Grounding a generator

[Ramper]

I have read TOO MANY posts regarding this topic and I am more confused than when I started so I will ask for the rule for MY SITUATION:

7000Watt portable generator
Connected at the power pole to the house lead (the main lead will be OFF)
Connected through a 50AMP 125/250 plug and inlet
120/240 twistlock plug (L14-30P) on genertator

I know that I am only supppling 30 amps, but I am having a 50AMP inlet installed to support future generator upgrades

THANK YOU. I feel that I am technical savvy, but this is maddening

 

[wyliesdiesels]

Are you using a transfer switch or interlock?

Switched neutral in TS?

 

[theoldwizard1]

Most portable generators do not have their ground bonded to the neutral. It is usually just attached to the frame.

As Wylie said, use of a transfer switch or an interlock makes a big difference.

 

[American Locomotive]

Are you sure about that? Every small generator I've seen has the neutral bonded to the chassis along with the ground. If the ground and neutral were not bonded at the generator, you would not get any protection during a fault situation.

 

[wyliesdiesels]

Most portable generators do not have their ground bonded to the neutral. It is usually just attached to the frame.

As Wylie said, use of a transfer switch or an interlock makes a big difference.

incorrect.

Portable generators MUST have a bonded neutral because theyre made for standalone use. This bond is needed for breakers to be able to clear ground faults.

Are you sure about that? Every small generator I've seen has the neutral bonded to the chassis along with the ground. If the ground and neutral were not bonded at the generator, you would not get any protection during a fault situation.

yup

 

[Lamakocklee]

Hmm..

You guys are more familiar with this.. but I was under the impression that in order to use any sort of generator transfer switch that does NOT switch the neutral, you need to unbond the ground from the neutral at the generator as the main panel has the ground bonded to the neutral already.

edit..Whoops.. I think that is what wyliesdiesels was getting at in his initial response.

 

[American Locomotive]

IIRC, you only have to mess with generator grounding when it's a permanent install, hardwired to your home.

 

[pattenp]

If connecting a portable generator to your home wiring system the neutral bond at the generator should be removed. Doesn't matter if hardwired or using a power inlet. When using the generator as standalone the neutral should to be bonded at the generator. You can use a bonding plug in one of the gens outlets to reestablish the neutral bond when using the generator as standalone.

 

[American Locomotive]

If connecting a portable generator to your home wiring system the neutral bond at the generator should be removed. Doesn't matter if hardwired or using a power inlet. When using the generator as standalone the neutral should to be bonded at the generator. You can use a bonding plug in one of the gens outlets to reestablish the neutral bond when using the generator as standalone.

If that were true, then if the neutral connection in the cord between your generator and house broke, your whole entire house would be at 120v potential. Including all the metal enclosures of grounded appliances and your plumbing. You would have a very unsafe situation.

"Ground" doesn't really exist on a portable generator that has rubber wheels and plastic feet. The ground pin on its plugs only work because they're bonded to neutral, which is held at 0 volts at all time by the generator head. If you remove the neutral/ground bond on the generator, the generator's chassis and ground connections will float at whatever voltage is present on the ground circuit.

So if you run into a situation where a device has a short to ground, or the neutral breaks, the entire chassis will be at line voltage. This is because the generator's ground isn't bonded to the 0v neutral point in the gen head, and the generator's wheels and plastic feet isolate it from earth ground. There is no where for fault current to go.

 

[pattenp]

It is true and is what is recommended when using a portable gen to power your house electrical system. Stating what if the neutral is lost is just hypothetical and doesn't change the fact that the neutral should only be bonded at one point in the house electrical system. The gen is grounded via the house EGC.

 

[American Locomotive]

It is true and is what is recommended when using a portable gen to power your house electrical system. Stating what if the neutral is lost is just hypothetical and doesn't change the fact that the neutral should only be bonded at one point in the house electrical system. The gen is grounded via the house EGC.

Earth ground is irrelevant when the generator is the voltage source, and is physically isolated from earth ground via its wheels and plastic/rubber feet. If the neutral breaks in the cord between your generator and house, and your generator is unbonded, everything in your house will be live.

