Portable generator question

[Bernard1599]

Scenario:
8000 watt Portable generator connected to main panel in residence with 30 amp DP breaker using an interlock kit from interlock.com.

Question:
If the generator?s internal neutral is bonded to the generator frame as shown below in the generator schematic, should the bond be disconnected?


Thank you,
Bernard

 

[ceb58]

Take a look at this thread http://forums.mikeholt.com/showthread.php?t=139991

 

[Bernard1599]

Take a look at this thread http://forums.mikeholt.com/showthread.php?t=139991

Hi ceb58,

Thank you for the link to the above thread. I found it very informative. Maybe I did not ask my question correctly in the OP. What I was questioning was since the neutral and ground are bonded in the main service panel and then the neutral and ground are bonded in the generator, should the neutral to ground bond in the genny be removed?

Regards,
Bernard

 

[jumper]

AFAIK, yes- you would have a parallel path for neutral current. The genny frame would have to be rebonded for cord connected loads.

I am probably wrong, but that is how I see it at the moment.

 

[augie47]

Sticky situation.
I agree with jumper.. and i too may be wrong, but, as he says, when connected to the house the neutral ground bond is a violation, but for stand-alone operation you need it.

 

[Bernard1599]

I agree with both jumper and augie 47. Since hurricane Irene I have read several online generator manuals and manual transfer installation instructions. What is troubling is that I have not seen any mention of the genny bonding jumper being removed/disconnected when hard wiring them to the house wiring. Seems odd that the manufacturer would omit a possible liability issue. Don?t you think?

Bernard

 

[Bernard1599]

Couple of other questions for those of you who have installed whole house standby generators. Do these standby generators have the ground & neutral bonded? Is this jumper mentioned in the installation manuals? Is the neutral required to be switched?

Regards,
Bernard

 

[M4gery]

Leaving the neutral bonded to ground in both the generator and main panel will give it a parallel path, but is there any danger in this exact situation since it's upstream (vs. bonding in both the main panel and a sub panel downstream)?

Some generators don't give you a way to disconnect the neutral to ground bond. On the other hand, some generators (such as the popular Honda EU2000i) don't have a neutral to ground bond at all, even when you cord and plug directly to it.

 

[hillbilly1]

My Uncle had a 6 or 7 thousand watt Honda generator that had built in ground fault protection and would trip when connected to a standard manual transfer switch that did not switch the neutral. It was not a ground fault receptacle, but a CT that fired a 30 amp shunt trip breaker. The neutral and ground was bonded at the generator.

 

[Howard Burger]

what's wrong with no G to N bond in generator?

what's wrong with no G to N bond in generator?

Augie - dumb question, because I know services have ground and neutral bonded, but:

why is it bad to not have G and N bonded in generator you are not using for standby power? My genny has a breaker on each receptacle. If there is a ground fault or short circuit, would the breaker NOT trip if the N and G were not bonded? Thanks

 

[Howard Burger]

engage brain before hitting 'send'

engage brain before hitting 'send'

Sometimes I think I forget to put my brain in gear before I hit the 'send' button. Thinking about my question, I conclude that since the genny doesn't have a GEC, and is just sitting on the ground, that the N-G bond is what will trip the breaker in the event of a fault of any kind.

So I guess the problem is if you have a generator for backup plus other utility uses around the farm, you either violate code by leaving it bonded when you use it as emergency backup power, or risk a shock if you use it to power equipment somewhere else. Sheesh.

 

[tom baker]

My Uncle had a 6 or 7 thousand watt Honda generator that had built in ground fault protection and would trip when connected to a standard manual transfer switch that did not switch the neutral. It was not a ground fault receptacle, but a CT that fired a 30 amp shunt trip breaker. The neutral and ground was bonded at the generator.

The 2011 NEC requires GFI protection for generator 15-20-30 receptacles, as these generators become available with GFI, tripping issues will result when the generator is used to power a system with a main bonding jumper. The CMPs answer is to install a switched neutral transfer switch.

 

[jwelectric]

The 2011 NEC requires GFI protection for generator 15-20-30 receptacles, as these generators become available with GFI, tripping issues will result when the generator is used to power a system with a main bonding jumper. The CMPs answer is to install a switched neutral transfer switch.

I have two Honda generators that are 10 years old that have GFCI protection on the 30 amp receptacle.

