Generator Size and Wiring Questions

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  #1  
Old 08-25-15, 10:15 AM
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Generator Size and Wiring Questions

Hello, first post here.

I'm a new homeowner and looking to get a portable generator. I'd like to be able to comfortably power the essentials: Well pump, oil furnace and kitchen circuit with fridge/freezer, lights and plugs.

The home had a GE 200a transfer switch installed that feeds the 200a panel - wiring from the street goes through the switch to allow selection of street/generator. 10 gauge (4 wire I believe? 2 hots red/black, white neutral and ground) runs 65' from the switch to a junction box in the shed, and from there it's a 25' rigid cable with L14-30 plug. All passed home inspection and a look over by my electrician.

I have two questions:

1. What is the maximum size generator I can purchase for my current wiring?
2. Will that generator be able to power the well pump, furnace and fridge?

I can get a good deal on a Honda EM6500SX (5500 continuous, 7000 surge) but I'm concerned if that will be enough to handle the draw from the well pump starting. I'm trying to determine the depth/hp of the pump to better estimate that. The pump is 240v on a double 15a breaker...

I'm also contacting the fridge/freezer maker (it's a new LG side by side) as I can't seem to find a ratings sticker on the back of the unit. I did determine that the oil furnace (burner/motor/igniter/circulator/zone valves) would be a little over 1000w based on the v/amp rating tags… I could use advice on calculating starting watts as well.

Any advice is appreciated.

Thanks,
Brian
 
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  #2  
Old 08-25-15, 10:29 AM
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The maximum power your generator can supply through your existing wiring is 30 amps at 240 volts. The 10 gauge line from the transfer switch generator side to the generator wall inlet is the limiting link.

Thirty amps will cover your essentials [excluding all electric water heating, air conditioning, and all electric space heating] but you may need to do some planning and management of power.

If you upgrade the generator feed from the transfer switch enough, you could conceivably use a 200 amp generator.

You would probably be better off keeping it as a 30 amp or smaller generator (no air conditioning, no all electric water heating) since at low loads a smaller generator on average consumes less fuel than a larger generator.
 

Last edited by ray2047; 08-25-15 at 10:53 AM. Reason: Add edit member couldn't make.
  #3  
Old 08-25-15, 11:08 AM
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The maximum power your generator can supply through your existing wiring is 30 amps at 240 volts. The 10 gauge line from the transfer switch generator side to the generator wall inlet is the limiting link.
7200 watt gen? Should power the well pump @ 240v

On the 120v side you need balance your loads... ( If fridge and high loads are all on one side of panel you may not be able to run them at the same time.)

Youll have 3600 watts per winding, or per side of panal. ( I assume when you throw the switch the gen will power your whole panel?)

Is this what you have as a transfer switch?

[ATTACH=CONFIG]55131[/ATTACH]


Honda generators are good that they have floating nuetrals AFAIK... I assume if you start looking at other gens without floating neutrals you will have other issues to deal with..

But thats a whole other topic..
 
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  #4  
Old 08-25-15, 11:47 AM
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I'll add that there really is not a good way to estimate whether a marginally-sized portable generator will start the well pump. You can run the numbers every way you can think and still have it not work, or sometimes work. The head pressure on the pump all the way down to the wiring, design and maintenance on the generator engine and windings will affect it. The options are really to oversize the unit a pretty significant amount to ensure you'll have the inertia to start the pump, or just buy or borrow a generator of a size you think should work, test it and return it if it doesn't work.

That said, Honda makes excellent quality generators. If you keep the engine in good condition and either run it for 15 minutes once a week or follow the long term storage procedure every time you shut it down, it should perform very well for a long time.
 
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Old 08-25-15, 11:53 AM
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Thanks for the replies. Here's the transfer switch:

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I had not considered balancing… Everything I want to run is on the right side of the panel. The furnace (10) fridge/freezer (12), GFCI kitchen outlets (20/22), well pump (24/26).

