how many amps is this?

[sky jumper]

this is likely a stupid question but I'm going to ask it anyway. with everything on simultaneously in my house I measure 44A on one hot leg and 59A on the other. I did not measure the neutral but I assume it is the difference bewteen the 2. how many amps am I drawing from the 200A 240V service?

 

[rlitman]

59A. The breaker only cares about the higest drawing leg.

 

[dogdog]

I think it's a trick question here .....

 

[sky jumper]

lol no trick question. just trying to understand how the loads add up in relation to the rated service. I have a 100A subpanel in the house and was measuring 31A and 44A on that one and I was wondering if that meant at 75A it was nearing its capacity (no, it is not). Oddly, the 200A "main panel" appears to carry very little load aside from the oven, and the 100A feeder to the subpanel. The subpanel has the AC units, furnaces, well pump, sump pump, etc.

But with 60A total draw with (nearly) everything on, I'm thinking I should be able to run the whole house and the new detached garage with a 24kW generator.

This informs the installation of the generator and method to hook up the feeder to the detached garage.

 

[dogdog]

Not sure, maybe wait for the electromagician to show up... but as far as I understand it...

44A on one leg , 59A on another... your wires are sized correctly for 200A (each wire)and your breaker are tied together, the one with the highest load will trip both breakers... (what rlitman mentioned)

There is a 180 degree phase difference on each legs I think if I remembered those AC correctly...

maybe its easier if you convert everything to KW instead of just looking at AMPs...

 

[Robbie B]

Your 200A main is a DPST breaker. Dp-double pole means it controls 2 individual circuits. ST means it’s on or off. Each side of the breaker will see its individual load but if both or either side goes over it’s rating then it will trip. You have to take the total load on both circuits into consideration when sizing it. You have 59 on one side and 44 on the other for a total load of 103 amps.

 

[rlitman]

...You have 59 on one side and 44 on the other for a total load of 103 amps.

NO! Your total load is 51.5A @ 240V, but the only important number is 59A.
You do NOT sum up the amps on the legs to get the total load. The sum gives you load at 120V, not 240V.

 

[alfredeneuman]

You have 59 on one side and 44 on the other for a total load of 103 amps.

It's not the proper way of figuring it.
Each pole will carry 200A before tripping, and each should be considered independently.

 

[Shiftless]

Rlitman and Aeneuman are correct. Here is another way of explaining it.

RobbieB added up the amps to be 103 but that is the total of amps @120 volts.

Watts = Amps x Volts

So you need 103 x 120 or 12,360 watts

So your proposed 24kw generator should be able to handle that no problem.
Since you won’t be operating every single appliance and tool at the same time during a power failure, you could get by with a much less expensive and much less fuel thirsty generator for back up purposes.

If it’s gasoline or propane or diesel powered, how many gallons per hour does a 24kw generator use even when running 10-20% of capacity?

How many days (Worst case scenario) do you expect to be without power?

 

[wyliesdiesels]

24KW would be more than enough to cover that.

The other bigger question here is are you using an ATS? If so, youre gonna run into some challenges if you have a combination meter main.

 

[rlitman]

...RobbieB added up the amps to be 103 but that is the total of amps @120 volts.

Watts = Amps x Volts

So you need 103 x 120 or 12,360 watts

So your proposed 24kw generator should be able to handle that no problem...

Almost. For residential utility usage, the watts matter. That is (59A+44A)x120V = 12360W. That's what you'll be paying the PoCo for on your meter.

For the 200A breaker, only the highest current leg matters, which is 59A.

For a generator, too much imbalance can matter a lot (as can power factor). For sizing a generator, I would say that load is closer to (59+59)x120=14160W. I know that the actual wattage is less, and this much imbalance is not unreasonable, and it's still well under a 24kW load, but it means that a 14kW generator may (some generators oversize their windings to compensate for imbalance, but not all do; read the spec sheets closely!) be overloaded on half the windings, when you'd think otherwise.

 

[nadogail]

IMHO, based on the information given, the 24 KW generator should be able to handle that load.

I suggest you move some of the load off the 59 Amp leg and on to the other leg to better balance the load.

My advice is guaranteed to be worth exactly what you are paying me for it.

 

[Shiftless]

IMHO, based on the information given, the 24 KW generator should be able to handle that load.

I suggest you move some of the load off the 59 Amp leg and on to the other leg to better balance the load.

My advice is guaranteed to be worth exactly what you are paying me for it.

The O.P. said he took those current readings with EVERYTHING in the house running. To me, this is not a realistic situation to base load balancing on.

When would a family be using all 4 stove elements, the oven, the AC, the microwave, TV’s in every room, the toaster the big shop air compressor, etc. all at the same time?

With a 24kw generator, you’d have almost 10,000 watts for adding a Tesla charger to the load and still be OK.

 

[sky jumper]

so one electrician I talked to told me I couldn't use a 24kw generator for the whole house because I have 200A service and the generator can only supply 100A, so I'd need to add a 3rd "emergency" panel in the house and switch over emergency circuits to it. I knew this wasn't true, but it got me thinking about how many amps I'm actually using.

to be clear --- I did not literally have EVERYTHING on at the same time. I had 2 AC units and furnaces, the well pump cycling, radon fan, the oven on preheat, 2 TVs, a bunch of lights, a bunch of Wifi stuff and computers, a couple bathroom fans, 2 dehumidifiers, 2 refrigerators, 1 freezer all running. Not sure if the fridge/freezer compressors were running at the time. The cooktop and dryer are gas. I did not have the mircrowave or toaster on. individually I measured
AC1: 12A @240V
AC2: 10A @240V
Well: 11A@240V
Oven: 11A @240V

the sump wasn't running, but its 5A @120V.

I don't have a meter combo. the plan is to come out the meter and into the ATS, then into an outdoor main breaker panel with feed-thrus. run the house off the 200A feed-thrus, and run a 125A breaker to the detached garage (yes I have modified that part of my plan if you saw my other threads). I burried 2" conduit to the garage so figured might as well put in 1ga copper and a 125A panel, since that was the only panel menards had in stock at the time.

btw the inspector busted me for trying to use PVC elbows to come out of the ground. the elbows have to be RMC, and the vertical stubby above ground has to be at least IMC, and the LB has to be metal (I had PVC LBs). who knew? funny thing, the inspector said 3ga copper was good for 130A... he even pulled out the NEC book and showed me the table...huh? I think he was looking at the wrong table.

 

[Stuart in MN]

so one electrician I talked to told me I couldn't use a 24kw generator for the whole house because I have 200A service and the generator can only supply 100A, so I'd need to add a 3rd "emergency" panel in the house and switch over emergency circuits to it. I knew this wasn't true, but it got me thinking about how many amps I'm actually using.

Yeah, as long as the generator has a 100 amp circuit breaker on its output there's no problem. The transfer switch does have to be sized for 200 amps, since the main power goes through it.

 

[rlitman]

Yeah, as long as the generator has a 100 amp circuit breaker on its output there's no problem. The transfer switch does have to be sized for 200 amps, since the main power goes through it.

I don't believe a circuit breaker is required on generators. In theory, they can be designed to stall before overloading.