Embarrassing circuit breaker/generator question

[Roger Feeley]

My house’s breaker box is actually a sub panel supplied from my daughters house 30 feet away. In their cellar, there’s a 125A 240v breaker. We don’t draw anywhere near that much power. Most of the time we draw we draw under a kilowatt. I have an energy monitor to work out our share of the monthly bill. As I write this, our house is pretty quiet, drawing 338w. The fridge is running at 130w.

If I multiply volts x amps, 120x125 is 15,000 watts. So if I wanted to supply my house with a generator at that 125A. Would I need a 15K generator or twice that. Put another way, do I use the amperage on the breaker or multiply by two legs?

I’m sure this has been explained to me many times and for some reason it refuses to stick. I remember all sorts of useless stuff but not this. Maybe I should write it down someplace..

Sheepishly,
Roger

[Malcolm Schweizer]

With every fan in the house going, plus a portable fan, the fridge, a computer, and batteries charging for tools and cameras, I’m pulling 0.5 kWh.

460436

Edit: I’m cross eyed this morning. It’s 0.3, not 0.5.

[Charlie Velasquez]

Why would you need any more than a smaller gen set, say a 5,000 watt one?

edit: maybe I am reading too much into this. Are you trying to replace your feed from the other house or looking for emergency power.

To supply your sub with the same power you have from the other panel you need 30,000 watts.
To feed your panel for your needs in an emergency you can get by with much less.

[Malcolm Schweizer]

…sorry, my point was your numbers seem high. 125A would be running all breakers at capacity and you would never be doing that. You’re running now at 0.338kW.

[Roger Feeley]

I know I would need less. I think I muddied the waters.

I want to know if a 120A double pole breaker is the equivalent of two single pole 120A breakers or two 60A single pole breakers.

This question is hypothetical only. I don’t have tied single pole breakers.

(the dryer is running now and I’m still under 1KW)

[Roger Feeley]

…sorry, my point was your numbers seem high. 125A would be running all breakers at capacity and you would never be doing that. You’re running now at 0.338kW.

Malcom, you are right that 10KW is a lot. I’m looking into having an electrician put in a single transfer switch on our house and running a cable out a window well to a portable generator in the driveway. I think I can easily supply my house and have enough leftover to power my daughters fridge and another fridge in the garage. I’ll just stay out of my shop during the outage.

I know I can get a smaller generator but the difference isn’t that much.

[Paul F Franklin]

125A double pole breaker is 125 amps on each leg of the service. You can provide a max of 125A to 240 volt loads, or 250 A to 120 V loads, or any combination of 120 and 240 volt loads that don't exceed 125 Amps on either leg. So you have a theoretical maximum power of 125A x 240V or 30,000 watts (30 Kilowatts). It would be equally valid to calculate this as (125A x 120V) + (125A x 120V) which gives the exact same result.

[Mike Henderson]

Malcom, you are right that 10KW is a lot. I’m looking into having an electrician put in a single transfer switch on our house and running a cable out a window well to a portable generator in the driveway. I think I can easily supply my house and have enough leftover to power my daughters fridge and another fridge in the garage. I’ll just stay out of my shop during the outage.

I know I can get a smaller generator but the difference isn’t that much.

If you don't have a lot of power outages, when you do have an outage, put the generator in a reasonable place and run long extension cords to the appliances you need to keep going. Putting in a transfer switch is somewhat expensive.

Mike

[Lee Schierer]

If you don't have a lot of power outages, when you do have an outage, put the generator in a reasonable place and run long extension cords to the appliances you need to keep going. Putting in a transfer switch is somewhat expensive.

Mike

You would also need a tranfer switch for whatever you plan to power in your daughter`s house.

[Alex Zeller]

Are you looking for a standby generator or a portable one? I ask because a 10kw standby is not half the price of a 20kW. Since your house is tied to your daughter's house I would see if they wanted a generator too. I say this because you could tie it into their main panel to feed both houses. To figure out how big you need go through your house and determine what you will need to run. Things like a furnace and fridge/ freezer you would want to power. Things like well pumps can be controlled if needed to only come on when other loads are not required. By doing both houses together it reduce the amount of "extra" you would need. There's several on-line calculators to help figure out what size generator is needed.

[Roger Feeley]

You would also need a tranfer switch for whatever you plan to power in your daughter`s house.
I’m not sending that kind of money on her house. We’ll run extension cords to the fridge.

[Charlie Velasquez]

I would suspect a 10,000 watt portable would handle both loads for most events. A transfer switch would work, but an interlock is cheaper and more versatile. Run the power to the kids' house.

[Kev Williams]

Speaking of generators, I have a question-

I'm considering picking up 2 HF 9500 watt Predator generators, which will supply 15,200 running watts when parallel-connected. ($4000 total for both generators is a good price IMO, I have a 3500 version and it works great!)

My question is, can the 120v output of each generator be connected to a breaker box's separate incoming legs so the 240 breakers would be usable? Or will the AC be out of phase, or?

[Larry Frank]

Two years ago, we had a 21 KW Generac generator and transfer switch installed. It was about $6500 and well worth it. It can power the well, AC and everything else in the house.

[Charlie Velasquez]

Speaking of generators, I have a question-

I'm considering picking up 2 HF 9500 watt Predator generators, which will supply 15,200 running watts when parallel-connected. ($4000 total for both generators is a good price IMO, I have a 3500 version and it works great!)

My question is, can the 120v output of each generator be connected to a breaker box's separate incoming legs so the 240 breakers would be usable? Or will the AC be out of phase, or?

Running two 120 volt gen sets will not give you 240 volts. But I don’t know of any 9500 watt units that can not produce 240 volts.

