Wiring a Generator to an Interlock

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Old 03-12-18, 05:52 AM
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Wiring a Generator to an Interlock

I picked up a generator and transfer switch off a guy who had a standby generator installed. The generator is an older 5k Milwaukee Generator and has no hours on it. He gave me everything he had for it and said that it worked fine but he upgraded to something automatic.

I recently upgraded my service from 100amp to 200amp. I did the work myself and had no issues with inspection. When I did the upgrade, I installed an interlock kit and ran 6/3 to an outside receptacle for a generator.

I would like to use the Milwaukee generator with my interlock kit but I am struggling on how to wire it properly. It seems that the neutral and ground must be bonded because it only has three prong receptacles. Also it appears to have a 250v receptacle and a separate 125v receptacles but no 125/250 receptacle. Can I use the 250v receptacle to back feed my interlock? Should I take the generator apart, separate the neutral and ground bond and wire a newer 4 prong 250v receptacle in? (I will note on the generator that it has a Floating Neutral)

The original owner had it wired with a 3 prong to 4 prong cable. The 3-prong plugged into the generator and the 4-prong plugged into the transfer switch receptacle. I have everything to install the transfer switch and I know how to do that. I would prefer to use the interlock kit as its already installed and allows me to selectively use any circuit in the house vs the few on the switch.

Lastly, I know that I can hire an electrician to do the work or buy a new 4 prong generator. I would like to use this generator as it is heavier duty then any of the new ones and itís the right size for what I need. I would like to do the work myself so I can learn how they system works. When an emergency occurs and we need the generator I would like to know the ins and outs of my system because electricians are typically not available then. Thank you all for your assistance with this. I do appreciate it.
 
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Old 03-12-18, 06:11 AM
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Here is the wiring Diagram for the generator.
 
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Old 03-12-18, 06:22 AM
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It seems the previous owner did not connect the Neutral (white) wire on the gen to transfer switch cable and used the 250v receptacle. Is this dangerous to use it this way?
 
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Old 03-12-18, 06:46 AM
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You need to find out hether the "250 volt" receptacle is 240 volts only or 120/240 volts.

How old is the generator? Is it still under warranty?

The generator neutral must be connected (via its output cable and the house wall inlet) to the house electrical system neutral. Failure to connect the neutral may result in seesawing voltages from hot to neutral on the regular 120 volt circuits. Very very bad,

Modern generator connections require a 4 prong receptacle for 120/240 volt usage. You can go ahead nd instlll one of those and while doing so, separate neutral and ground in the generator.
 
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Old 03-12-18, 07:37 AM
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The generator is wired for a 250v three wire circuit with a bonded neutral. It is not a 120/240 circuit. The generator is older. 20-25 years old but has no hours on it. I do think it would be best to install a 4 prong outlet. I think that would solve a lot of these issues. I may pay an electrician to change out the 3 prong receptacle for a 120/240 4 prong. How much would i be looking at to change it out?
 
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Old 03-12-18, 08:42 AM
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Before you put too much money into this, have you load-tested the generator? If it has sat that long without regular exercise the excitation field in the alternator might be shot which causes reduced output.
 
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Old 03-12-18, 08:56 AM
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I load tested it with a circular saw when i got it. It didn't stumble. What goes wrong with them from sitting. I have a lead on a Honda eb6500 that has sat unused. Its about 20-25 years old too. Its not running (bad gas) so i cant test it.
 
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Old 03-12-18, 02:19 PM
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Aside from the mechanical problems from the engine sitting, the electrical alternator can go bad too. The windings lose magnetism if the generator doesn't run regularly which will result in the generator producing no voltage or low voltage. Sometimes you can revive them using a process call "flashing the coil", but it's not a guaranteed fix and requires a bit of luck and skill with motor windings to get it right.

To make sure the generator is OK, you'll want to get it started and let it warm up a few minutes. Apply about 80% of the rated load on each leg (for a small generator two space heaters will work). Measure the voltage as you apply the load and see how much it drops and how the engine compensates. If it stalls out or if the voltage drops down below about 112-110V the generator has some problems.
 
 

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