They are actually quite large, the photo does not do them justice.
My plan is to place interlocks so that either the generator's disconnect is closed, or the main panel breaker is closed, but never both.
That's what they were designed for, if it is unclear to anyone, I can explain it in more detail, or see:
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I would lock up another key (they are keyed alike) in my safe so that its use cannot defeat this system.
I believe that this arrangement fully satisfies the rule that a mechanical interlock device should prevent both sources of power from coming in contact.
I don't think your local inspector is likely to approve of such a setup. You would be better off with an approved interlock system produced by the manufacturer of the electrical panel such as the Square D setup I use.
AT&T had this arrangement on a battery plant that was in two cabinets. The interlock depended on one key that had to turned to release the key so it could be used in the other cabinet..
So some idiot had a spare key made so he didn't have to move the key. Some time later he disconnected both battery strings and failed the service.
Currently approved mechanical interlock devices physically do not permit both breakers to be on.
With this, a second key already exists, and if it did not, a hardware store could make one - nothing to prevent both from being turned on at once, other than the assumption that there's only one key. A key in a safe can be removed from a safe, a key in place can be copied. Your taste for weird old surplus has got the better of you - there's a reason this stuff is surplus.
Mark, thanks. To answer other people's concerns, I am not going to duplicate the keys. I think that to prevent use of the second key, I may simply put both keys on one steel "connecting link" (a shackle used to connect chains) and will weld the link shut so that they cannot be separated. Or else I will bolt it to a wall in some secret location or save it in the safe.
These interlock keys are indeed used relatively widely in industry for all sorts of purposes. See the kirkkey.com website for examples.
A power station which is presumed to be accessible only to qualified persons. A residential setting which is presumed to be accessible to unqualified persons. Your interlock may well be acceptable in a power station, it will not however be acceptable in a residence. Inspection requirements and codes applicable are also very different between residential (NEC) and power station (NESC).
I suppose that being a somewhat ethical and caring person, and like the KISS principle (Keep it Simple Stupid), I would have to go with the tradition 3-pole, 3-position, transfer switch. On these, one position puts your home on grid power, in the center postion it is connected to nothing, and in the thrid position it is connected to your generator.
Only a week or two ago I was running my home on generator power, with the generator connected to the house with a "suicide cord", and the master breakers to the house pulled. I went outside and spent some time talking with the line crew that was replairing the down line in front of my home, in the rain. Having noticed that I was running a generator, one of the guys asked me if I was sure that I was disconnected from the grid. I replied that I knew I was, because the breaker connecting me to the grid was not only turned off an pulled, so I could see about 2-3 inches of physical separation.
No problem, he replied to me, and also informed me that the top like supplying the transformers on my street was an 8,000 volt line. I'm not a lineman but am an electrical engineer, and would not sleep at night if I were risking backfeeding a distribution transformer that stepped the voltage up to 8,000-volts, or even 2,200, no matter how clever the interlocking arrangement. I am not that desperate to power my home, and as an engineer I recognize the too frequent failure of such arrangements, let alone to build one myself. It's not so much the design of such interlocks, but the failure modes that amateur designers often fail to take into account, with tragic consequences.
Especially the retarded lineman that doesn't use equi-potential technique grounding devices to protect himself from induction and static charges that exist on lines running accross the countryside just by laws of nature. Your little generator is not a problem for any lineman that isn't a lazy and lucky jerk.
Interlocks are still necessary to help prevent frying the lazy and lucky jerk though. You are right. You don't want to run the child over, green light or not.
Before you invest allot of time and effort check with your local inspector as in the end he's the final authority. If he doesn't like it go with whatever he recommends, he's the one you need to keep happy. If he's OK with it you should be good. Kirk keys are a common interlocking means in power distribution schemes, and in settings other than the power company. You'd have a tough time duplicating the key as they are only available from Kirk, I don't know what they require before they sell you another. The only problems apparent are the presence of the second key, remove it from the premises to a safe deposit box or such, and the ultimate design of the locking mechanism that the locks are applied to.
Yeah, I don't think an inspector would go for it. The inspector would say "but if someone had the other key..." and you'd say "but it's in the safe" and the inspector would say "but if someone had the other key..." and out would come the [REJECTED] stamp.
That kind of stuff, the safety is in physical impossibility of linking sources, not the reliance on a meat puppet to do the right thing and not throw both switches at once.
In a restricted industrial setting, there can be different rules. Residential is another matter...
The code inspector is likely to treat this with the same respect he treats a Wilma interlock.
What's a Wilma interlock? A piece of electrical tape across the main breaker handle. What every household was using with a portable generator and suicide cord for a disconnect after Hurricane Wilma here in Palm Beach County, Florida.
Sure, it works, but they won't trust your discipline and brains. Nor should they.
Certainly not wishing anything but how could you know that? Anything can happen.
Part of the reason for doing a safe/standard installation is so that no "hocus pocus" is required so it will be safe if you aren't there or are incapacitated etc.
Mark I don't know were you or the OP are located so I'll answer as if both of you are in the United States. It may indeed be acceptable in a power station that is operated by a utility under the National Electrical Safety Code (NESC). The NESC is the code that is enforced by the public utility regulatory bodies in most states to govern the installation and operation of electrical generating and distribution systems. It is not however compliant with the National Electric Code (NEC) that is adopted and enforced as law by the vast majority of local or state governments in the United States. The NEC is also incorporated by reference into the vast majority of insurance contracts in the US. The NEC requires that materials be approved by the Authority Having Jurisdiction (AHJ). The AHJ can be the local building official, electrical inspector, or the insurance companies loss prevention department. No responsible AHJ will approve the use of an interlock that is not listed by a national electrical testing laboratory.
some people will do endless work to save a buck but create possible hazards later. The OP asked his question so posters could agree, and must be disappointed so many dont.........
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