Generator inlet plug-30A or 50A?

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Badfish740

Minister of Fire
Oct 3, 2007
1,539
I was looking at various generator inlet boxes and noticed that there are boxes rated at 30 Amps and 50 Amps. The 50 Amp boxes seem to be about twice as expensive as the 30 Amp boxes (about $80 as opposed to $40), and my generator (4500W) puts out 30 Amps max from the 240V outlet. However, I would like to go with something larger one day because I'm pretty sure that the generator I have is probably close to maxed out just running critical systems in the house which I try to cycle. It would be nice to be able to power some lights at the same time and be able to run my electric HWH (by itself) without fear of overloading. At what wattage generator do you get into the 50 Amp range? I Googled and all I can find is wattage. Are we talking 10kW? 15kW? I would probably only go as high as 10kW, maybe 12kW.
 

thinkxingu

Minister of Fire
Jun 3, 2007
1,125
S.NH
Mr. Badfish,
I asked a similar question a couple days ago, and what I found out was this: to determine maximum wattage, you multiply voltage times amperage, so: 120 x 30 = 3600. Running 240 would be twice as much, so our 30 amp inlets would allow up to 7200 watts whereas a 50 amp would allow up to 12000. I have a 5500, and I can run my hwh and fridge but nothing else. I'll be picking up a 7000 soon, which will allow lights and maybe a single burner on my stove.

S

PS I assume you have an electric stove, too: I discovered that one burner takes much less power than a microwave.
 

Badfish740

Minister of Fire
Oct 3, 2007
1,539
thinkxingu said:
Mr. Badfish,
I asked a similar question a couple days ago, and what I found out was this: to determine maximum wattage, you multiply voltage times amperage, so: 120 x 30 = 3600. Running 240 would be twice as much, so our 30 amp inlets would allow up to 7200 watts whereas a 50 amp would allow up to 12000. I have a 5500, and I can run my hwh and fridge but nothing else. I'll be picking up a 7000 soon, which will allow lights and maybe a single burner on my stove.

S

PS I assume you have an electric stove, too: I discovered that one burner takes much less power than a microwave.
Thanks! I think the 50A is definitely the way to go then. I do have an electric range but at least this time, cooking on the propane grill outside worked well. Not sure how well that would work with the power out in the middle of a driving snow storm though ;)
 

thinkxingu

Minister of Fire
Jun 3, 2007
1,125
S.NH
If you're going to start thinking 50 amp and the associated generator, you might look into a standby unit.

S
 
M

MasterMech

Guest
Bigger is def better if you can swing it but my 7500 watt genset powers 80% of my home through a 30A hookup. (Doesn't power the elec. stove/oven or washer/dryer, Hot water is via oil boiler.) 50A will also hit you in the pocket for the heavier wire to hookup. If you go with the 50A, make sure the genset has a 50A output too as some units do not despite being rated for 8000 watts or more.

Watts / Volts = Amps

Your 4500W Gen is only really capable of 18.75 Amps @ 240V
You'd need a 7200W Gen to max out a 30A connection, a 12000W unit for 50A.


Figure out what you need, If you have to run an elec. range, elec. HW, and Fridge/Freezer, etc. then 50A is a must.
 

bogydave

Minister of Fire
Dec 4, 2009
8,426
So Cent ALASKA
Remember pie.
PIE
P=I X E
P - power (watts)
I - current (amps)
E - voltage

Watts = 50 amps X 220 volts
11,000 Watts, 11kw

50a X 240v = 12000 watts.

There are power losses involved. Generator ratings are like anything, a 5k rating may not run at a full 5k load, & is more like 20 amps usable, at 220 volts. (5000/220 = 22.7 amps)
Ratings & usable power vary. Some I've seen, use 220 volt, 230 volt, or 240 volt for their output.
Wire size current rating is another factor. 20 amps - #12 wire, 30 amps - #10 wire, 50 amps, # 6 to #8 wire, type of wire also (solid,stranded number of conductors). So do the research.
Going over 30 Amps, everything has to be "up sized" from the "off the shelf, basic house wiring". Wire, switch, plugs sizes. Know when to call on the experts. Consult your local utility.
Fuel consumption? ***"So do the research.""

