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If your transfer panel does not switch neutral, the generator should have its neutral conductor floating, not bonded to the chassis. Having a second bonding point will not prevent the system from working. Your lights will come on, but your safety will be jeopardized. If you are going through the expense and effort to purchase and install a backup power system do it properly.
Take a look at return current flow along the neutral and ground conductors. If you have only three conductors, such as with the neutral bond in the main panel and in the generator (or with just a 3-conductor cord), there will be no separate and independant ground conductor bonding the generator frame back to your house ground. There is a potential of the chassis becoming live as there is current flow along the ground conductor.
Remove the neutral bond and now all return current flowing from the live conductors will flow along the neutral conductor only. It will not flow along the ground conductor. This will ensure the chassis remains at the proper potential.
To meet electrical code requirements for stand alone operation, neutral and ground should be bonded together. This can be accomplished quite simply with a standard 120V 15A plug with ground and neutral jumpered and plugged into an outlet.
Picture is here. Many of the Chinese built generators with a built in 120/240V selector do some very odd things with the switch. I do not recommend using the neutral/ground jumper plug with those generators.
My personal opinion (and that of others who I have discussed the issue with) is that floating neutral is safer for stand alone operation. Consider having the generator chassis connected to a suitable ground rod. You are a few feet away, standing in a puddle of water with bare feet. Holding one of the live wires in your hand, there is no return path from the neutral conductor or the other live line through the chassis. With no path for current to flow you will not experience an electric shock. If the output uses a GFCI outlet it will not trip. Let's install the neutral / ground bond again and the return current path exists through your feet to the grounded chassis, through the bond jumper to the neutral conductor. You can be assured of a nasty jolt. If there is a GFCI outlet in place it should open. Which situation is safer? In my opinion floating neutral is better, but the electrical code says it should be bonded. It may seem I'm going against my own advice and I won't tell people to go against code requirements, so follow the rules.
Rewiring will likely void any remaining warranty as well as UL/CSA certification of the generator. In my case warranty is not important, and I feel safety has not been jeopardized in any way. In fact the system is safer now than it was originally.
Proceed at your own discretion and risk.
To determine if your generator uses a floating or bonded neutral perform this simple test. With the engine off, use an ohm meter between the chassis and neutral conductors in the outlet. If it indicates open circuit, the neutral is floating. A short circuit will indicate neutral bonded to ground. I don't recommend doing this to household circuits due to the possibility of exposed AC and damage to the meter.
Don't trust the generator label. I've seen many in which it is incorrect. Confirm for yourself either way.
It is normal for to read very low resistance between the neutral and live terminals on the outlets. You are measuring the DC resistance of the output coils.
Plug in an electrical tester as shown and start the engine. If it indicates open neutral, live/neutral reversed, or live/ground reversed do not use the generator and have someone qualified check the wiring and make the necessary repairs. Use the tester throughout your house to ensure it is wired correctly. This sort of tester is often inaccurate for determining whether the neutral is bonded or not. Even with a floating neutral, the second light will often be on. I suspect this is due to very low leakage currents and a high impedance bulb in the tester.
My former generator, a DeVilbiss GT5000 was supplied with a duplex outlet for 240VAC. The three wire connection with bonded neutral and ground was not suitable for my transfer panel. It was rewired to use a four conductor twistlock outlet, type NEMA L14-30 30A 125/250VAC. The outlet shown in the picture was later replaced with a L14-20 20A outlet. As a backup power supply for my home, I required the neutral line to be isolated from ground.
There are two output coils in the generator and four wires coming to the output panel.
They are paired as red/green and orange/black. Each coil generates 120VAC.
Orange and green are used as neutral and connect together and attach to the neutral connections on both outlets.
Red and black are used as live lines and both connect directly to the circuit breakers.
From the circuit breaker outputs, connect red to one of the 120VAC outlets and black to the other. Red and black also connect to the live lines on the twistlock plug.
Remove the jumper from ground to neutral, likely on the 120VAC duplex outlet and connect ground connections on both outlets to the chassis.
Note the green wire from the generator coil is not the same as the green wire used for grounding. Be careful not to get the two mixed up!
Make a new label for the electrical panel stating FLOATING NEUTRAL.
Each output coil creates 120VAC up to 2500 watts maximum, and when operated together supply up to 5000 watts. If required, both output coils can be permanently wired in parallel to provide full 5kW output at 120VAC. 240VAC will not be available in this configuration. Alternately, a switch can be installed to select either normal 120/240VAC operation or full 5kW output at 120VAC only.
I've hand drawn a
diagram for both methods.
Top of drawing shows twistlock 120/240VAC plug.
Bottom diagram has 4PDT switch to select either 120VAC only or 120/240VAC operation.
On the GT5250, there is a green jumper wire on the duplex wire going from the neutral connection to ground. Remove it for floating neutral.
Here are
wiring diagrams for the full DeVillbiss generator lineup, including many Porter Cable models.
DeVilbiss equipment manuals can be found at DeVilbiss manuals/breakdown web site.
Other Generac manuals here...
Here are
wiring diagrams for the full DeVillbiss generator lineup, including many Porter Cable models.
Honda EB series generators with GFCI outputs will cause the breaker to trip when connected to some transfer panels. To correct this the neutral bond must be removed.
Check Honda Service Bulletin #20 for details.
warrens@ns.REMOVE.sympatico.ca
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ThanksWarren