Backup Generator for House Panel

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jonny1982

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Backed up a 200 amp residential panel with a 3500 watt 240 volt honda generator (properly with innerlock). Fed it from the L-1430 outlet on the generator (2P, 4W). After troubleshooting, found that the breaker on the generator was tripping because of the GFI protection ( would trip with ground and netural landed, but when I took off the ground in the panel, didn't trip). Is it legal to feed the panel comming out of the L14-30 outlet on the generator with just 2 hots and a neutral (leave the ground disconnected)? Or is the breaker just being to sensitive?

Thanks
 

GoldDigger

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If both the generator and the utility service bond the neutral to the EGC, then your transfer switch must switch the neutral too.
If the generator has a ground to neutral bond, you can possibly remove that, converting from a seperately derived to a non separately derived source. But if the bond remains you must run both neutral and EGC to the TS.
 
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jonny1982

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If both the generator and the utility service bond the neutral to the EGC, then your transfer switch must switch the neutral too.
If the generator has a ground to neutral bond, you can possibly remove that, converting from a seperately derived to a non separately derived source. But if the bond remains you must run both neutral and EGC to the TS.

It's not a transfer switch, it's called innerlock. It's a legal way to backfeed the panel using basically a piece of metal that slides that prevents the main from being on if the backfeed generator breaker is on and vice versa. \

I originally ran 2 hots, a neutral, and a ground out to the generator. The breaker would trip. Then I disconnected the ground from the cord so only 2 hots and a neutral ran from generator to panel. Should I run 2 hots and ground instead from generator to panel and disconnect neutral?

Thanks
 

rlundsrud

Senior Member
Location
chicago, il, USA
GoldDigger's answer was on the money. What you are calling an interlock still functions as a transfer switch and doesn't change the requirements for correctly connecting it. As he said, if the neutral is bonded at the generator you must switch the neutral.

As to the ground, I would not disconnect it. I am just guessing but if the neutral was bonded at both the generator and the panel, that might cause a ground fault because of parallel paths. Since you are not switching the neutral with your interlock, just verify the bonding at the generator and remove if connected. This should alleviate your problem.
 
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jonny1982

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GoldDigger's answer was on the money. What you are calling an interlock still functions as a transfer switch and doesn't change the requirements for correctly connecting it. As he said, if the neutral is bonded at the generator you must switch the neutral.

I guess my question is, why is the generator breaker tripping when I have all four wires landed at the panel, but then when I either remove the ground or remove the neutral, it funcions?
 
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jonny1982

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I guess my question is, why is the generator breaker tripping when I have all four wires landed at the panel, but then when I either remove the ground or remove the neutral, it funcions?

Do newer generators tend to have the ground and netural bonded, unbonded, or 50/50?
 
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jonny1982

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GoldDigger's answer was on the money. What you are calling an interlock still functions as a transfer switch and doesn't change the requirements for correctly connecting it. As he said, if the neutral is bonded at the generator you must switch the neutral.

As to the ground, I would not disconnect it. I am just guessing but if the neutral was bonded at both the generator and the panel, that might cause a ground fault because of parallel paths. Since you are not switching the neutral with your interlock, just verify the bonding at the generator and remove if connected. This should alleviate your problem.

I see what you are sayin. What is the typical procedure for removing a neutral to ground bond in a portable generator?
 
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jonny1982

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I see what you are sayin. What is the typical procedure for removing a neutral to ground bond in a portable generator?

Also, how would I determine if there was a bond in the generator? I guess just make sure nothing is plugged in and do a contnuity check between ground and neutral in the 240 volt outlet?
 

jaggedben

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Northern California
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Solar and Energy Storage Installer
Also, how would I determine if there was a bond in the generator? I guess just make sure nothing is plugged in and do a contnuity check between ground and neutral in the 240 volt outlet?

What rlundsrud said.

If the generator is allowed to be configured with or without the bond, it will have instructions in the product literature, or perhaps in some kind of official technical application note that you could obtain from the manufacturer.

If the manufacturer can't tell you how to disconnect the bond then you probably should have used either a different generator or a different type of transfer switch.
 

GoldDigger

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Location
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What rlundsrud said.

If the generator is allowed to be configured with or without the bond, it will have instructions in the product literature, or perhaps in some kind of official technical application note that you could obtain from the manufacturer.

If the manufacturer can't tell you how to disconnect the bond then you probably should have used either a different generator or a different type of transfer switch.
If the generator has GFCI protection built in for all connections, you can be pretty sure that there is a bond and it is not intended to be removed.
Unfortunately there is an interaction between the UL requirements for the generator and NEC requirements on bonding which usually cannot be reconciled except by switching the neutral.
 
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jonny1982

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After having run into this problem before, I decided not to use the "interlock" set up anymore. I buy transfer switches that switch the neutral and move individual circuits out of the main panel. Don't like the idea of altering someone else's
generator. Someone can do it cheaper using the interlock, but they run the risk of problems down the road.
http://www.electricgeneratorsdirect.com/Reliance-Controls-XRC0603C/p3714.html

Thanks for all the info.

One more question is, lets say I leave the frame bonded to the neutral at the generator. To make it work, is it safer to disconect the ground wire going to the panel from the generator, or disconnect the neutral going to the panel from the generator. Don't worry, I don't plan on doing anything that isn't proper. I just want to be educated on the matter.

Thanks
 

iwire

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Location
Massachusetts
After troubleshooting, found that the breaker on the generator was tripping because of the GFI protection ( would trip with ground and netural landed, but when I took off the ground in the panel, didn't trip).

What GFI?

The generators output has a GFCI breaker???

There is no reason a 240 volt 30 amp receptacle on a generator should have GFCI protection.

Is this generator really designed to feed a panel or is it really designed for portable use only?
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Units designed for portable use in OSHA environments are likely to have the entire output GFCI protected to reduce the need to GFCI individual circuits.

OP:
Not connecting the neutral is simply not an option as it would force normal current through the EGC.
Not connecting the EGC could force fault current to travel through the earth, preventing proper breaker tripping. Also not safe.
 
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jonny1982

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Units designed for portable use in OSHA environments are likely to have the entire output GFCI protected to reduce the need to GFCI individual circuits.

OP:
Not connecting the neutral is simply not an option as it would force normal current through the EGC.
Not connecting the EGC could force fault current to travel through the earth, preventing proper breaker tripping. Also not safe.

Wouldn't the neutral current come back to the panel and then travel through the service neutral before it would travel back to the generator?

Wouldn't the fault current come back to the panel and then travel through the normal channels as well before going to the generator?

Again, I realize neither one is an option, but I just want to understand it.

Thanks
 

GoldDigger

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Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Without a neutral to the generator, but with a ground rod, most of the return current would flow in the generator EGC. The paths through panel GES and through service neutral to POCO ground, followed by up generator ground rod will have a much higher resistance than the EGC to the generator. The service neutral by itself cannot form a return path to the generator winding. The current flowing through the EGC would then cause the breaker GFCI to trip.

The situation with no EGC connection is more complicated, but it is true that in most cases the fault current will flow down the house EGC to the panel EGC/neutral bond and then through the generator neutral back to the generator. This is still fairly low resistance as long as that neutral is not compromised, but it will totally defeat the action of the GFCI at the generator, so you would be better off disconnecting the GFCI and connecting both wires in that case. (But still not up to code.)
 
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