Take a 12v battery, and tie the positive terminal to a copper pipe in your house. If you measure between the ground pin of an outlet, and the negative terminal of the battery, you will measure 12v. The battery is an isolated power source, and the earth ground of your house is irrelevant as far as its concerned. A portable generator on rubber wheels with plastic feet is an isolated power source like that battery.

 

[48RON54]

I rent and sell generators for a living. What is all this unbond the neutral at the generator stuff about? All of our generators have a bonded neutral. Whether using the ceptacles, or hard wiring the generator to power up a building, I have never once heard a story of someone breaking the neutral bond at the genset whether a transfer switch was involved or not. You would think in 21 years of doing this job, this question would have been brought up at least once. Or, with some frequency, I'd see some wiring disconnected where everything grounds on the frame of the genset. It does not happen.

 

[pattenp]

The generator frame is grounded via the EGC (equipment ground conductor) which the neutral is bonded to at the service disconnect. All you have to is search the web about unbonding portable gen neutral when gen is used to power house electrical system.

I'm talking about when the neutral is not switched. If neutral is switched then neutral should be bonded at gen.

 

[American Locomotive]

The generator frame is grounded via the EGC (equipment ground conductor) which the neutral is bonded to at the service disconnect. All you have to is search the web about unbonding portable gen neutral when gen is used to power house electrical system.

I'm talking about when the neutral is not switched. If neutral is switched then neutral should be bonded at gen.

Think about this logically:
- The generator has three wires in its cord to the house: Hot, Neutral and Ground (possibly two hots for a 240v generator)
- The generator is an isolated power source. Since it's on rubber wheels and plastic feet, it has no reference to earth ground
- Ground and Neutral are bonded together at panel inside the house

On most generators, the ground pins on the outlets are bonded to the generator chassis, and the chassis is bonded to the neutral. If you un-bond the neutral from generator chasis, the ground pins and the generator chassis are now "floating". They have no 0v reference.

When connected to house panel, the generator's chassis becomes connected to neutral inside the panel via the ground wire in the cable joining the generator to the panel.

Now take your cord connecting the generator to your panel, and severe the neutral connection, but leave the hot and ground wires intact. You now have no neutral path back to the generator. So now the neutral bus inside your panel is now floating at 120v. Your grounding system is also now at 120v, since it's bonded to neutral inside the panel. No problem, the ground is hooked up to the generator, right?

Well no, since you unbonded the generator's chassis from the genhead's neutral, the generator's chassis (and therefor ground connection on its outlets) are no longer referenced to 0v, and are not capable of sinking any fault current. So now all of the piping and faucets inside your home are now at 120v potential relative to neutral on the generator.

 

[Lamakocklee]

I'm under the impression that if the ground is bonded to the neutral at the generator it is considered a separately derived system..

https://cpower.com/PDF/InfoSheets/44.pdf

Out of curiosity, does the manufacturer of the generator specify how to wire it up backfeeding a home thru a transfer switch?

 

[electroman187]

I love this conversation. While I don't work in the field, I do maintain a master's license just in case. Full disclosure, I do not stay tight with the NEC anymore.

I see both sides of the argument and I believe pattenp is correct. I think it's in the 2011 or 2014 code update. When the neutral is not switched, then the main bonding jumper is still in tact and redundant connections are illegal. The bonding jumper on the generator should be removed. The frame is grounded through the jumper installed at the house.

Think about it. If both bonding jumpers are in place, then half the neutral current will travel on the EGC because they are in parallel. That's not good.

Now consider the case when the generator bond is removed. In the event of a ground-fault, the fault path will follow the EGC until it meets main bonding the jumper and continue down the neutral back to the generator until the generator or house breaker trips.

American Locomotive, I understand your broken neutral argument, but the same thing can happen if the utility neutral breaks. The neutral will be the tap of a voltage divider between the loads of the two phases. More load on one phase and the other phase will have a higher voltage. The neutral and grounding system shouldn't wander too far with a proper grounding electrode.

Now, if you're going to use the portable generator as a standalone, keep the bonding jumper.

