Clarifications about portable generator grounding

Status
Not open for further replies.

M4gery

Senior Member
I have some questions about portable generator grounding and bonding that I would appreciate help with.

1) When backfeeding a panel with an interlock kit or using a simple manual transfer panel, the neutral isn't switched. Because of that fact, the neutral-ground bond in the service disconnect still applies. In this situation you would remove the neutral-ground bond in the generator, correct?

2) When using manual transfer switch that switches the neutrals, you lose the neutral-ground bond in the service disconnect. In this situation you would have to either leave the neutral-ground bond in the generator intact, OR bond the neutral to ground on the generator side of the transfer switch, is that correct?

3) The reason you don't want the neutral-ground bond in both the service disconnect and the generator is so that there are not 2 paths for the current to flow. However, in this situation those two paths would only be thru the generator cord unlike when dealing with a sub-panel in a house in which current can flow thru appliances, etc. Is that correct? Is there a reduced danger in the generator situation? The reason I ask is because I think a lot of homeowners who have this portable generator/inlet/transfer panel setup don't break the bond when connecting the generator to their house.

4) First, thank you for getting this far ;) Finally, what is the purpose of a grounding conductor on a generator without a neutral-ground bond at all? For example, the popular Honda EU2000i:

Code:
GROUND SYSTEM
Connections for standby power to a building electrical system must be
made by a qualified electrician. The connection must isolate the
generator power from utility power, and must comply with all
applicable laws and electrical codes.

Honda portable generators have a system ground that connects
generator frame components to the ground terminals in the AC output
receptacles.[B][I] The system ground is not connected to the AC neutral
wire. [/I][/B]If the generator is tested by a receptacle tester, it will not show
the same ground circuit condition as for a home receptacle.
 

skeshesh

Senior Member
Location
Los Angeles, Ca
1) When not switching the neutral, the neutral and ground should not be bonded at the genset.

2) When switching the neutral you want to establish a seperately derived system the neutral and ground should be bonded.

3) That is right, doing so will create parallel ground loops. Where the current flows depends on how and to parts of the system the generation is connected. I don't have much experience with portable gensets for residentials but I'm sure someone experienced will chime in shortly.

4) The purpose of EGC is the same as the rest of the system that is to connect non-current carrying metallic surfaces in order to carry fault current to ground as well as trip the overcurrent protection.

Sounds like its time for you to take a stroll down to article 250 street, a trip I find myself taking quite often :roll:
 

M4gery

Senior Member
4) The purpose of EGC is the same as the rest of the system that is to connect non-current carrying metallic surfaces in order to carry fault current to ground as well as trip the overcurrent protection.

How is that possible if neutral is not bonded to ground in the generator? How would you trip an OCPD?
 

M4gery

Senior Member
There are some variables. Have you looked at 250.34 ?

Yes, but I am still looking for a bit of clarification. Especially on the part about some generators not having a neutral-ground bond. When used directly with an extension cord, what is the purpose of even having the EGC?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
How is that possible if neutral is not bonded to ground in the generator? How would you trip an OCPD?

When the T/S does not open the neutral, the neutral and ground are bonded at the service equipment so a ground fault would flow back to the service then to the neutral and trip the Gen OCP.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
Yes, but I am still looking for a bit of clarification. Especially on the part about some generators not having a neutral-ground bond. When used directly with an extension cord, what is the purpose of even having the EGC?

Because in theory, it isn't a hazard. If there is a fault against the case of a metal portable tool, since the generator isn't connected to the earth there is no way to be shocked.

Supposedly, in larger generators, there can be some capacitive coupling to the earth so then you could be shocked.

With all the pins and wires there, you could make a "bonding plug" which is just a plug with a wire connecting neutral to ground. Now you have a fault path to the EGC.
 

M4gery

Senior Member
When the T/S does not open the neutral, the neutral and ground are bonded at the service equipment so a ground fault would flow back to the service then to the neutral and trip the Gen OCP.

In this instance I am talking about using just the generator. If I plug devices and alliances directly into a generator, what is the purpose of having an EGC if neutral isn't bonded to ground?
 

M4gery

Senior Member
Because in theory, it isn't a hazard. If there is a fault against the case of a metal portable tool, since the generator isn't connected to the earth there is no way to be shocked.

Supposedly, in larger generators, there can be some capacitive coupling to the earth so then you could be shocked.

With all the pins and wires there, you could make a "bonding plug" which is just a plug with a wire connecting neutral to ground. Now you have a fault path to the EGC.

I see what you are saying, thank you.
 

SG-1

Senior Member
In this instance I am talking about using just the generator. If I plug devices and alliances directly into a generator, what is the purpose of having an EGC if neutral isn't bonded to ground?

If the generator is being used for cord & plug connected loads the grounded conductor (neutral) & EGC should be bonded at the generator. It does not matter if the grounded conductor is not actually connected to a Grounding Electrode System ( GES ). The fault path is as follows:
1. Ungrounded conductor comes into contact with the metal frame of appliance.
2. EGC carries fault current back to the generator ( neutral ) via the bonding jumper.
3. Generator OCPD trips.

The earth has nothing to do with providing a current path for the fault. The EGC provides the path. This is true even when the neutral is connected to a GES.

The Honda may have ground fault protection built in, and does not require a solid connection between the EGC & the neutral.
 
Last edited:

kwired

Electron manager
Location
NE Nebraska
Yes, but I am still looking for a bit of clarification. Especially on the part about some generators not having a neutral-ground bond. When used directly with an extension cord, what is the purpose of even having the EGC?

The frame of the generator and anything connected to the EGC leaving the generator are at the same potential. All non current carrying parts still need connected together even if supplied by an ungrounded system. (250.4(B))
 
Status
Not open for further replies.
Top