Max load for 100 amp circuit.

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Old 01-29-06, 12:25 AM
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Max load for 100 amp circuit.

I have 100amp main box
I read elsewhere that you can put 200 amps total in a 100amp circuit.
that is 100amps per side.

Is this correct?

I have 70's home 3 bedroom with no A/C we dont use gas heat, (electric blower unit). I have dish washer, and washer/Dryer as main sources. I want to add a 220/ 50 circuit for Jucuzzi? Is this going to be too much.
 
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Old 01-29-06, 02:05 AM
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need heavy upgrade

Originally Posted by bedtime211
I have 100amp main box.
I read elsewhere that you can put 200 amps total in a 100amp circuit.
that is 100amps per side.

That's the essence of it.
But what do you mean by "side"?

A 100-amp 250-volt service gives you 200 amps at 125 volts.




> I have 1970s home, 3 bedroom, with no A/C.
> we don't use gas heat (electric blower unit).
And you have only 100A?


> I have dish washer, and washer/Dryer as main sources.
Actually, those are appliances.


> I want to add a 220V 50A circuit for jacuzzi.
> Is this going to be too much?

Yes. Think about it. That circuit is up to 100A all by itself.
Then you have 50A for lights and appliances other than the dryer, another 20A for the clothes dryer, 18A for the water heater, and that leaves you maybe 20-30A for heating and anything else I missed before the main pops - and that's if you have load on both poles balanced.

Do your present breakers add up to much more than 100?

Could it work? Most of the time it would.


You need the next level higher of service, preferably 200A.
 
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Old 01-29-06, 05:26 AM
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The sum of the breakers is of absolutely no consequence. It tells us nothing.
The only way to tell if you are nearcapacit, or if the spa will put you over, is with a load calculation of your service.
Do I think you should upgrade to 200a? I'd say yes.
Do you have to upgrade? Only a load calc will tell.


Also, 50a @ 240v is not 100a @ 120v in reality. The wattage is the same regardless but if a load is rated @ 240 it is not realistic to say the amperage is doubled at 120 since the load will never see 120v.
So NO, your 100 amp serive cannot handle 200 amps. It can handle 100 amps on each of two legs, or 24,000 watts total.
And a 240 volt, 50 amp spa cannot be said to be 100 amps @ 120v since the circuit is 240v. On paper maybe but not in reality.
 
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Old 01-29-06, 09:21 AM
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Just because the spa uses a 50 amp breaker doesn't mean it draws 50 amps. Probably a lot less than that actually.
 
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Old 01-29-06, 09:26 AM
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I am confused by the statement 'no A/C we dont use gas heat, (electric blower unit). ' Does this mean that you have a central AC that you don't use, or that you don't have a central AC, and does it mean that you do or don't use gas for heating?

As Speedy Petey has said, the question can only be answered by doing a load calculation. You can search this forum for descriptions of load calculations, and you can also find load calculations on the web, eg. http://www.electricalknowledge.com/SFDLoadCalc.asp

Figure out your house's current load, and use the information about the Jacuzzi to figure out how much additional load the Jacuzzi will place on your system. The fact that it requires a 50A circuit is not the correct information; what you need is the total VA requirement. The use of a 50A circuit means that the maximum VA that the Jacuzzi could possibly use is 12000VA, but it probably uses less than this.

One option to consider: some Jacuzzi's can be wired to run at 120V on a single 20A circuit. They do this by connecting the 240V heater to a 120V supply, which cuts the power that the heater can put out. This lowers the _instantaneous_ VA consumption of the Jacuzzi, at the cost of slower heat up times. The heater has to run for longer periods at lower VA, using the same total kWh, but putting less of a strain on your electrical system.

-Jon
 
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Old 01-29-06, 09:27 AM
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Very true Joe. I should have written it: "A 50 amp spa circuit...".
 
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