 

[Bernard1599]

The following link will take you to a pretty decent article from Cummins Power Generation discussing ground-to-neutral bonding of generators in separately derived systems.

http://www.cumminspower.com/www/literature/technicalpapers/PT-6006-GroundingAC-2-en.pdf

Bernard

 

[don_resqcapt19]

...
So I guess the problem is if you have a generator for backup plus other utility uses around the farm, you either violate code by leaving it bonded when you use it as emergency backup power, or risk a shock if you use it to power equipment somewhere else. Sheesh.

Many portable generators do not have the neutral bonded to the frame. You have to look close at the wiring diagram for the generator. Some manufacturers, like Honda, have the bond in some models and not in others.

 

[kwired]

A portable generator with no neutral - ground bond that is not connected to a premesis wiring system is (regardless of what code requirements may or may not be) fairly safe. It is no different than the allowed ungrounded systems that are permitted in the NEC, other than there is no ground fault detection system. Since there is no grounded conductor the shock risk is greatly diminished as there is no reference to ground. Once a conductor becomes grounded you have a reference and overcurrent devices will operate if a second conductor becomes grounded. When tying this generator to a premises wiring system, the service does have a conductor that is grounded and this changes everything compared to having the generator standing on its own, the generator becomes part of the system.

 

[iwire]

I have two Honda generators that are 10 years old that have GFCI protection on the 30 amp receptacle.

Seems like a really poor design.

 

[tkb]

Scenario:
8000 watt Portable generator connected to main panel in residence with 30 amp DP breaker using an interlock kit from interlock.com.

Question:
If the generator?s internal neutral is bonded to the generator frame as shown below in the generator schematic, should the bond be disconnected?


Thank you,
Bernard

In MA we have an amendment to the 2001 NEC that allows this configuration up to 15kw.

702.11. Insert a new 702.11(C) as follows:

(C) Classification of Supply. A generator with a grounded circuit conductor connection as part of its output shall be wired as a separately derived source unless its grounded circuit conductor is not bonded to the frame, or where used to supply a premises wiring system it shall be permitted to be wired as a nonseparately derived source if all of the following conditions are met:

(1) The generator rating does not exceed 15 kw.

(2) The generator is connected through a flexible cord and a cord connector to a flanged inlet.

(3) The flexible cord does not exceed 4.5 m (15 feet) in length.

(4) The flanged inlet connection point is not more than 3.0 m (10 feet) from the main bonding jumper or system bonding jumper for the supplied premises.

(5) The point of connection is marked ?Disconnect cord when generator is not in service.?

(6) Ground-fault protection of equipment has not been installed on any portion of the premises wiring system supplied by the generator.

Informational Note: Current product standards require all portable generators rated 15 kw and below and supplying grounded output circuits to have the grounded circuit conductor connections bonded to the generator frame.

 

[jwelectric]

Seems like a really poor design.

seems like there are some electricians that sees nothing wrong with using one of these small generators to power a panel and they are putting a stop to it

 

[Bernard1599]

In MA we have an amendment to the 2001 NEC that allows this configuration up to 15kw.

702.11. Insert a new 702.11(C) as follows:

(C) Classification of Supply. A generator with a grounded circuit conductor connection as part of its output shall be wired as a separately derived source unless its grounded circuit conductor is not bonded to the frame, or where used to supply a premises wiring system it shall be permitted to be wired as a nonseparately derived source if all of the following conditions are met:

(1) The generator rating does not exceed 15 kw.

(2) The generator is connected through a flexible cord and a cord connector to a flanged inlet.

(3) The flexible cord does not exceed 4.5 m (15 feet) in length.

(4) The flanged inlet connection point is not more than 3.0 m (10 feet) from the main bonding jumper or system bonding jumper for the supplied premises.

(5) The point of connection is marked “Disconnect cord when generator is not in service.”

(6) Ground-fault protection of equipment has not been installed on any portion of the premises wiring system supplied by the generator.

Informational Note: Current product standards require all portable generators rated 15 kw and below and supplying grounded output circuits to have the grounded circuit conductor connections bonded to the generator frame.

Please do not take the following questions as being adversarial in nature, but……

What is it, exactly, that makes the above a safe installation with the neutral-to-frame connection at the generator? Is it the fact that the flexible cord and the inlet box wiring combined length is 25’ or less from the MBJ and not say 30’?; or is it the fact that there is no GFP for equipment and not GFP for personnel?; or is it that the genny is 15kw or less?; or etc.? Why does the combination of 1 through 6 make this a safe use of a portable generator used to power the structured wiring.

Regards,
Bernard