generator to plug into my plug? Since the neutral will be in the sub panel tied to the same bus as the ground.

Anyone have experience with the simple lockout switch hook up and either blowing the GFCI breakers because of the neutral or not?

Thanks!

Generally a subpanel doesn't have a bonded neutral, so if you're backfeeding that with generator with bonded neutral, no worries. The issue is if you're backfeeding the main panel, in which case that's 2 bonded neutrals, won't work. The solution in that case is to unbond the neutral on the generator, no biggie there.

Just make sure you fabricate or buy a bonded neutral plug, and leave that plugged in one of the generator's inlets at all times other than when you're backfeeding the house.

 

[CobyRupert]

Generally a subpanel doesn't have a bonded neutral, so if you're backfeeding that with generator with bonded neutral, no worries. The issue is if you're backfeeding the main panel, in which case that's 2 bonded neutrals, won't work. The solution in that case is to unbond the neutral on the generator, no biggie there.

Just make sure you fabricate or buy a bonded neutral plug, and leave that plugged in one of the generator's inlets at all times other than when you're backfeeding the house.

The sub-panel, via its connection to the main panel, has a “bonded” neutral and ground bus. When the sub panel feeder’s disconnect device is opened, that bond is still there.

And as always there should only be one location where the N + G are bonded (with few exceptions).

 

[stumblinhorse]

Generally a subpanel doesn't have a bonded neutral, so if you're backfeeding that with generator with bonded neutral, no worries. The issue is if you're backfeeding the main panel, in which case that's 2 bonded neutrals, won't work. The solution in that case is to unbond the neutral on the generator, no biggie there.

Just make sure you fabricate or buy a bonded neutral plug, and leave that plugged in one of the generator's inlets at all times other than when you're backfeeding the house.

I think all portable generators have to be bonded neutral these days.

So if the generator is used on a house you have to convert to floating when you feed a panel that is bonded. Which as @CobyRupert mentions is typically bonded with the main panel. I actually think, as someone mentioned before, it is code to do so.

 

[CobyRupert]

I guess you will have to explain that better for me to understand. You’re saying that plugging into a generator with a bonded neutral and ground into a panel that also has a bonded neutral and ground won’t blow the GFCI breaker? Because what I was trying to say is simply that it will trip the GFCI breaker.

The GFCI doesn’t trip because the neutral current returning from GFCI receptacle’s load is the same as in the “hot” leg going to the load.
However the current in the neutral conductor returning to the generator from the panel won’t equal the sum of the hot leg’s current, as it should, because some neutral current can take a parallel path on the ground conductor back to the generator (when bonded at both locations).

 

[CobyRupert]

Here is a drawing of how to connect a generator. Note the neutral is not bonded to the ground wire at the generator. The ground is bonded to the neutral at the meter socket(the preferred method) or a the main electrical panel.
View attachment 778766

I’ve never seen a transfer switch drawn like that.
That diagram is for when only 1 load (perhaps a sub-panel?) is transferred onto the generator system during an utility outage; and the loads on the main panel are not. That is, the main panel is not transferred to the generator system in this setup.

Other installations might switch the whole panel, like this diagram I found on the internet.

 

[GeneV]

The sub-panel, via its connection to the main panel, has a “bonded” neutral and ground bus. When the sub panel feeder’s disconnect device is opened, that bond is still there.

And as always there should only be one location where the N + G are bonded (with few exceptions).

Well first I'll say I'm not an electrician by any stretch, so everything I blabber here is speaking w/o authority on the subject. But with that outta the way, it sounds like he's using a transfer switch. There are different kinds, and if his is the switch neutral type, he's good to go with the generator having bonded neutral.

I only know about this stuff coz I was researching it for my setup. I ended up just doing an interlock on the main panel.

 

[CobyRupert]

Well first I'll say I'm not an electrician by any stretch, so everything I blabber here is speaking w/o authority on the subject. But with that outta the way, it sounds like he's using a transfer switch. There are different kinds, and if his is the switch neutral type, he's good to go with the generator having bonded neutral.

I only know about this stuff coz I was researching it for my setup. I ended up just doing an interlock on the main panel.

It would be the odd transfer switch that switches the neutral, typically not found in commercial or residential applications.

 

[stumblinhorse]

Most simple home installations don‘t have a ”transfer” switch. But on the inter webs if you don’t say a word like a transfer/cutover/breaker, people will assume a back feed suicide setup. I have a sub panel off the main panel with a main power breaker and a lockout on the generator breaker. Typical install for residential generator setups. They do sell fancy true “transfer” switches for people that want automatic cut over or wanted To pay extra for a neutral transfer, not sure why to do that other than you don’t need to modify your portable generator.

 

[Egon]

After we go thru all the personnel installation procedures perhaps a reference to what is officially required may be in order.

 

[stumblinhorse]

After we go thru all the personnel installation procedures perhaps a reference to what is officially required may be in order.

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]

It would be the odd transfer switch that switches the neutral, typically not found in commercial or residential applications.

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]

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]

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.

 

[GeneV]

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.

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:

https://www.amazon.com/dp/B07F4R7BDL/?coliid=I1ZKMG8821V3OX&colid=TJYU61LC7LU&psc=1&ref_=lv_ov_lig_dp_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]

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 to the neutral conductor (N).

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) N + G bars in the main panel.
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 only has about .491 ohms per 1000’ feet, 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.

Oh wow man, you know WAY more about this than I do, this all greek to me lol!

 

[GSVette]

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:

https://www.amazon.com/dp/B07F4R7BDL/?coliid=I1ZKMG8821V3OX&colid=TJYU61LC7LU&psc=1&ref_=lv_ov_lig_dp_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.

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]

Oh wow man, you know WAY more about this than I do, this all greek to me lol!

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!

 

[stumblinhorse]

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.

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.