[homeowner357]

I have wired a generator into my 200amp breaker box. The generator power enters the box via a 50 amp breaker.

My local utility representative tells me that the 200 amp main breaker does not have enough clearance to safely isolate my generator from the power grid. He is telling me that there is only 1/32 air gap between the contact points. I don't believe them. Can someone help me with this?

[tkrussell]

Can you provide any photos? I have no idea what clearance is being referred to. Does the utiltiy have requirements published? Check their website.

[homeowner357]

I am referring to the clearance of the contact points inside the breaker. They say there is only a 1/32 air gap which could cause an arc back to the power grid. Everything that I can find uses breakers to manually shift from generator to incoming line power. I want to use the main breaker to isolate the panel from the incoming voltage from the power company. If there is a chance of my generator arcing back to the pole through the main breaker then what use is it to protect me when I am working on the panel from their voltage arcing across to the panel. I have found pictures of smaller breakers in the panel that show an air gap of close to and inch. Thank you for your input.

[stanfortyman]

I am getting the impression that you are not using a transfer switch or main breaker interlock. Are you?

If not you MUST.

[tkrussell]

Stan my thought exactly as to something missing. I wanted to get how was this done. I tend to beat around the bush a bit, and your direct, like a snipers bullet.

If you are trying to back feed a panel with a 50 amp breaker in a branch slot, and expecting the main to keep you from connecting from the grid, not only are you wrong, but so is the utility.

If they looked at it, or otherwise understand what you are trying to do,without a breaker interlock or a transfer switch, the issue is not the gap at a breaker, but that the grid is not intentionally disconnected when the generator is connected.

With an approved interlock kit, the gap of a breaker is all that disconnects the service from the grid.

Like I said, ask the utility for their requirements, or standards, for installations. They may not allow interlocks and only want a transfer switch, until you check, only guessing.

[homeowner357]

Ok let's see if I can explain what happened. The power company had a planned power outage to do repairs. When the power went down I turned the main breaker off. I switched the 50 amp breaker on after I started the 17k generator. Two guys showed up from the power company because I was the only one on the street with power and told me I needed some kind of disconnect between the meter and the main breaker. He asked me how I expected the main breaker to stay in the off position and I told him that is why I was standing by. He then told me that the breaker only had 1/32 of clearance in internal contacts.
This person is known to me to be the electrical engineer for the PUD. I could not believe that turning that breaker off would not protect the linemen. You have convinced me that he was blowing smoke you know where. Now I understand what you you mean by a breaker interlock, and couldn't agree with you more that it is either that or transfer switch.
You have help me a bunch. Now I will contact the PUD and ask them which one they prefer.
Thanks again for your help. Nick

[KISS]

See Generator InterLock Kit

[tkrussell]

The utility workers were exaggerating a bit on the contact clearance, but to make a point. I have taken apart many 200 amp breakers, and the contact clearance is much greater than 1/32".

All they needed to do is tell you that your method of connecting the generator was illegal, since it must rely on human action to insure the grid is clear before the panel receives power from an alternate source.

And there is no method of insuring the Main Breaker could not be closed while the service is energized by the alternate source.

Your lucky they did not call in the local inspector, who could order the utility to cut your service free from the grid due to an illegal installation.

As a lesson to anyone reading this, a service with a generator must have a mechanical means, whether manual or automatic, to insure the generator cannot send power out onto the grid. Keep in mind, while you are dealing with 120/240 volts, that voltage comes from a utility transformer supplied by high voltage, 2400, 4160, or even higher.

A transformer works in reverse also. So if you send 240 volts onto a dead grid, a lineman working on the high voltage side will be exposed to that high voltage, when he thinks it is off because the power lines are down feeding that transformer.

Fortunately they work on dead lines as if they are live, but something can still happen. They are constantly checking for power on lines they believe are dead. If they detect power, they will track it down, cut your lines free from the grid, call in the inspector, and you can be subjected to a summons to have the installation corrected, and trust me, you will be the LAST house in town to be re-connected to the grid.


So, to anyone connecting a generator by plugging in the generator to an outlet and only shutting off the Main Breaker, stop it, and get it connected properly. You do not want to piss off a lineman, or kill one.

[Missouri Bound]

TK.. If I may... I have heard the reasons explained hundreds of times why you can't just backfeed through an outlet, such as a dryer outlet. But you are the only one who took the time to explain the transformer issue, and the job of the lineman. I think if everyone would read your post, there would be less occurrences of illegal and unsafe hook ups and the consequences they could cause... Well said.

[KISS]

I've said it before on AMHD, but I must agree that post from tk was well written.