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Author Topic: Electric/Heatpump hookup for generater power  (Read 591 times)

shepherd boy

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Electric/Heatpump hookup for generater power
« on: March 03, 2018, 06:02:12 PM »

  We have had a major wind storm in the east with a lot of power outages. How would you hook a electric furnace or a heatpump air handler into a generator sub panel if all you have is a 30amp panel and a 5000 watt generator (which could pull the fan only), but the air handler is run with one or two 60amp breakers in the main panel. All we want to do is run the fan and the outdoor furnace to get some heat.
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greasemonkoid

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Re: Electric/Heatpump hookup for generater power
« Reply #1 on: March 03, 2018, 08:03:22 PM »

You mean a transfer switch panel? If your xfer switch doesn't have the same or higher rating then you'll have to get a single box transfer switch. Home depot use to sell them for $100, good for 100 amps. I've got 3 of them and put the digital ebay induction ammeters in line to monitor the generator load on each phase. I think I answered that with what you're wanting.
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shepherd boy

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Re: Electric/Heatpump hookup for generater power
« Reply #2 on: March 04, 2018, 05:40:54 AM »

 I have run into some auto switch panels that just don't have the capacity to handle that kind of load. They are matched to the auto start generator. If you have a main double throw switch between the meter and breaker panel your good but it's manual and most add on auto start units I've seen don't have panels heavy enough to handle the heat. But when adding a outdoor furnace they want their heat on the generator. Your answer is probably right but it's over my head.
« Last Edit: March 04, 2018, 10:41:06 AM by shepherd boy »
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greasemonkoid

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Re: Electric/Heatpump hookup for generater power
« Reply #3 on: March 04, 2018, 08:54:36 AM »

Generac seems to be dominating the market for that application. Unfortunately, there are no double throw motor or lighting contactors with that amperage in industry - not common anyways.

Sounds like you would have to add and parallel from the existing generator and transfer switch with a 2 pole 100 amp unit dedicated to operating the HVAC/air handler. Of course, if the coils or something big is turned on it will trip the main breaker.

The other option is to find the circuit responsible for the blower alone and run it directly to the xfer switch (a lot of work).

In summary I would find it easiest to junction/splice the generator lines and run them to the new 100A automatic XFER switch, pull (extend) the air handler lines from their box and run to the xfer switch then back to the original breaker.
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shepherd boy

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Re: Electric/Heatpump hookup for generater power
« Reply #4 on: March 05, 2018, 05:14:31 AM »

  Just toying with a idea, Could you run a low amp (15) circuit from from the generator panel to the air handler, through a double throw 220v contactor that would separate the control board from the 60A circuit in the air handler and energize that with the line from the Gen panel. The fan relay is in the board on a lot of these units anyway and that would energize the fan as well without the strip being effected? When the contactor loses it's power from the gen panel it would automatically switch back to the 60A in the air handler. Missing anything?   If I'm thinking right this would only take a #14 wire from the Gen panel and a double throw 220v contactor.
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greasemonkoid

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Re: Electric/Heatpump hookup for generater power
« Reply #5 on: March 05, 2018, 06:52:16 PM »

Hopefully I'm understanding that scenario correctly. As long as it's in the blower sub-circuit (outside of the heating strips), sure, don't see why not. You'll still have the hassle of running a set of lines to the hair handler. The caveat is many air handlers today are variable speed DC motors (or AC with a variable speed motor drive). I'm not an HVAC guy so I don't know the implications, but if you could figure out where to feed the signal into the board to make it think the strips are on it would kick into high gear. That information should be in the air handler install manual. The signal may need to be 24 VAC so source your power accordingly and make sure there is no way possible for your generator voltage to feed back some place you don't want it.
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greasemonkoid

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Re: Electric/Heatpump hookup for generater power
« Reply #6 on: March 05, 2018, 10:26:45 PM »

Was looking up something for work, ran into these -

https://www.ebay.com/itm/ELPRO-CEM-65-Contactor-Pair-Set-3P-65A-120-208V-50-60Hz-with-interlocking/202162052467?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D50074%26meid%3D94dd71c6843f4950bc8215b872fb5017%26pid%3D100005%26rk%3D4%26rkt%3D5%26sd%3D202162053250%26itm%3D202162052467&_trksid=p2047675.c100005.m1851

The price is right. Basically a 3 phase reversing motor contactor, but at a fraction of the cost. This will probably be your easiest bet. Even comes with NC and NO aux contactors and silver coated contacts. Use your existing low amp automatic xfer switch to control this one.

As far as that goes, you could probably use about any reversing motor contactor with correct amperage and coil voltage.

Edit - nevermind, I see now the UL continuous current is too low, need a heavier version.
« Last Edit: March 05, 2018, 10:32:35 PM by greasemonkoid »
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shepherd boy

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Re: Electric/Heatpump hookup for generater power
« Reply #7 on: March 06, 2018, 01:12:53 PM »

  We have hooked up a separate t-stat on variable speed units and know how to make them ramp up on high and keep the outdoor unit and strip off. Had a thread a while back on this forum on that, but was just looking into the way to bypass the large breaker to get all those controls to work on a low amp auto start Gen panel. I have a variable speed 5 ton air handler we changed out here now. I think I'll hook it up  and if I blow it it won't mater. If it works out I'll have a demo unit.
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