Interlock locks to be used in lieu of transfer switch

I have this generator:
formatting link

I bought these interlocks on eBay:
formatting link

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:
formatting link

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.
Any comments?
i
Reply to
Ignoramus23720
Loading thread data ...
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.
Pete C.
Reply to
Pete C.
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.
Not much is idiot proof
Bill K7NOM
Reply to
Bill Janssen
Not acceptable.
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.
Reply to
Ecnerwal
It's a perfectly acceptable solution and I've used it on power station transfer boards.
Regards Mark Rand RTFM
Reply to
Mark Rand
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.
i
Reply to
Ignoramus3938
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).
Reply to
Pete C.
Yes but many of these "Kirk key" locks have keys that cannot be duplicated easily.
Reply to
Solar Flaire
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.
Harry C.
Reply to
hhc314
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.
Reply to
Solar Flaire
What you did was considerably more failure prone than an interlock arrangement.
i
Reply to
Ignoramus23720
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.
Paul
Reply to
Paul
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...
DJ
Reply to
DJ
Who will live there after you leave?
Reply to
Solar Flaire
Our situation is a little different, were too far from the grid to be connected. But have the same problem So we have our own power making setup. ie generators. that means 2 off . One 6KW for daily use and a 15KW when I need lots of power @240Volts.(Were in the UK where all normal domestic supplies are at this voltage). How do we seperate the 2 ? to make sure there never connected at the same time when either one or the other is running? Its simple we have a board to which the 2 generator outputs come into 2 identical but seperate sockets. one labeled BIG and the other SMALL the domestic connection is wired into 1 plug. So you can only plug this into 1 or the other socket. Which we do before we power up . Both gemerators also have big cast iron breaker boxes on their own panels. these have knife switches inside a well as fuses. I know it doesnt have the convenience of a change over switch but does the same thing with the same safety in my opinion. Also a lot cheaper that a 20KW change over switch.
Reply to
ted frater
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.
Locking things in a safe? C'mon.
Reply to
Richard J Kinch
If your question is addressed to me, I am not going to leave this stuff to the next owners, I will remove it and take with me.
i
Reply to
Ignoramus17686
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.
Reply to
George
Why would you care? A few posts back you claimed that a generator backfeeding into the utility was only a safety issue if the lineman was retarded.
Reply to
trader4
Cross posts deleted
In a word, NO!
If your system requires instructions or training to make it function, it isn't safe for residential use.
I'm all for keeping the cost down, this is not one of those places.
Ignoramus23720 wrote:
Reply to
RoyJ

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.