• We will be performing upgrades on the forums and server over the weekend. The forums may be unavailable multiple times for up to an hour each. Thank you for your patience and understanding as we work to make the forums even better.

1 portable generator to feed 2 200 Amp panels with generator interlocks.

Learn the NEC with Mike Holt now!
M

MikeyFSE

Member
Location
Edmonds WA
Occupation
Electrical Contractor
How to safely have 1 portable generator feed 2 200 Amp panels with generator interlock. Addressing isolating grounded conductor between panels.
 
R

ruxton.stanislaw

Senior Member
Location
Arkansas
Occupation
Laboratory Engineer
Here's how to safely have 1 portable generator feed 2, 200 Amp panels with a generator interlock, addressing the isolation of the grounded conductor between panels:

Important Disclaimer: Electrical work, especially involving generator installations and modifications to electrical panels, can be dangerous if not done correctly. This information is for informational purposes only and should not be a substitute for consulting with a qualified electrician who can assess your specific situation and ensure safe and code-compliant installation.

Generator Requirements:
  • Size: The generator needs to be adequately sized to handle the combined load of both 200 Amp panels. Determine the total wattage or amperage of all appliances and equipment you plan to power simultaneously across both panels. Choose a generator with a continuous output rating that exceeds this total by 20-30% to account for starting surges.
  • Transfer Switch or Interlock Kit: A transfer switch or interlock kit is crucial to prevent accidentally backfeeding power to the utility grid. This ensures your home's electrical system is completely isolated from the utility while operating on generator power.
Addressing Isolation of Grounded Conductor:

Here's the key point regarding the grounded conductor:
  • In the United States (NEC standards): The 2023 National Electrical Code (NEC) typically requires a 4-wire transfer switch for generator installations with a separate neutral and grounding conductor. This ensures the neutral and grounding conductors remain isolated between the generator and utility supply.
Here's a breakdown of the installation process (refer to a qualified electrician for actual work):
  1. Identify Panel Types: Determine if your existing panels are main breaker panels or subpanels. This will influence the specific installation approach.
  2. Install Transfer Switch: Install a 4-wire transfer switch with a capacity exceeding the generator's output rating. The transfer switch will be connected to the utility feed, generator output, and the two 200 Amp panels.
  3. Isolating Grounded Conductor: During the transfer switch installation, ensure the grounded conductor (neutral wire) coming from the generator is isolated from the grounded conductor of the utility feed. The transfer switch should have separate terminals for the neutral and grounding conductors from both sources.
  4. Panel Bonding: The grounding conductor from the generator will connect to the grounding bus bar in the transfer switch. In most cases, the neutral conductor from the generator should not be connected to the grounding bus bar or any other equipment grounding conductors within the transfer system. Consult a qualified electrician for specific bonding requirements based on your panel types and local codes.
  5. Interlock Kit (Alternative): If using an interlock kit instead of a transfer switch, ensure it's a 4-wire kit designed to isolate the neutral conductor. However, transfer switches are generally considered a safer and more reliable option for generator installations.
Additional Considerations:
  • Permit Requirements: In many areas, permits are required for installing a generator and modifying electrical panels. Check with your local building department to understand the permitting process.
  • Qualified Electrician: While this information provides a general overview, it's highly recommended to consult with a qualified electrician to ensure a safe and code-compliant installation that meets your specific needs and local regulations. They can assess your existing electrical system, select the appropriate transfer switch or interlock kit, and perform the installation according to best practices.
Remember, safety is paramount when dealing with electrical wiring and generators. Don't attempt any electrical work yourself unless you are a qualified electrician.
 
qcroanoke

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
Switching it correctly to not backfeed onto the grid would concern me more than neutral currents
 
H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
augie47 said:
True but a great percentage of generator installs that size are not SDS
Click to expand...
qcroanoke said:
And the utility neutral is still connected even when genset is running. I see no reason to use a contactor.
Click to expand...
You still have a small neutral from the generator paralleled with the larger panel neutrals, but usually is a non issue on that small of a service. As you said, a vast majority of the installations are that way. Just technically not right.
 
tom baker

tom baker

First Chief Moderator & NEC Expert
Staff member
Location
Bremerton, Washington
Occupation
Master Electrician
ruxton.stanislaw said:
Here's how to safely have 1 portable generator feed 2, 200 Amp panels with a generator interlock, addressing the isolation of the grounded conductor between panels:

Important Disclaimer: Electrical work, especially involving generator installations and modifications to electrical panels, can be dangerous if not done correctly. This information is for informational purposes only and should not be a substitute for consulting with a qualified electrician who can assess your specific situation and ensure safe and code-compliant installation.

