Connecting generator to gas furnace

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  #1  
Old 01-26-15, 10:54 AM
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Connecting generator to gas furnace

Please advise a simple emergency electrical connection for my Burnham gas furnace, before we lose power tonight? I'd rather install before losing power; and I don't have time or money for a transfer switch. House is 90 years old, Burnham natural gas furnace looks pretty old too. I have a 5,000 Watt generator that I'd like to power the furnace and forced hot water and thermostats with, but not quite sure how to wire it.
There are two sheathed wires coming from outside the furnace area (finished basement, so cannot see from where they come or go) into a steel conduit, then into an unlabeled two-gang toggle switch box (with two toggle switches). They appear to power the furnace; one cable is a white-sheathed Romex labeled NM 12-2, but the second one is black with no labeling visible. There are three additional two-gang boxes with switches, attached to that first unlabeled box; and each of those three is labeled either zone1, zone 2, or zone 3. It appears that each of the cables entering the conduit and then the first box are 12-2; so between the two, there are two black, two white, and two ground wires. I could either directly connect the generator cable to the power feeds with wire nuts; or I could try to install a receptacle, which sounds safer. Rather than splice directly into the feeder lines, I'd liked to install a receptacle; but I've never added a male plug to a cable set of wires. Whether I install a receptacle or just directly connect with wire nuts; How do I determine which of these sheathed 12-2's I connect the generator cable to?
Or do I pigtail (or install two separate receptacles) the generator cable to both white- and black-sheathed cables entering that first unlabeled box?
I Know the main power breakers for both panels in the house need to be shut off while powering the furnace with the generator.
Thanks for any guidance!
Do I need to install two separate outlets; one for each of these cables?
 
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  #2  
Old 01-26-15, 11:06 AM
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Are there switches on the boiler?are the circuit breakers labeled to indicate which one feeds the boiler?
Geo
 
  #3  
Old 01-26-15, 11:56 AM
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NONE of the circuit breakers are labelled for the boiler.
- There are only TWO two-gang metal boxes (sorry, not 4 as originally written) each with two switches, installed on the plywood directly behind the furnace. The first has one unlabeled switch, and one labeled ZONE 1; the second's 2 switches are labeled ZONE 2, and ZONE 3 respectively. I'm uploading photos; the upper box receives the electrical feed, and one of its switches is labeled ZONE 1. You'll see the two sheathed cables entering the conduit feeding that upper switch, one white and one black; and they go to different directions and outside the small boiler room.
The house has 3 heating zones; basement, 1st floor, then second floor.

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Name:  pdoyle electrical switches 2.jpg
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Last edited by PJmax; 01-26-15 at 02:22 PM. Reason: reoriented pictures
  #4  
Old 01-26-15, 12:37 PM
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Do you feel comfortable about opening the box that has the feed in it? If so find out which circuit breaker feeds that switch and shut it off,let us know what you have in that box.
Geo
 
  #5  
Old 01-26-15, 01:52 PM
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Will do. I'll shut the breakers until Klein non-contact voltage tester stops showing voltage. Is it possible that the two feeds are on different circuits?
I'll cross that bridge if I come to it. Will post again in an hour or so, I want to get this set today.
thanks!
 
  #6  
Old 01-26-15, 02:24 PM
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As a guess.... it looks like the white NM cable is the feed and that black cable may be for the water heater. The unlabeled switch may be master power.

I don't see the black wire connecting at the switch location.
 
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Old 01-26-15, 02:29 PM
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Moved to the electrical forum because this is an electrical question.

A non contact tester is not really reliable enough. You will need to test between hot and neutral with a multimeter, preferably analog, to be sure. A non contact tester could show power when there is none which would confuse you about what breaker is correct.
 
  #8  
Old 01-26-15, 07:26 PM
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wiring pics of switches, circuit breaker found

I hope this is enough for your guidance; my wife doesn't want the furnace off for long as it's struggling, only getting to 68 temp when thermostat is set for 70; and it's only 26 degrees now; expected to drop to 17 tonight.
I've found the 20A breaker; when I threw it, all the sounds from the furnace stopped. Put back on, all the sounds pick up again.
The upper 2gang has 2 switches; the Left (see pics) is unlabeled; the Right is labeled Zone 3. Both switches are only wired with black wire. There are two 12-2 cables feeding into that upper box from Top right conduit above (and outside the room); from these, [LIST][*]one black wire is wire nut connected to another black wire coming into the left side of box from the zone 3 thermostat conduit.[*]the other black wire is pigtailed to three additional black wires. The first of These three pigtailed black wires then runs to the master switch lower screw; from that switch's upper screw, a black runs into the Left conduit to zone 3 thermostat. Second pigtailed black runs to the zone 3 switch, and the third pigtailed goes to the lower 2gang box which has switches labeled zone 2 and zone 1.
Both white feeder wires entering from above, join two pigtails with two additional white wires each. From the pigtails, the whites run into the Left, bottom, and Top left conduits.
blacks are only pigtailed to blacks; white are only pigtailed to whites. Then there are very small guage blue and other color wires connected with wire nuts.

