Backfeed generator through dryer outlet?

Page 8 of 9  
"Pete C." wrote:

Come to think of it, if it is the RV type it could indeed switch the neutral by using the contactors together and utilizing the NC and NO sets of contacts with no provision for an "off" state. NC to connect to one source until the other source is available, cycles the time delay relay and then energizes both contactors. Of course this type of setup has the potential for a nasty failure mode if one contactor fails.
Pete C.
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Pete C. wrote:

The relay on the left switches the neutral, the relay on the right switches both hots. they are interlocked.
--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
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Steve Spence wrote:

What happens if a coil burns out on one of the contactors? One side switches and the other does not, you could end up with a situation where you have lost your neutral, i.e. hots from one source and neutral from the other source. Could be ugly.
On the transfer switch I built I had a solid neutral, but only used the NO main contacts on the contactors. If a contactor coil were to fail I would not have a situation where I lost a neutral or a phase. The NC auxiliary contact blocks on the contactors were used to provide the interlock to prevent any possibility that both contactors could be energized at the same time. It would require two failures for that to occur, both the upstream control to try to energize both contactors and the failure of one of the aux contacts to allow it to actually happen.
Pete C.
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If the coil fails, most contactors will be unenergized and that makes the contacts OPEN in most cases. This is standard for MOST electrical systems design. You design the system so that if therer is a failure, It is in the unenergized way and all contactors are OPEN.....
Me
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Me wrote:

Right and that was my point and also the way I designed my electrically interlocked transfer switch using only the NO contacts on the contactors and one contactor per source.
In the RV style auto transfer switches I've seen that use DPDT relays, they use a single DPDT relay and switch either a 120V source with neutral, or a 240V source with a solid neutral. A relay coil failure will leave you stuck on one source but will not create a hazardous situation.
The transfer switch as described by Steve appears to be using two DPDT relays to emulate a 4PDT relay with one source on the NO contacts and the other on the NC contacts, the common feeding the load. With one relay you are safe, but with two relays a failure of one will put you in a half switched state which could be hazardous.
Steve stated that the relay on the left was switching the neutral and the relay on the right was switching the two hot legs of the 240V feeds. If one of these relays were to fail you would get the two hot legs from one source and the neutral for the other source which could certainly cause significant problems.
My recommendation is that Steve review carefully the "what if" scenarios for the cases of the failure of either relay. I think a safer route would be to locate a suitable 3PDT or 4PDT contactor to replace the two relays or to go with a solid neutral.
Pete C.
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Probably never pass inspection like that.
wrote:

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Solar Flare wrote:

Er, like what? The way Steve apparently has it currently?
Pete C.

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Yeah, I couldn't find it in our code right now if my life depended on it but I doubt you would be allowed to switch a neutral on an independant device.
wrote:

where
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On Tue, 1 Nov 2005 23:08:13 -0500, "Solar Flare"

The short answer is if the generator has the neutral bonded to the frame (equipment ground) the transfer equipment will have to switch the neutral. You can't have 2 bonding jumpers in one system, switching the neutral isolates one of them.
Look at "separately derived systems" in the NEC art 250
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snipped-for-privacy@aol.com wrote:

Yes, but that's not relevant to the apparent situation. Essentially he has portions of a single circuit switched by what is effectively two separate transfer switches that are supposed to operate in parallel (neutral on one transfer switch and two hots on another transfer switch).
Pete C.
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wrote:

That is right. When you switch the neutral it has to also switch all ungrounded poles simultaniously.
I have to admit this thread has wandered around so much I am not sure I responded to the right post. I was just referring to the idea that transfer equipment does/does not switch the neutral and when that was appropriate.
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I have to reapeat my previous post since your response seemed unrelated.
"I doubt you would be allowed to switch a neutral on an independant device."
wrote:

I
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JoeSixPack wrote:

Many areas operate with primary voltages higher than 7200 volts.

It's the same current that it takes to kill you at 120/240 volts. The difference in not in the current requirement, it is in the amount of insulation required to protect you.

Your limited knowledge is forming incorrect assertions.
The amount of current flowing across the heart required to kill you is small and a constant. The voltage necessary to achieve this current varies depending on the contact conditions. Once you exceed the voltage necessary to produce that current across the resistance of the human body over the distance between the contact points, you're toast.
Pete C.
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JoeSixPack writes:

You know nothing of who I am, and are quite mistaken.
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True. I can only comment on the lack of reason and knowledge in your post. You may be a genius in other respects.
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JoeSixPack writes:

Trolling anonymous coward.
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You know nothing of who I am, and are quite mistaken.
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On Thursday, October 27, 2005 11:49:15 AM UTC-5, snipped-for-privacy@yahoo.com wrote:

doing it (I have a new generator and new uninstalled transfer switch) so sa ve your flames. I plan on installing my transfer switch when I get some tim e in the next month or two.I read a post suggesting that in a power outage, you could flip your main breaker off to prevent anything going to the line s and killing a line worker, and use a suicide cord from your generator to you clothes dryer outlet (240 vac) and then your main panel would serve as your switch for what circuits are using the generator--and that this would power both 240 and 120 outlets.As dangerous as this is, is this even possib le?
Yes, it can and has been done (by me) in an emergency. Whether you feed th e 240V back thru the dryer cord outlet or directly tap in at the breaker bo x, either way you must open the main circuit breaker to disconnect your hou se from the mains to avoid electrocuting a worker, or heavily overloading y our generator trying to feed your entire neighborhood.
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snipped-for-privacy@sbcglobal.net wrote:

When finished my wiring will have a breaker in the panel for just this purpose . Out here in the woods we can be left without power for days if we get another bad ice storm . Also part of the reason we heat with wood ...
--
Snag



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