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Thread: Emergency Generator Test with questionable results

  1. #1
    DIY Junior Member krnva's Avatar
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    Default Emergency Generator Test with questionable results

    When I remodeled my house about 3 years ago, an electrical upgrade was done that included replacing all non-temperature rated wiring (cloth wrapped, without ground wires) and adding a pre-wired automatic transfer switch with service connection located on the side of the house. The ATS panel is rated 240v/50A and is connected to the main breaker panel via a double pole 50 amp breaker. It has several important circuits on it, including sump pump, refrigerator, freezer, gas burner equipped heat pump, boiler, strategic general lighting circuits, and alarm system. I have not gotten to the point to put in a permanently installed generator, but I do have a portable generator rated 7000 watts with L14-30 connector that matches the service connection to my house for the emergency generator, also a L14-30 connector.

    I recently decided to test this setup and see how it works, so I could see if I am ready for an outage. So, I set the thermostats down on my heating systems and switched my heat pump to emergency heat so it would only run gas heat. Then, I connected up my generator to the house and started it up and let it run for a few minutes to warm up. Next, I threw the 50 amp double pole breaker in my main panel to kill utility power to the ATS. After the 20 second timeout, I heard the ATS pick up on generator power and the emergency circuits came back on. All seems as it should, so I moved on to the next test - filling up the sump pump crock to get the sump pump to kick in and empty out the crock. Before I get the sump crock filled with water, I heard the generator governor kick in and then smelled electrical burning, so I canceled the test and went back and restored utility power to the ATS by resetting the 50 amp breaker in the main panel and letting the generator run unloaded and disconnected to cool down. Found out that the transformers (120v-24v) in both the heat pump and the boiler had burned up and had to replace them. Never even got to do the sump pump test on the generator, but did complete it on utility power, just to make sure the sump pump still works. No other equipment has been identified as damaged in this test.

    So, any thoughts to share on what might have happened that would have burned up those transformers? If there was a surge, wouldn't a circuit breaker on the generator or ATS trip? Would a brown out burn up a transformer? Is it likely that the generator can surge to that level of damage? Granted, the transformers are probably the most sensitive devices in this scenario.

    How should I test this out, without destroying any more expensive parts or equipment?

    Everything is fine now that I am back on normal power and after replacing the burned transformers.

    Any thoughts would be appreciated, and having the system tested by a licensed electrician is also a fair recommendation, but I just want to make sure I have checked all the easy suspects.

  2. #2
    Electrical Contractor/Instructor jwelectric's Avatar
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    These small generators do not have a voltage regulator on them so when the generator goes into a load the voltage varies and a coil does not like this therefore it lets go of its smoke and quits.

    I don’t know how many times I have said that a generator than has receptacles on their frame is not designed for what you are proposing to do. You are looking for trouble each and every time you try to use something designed for a thirty amp load max and putting large surges of starting motors on them.

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    DIY Junior Member Igor's Avatar
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    My guess is that the neutral and one of the hots were swapped somewhere, so those 120V transformers were getting 240V.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Igor View Post
    My guess is that the neutral and one of the hots were swapped somewhere, so those 120V transformers were getting 240V.
    Should this have been a neutral problem it would have shown up long before the pump test.

    It was without a doubt the inrush of current due to the starting of the motor. To start a 1/2 horse power 120 volt motor the motor will have an inrush of about 58 amps which is far more than the small generator will deliver.
    When the motor started the load on the generator caused the gasoline motor to load and speed up which in turn caused a voltage drop followed by a surge in voltage that the transformer could not handle.

    Once again, these small generators were not designed to be connected to a house load. The proper way to use one is with the use of cords plugged directly into the devices (receptacles) on the generator.

    On a side note, I have two small generators. I have horses that need water during an extended power outage (24 hours or more). I use the 7500 watt generator to power the well pump for water at the barn. The other generator is used for emergency lighting at the house. This lighting is a table lamp plugged into a drop cord ran to the generator outside. I have no transfer switches connected to my house at all.

    A power outage is a very rare event and one in which my everyday way of living is interrupted and one which I live on a limited amount of electrical use. I do not try to watch TV or surf the internet during these times.

    Should I for some reason or another need more than a cord during a power outage I will purchase a generator big enough to handle the load. What I wouldn’t do is try to haul 17 ton of rocks on a half ton pickup truck or use a portable generator to power my house. Think of it this way and see if it doesn’t make a little more sense than just saying I have a generator and I want to power up this and that during a power outage.

  5. #5

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    I can start my 3/4 HP deep well pump using my 6500W portable generator with my air handler and all general lighting circuits already on. I'll admit it is a close call though, but during an outage the generator can handle this condition 20 times a day.