With breaker off, the analog voltmeter showed zero volts AC from all black wires on the 2 switches. It also showed 0 ohms (the needle jumped all the way) resistance with the black probe on the ground feed. With breaker turned on, both screws on the Left unlabeled switch showed 12 Volts, with black probe on the ground. On the Zone 3 switch, only one screw showed 12 volts; the other screw showed 0 volts.

So it does appear the unlabeled is the master and emergency cutoff switch. If I lose power, I should first throw the main panel 200A switch off.
Then I'll throw off the 20A circuit breaker to the furnace. Then I'll turn the master switch toggle off.
Then from the master switch, I'll disconnect and cap separately the black wire coming from the four pigtailed black wires (fed by the feeder from Top right conduit). To that empty screw, I'll attach the black wire from the generator extension cord. I'll connect the white wire from extension cord, to either of the two white 3-wire pigtails. (Should I remove either of the white wires from the feeder cables attached to the pigtails, or just leave them attached?
I'll connect the extension cord green wire to one of the ground wires coming in from the feeder cables; though I don't believe either of those are connected to anything in the upper box. They're both just loose, not connected to anything. Or, should I connectd the green wire to a grounding screw in the box itself? I didn't see any.
Then after the generator has been running for a minute or so, I'll throw the master switch on.
Does this make sense? I don't know that I have enough slack wire from the feeder cables to wire a receptacle; and I'd rather avoid that if possible. I just need to disconnect the generator extension cord from the master switch, and reconnect the house wiring, before I turn the 200A panel breaker back on.
(Will try to upload my pics later; it's failing right now.)

thanks!
 
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Old 01-26-15, 08:26 PM
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Here's another thread with virtually the same question & the replys, http://www.doityourself.com/forum/bo...ator-like.html
 
  #10  
Old 01-27-15, 06:20 AM
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That should be fine,isolate all the feed conductors and connect the ext. in place.I am trying to confirm if a pigtail with a male cap hanging from the boiler controlled by a 2 pole switch is legal.
Geo
 
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Old 01-27-15, 06:46 AM
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It is not. Permanent HVAC equipment cannot be connected by cord and plug. It's a better solution during an emergency situation than an illegal back feed, but it should be put back the way it was and a proper transfer installed as soon as the storm is over.
 
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Old 01-27-15, 08:05 AM
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Please advise a simple emergency electrical connection for my Burnham gas furnace, before we lose power tonight?
You had a power outage scheduled?
 
  #13  
Old 01-27-15, 10:03 AM
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Not so far; thankfully I'm not one of the 26,000 who lost power in MA
 
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Old 01-28-15, 09:50 AM
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Please show me the code vilolation.
Thanks
Geo
 
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Old 01-28-15, 10:49 AM
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I don't think your question will be seen unless it's added to the other thread; http://www.doityourself.com/forum/bo...ator-like.html

. After my initial post was later relocated to Electrical, and I was sent a link to a similar question, I started replying to that other thread...which is where you'll find the other replies.
Thanks for your suggestion; It makes sense to me, to add the transfer switch to the breaker panel, rather than at the Master Switch at burner. Is it important to change the breaker from 20Amp to 15Amp, because I'm adding the transfer switch?
Trooper suggested combining the low voltage control wires, with the 120VAC wires in the same box was "a big no-no." He also stated he did not read my description of the wiring, nor look carefully at the pics. The NEC code is always changing, perhaps when this system was installed it was within code of the time. You are not seeing a code violation?
Thanks for your help! I appreciate it.
 
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Old 01-28-15, 07:45 PM
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Trooper suggested combining the low voltage control wires, with the 120VAC wires in the same box was "a big no-no." He also stated he did not read my description of the wiring, nor look carefully at the pics. The NEC code is always changing, perhaps when this system was installed it was within code of the time. You are not seeing a code violation?
Maybe I missed something, but I didn't see a junction box with both line voltage and low voltage wiring. Low voltage and line voltage cannot be combined in the same junction box unless there is a divider separating the two spaces. This has not changed in the NEC for at least the last 50 years.
 
  #17  
Old 01-28-15, 08:00 PM
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Joe, See the last picture in the thread here: http://www.doityourself.com/forum/bo...generator.html
 
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