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.