All IMO. But if you are on back up power, you are already involved in something out of "the norm". Maybe you aren't home. You don't want your back up system to add to the situation.
Maybe use a propane stove for cooking & hot water.
 

Badfish740

Minister of Fire
Oct 3, 2007
1,539
MasterMech said:
Bigger is def better if you can swing it but my 7500 watt genset powers 80% of my home through a 30A hookup. (Doesn't power the elec. stove/oven or washer/dryer, Hot water is via oil boiler.) 50A will also hit you in the pocket for the heavier wire to hookup. If you go with the 50A, make sure the genset has a 50A output too as some units do not despite being rated for 8000 watts or more.

Watts / Volts = Amps

Your 4500W Gen is only really capable of 18.75 Amps @ 240V
You'd need a 7200W Gen to max out a 30A connection, a 12000W unit for 50A.


Figure out what you need, If you have to run an elec. range, elec. HW, and Fridge/Freezer, etc. then 50A is a must.
Maybe I'm just better off going with the 30A then. I would think something like this:

http://www.northerntool.com/shop/tools/product_200402913_200402913

would be about as large as I would need.
 

bogydave

Minister of Fire
Dec 4, 2009
8,426
So Cent ALASKA
"Any" is better than "None".
Some lights,a cold fridge & a Coleman stove, as long as it's just a short temporary outage, "making do" isn't so bad.
If you are going to spend tens of thousands $$$ for power back up system to run the whole house as if you never lost power, call the pros. You want a safe system.
 

BrotherBart

Modestorator
Staff member
bogydave said:
"Any" is better than "None".
Some lights,a cold fridge & a Coleman stove, as long as it's just a short temporary outage, "making do" isn't so bad.
If you are going to spend tens of thousands $$$ for power back up system to run the whole house as if you never lost power, call the pros. You want a safe system.
Yep. We have lost power for five to seven days three out of the last five years. But I am sticking with the two gennys and cords. I can take a lot of showers in five star hotels for the twenty grand my neighbor spent after losing power for the first time in twenty years for a few days.

That leg they are on never goes down. Well, it did once. Ours, all the time.
 

Shadow&Flame

Minister of Fire
Jun 6, 2011
787
Central Arkansas
It really depends on how much money you want to spend. I have a friend whos
power was off for two days and he spend over 10K on a small standby generator.
In the 4yrs since it was installed he has never lost power... I have three generators
(one main and two small backup units) and I just built small boards to go into the widows
with outlets mounted on them. Works essentials until I get power back. I always
have someone coming over to borrow one of them for one reason or another...
I even had a neighbor, when the power was off, come over to borrow the big gen.
It was running hooked to the house and he still had the nerve to
ask...let me think about that NO!
 

bogydave

Minister of Fire
Dec 4, 2009
8,426
So Cent ALASKA
I've wheeled mine over to the neighbors to get his well running & he fills up some water jugs, tub etc. Take a shower etc. if it's a long outage.
His is 120 volts & Runs the furnace & a few lights but not the 220 volt well pump. He'll upgrade one of these days.
He wheels it back when he's got what he needs.
 

jebatty

Minister of Fire
Jan 1, 2008
5,775
Northern MN
I was amazed at how little power we regularly use in our house. I put a whole-house monitor on the meter, and our normal base load is less than 1000 watts. The big consumer is the 240V electric HW htr, and the big demand consumer is the 240V well pump. Except for the HW htr (and the dehumidifier in summer), average electric for our home is less than 600 kwh/month, which is less than 20 kwh/day, which is less than 1 kw/hr. The 5500 watt generator does everything that's really needed in a power outage emergency, including the well pump, even if the outage lasts a long time.
 