Generator Requirements:
  • Size: The generator needs to be adequately sized to handle the combined load of both 200 Amp panels. Determine the total wattage or amperage of all appliances and equipment you plan to power simultaneously across both panels. Choose a generator with a continuous output rating that exceeds this total by 20-30% to account for starting surges.
  • Transfer Switch or Interlock Kit: A transfer switch or interlock kit is crucial to prevent accidentally backfeeding power to the utility grid. This ensures your home's electrical system is completely isolated from the utility while operating on generator power.
Addressing Isolation of Grounded Conductor:

Here's the key point regarding the grounded conductor:
  • In the United States (NEC standards): The 2023 National Electrical Code (NEC) typically requires a 4-wire transfer switch for generator installations with a separate neutral and grounding conductor. This ensures the neutral and grounding conductors remain isolated between the generator and utility supply.
Here's a breakdown of the installation process (refer to a qualified electrician for actual work):
  1. Identify Panel Types: Determine if your existing panels are main breaker panels or subpanels. This will influence the specific installation approach.
  2. Install Transfer Switch: Install a 4-wire transfer switch with a capacity exceeding the generator's output rating. The transfer switch will be connected to the utility feed, generator output, and the two 200 Amp panels.
  3. Isolating Grounded Conductor: During the transfer switch installation, ensure the grounded conductor (neutral wire) coming from the generator is isolated from the grounded conductor of the utility feed. The transfer switch should have separate terminals for the neutral and grounding conductors from both sources.
  4. Panel Bonding: The grounding conductor from the generator will connect to the grounding bus bar in the transfer switch. In most cases, the neutral conductor from the generator should not be connected to the grounding bus bar or any other equipment grounding conductors within the transfer system. Consult a qualified electrician for specific bonding requirements based on your panel types and local codes.
  5. Interlock Kit (Alternative): If using an interlock kit instead of a transfer switch, ensure it's a 4-wire kit designed to isolate the neutral conductor. However, transfer switches are generally considered a safer and more reliable option for generator installations.
Additional Considerations:
  • Permit Requirements: In many areas, permits are required for installing a generator and modifying electrical panels. Check with your local building department to understand the permitting process.
  • Qualified Electrician: While this information provides a general overview, it's highly recommended to consult with a qualified electrician to ensure a safe and code-compliant installation that meets your specific needs and local regulations. They can assess your existing electrical system, select the appropriate transfer switch or interlock kit, and perform the installation according to best practices.
Remember, safety is paramount when dealing with electrical wiring and generators. Don't attempt any electrical work yourself unless you are a qualified electrician.
Click to expand...
Notice this post is AI generated. How the generator is bonded and grounded is determined by the transfer switch
 
qcroanoke

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
tom baker said:
Notice this post is AI generated. How the generator is bonded and grounded is determined by the transfer switch
Click to expand...
Step 5 says to use a 4 wire interlock kit..... I don't think I've ever seen one of those.....
 
H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
tom baker said:
Notice this post is AI generated. How the generator is bonded and grounded is determined by the transfer switch
Click to expand...
I had an AI response to a question for a mini split, the seller did not list the amps, only volts, and btu. Instead of answering the question, it said that information was not specified, and to call the manufacturer. Duh! The seller should have this info if they want to sell it. BTU’s mean nothing to an electrician!
 
R

ruxton.stanislaw

Senior Member
Location
Arkansas
Occupation
Laboratory Engineer
tom baker said:
Notice this post is AI generated. How the generator is bonded and grounded is determined by the transfer switch
Click to expand...
This post covers generator installations with a separate neutral and grounding conductor, as previously mentioned.

qcroanoke said:
Step 5 says to use a 4 wire interlock kit..... I don't think I've ever seen one of those.....
Click to expand...
It is like the kits that you see at Costco every now and then.

hillbilly1 said:
I had an AI response to a question for a mini split, the seller did not list the amps, only volts, and btu. Instead of answering the question, it said that information was not specified, and to call the manufacturer. Duh! The seller should have this info if they want to sell it. BTU’s mean nothing to an electrician!
Click to expand...
I am sorry for your bad experience with AI! Sometimes, that is the best it can do - it's not a magic bullet. It is for sure not possible to guess the ampacity from BTU alone, only to get a general idea of course (e.g. NN A or NNN A).
 
Last edited:
You must log in or register to reply here.
Top