    I doubt this is an overload problem. It sounds more like someone screwed up. I'd say you have a wiring problem between the generator and your service panel. And I agree with Igor, it is most likely a hot/neutral swap. Do not try the generator connection again until you have it fixed. Consider yourself lucky if this is the problem and all that happened was 2 transformers were cooked.

    -rick

  6. #6
    General Engineering Contractor ballvalve's Avatar
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    Submersible franklin pump motors have huge service factors, 1.5 -1.8 in some cases, and they are designed to start on LOW voltage.

    Take a look at Franklins AIM manual, they give extreme lengths of wire runs that a normal electrician would laugh at for such small size. I have had to fight with electricians to use the Franklin designed wire runs because they give great cost savings, and provide a soft start, which greatly reduces starting torque, and the associated lifespan reductions with that in a pump.

    Which all means that portable generators are more than adequate to run submersible motors. I ran a 1 HP pump for 3 days non-stop on a 13HP Briggs genset, along with 2 freezers, a fridge and some lights. Although I wired it into the panel in an "emergency" mode. AND adjusted the motor speed-governor under the full load to 240volts, something few ever bother to check.

    It was without a doubt the inrush of current due to the starting of the motor. To start a 1/2 horse power 120 volt motor the motor will have an inrush of about 58 amps which is far more than the small generator will deliver.
    When the motor started the load on the generator caused the gasoline motor to load and speed up which in turn caused a voltage drop followed by a surge in voltage that the transformer could not handle.


    Seems if that were so, 58 amps [?] would have just killed the genset motor. And If it was a cap start blower motor, that load would have been simple for the generator. And I never could get any surge out of any of the gensets that I have used, and its many. The gen set motor slows down and regains speed as the motor begins its turning.

    The OP needs to tell us if his gas heater and boiler were even engaged. He said he turned the thermostats way down, so perhaps there was no motor turning at all.

    Then one must assume that the 120v transformers got a LONG dose of 240volts. Small transformers do not burn up on low voltages induced by a motor starting.

    I am guessing that the OP heard the governor speed UP [reduced amp draw] when the load on the transformers ceased by melting.
    Last edited by ballvalve; 03-02-2011 at 02:35 PM.

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    DIY Senior Member Rich B's Avatar
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    The first thing that needed to be checked before the test was the voltage and frequency of the generators output. How many KW is it ? What brand is it? Many decent sized portables DO have voltage regulators. Any quality built unit of about 4-5kw or higher will have a voltage regulator. These regulators are small and can only keep the voltage in the proper range if engine speed is close to correct. 3600 rpm is the usual rpm for a small unit and that is also the frequency or called HZ or cycles per second. A Fluke meter with HZ measuring capability is what we use to check engine speed. I work in the backup generator field.....18 years. Big, small....Commercial, RV....Homeowner.....You name it we do it......I also repair other electrical equipment.....Miller and Lincoln welders......I am a certified tech for both companies as well as on Onan RV's and work on them all the time.......

    Motor starts can and do cause a small generator to bog down in speed. Voltage goes down.... generator breakers usually do trip under that scenario.

    One more likely scenario.....your voltage was too high for some reason on the generator......takes a while for stuff to burn up under a condition like that. Another possibilty your generators governor did not respond properly.....and engine speed went high.....the voltage regulator can only regulate so much and if your voltage went high it would burn up some things easily........most electrical items can tolerate plus or minus 10 % or even more but not for long.......

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    DIY Junior Member krnva's Avatar
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    First and foremost, thanks to all for considering this and sharing your opionions . . .

    In response to thoughts about more details:

    1. The generator is a Northshore Power Systems Model NSP7000EH (http://www.nspsystems.com/products/hw7000eh_566992039). I appears from the website that it is a Honeywell system, or at least closely related to Honeywell. It is powered by a Honda engine.

    2. As was stated, the thermostats for the heating systems were set down to prevent/delay/control their operation until later in the test. I do not believe that either system started up on the generator, but rather set idle. However, the refrigerator and freezer were still on the panel and may have started while I was filling the sump crock. Don't know for sure either way. Otherwise, just general lighting and outlet circuits.

    So, am I interpreting the replies correctly that the issue may be in two distinct areas: Surge from the generator or wiring fault between the generator connection and the ATS/Panel, since the circuits work fine under utility power provided by a 50 amp double pole breaker? Would the wiring fault premise that a neutral is energized and providing voltage to 120 volt circuits from both sides suggest that other devices like the freezer and refrigerator and sump pump would have been compromised as well? If there is a problem with regulating the voltage that is inherent to portable generators, would that make them unsuitable for use with extension cords to the devices independently from the duplex outlets on the side of the generator?

