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post #1 of 27 (permalink) Old 02-07-2020, 08:54 AM Thread Starter
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Generator Size

Here is what I have:




https://www.homedepot.com/p/Siemens-...230U/100002289
And approximately 40 feet of 8/3 wire connecting them.

I have a pool pump that I need to run if I lose power in the winter months - 230v x 9.3a = 2,139 running watts
Refrigerator approximately 800 running watts

What I donít know is the running/starting wattage of my gas furnace blower (should I choose to use it because we have gas logs). I also plan to have a window unit for AC That would cool about 800 sq ft on standby in case of a summer outage. I also know that during summer months I could kill the pool pump and, depending on the running/starting wattage of the HVAC, possibly run that. Other than that, maybe a 225 watt tv and some random comfort related extras.

Having said all of that, I havenít purchased a generator yet. What size portable generator will my current setup handle? Once I know the largest generator I can run, Iíll know what all I can possibly run during an outage.

Thanks in advance, Danny
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post #2 of 27 (permalink) Old 02-07-2020, 12:07 PM
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Garage
well you are going to need a 240 volt gen.
at least to do the pool pump..
unless you get a second pool pump for the back up that is 120 ac..
so what is the pool heater?? electric or gas?
and house water heater? electric or gas?

yea do a site survey and it is best to have a meter system for the breaker panel..
that helps to see loads when you are on grid so you can label the breaker box when you see the loads...

lucky on my system here as I wired it all my self!!
over kill dedicated runs. lol
so at least I know what runs where!! and it is marked in the printed box cover.
square d has software for that on their site. or a template for MS word. fill in the blanks and print!!

for most homes the honda eu7000is is the best in class.
https://www.northerntool.com/shop/to...0183_200640183
right now 02/07/2020 they have free shipping and $4449.00 price tag..
but they are quiet!!
and if you need tri fuel there is an optional kit now for $500.00 plus hoses to the house.

so the big question is are you able to install this your self?
or are you hiring it out?
if you are good with electrical these are not bad to put in!!
take your time!!

I used 6 gauge on my gen inlet feed to the interlock breaker panel... that gets me a better rating for power..
that is what worked for me. 50 foot was 110.00 retail I catch that on the 11% at menards and get it for 11 bucks less.
see the chart here
https://www.cerrowire.com/wp-content...city091418.pdf

always room for expansion!! run the wire once!! lol!!

Thanks Paul in Iowa
see my Honda generator Group at https://hondagenerator.groups.io/g/main
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post #3 of 27 (permalink) Old 02-07-2020, 01:32 PM Thread Starter
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The house is already set up for a generator. I suppose I could re-wire and/or change the inlet box or breaker if I needed to. I guess Iím just trying to find out, with the current setup, what the largest size generator I can run?
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post #4 of 27 (permalink) Old 02-07-2020, 01:42 PM
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Need some more info to make a proper call.

What state do you live in? Whats your home heating situation, Natural Gas, Propane, heating oil or heat pump?

Do you have any intention on running an alternative fuel... Propane or Natural gas?

Gas or electric stove/oven?

Gas or electric Dryer?

Well pump or city water?

Most Important, whatís your budget? Iíd love to say 240v inverter gen, but $3-4K is a hard pill to swallow.
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post #5 of 27 (permalink) Old 02-07-2020, 02:37 PM
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So Danny,
You must be planning to back feed the house and use a lock out device.
I am not a fan of these devises, but to each his own.
I took a tally of the wattage and amperage you need to keep the items running.
@ 746 watts per HP.
2139 watts for the pool pump. 120 or 240 vac ?
That wattage equates to nearly three hp or 8 to 9 amps @ 240 vac.
Most furnace blowers are 1/4 hp unless it is a huge furnace.
@120 vac that is 1.75 amps.
Then a 225 watt TV is another 2 amps.
So your needed power does not add to a lot of amps.
Then I see that IowaGold is recommending a $4400 generator.
You should check Generatorsdirect.com.
I got my 16 KW Generac for $3100 shipped. Add to that the cost of the transfer switch.
At present we are without power due to the winds in NC.
The Generac is purring and we are comfortable.
I installed a transfer switch and a sub panel to be selective on the things I wanted to run. Works good.
A whole house generator adds value to a home and allows the wife to be comfortable on an outage if I am not home as was the case this morning.
Ask your wife if she can power up the generator if you are not home, then decide.
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post #6 of 27 (permalink) Old 02-07-2020, 03:38 PM Thread Starter
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Let me try asking this a different way. Sometimes things make sense in my mind but not when I type them out.

My wife and I bought a house that is already set up for a portable generator. It is set up with the inlet box, 8/3 wire, 30 amp 2 pole breaker, and interlock switch I mentioned in my original post. Iím simply looking to buy a portable generator.

Does the currently installed set up limit the size generator I can use? If so, what is the largest one it will handle?
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post #7 of 27 (permalink) Old 02-07-2020, 04:41 PM
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If you are sure that the feed wire is 8 Gauge THHN wire, then it is good for 40 amps, but the connector is only good for 30 amps.
That being said, 30 amps times 240 volts is 7200 watts for the maximum the connector box can safely be loaded to.
The general rule is not to load a device over 80%.
You should be the judge, but 80% of the connector is 5760 watts, that leads you to a 5500 watt generator.
The 80% rule assures that the devices connected to your home will not over heat and cause fire.
Now a note concerning the twistlock connector box you are considering.