Badfish740

Minister of Fire
Oct 3, 2007
1,539
jebatty said:
I was amazed at how little power we regularly use in our house. I put a whole-house monitor on the meter, and our normal base load is less than 1000 watts. The big consumer is the 240V electric HW htr, and the big demand consumer is the 240V well pump. Except for the HW htr (and the dehumidifier in summer), average electric for our home is less than 600 kwh/month, which is less than 20 kwh/day, which is less than 1 kw/hr. The 5500 watt generator does everything that's really needed in a power outage emergency, including the well pump, even if the outage lasts a long time.
I'm debating on whether it would be wise to go all propane in the long run. Right now I have forced air oil heat, electric DHW, and an electric stove-the two of which take up 80A worth of my 200A service. Ideally I'd like to convert to hydronic heat (my wife has bad allergies and we "tolerate" the forced air heat for now), install a small propane boiler and a gasifier with a sidearm for DHW. I'd also like to throw a solar loop in there as well so that DHW heat would be taken care of with wood in the fall and winter and the solar in spring and summer.
 

BrotherBart

Modestorator
Staff member
jebatty said:
I was amazed at how little power we regularly use in our house. I put a whole-house monitor on the meter, and our normal base load is less than 1000 watts. The big consumer is the 240V electric HW htr, and the big demand consumer is the 240V well pump. Except for the HW htr (and the dehumidifier in summer), average electric for our home is less than 600 kwh/month, which is less than 20 kwh/day, which is less than 1 kw/hr. The 5500 watt generator does everything that's really needed in a power outage emergency, including the well pump, even if the outage lasts a long time.
That is what I found. And the reason why I added the new 2500/3250 genny last year. The 5000 is a gas hog. When we lost power in the last big snow storm the little guy hauled the freight for five days. Using a fraction of the gas the other one usually does.

We don't run the well pump though. If we did I would just fire the big one for the pump and to make coffee and fry some eggs on the griddle of a morning.
 

Badfish740

Minister of Fire
Oct 3, 2007
1,539
BrotherBart said:
We don't run the well pump though. If we did I would just fire the big one for the pump and to make coffee and fry some eggs on the griddle of a morning.
It's amazing how much power resistance heating consumes. One morning when I fired up the generator (4500W) I figured I'd hook up the coffee maker before I connected anything else and you might have thought I just flipped the switch for a large A/C unit with the way it bogged for a moment before chugging back up to speed.
 

btuser

Minister of Fire
Jan 15, 2009
2,069
Principality of Pontinha
I looked into the standby units and decided even if I could afford to buy one I would not be in the mood to run it. We don't have NG so propane/oil is really the only option. Propane units are cheaper, but I do heat with oil so I could connect to the same tank. 12kw-18kw to run the whole house because at this point "you mine as well" and not a huge difference in price. I stopped looking when it noticed that most units were 1g/hr at 50% load and up to 2-3g/hr at rated load. 2g/hr x 24hr x $3.00/g = a hotel room where you can take a shower, watch tv and do your laundry down the hall. Plus I can keep my 10-20 grand. My boss just got a standby unit and spent 36 hours in the dark because a govenor spring broke. Not a foolproof option.

I've got a quality jobsite generator that's rated for 6500w/8150w. Because we have an in-law apt its really running for two households. This time around I got 14hrs (leave it running for the old folks) on 7 gallons so its fuel rating is pretty accurate. With this size genset I dont' have to worry about the well pump kicking on if the furnace or fridge is running. I do however, like the idea of the two little gensets. Even though it would be more work to run/maintain two its redundancy so if one breaks at least you have 1/2 your power.

A friend of mine got me thinking about a UPS between the transfer switch and the genset so I could use the idle feature (which really shouldn't be used when you've got inductive loads plugged into it) and cut down on all the wasted revs/fuel.
 