I understand the well pump at 240 splits both. Would it be wise to have either the fridge or furnace moved to the other side to balance the two of them?

When using the generator, I plan on keeping on the furnace/well/kitchen breakers. Everything else gets shut off including the electric water tank and bypassing it with the shutoff valves. I don't plan on using the stove or any other 240 appliances.

Thanks,
Brian
 
  #6  
Old 08-25-15, 12:03 PM
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The panel is laid out like this:

1 A--A 2
3 B--B 4
5 A--A 6
7 B--B 8



So circuits 1, 2, 5 & 6 are on the same leg "A" and 3, 4, 7, & 8 are on the other leg "B". Compare to your own panel to see where the important loads land. You should adjust the panel so the 120V loads are spread as evenly as you can across the two legs. The 240V loads don't matter as they are balanced by design.

The hot water tank will stay warm for a surprisingly long time if you flip the breaker off and limit your hot water usage -- no bypass necessary; or you can just cycle it on when you're asleep to burn up a little fuel but still have a hot shower in the morning.
 
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Old 08-25-15, 12:40 PM
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When using the generator, I plan on keeping on the furnace/well/kitchen breakers. Everything else gets shut off including the electric water tank and bypassing it with the shutoff valves. I don't plan on using the stove or any other 240 appliances.
Since you have 240 loads I would get the 7500 watt gen. Probably 10000 surge.. Especially if I had electric HWH and stove..

Like this.. Just need to make sure floating neutral. ( I have a coleman I believe they are all floating)

A honda with same wattage will cost you 5k $$$$$

Powermate PM0148000 Wx Series - 8000 Watt Electric Start Portable Generator



Since I run a small 3000 watt gen and have no 240 loads I simply run what I want with the high draw loads with others off..

Whats on my circuit for example.

120 well pump ( 800 watts run )
Ceiling fans x3
many outlets and lights ( All cfl's)
TV.s about 50 watts each
Fridge (400 watts run)
Microwave ( 1000 watts)
boiler gas ( 50 watts )

Im gas boiler and hw water.

During hurricane sandy I sipped 12 gallons of fuel only. ( benefits of small gen)
Fuel was a very scarce commodity for 9 days of no power.

When it was time to shower in my home I got the wife and all the kids togther and said " Shower time" !!! I turned off fridge, and most all circuits but a few lights and we all showered one after the other.. ( left shower running as it kept the well pump on so it would not cycle)

After that , well pump off, fridge and heat back on as well as TV.

If anyone wanted to use water it was OK sparingly. ( I explained to them about the well tank ) Even if they used all the water in the tank, I just flipped the breaker to refill.

Id run the gen in morning 4 hours to cool the fridge, heat the house, and let everyone wash up. Then 4 hours off.
Then 4 hours on and dinner time.
Then 4 hours off till dark.
Then on till about 12 pm then off till I got up at 5:30.
( I made sure to crank the heat up to 75F in the house, cause by morning it was chilly
 

Last edited by lawrosa; 08-25-15 at 01:59 PM.
  #8  
Old 08-25-15, 01:32 PM
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Thanks.

Based on the panel layout the furnace is on leg A and the Fridge is on leg B so I should be good with balancing the load.

I'll just have to ensure I get a 30amp generator with enough watts to handle the 240v well pump startup and the fridge on one leg and the furnace on the other. The outlets for charging devices and a single bulb overhead light I assume are negligible.

I liked the Honda generators quality, the auto-throttle and the fact that the neutral/ground are not bonded on the EM series. The problem as mentioned is the jump between the 6500 and the 10000 is too much money, so I may need to look at something else, or find a way to rent/borrow a 6500 and see if it has what I need before buying.

Brian
 
  #9  
Old 08-26-15, 06:22 AM
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So last night I was looking at other brands of generators thinking I'll target 7000-8000 running watts with a higher surge.

I noticed on some models the max rated amps vary. In particular some of the Generac models have max rated listed in the 31a-33a range. Is this anything to be concerned about given the length/gague of my wiring or is this negligible?