In the early seventies we were required to run a safety check on all devices we were using.
Believe it or not the twistlock plugs both male and female were found to be dangerous.
Electrical shock was the culprit.
If a hand tool was connected via twistlock then the cable could not be quickly pulled apart creating a potential electrocution situation if a device failed.
If you choose to use the male plug you have shown in your post, be sure to install an on site GFI circuit breaker to assure the plug is rendered inoperable.
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Last edited by ToolLover; 02-07-2020 at 05:31 PM.
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post #8 of 27 (permalink) Old 02-07-2020, 05:46 PM
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Quote:
Originally Posted by Danny Womack View Post
Let me try asking this a different way. Sometimes things make sense in my mind but not when I type them out.

My wife and I bought a house that is already set up for a portable generator. It is set up with the inlet box, 8/3 wire, 30 amp 2 pole breaker, and interlock switch I mentioned in my original post. Iím simply looking to buy a portable generator.

Does the currently installed set up limit the size generator I can use? If so, what is the largest one it will handle?
lol, thatís a very different question. There is no harm in a generator capable of the full 30amps. Both the generator and load center have over current protection and the greatest amperage draw is Inrush from induction loads(electric motors) which spikes very high for only a moment then settles to much lower numbers. But do you actually need a 7200 watt generator???

Bigger rated gen = more fuel usage. What if fuel is hard to come due to disaster, hurricane, earthquake, etc. The only thing youíve told us is that you have a pool and want to be able to run the pump during an outage.

Iíd feel better knowing at the very least the answers to the questions I posed earlier before making a recommendation.
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post #9 of 27 (permalink) Old 02-07-2020, 08:30 PM Thread Starter
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Quote:
Originally Posted by ToolLover View Post
If you are sure that the feed wire is 8 Gauge THHN wire, then it is good for 40 amps, but the connector is only good for 30 amps.
That being said, 30 amps times 240 volts is 7200 watts for the maximum the connector box can safely be loaded to.
The general rule is not to load a device over 80%.
You should be the judge, but 80% of the connector is 5760 watts, that leads you to a 5500 watt generator.
The 80% rule assures that the devices connected to your home will not over heat and cause fire.
ToolLover, Iím sure of what is already here but given what youíve said, I could replace the input box with a 40amp (if one exists) and then swap the 30 amp 2 pole breaker with a 40 amp 2 pole?

Quote:
Originally Posted by drmerdp View Post
lol, thatís a very different question. There is no harm in a generator capable of the full 30amps. Both the generator and load center have over current protection and the greatest amperage draw is Inrush from induction loads(electric motors) which spikes very high for only a moment then settles to much lower numbers. But do you actually need a 7200 watt generator???

Iíd feel better knowing at the very least the answers to the questions I posed earlier before making a recommendation.
Given what ToolLover said and Iím limited by a 5500 watt unit, would that be 5500 running watts? Iíve seen some estimates that say running wattage of an electric motor should be multiplied by 3 to get the wattage it would take to start the motor? My pump is 240 volts and 9.3 amps. That calculation tells me that itíll take 6,700 watts to start the pool pump?

I live in Georgia. Iím not planning to run our electric stove, our electric dryer, and we have city water.
We have natural gas, central heat and air but I plan to use neither unless I have a lot of wattage/amps to use. We have natural gas logs.

As far as the pool goes, itís only a concern in sub-freezing temps. Also I only need to run the pump long enough to drain the pool below the skimmer and recirculation lines. Once I do that, I open all the above ground valves, blow the remaining water out and leave the system off until power is restored. Running the pump to drain should take less than an hour. After that, the generator will keep us semi-comfortable.
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post #10 of 27 (permalink) Old 02-07-2020, 09:05 PM
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There is no reason to derate your generator circuit to 80%. And the fact that you have 8/3 shows the electrician wanted to keep voltage drop at the rated 30amps in consideration.

All of your important appliances are electric, why not consider that?

Yes, induction motors require up to 5x their running wattage. But there is no head pressure on your water pump so itís much less.

If you choose to do a trifuel conversion in the future and run on natural gas, your generators output needs to be derated by 20% based on your operating load. So if you buy a 5000 watt continuous unit your effective continuous output should be considered around 4000 watts. This is a rule of thumb estimate.

Generators rated output contain 2 numbers. Continuous rated wattage and surge rated wattage. Example 7000/9000 is 7000 Continuous or running. 9000 is surge.

An slightly undersized generator starting an electric motor will cause a voltage drop, a peak in amps, and bump in heat, and a some wear and Tear on the motor. A way undersized generator will not start the motor. And could stall the generator and/or cause a voltage drop that could potentially harm and sensitive electronics that are also connected.

Iím assuming your central heat is a natural gas furnace. An eu2000 can run that. Window air conditioners are also pretty small loads.

I forgot to ask if you have an electric water heater, but you said you have an electric stove. If your water heater is electric then a 5000 watt generator is barely adequate and Iíd be looking bigger. A 5000 watt generator would require much more attention to load management.

Especially if you convert to natural gas, which I strongly recommend. Itís basically an endless supply of fuel, with zero carburetor maintenance.
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