[Lee DeRaud]

I know I can get a smaller generator but the difference isn’t that much.I can believe the price difference isn't that much, but size/weight may matter when you need to move it for use.

[Mike Henderson]

Speaking of generators, I have a question-

I'm considering picking up 2 HF 9500 watt Predator generators, which will supply 15,200 running watts when parallel-connected. ($4000 total for both generators is a good price IMO, I have a 3500 version and it works great!)

My question is, can the 120v output of each generator be connected to a breaker box's separate incoming legs so the 240 breakers would be usable? Or will the AC be out of phase, or?

A problem I can think of when putting two generators in parallel is getting them "in-phase" and matching the voltage levels. My college studies focused on electronics but I had to take a few courses in power transmission. I remember there were some challenges in putting multiple generation stations "on-line".

Personally, I'd keep the two outlets separate and use them to power different things.

Mike

[Rod Sheridan]

I know I would need less. I think I muddied the waters.

I want to know if a 120A double pole breaker is the equivalent of two single pole 120A breakers or two 60A single pole breakers.

This question is hypothetical only. I don’t have tied single pole breakers.

(the dryer is running now and I’m still under 1KW)

Hi, if you’re under 1Kw with the dryer running and it’s an electric dryer, there’s something wrong with your instrumentation

A dryer is about 5Kw.

If you want a transfer switch you move all the circuits you want to supply from the generator to a generator panel and size your generator to suit.

If you do that you need a generator with an Isolated Neutral (floating neutral) to feed the transfer switch. Such generators can’t be used as a standalone set as the neutral is floating.

If you want to use a portable generator with an extension cord to run a load you needed a bonded or grounded neutral generator and the generator frame needs to be connected to a good ground


Regards, Rod

[Rod Sheridan]

Speaking of generators, I have a question-

I'm considering picking up 2 HF 9500 watt Predator generators, which will supply 15,200 running watts when parallel-connected. ($4000 total for both generators is a good price IMO, I have a 3500 version and it works great!)

My question is, can the 120v output of each generator be connected to a breaker box's separate incoming legs so the 240 breakers would be usable? Or will the AC be out of phase, or?


Yes, the voltage will vary from zero to 240 volts as the generators drift in and out of phase.

The 120 volt loads would be fine…Regards, Rod

[Roger Feeley]

Rod,
my dryer is ventless. As I understand it, early in the cycle, it recirculates the air through a dehumifier. It uses a small heat pump for heat. It’s a mystery to me which is why I have a very long extended warranty.

BTWwe really like this dryer. It emits no humidity into the house. It does take about 100 minutes to dry a load, but they come out nice and dry. To be fair, we have a good washer with an awesome spin cycle so the dryer starts with a big advantage.

[Charlie Velasquez]

Yes, the voltage will vary from zero to 240 volts as the generators drift in and out of phase.

The 120 volt loads would be fine…Regards, Rod

Rod, trying to understand this. Are you saying connecting two 120 volt generators in parallel will double the volts instead of increase the amps?

[Rod Sheridan]

Rod, trying to understand this. Are you saying connecting two 120 volt generators in parallel will double the volts instead of increase the amps?


Sorry I was assuming that you wanted 240/120 volts.

If you parallel the 2;generators then you would double the current and power capability….Rod

[Roger Feeley]

I would suspect a 10,000 watt portable would handle both loads for most events. A transfer switch would work, but an interlock is cheaper and more versatile. Run the power to the kids' house.
Charlie,
Thanks for the hint about the interlock but it won’t work for me. My main panel has no main breaker. It’s a sub-panel supplied by a 125A breaker in the main panel in my daughters house.

[George Yetka]

I would size it for you both to run off it in a hot day. Install it at the main house. Cost is not going to be that different between sizing for just you and for both. If you have it power the main panel you would be wired in. If you wire it down by your house you would have to have the switch disconnect you from the main house for safety.

Plus as a bonus the noisy generator will be kids problem;)

I have a manual transfer switch and a portable 6.5 kw. I find that when the power goes out I wait 2 hours to make sure it doesnt come right back on. Then I have to brave the elements to get the generator outside, wired, and started. I would love a built in

[Charlie Velasquez]

Charlie,
Thanks for the hint about the interlock but it won’t work for me. My main panel has no main breaker. It’s a sub-panel supplied by a 125A breaker in the main panel in my daughters house.

Yes, that is why I suggested running it the genny to your daughter's house. With judicious use of circuit breakers you could easily run both buildings on the one 7000-10 000 watt genny. She runs her refrigerator on even hours, you on odd sort of thing. Just call her and sort out start-ups to manage that initial rush.

My son has a 3500 watt genny we hooked up, 120 volts. He loses power maybe 2-3 times every few years. Wet basement so the sump pump is critical.
Three days with no power and didn't miss a beat. He has a "cool room" in the basement with a tiny window air conditioner, a low voltage auxiliary pump, all LED lighting, a single burner hot plate that only uses 250 (?) Watts on its low setting, gas heat and hot water. By flipping circuit breakers he has access to everything except his central air, clothes dryer, and stove.

[Roger Feeley]

Charlie,
My daughters house is an 1860 can of worms. When we first moved here, we needed some plumbing work. I called a leading company and when they heard the address, they said they wouldn’t come. It seems that previous owner would call trades people out for an “estimate”, pump them for information and then go hire someone from the Home Depot parking lot. There’s a lot of plumbing and electrical in that house that just plain scary to me. My point here is that I’m hesitant to hook anything up to that house.

But we had our house built on the property about five years ago and I was very impressed with the workmanship. The main breaker box is a thing of beauty. The wires move vertically and horizontally with right angle bends. Hooking up to our house would be much easier.