NEC 702.10 requires that households with an optional standby system to have either:
(A) Transfer equipment that switches the grounded (neutral) conductor and a generator with its grounded (neutral) conductor bonded to the case.
OR
(B) Transfer equipment that does not switch the grounded (neutral) conductor and a generator with its grounded (neutral) conductor not bonded to the case, also known as a “Neutral Floating Generator.”
Several companies market manual transfer equipment (generator panels) with a 120/240V power inlet. A portable generator is then to be connected to the generator panel with a twist lock cord. All of the generator panels that I have looked at switch the ungrounded conductors only. The neutral remains solidly connected at the generator panel.
Most portable generators have the neutral bonded to the frame.
The use of neutral bonded generators and the above referenced manual transfer equipment is a code violation (neutral bonded to ground in two locations) and would cause current to flow in the grounding conductor, creating a safety hazard.
What is the appropriate solution to this problem? I would wager that this scenario exists in most homes with a generator panel and portable generator.
You could alter the portable generator so that the neutral is no longer bonded to the frame. But, what if this generator (likely to have 120 V receptacles) were to then be used to energize plug and cord equipment? A safety hazard would be created. Additionally, would a manufacturer permit this alteration?
As an alternative, could you omit, or sever, the grounded (neutral) conductor between the generator and the generator panel? This would effectively create a 2 pole, 3 wire 240 V connection between the generator and the generator panel. Current for 120 V circuits in the generator panel would then return via the unswitched grounded (neutral) conductor to the main panel. Would this proposal satisfy the requirements of NEC 702.10 and NEC 250?
(A) Transfer equipment that switches the grounded (neutral) conductor and a generator with its grounded (neutral) conductor bonded to the case.
OR
(B) Transfer equipment that does not switch the grounded (neutral) conductor and a generator with its grounded (neutral) conductor not bonded to the case, also known as a “Neutral Floating Generator.”
Several companies market manual transfer equipment (generator panels) with a 120/240V power inlet. A portable generator is then to be connected to the generator panel with a twist lock cord. All of the generator panels that I have looked at switch the ungrounded conductors only. The neutral remains solidly connected at the generator panel.
Most portable generators have the neutral bonded to the frame.
The use of neutral bonded generators and the above referenced manual transfer equipment is a code violation (neutral bonded to ground in two locations) and would cause current to flow in the grounding conductor, creating a safety hazard.
What is the appropriate solution to this problem? I would wager that this scenario exists in most homes with a generator panel and portable generator.
You could alter the portable generator so that the neutral is no longer bonded to the frame. But, what if this generator (likely to have 120 V receptacles) were to then be used to energize plug and cord equipment? A safety hazard would be created. Additionally, would a manufacturer permit this alteration?
As an alternative, could you omit, or sever, the grounded (neutral) conductor between the generator and the generator panel? This would effectively create a 2 pole, 3 wire 240 V connection between the generator and the generator panel. Current for 120 V circuits in the generator panel would then return via the unswitched grounded (neutral) conductor to the main panel. Would this proposal satisfy the requirements of NEC 702.10 and NEC 250?