 

[pattenp]

Read this..
http://help.championpowerequipment....at-does-floating-neutral-on-my-generator-mean

 

[American Locomotive]

Think about it. If both bonding jumpers are in place, then half the neutral current will travel on the EGC because they are in parallel. That's not good.

I do agree that in such a configuration some current would flow through the EGC to the generator chassis, but I'm not sure that would really be an issue.

Now consider the case when the generator bond is removed. In the event of a ground-fault, the fault path will follow the EGC until it meets main bonding the jumper and continue down the neutral back to the generator until the generator or house breaker trips.

We agree there

American Locomotive, I understand your broken neutral argument, but the same thing can happen if the utility neutral breaks. The neutral will be the tap of a voltage divider between the loads of the two phases. More load on one phase and the other phase will have a higher voltage. The neutral and grounding system shouldn't wander too far with a proper grounding electrode.

Ah, but the utility usually has earth-ground rods driven into the ground all over the place connected to the neutral line. So in the event your neutral on the house does break, the neutral current should shunt to earth ground. I've heard some very rural areas only use a 1 wire feed, and rely on earth-ground for the return current?

Read this..
http://help.championpowerequipment....at-does-floating-neutral-on-my-generator-mean

In a center-tapped dual-voltage 120/240 generator, there is a "real" neutral that is at 0 volts. Most 120/240 generators I've seen utilize a center-tapped gen head. Now I suppose inverter generators or specialty gen heads would not have that center tap, and would have separate 120 and 240 windings.

 

[mrobins297aaa]

I have a Generac GP7500E and I have not removed the bond, below is what I got from the manufacturer:

on the phone: generac told me that they don't recommend removing the bond that the generator can be used right out of the box with the 2 pole transfer switch without the neutral switch, she said the notes in the instructions for the transfer switch only pertain to the xp models because they are there only generators with gfi protection.

she also said you should only remove the bond if local codes require it and if you do it should be done by the a generac service center, if you remove it yourself it could void your warranty. end of phone call.

They also sent me a email about it.
below is a copy and paste response from the generac email:


"Good morning,



Thank you for contacting Generac Power Systems. My name is Sara and I will be assisting you today. You can use the unit out of box with a Gen tran switch. You should not need to remove the bond. These units do not have the gfci. If you have any other questions please let us know. Again thank you for contacting Generac and have a great day!



Sara

Customer Support

888-436-3722"

 

[nsula_country]

Read this..
http://help.championpowerequipment....at-does-floating-neutral-on-my-generator-mean

I have personally dealt with floating neutrals. In many older industrial control cabinets using a xformer to step 480v to 120v. On the 120v (secondary) side of xformer, the neutral was not bonded to earth. When using a meter to check voltages, the line will be low and show voltage on neutral. Some times as much as 60v on neutral. But when checking line to neutral its always 120v. Because neutral is "above ground"...

CT

 

[kd3pc]

OSHA says:

https://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.html

 

[lakelandcat]

related/nonrelated don't know, but here goes, help if you can.I hooked my shop power past my meter and before my house panel. Can I hook a transfer switch into my 200A shop panel and run my gen. to power my house and shop? neutral is bonded to ground in the shop

 

[TractorJeff]

Seen as there have been 2 Hurricanes smashing the East Coast in the past 6 weeks.
This thread should maybe come back to the top?

 

[sberry]

I fugged this up along the line somewhere. I had my guy install an outlet boogered on one and told him to make it 240, I forgot about it and hooked it on to my folks house. Burned up a bunch of stuff. It was a dumb mistake as there was a 4 wire recept on the machine. I had one back in the day I was metering,,, duh, had current on the ground wire and I wonder wtf.
These incidents were some time ago.

 

[TRWham]

... I've heard some very rural areas only use a 1 wire feed, and rely on earth-ground for the return current?
...

I think that earth return is only for the distribution voltage (something over 10kV) to limit the ground current, but each customer transformer is three wire from pole to house. I have seen a case where a house lost its neutral, thanks to a tree cutter, but most of the 120V circuits continued to operate using the ground to return current, but it was less than 200 ft to the transformer. Some equipment was damaged by the voltage spike, but I don't know what the voltage measured or how stable it was.