    Again, thanks for consideration and sharing.

  9. #9
    General Engineering Contractor ballvalve's Avatar
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    I would spring for an electrician that also advertises as doing the B&S propane genset installs.

    I once had the pleasure of digging up the main 200amp service run to a rental of mine and it seems the neutral became energized. Every 120v appliance of any sort that was on needed to be replaced.

  10. #10
    DIY Senior Member Rich B's Avatar
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    I looked at the electrical print for the Honeywell generator. There is an AVR on the drawing. That stands for automatic voltage regulator.

    Assuming the engine stayed within a fairly normal speed range.....the units output should have been close to normal. 120/240.

    That would need to be checked and verified first at the generator and then at your Transfer switch. If the generators output is normal then your problem would have to be in the switch wiring.

    A generator is tested by using a resistive load bank. Think of it like a toaster...same thing. We do it all the time on big and small units. It verifies that the unit can "carry the rated load". Motor loads are definately not the same as resistive loads but you have not mentioned anything that would make me think the generator is overloaded. 7kw is good for 58 amps at 120v and 29 amps at 240v. If your wiring is correct maybe your 120 loads were not balanced. If you connect all your 120 volt loads to one leg of the generator it is not good...... Methodical testing by someone with a little knowledge and a Fluke meter is all you need too figure out your problem. To be very truthfull.......and I might get bombed on here for saying this.....many electricians don't do to well with backup generators and the switch gear that accompanies one. I have seen it many times......

  11. #11
    DIYer, not in the trades LLigetfa's Avatar
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    One theory that has not been put forth yet is the possible effect of power factor. While I am not an EE, I do work with EEs in an industrial setting and know first hand some of the effects of power factor on sensitive equipment.

    http://en.wikipedia.org/wiki/Power_factor

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    DIY Senior Member Rich B's Avatar
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    I have a Honda 3500 watt portable. I use it at the races I attend. I am a drag racer.....It powers my truck camper and various items in my trailer.

    Last June or July my electrical service drop was severed at the street. When I got home I discovered this and used that same Honda generator to power up some things in my house untill the cables were repaired. I have a 240 volt deep well. It worked fine but I did make a big mistake when I first powered up. My generator is 120/240 switchable. I had the ouput switch still on 120 as my camper is 120 only. My well pump tried to run and fortunatley the breaker tripped that feeds the pump. One leg was hot one leg was not........

    My point is even a 3500 watt generator will work. Some motors draw 3 or more times their running amps to start. Usually things like pumps, compressors........My well and some lights and my fridge worked fine for the few hours it took that day to restore normal power.....

    My camper has a 10,000btu AC unit, a dc converter/ battery charger and a fridge. The Honda 3500 will power all 3 and maybe a little more usually.

    I can't mention how the generator was connected to my house.......The moderator wouldn't like it....



    P.S. When a generator is loaded heavily......the engine's governor which is mechanical in this case......sends the carburetor to wide open throttle. The engine gives you all it has agsinst the electrical field that it is in the generator end. If the engine can't maintain speed amperage shoots up and the overload breakers almost always trip at the machine.......On an RV if you turn the AC units off and then immediately back on you will undoubtedly trip the generators output breaker(s) on any Onan RV unit. You are trying to start the AC compressor in a condition called locked rotor amp draw. You have to wait a few minutes for the pressures in the AC unit to equalize........and reset you generators breaker(s) This issue rarely causes any other problems as it happens withing seconds of trying to restart that Ac unit......I work on a lot of M-H's in the warmer months.....We did some work on 2 this week and one is right in front of me now. 39' Dutch Star...Generac diesel genset....out and on the bench......
    Last edited by Rich B; 03-03-2011 at 11:38 AM. Reason: spelling errors

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    General Engineering Contractor ballvalve's Avatar
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    And you can start a pretty large air compressor by holding the unloader open for awhile while it gets up to speed.

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    DIY Junior Member david_griffin's Avatar
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    Quote Originally Posted by Igor View Post
    My guess is that the neutral and one of the hots were swapped somewhere, so those 120V transformers were getting 240V.
    This is also my point of view. Surges from generator, even strong, would not kill primary windings of transformers so quickly.
    It must be hot neutral swap...

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Should this have been a hot and neutral reversed would it not have shown up during this?
    Quote Originally Posted by krnva View Post
    2. As was stated, the thermostats for the heating systems were set down to prevent/delay/control their operation until later in the test. I do not believe that either system started up on the generator, but rather set idle. However, the refrigerator and freezer were still on the panel and may have started while I was filling the sump crock. Don't know for sure either way. Otherwise, just general lighting and outlet circuits.

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