I understand at 30amps and 240volts I'd be drawing about 7200 watts on the L14-30 outlet…

Are the additional surge watts available for use on that line for a short period? Also, is the surge available at anytime while the generator is running?

I also understand I'll have to correct the neutral bond issue on the generator if I choose one that has that.

Thanks,
Brian
 
  #10  
Old 08-26-15, 07:09 AM
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Take all of the ratings with a grain of salt -- they are produced on brand new engines in laboratory conditions and massaged by the companies' marketing departments to get 0.1 bigger numbers than the competitors. I usually figure a 20-25% variation in what the manufacturer states vs. what you'll actually get during an ice storm with a can of old gas from the back of the shed. The 30A plugs and receptacles will be plenty adequate for the loads you're dealing with. I recommend focusing more on warranty, quality, etc than flat out specs.

The surge rating essentially means how much the bogging the engine can handle without stalling during an electric motor start-up. It will really only be maximally effective when the generator is lightly loaded when the motor kicks on, and should last just for a few seconds before the load levels out. The mass of the flywheel and/or rotor have a big effect on the surge capacity as do the response time on the throttle/governor and the overall tuning of the engine. If you tune it a little rich, it can throttle up more quickly to respond to a surge, but at the expense of less runtime due to greater fuel consumption per hour.
 
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Old 08-26-15, 08:00 AM
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The mass of the flywheel and/or rotor have a big effect on the surge capacity as do the response time on the throttle/governor and the overall tuning of the engine.
My theory is that the farther apart the run watts and surge watts the better the winding's are in the head unit..

I'd be drawing about 7200 watts on the L14-30 outlet…
IMO if you think you will be drawing that amount of watts constantly youll just kill/melt the gen from heat in no time.

Even though they rate them as a constant run wattage.

In particular some of the Generac models
They are loud!!! Also the briggs/stratton gens...

One thing I am considering when looking for a new gen, and because of what I experienced with hurricane sandy is propane gen.

This I say because gas stations were closed for some 5 days due to no electric.. But how many blue rhino propane exchanges were there? Many. All the home stores and wally world has them.

Would I be fighting for propane? Dont know. I dont think many have portable propane gens. Most are permenant installs at the home with large 250 gallon tanks.

But I have a camper and grill of course so always have 4-5 20 lb bottles on hand...

Just a thought.. ( propane has no shelf life)
 
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Old 08-26-15, 08:12 AM
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Would I be fighting for propane?
Went through several hurricanes and one really bad tropical storm and never lost natural gas. Of course if your neighborhood doesn't have it not an option.
 
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Old 08-26-15, 08:17 AM
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I'll also throw in that Yamaha makes really nice dual- and tri- fuel generators that can take natural gas, propane or gasoline.
 
  #14  
Old 08-26-15, 11:42 AM
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Thanks for the advice and input, there's some good information here. I will check out the Yamahas.

I found the ratings sticker for the fridge, it was on the inside. 750 watts running. The furnace is about 1000 watts running (burner/motor/circulator/zones) so provided not everything starts at the same time, that would leave 5000+ for starting and running the well pump. I'm still trying to determine the depth and hp.

If the well pump is 1/2hp - 3/4hp as I suspect, I'm going to see if I can rent/borrow the Honda and give it a shot.

Thanks,
Brian
 
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Old 08-26-15, 12:03 PM
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I'm still trying to determine the depth and hp.
There should be a starter box on the wall near the well tank. Often the info is in there..

High voltage inside so cut power if you open it up to look...
 
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Old 08-26-15, 12:15 PM
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Any gasoline engine can be converted to use gaseous fuel such as propane or natural gas. Generally speaking a conversion to straight gaseous fuel (no longer able to use gasoline) gives slightly better results than a so-called "tri-fuel" conversion and in most cases the loss of the gasoline option is of little consequence. I converted my Yamaha inverter generator to gaseous and use it with natural gas.