Badfish740

Minister of Fire
Oct 3, 2007
1,539
btuser said:
I looked into the standby units and decided even if I could afford to buy one I would not be in the mood to run it. We don't have NG so propane/oil is really the only option. Propane units are cheaper, but I do heat with oil so I could connect to the same tank. 12kw-18kw to run the whole house because at this point "you mine as well" and not a huge difference in price. I stopped looking when it noticed that most units were 1g/hr at 50% load and up to 2-3g/hr at rated load. 2g/hr x 24hr x $3.00/g = a hotel room where you can take a shower, watch tv and do your laundry down the hall. Plus I can keep my 10-20 grand. My boss just got a standby unit and spent 36 hours in the dark because a govenor spring broke. Not a foolproof option.
The way I look at it the built in standby units are for rich folks who can't fathom having movie night on their 65" flat panel interrupted by a power outage complete with microwave popcorn, lights on in every room, and the heat cranked up. That or critical infrastructure like fire stations, OEM headquarters, etc... A manual interlock and a good quality conventional generator will do just fine for you and I.
 

btuser

Minister of Fire
Jan 15, 2009
2,069
Principality of Pontinha
Eventually I'm going to have to figure something out for my parents, at which point the rich man's option may be the only option. My genset is battery-start so it would be a piece of cake to wire up a contact/timer board off an auto transfer switch, but no auto choke on the engine may leave me out of luck. As it is right now I really can't expect anyone but me to roll the generator outside, plug it in without bending over any tabs, prime + start the generator and then throw the breakers on the transfer switch. I've shown everyone else how to do it but somehow no one else is really interested in actually doing it.

Maybe a night without lights would peak their interest.
 
Sep 29, 2010
246
Southern NH
btuser said:
Eventually I'm going to have to figure something out for my parents, at which point the rich man's option may be the only option. My genset is battery-start so it would be a piece of cake to wire up a contact/timer board off an auto transfer switch, but no auto choke on the engine may leave me out of luck. As it is right now I really can't expect anyone but me to roll the generator outside, plug it in without bending over any tabs, prime + start the generator and then throw the breakers on the transfer switch. I've shown everyone else how to do it but somehow no one else is really interested in actually doing it.

Maybe a night without lights would peak their interest.
Btuser

I'm in the exact same boat. I heat with oil and had a couple of propane companies come in to give me a quote. The worst part about only using the propane for the generator is that you usually don't use much propane so the propane company wants to charge you a rental fee for the tank, or charge you a premium for propane, or both. One company was about $2 more per gallon. OUCH!!!
 

KarlP

Feeling the Heat
Nov 18, 2005
485
wannabegreener said:
I'm in the exact same boat. I heat with oil and had a couple of propane companies come in to give me a quote. The worst part about only using the propane for the generator is that you usually don't use much propane so the propane company wants to charge you a rental fee for the tank, or charge you a premium for propane, or both. One company was about $2 more per gallon. OUCH!!!
Some reason you're not considering a diesel genset if you want something automatic and already heat with diesel? Seems much cheaper and easier to run an extra line than install an extra tank.
 

btuser

Minister of Fire
Jan 15, 2009
2,069
Principality of Pontinha
KarlP said:
wannabegreener said:
I'm in the exact same boat. I heat with oil and had a couple of propane companies come in to give me a quote. The worst part about only using the propane for the generator is that you usually don't use much propane so the propane company wants to charge you a rental fee for the tank, or charge you a premium for propane, or both. One company was about $2 more per gallon. OUCH!!!
Some reason you're not considering a diesel genset if you want something automatic and already heat with diesel? Seems much cheaper and easier to run an extra line than install an extra tank.
The generators can get pretty darn expensive when you start looking into diesel. I went through the Listeroid setup, small portable diesel rigged for ATS, marine diesel pulled from a boat and rebuilt, military surplus ect. A friend who does service work for Onan said it would be a tinkering nightmare. I think I priced it out that a minimum diesel setup was about 10 years worth of propane tank rental or just buy the tanks outright (if they will let you). A diesel genset may be the ultimate doomsday setup but I'm not running a hospital. I just need a furnace and a hot plate. For my house I'd be running either an oil line 100' to the generator (though the house or burried/under asphalt driveway) or 1/0 from the panel to the genset. I'd end up siphoning heating oil and filling the tank manually, with all the associated problems. If the goal here is seemless ultra-reliable power during a temporary emergency then I don't want to worry about diesel.

