Home Backup Generator Wiring Question

[roblouvasz]

Hi all. MagicMarker's recent thread dealing with a loose neutral got me thinking about my brother's backup generator installation. He's installing a transfer switch that disconnects the mains input from the meter and then connects the generator output to the service (breaker panel) when there's a power outage. Anyway, from what I can tell, the neutral from the meter and the generator are always connected. The transfer switch only disconnects the two legs of 120v and NOT the neutral. Is this right? What would happen if the generator malfunctions and sends voltage out over the neutral during an outage? The generator does have a dual pole 50 amp breaker on it's output, would it just trip? Just curious.

 

[ForceFed70]

A proper transfer switch will also switch the neutral. I think that's a requirement of PoCo for the reasons you mention. It's also part of the reason why people will tell you that manually switching off your main breaker and backfeeding a 240V outlet with a generator is not a good idea.

 

[pattenp]

A lot of transfer switches do not switch the neutral, you need to buy a neutral switching kit. Basically if the Gen has bonded neutral you need to switch the neutral. If the Gen has a floating neutral then you do not need to switch the neutral. At least this is my understanding.

 

[cobratom]

A lot of transfer switches do not switch the neutral, you need to buy a neutral switching kit. Basically if the Gen has bonded neutral you need to switch the neutral. If the Gen has a floating neutral then you do not need to switch the neutral. At least this is my understanding.

This is 100% right. The general rule is if the generators neutral is not bonded to earth (EGC) you can get away without switching the neutral. If the generator has a floating neutral (which most newer 120/240V gensets do, because the manufacturer of most gensets is also the manufacturer of the switches)you are not required to switch the neutral.

The preferred method is to not switch the neutral as it prevents arcing in the switch, unless the switch is a high quality unit that uses tinned copper contacts and has a very fast transfer solenoid.

 

[roblouvasz]

The generator is a Generac and I pretty sure the transfer switch is too. Thanks for the replies.

 

[pattenp]

Is your Generac a whole house style gen or is it a portable? I have a Generac GP7500 portable and the neutral was bonded in the gen. I mainly use it for house backup so I removed the internal neutral bonding. If I need to use the gen as a portable I have a bonding plug to restore the neutral bond at the gen.

 

[roblouvasz]

It's a whole house style. It's not mine, it's my brother's.

 

[theoldwizard1]

This is 100% right. The general rule is if the generators neutral is not bonded to earth (EGC) you can get away without switching the neutral. If the generator has a floating neutral (which most newer 120/240V gensets do, because the manufacturer of most gensets is also the manufacturer of the switches)you are not required to switch the neutral.

CONCUR !


BTW, this does cause a problem with small generators (Honda 1000/2000) when you try to hook them up directly to a modern furnace If the furnace can NOT sense a "bond" between neutral and ground, the furnace will not run.

 

[Mustang51js]

It's a whole house style. It's not mine, it's my brother's.

Its fine like that,the generac whole house only switch the hot legs