FYI, you do not have a furnace, you have a hydronic heating system using a boiler, hot water, circulating pump and some type of heat emitter such as convection baseboards, convector cabinet heaters, cast iron radiators, radiant floors or possibly a fan/coil arrangement with ducts. The term "furnace" in regards to residential space heating denotes a heated air system, usually with a blower to circulate the air.
 
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Old 08-26-15, 01:07 PM
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FWIW, I had a Honda 5500 watt generator at my old house. I had a 1hp, 240 volt submersible well pump. The Honda would just barely handle the starting surge. It would groan and struggle for 5-10 seconds when the pump kicked in. I eventually replaced it with a 7500 Generac and it barely missed a beat when the pump started. Although Generac is not in the same league, quality-wise, as the Honda, it has served me well for nearly 10 years now, including running probably 8 hours a day for a week when I had to have my underground power line repaired.
 
  #18  
Old 08-26-15, 01:18 PM
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I've got a Pumptrol pressure switch which lists it's own max ratings but there's no information on the well pump itself noted anywhere around that I can find. My assumption (could be wrong) that it's a 1/2 or 3/4hp pump is based on the 15amp breaker and 20gal/38psi tank.

If the pump is 5-6 amps running, I'm thinking the 5500/7000w surge Honda should be able to get the pump going even with 1750-2000 in use for the furnace, fridge and a few lights.

It's just a lot of money to spend when you aren't sure…

Brian
 
  #19  
Old 08-26-15, 01:29 PM
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That is actually my concern with the Honda, it's an expensive unit to find out it's just not quite enough - why I started looking at the 7-8k Genracs as well.

With the Generac, did you have to address the bonded neutral or do you have a neutral switching transfer switch?

Thanks,
Brian
 
  #20  
Old 08-26-15, 07:46 PM
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Most rental houses rent generators. Maybe you could rent a 5500 for a few hours and test it?

OTOH, I've never heard anyone say "I wish I had bought a smaller generator".

Also, if you have an ammeter or could borrow one you can determine the size of your pump in a few minutes.
 
  #21  
Old 08-27-15, 05:35 PM
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I've decided to buy a Briggs & Stratton 30471 8000 watt generator. I found a neighbor who has one, similar house, same age/size well pump, etc. It meets all his needs and he gave a very good review of it. After comparing, I prefer the B&S over the Generac and the prices are similar.

Now this model also has the neutral bonded to the frame. My transfer switch is non neutral-switching, so I will have to modify the generator…

I just want to make sure the unit will be safe to operate with the neutral bond removed. I have no plans to use this as a standalone unit, just as a home backup power source.

I also want to be sure I'm not compromising any of the safety features like the circuit breaker/overload protection by floating the generator's neutral.

Thanks,
Brian
 
  #22  
Old 08-27-15, 07:39 PM
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some bonds are hard to find...

I found a neighbor who has one, similar house, same age/size well pump, etc. It meets all his needs and he gave a very good review of it.
Whats he doing? Did he lift his bond? or does he have proper transfer switch...?

I just want to make sure the unit will be safe to operate with the neutral bond removed. I have no plans to use this as a standalone unit, just as a home backup power source.
IMO and what I do if I want to use it stand alone is that I made an edison plug..

( Although there is a debate but IMO a floating nuetral is safer IMO on a stand alone gen but I do use the edison plug when using my gen on my non grounded RV)

The RV Doctor: My Honda Generator Will Not Power My Coach

and here

Generator Ground-Neutral Bonding | No~Shock~Zone

This gets very in depth on bonding and generators.. Its a good read if you spend some time on it...

Part 1

https://cumminspower.com/www/literat...ingAC-1-en.pdf

Part 2

https://cumminspower.com/www/literat...ingAC-2-en.pdf

And a very good one from this guy... I often post this as it explains a lot..

http://www.oshaprofessor.com/Portabl...rds%203-05.pdf

Hope you learn something...

Oh by the way I am not an electrician. Im a plumber...!!!!
 
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