I would change my tune if I could get my hands on a steady stream of WVO. I had visions of running my boiler, truck, generator/solar and even pool heater with the stuff but it never panned out. Too many hippies out there.
 

stub

New Member
Dec 8, 2005
12
During last years ice storm, I bought a 4500 W at Menards for about $500. It uses a 30 amp plug, which I back-fed into my welder outlet. I know...

I was able to run all house lights, kitchen apps., microwave, except stove, well pump (220V), furnace (propane), wood stove blower, etc. Basically everything except washer/dryer, water heater, and electric stove.

It has I think a 6 gal gas tank. I put in 5 gal before going to work, and again in the evening. I ran it for 4 days like that. Worked good.

I'm now in process of moving my electric meter, adding a 100a/60a manual transfer switch, and permanently installing a 30a power inlet to be safer and easier to connect.

I considered a bigger unit but everything is $$$ and this one is easy to pull-start and move around and gets us by as long as I can keep gas in it.

No more than our power is out, I don't need any more hassle than this.
 
BrotherBart said:
jebatty said:
I was amazed at how little power we regularly use in our house. I put a whole-house monitor on the meter, and our normal base load is less than 1000 watts. The big consumer is the 240V electric HW htr, and the big demand consumer is the 240V well pump. Except for the HW htr (and the dehumidifier in summer), average electric for our home is less than 600 kwh/month, which is less than 20 kwh/day, which is less than 1 kw/hr. The 5500 watt generator does everything that's really needed in a power outage emergency, including the well pump, even if the outage lasts a long time.
That is what I found. And the reason why I added the new 2500/3250 genny last year. The 5000 is a gas hog. When we lost power in the last big snow storm the little guy hauled the freight for five days. Using a fraction of the gas the other one usually does.

We don't run the well pump though. If we did I would just fire the big one for the pump and to make coffee and fry some eggs on the griddle of a morning.
I ended up in the same situation. I was given both of my gens. The Honda Eu3000is is small, quiet, easy to start, fuel-efficient and an inverter gen for my "sensitive" electronics. It's the first choice in an outage. The Generac 5000 watt with a 10 hp Briggs is hard to start, noisy and thirsty. I only run it when I need 240v. for the well pump or HW.

On the subject of HW, I was looking at the rating on my water heater. It says upper element 4500w, lower element 4500w, maximum 4500w. Does it switch from one element to the other? Trying to figure out if I need to put a switch on one element to prevent overload on the gen.
 
I'm in the exact same boat. I heat with oil and had a couple of propane companies come in to give me a quote. The worst part about only using the propane for the generator is that you usually don't use much propane so the propane company wants to charge you a rental fee for the tank, or charge you a premium for propane, or both. One company was about $2 more per gallon. OUCH!!![/quote]

A friend was in the same situation. Rather than get screwed by the propane company, he bought a 100 gal. tank and put it on a cheap HF trailer. Now he buys his propane wherever it's cheapest.

His standby generator was less than $2k. The beauty of propane is the stuff doesn't go stale or gum up the carb from sitting. I wouldn't have mine on automatic, though. He and his wife were both gone during a 3 day outage. The house was well lit and nice and warm.
 

BrotherBart

Modestorator
Staff member
MrWhoopee said:
On the subject of HW, I was looking at the rating on my water heater. It says upper element 4500w, lower element 4500w, maximum 4500w. Does it switch from one element to the other? Trying to figure out if I need to put a switch on one element to prevent overload on the gen.
Only one at a time turns on.
 
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