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Generac Generators (SEARS, etc.)

3 wire generator to 4 wire Xfr switch


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  #1  
Old 11-16-2011, 12:20:16 AM
hoghunter69 hoghunter69 is offline
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Default 3 wire generator to 4 wire Xfr switch

New to this forum so be gentle.

20 years ago I inherited a 1966 Sears generator when my dad went with a whole house unit. The genset is a Sears model 533.3211 with a 14hp Wisconsin turning 1800rpm, rope start, 4kw head, 120/240v. Starts on the 2nd pull every time. Several years ago I wired it to a GENERAC 1403 Xfr switch which is a 6 circuit model with break before make switches. My service panel uses a common neutral/ground. The config has been working flawlessly until I read the generac manual which said do not use with 3 wire generators and now I am nervous.

When wiring the TS I used the 240 receptacle wiring the T1 and T3 from the generator to the 2 legs of the service panel and the T2 ground pin to the neutral bar in the panel. According to GENERAC manual, if there is no ground bar in the panel, use the neutral bar. Doesn't that defeat the point of a 4th wire in the generator?

I am not running a ground rod based on an OSHA article related to portable generators under 5kw and 3 wire config.

Have not checked to see if the neutral is bonded or not (dark and pouring rain)

So here are my questions/concerns-

Since the TS does not switch neutral or ground, what risk do i run continuing to run this setup?


Why is this config not acceptable?
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Old 11-17-2011, 12:48:58 AM
Jim Rankin Jim Rankin is offline
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Default Re: 3 wire generator to 4 wire Xfr switch

A 230-240 volt 3 prong receptacle has no neutral connection. The only way your house panel has a connection back to the generator neutral is by using the ground conductor.

When you use 120 volt circuit, the power flows from a line through the load and back to the neutral. In your case, the get back to the generator neutral, the current must flow from the neutral bar through the ground wire of the connecting cable to the generator where HOPEFULLY the neutral is bonded to ground. The current can reach the generator neutral if there is a neutral to ground bond.

there has been a lot of discussion about this situation, but in summary, things that are supposedly grounded could become 'HOT' if there are breaks or poor connections in the wrong places of the ground wiring. AND ground fault breakers can experience nuisance trips.
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Old 11-18-2011, 09:35:18 PM
hoghunter69 hoghunter69 is offline
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Default Re: 3 wire generator to 4 wire Xfr switch

Jim - would it be possible to break a bonded N/G and try to add a 4 prong plug with G tied to the generator frame?
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Old 11-19-2011, 12:56:11 AM
Jim Rankin Jim Rankin is offline
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Default Re: 3 wire generator to 4 wire Xfr switch

Yes, it is possible and that is what you should do if you want to change anything from how it's working now.

That will eliminate the ground wire carrying anything other than fault current if there's a short circuit. You will have a neutral connection back to the generator neutral and a generator ground connection through the receptacle back to the panel ground.

The service panel is the one place where the neutral and ground conductors can be on the same bus. There is a bond there anyway, so they can be mixed instead of being kept separate like in a sub panel.
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