Wire & breaker size for water heater

[Jpflex]

If you google what the size breaker and wire should be for a water heater 120 gallon or less at 3,000 watts at 120 volts

You get answers ranging from 12 AWG wire and and 25 ampere breaker to 10 AWG wire and 30 ampere breaker

However, is 240.4 D OCPD rule for small conductors not applying or are inspectors not enforcing this?


Unless specifically permitted in 240.4(E) (taps) or (G) (specific applications water heaters not listed),

the overcurrent protection shall not exceed that required by 240.4(D)(1)through (D)(8) after any correction factors for ambient temperature and number of conductors have been applied.

We’re getting online advise to install either a 12 AWG or 10 AWG wire with a 30 ampere breaker for this 3,000 watt 120 volt water heater

3,000 / 120 = 25 i ( this is where online experts stop) using a 12 AWG or 10 AWG wire

However, wouldn’t it be properly calculated at 25 i x 1.25 (continuous load) = 31.25 i amperes MINIMUM



Answer #8 AWG wire at 75 degrees Celcius good for 50 i amperes and not subject to small conductor rule 240.4 D?

OCPD = 35 i ampere standard breaker minimum

 

[infinity]

If you reduce the voltage by 1/2 you also reduce the current by 1/2. #12 cannot be used with a 25 amp OCPD.

 

[Jpflex]

If you reduce the voltage by 1/2 you also reduce the current by 1/2. #12 cannot be used with a 25 amp OCPD.

Yes that’s why I’m saying you shouldn’t be putting on a 10 AWG conductor limited to 30 ampere breaker for a load at over 31 amperes

3,000 watt / 120 E = 25 i

NEC considers these continuous loads at 125% x ampere rating 25i = 31.25 i amperes

This exceeds the OCPD limit for 10 AWG small conductors

So my question is why are licensed electricians giving what appears to be incorrect advice online?

 

[tortuga]

 

[infinity]

Yes that’s why I’m saying you shouldn’t be putting on a 10 AWG conductor limited to 30 ampere breaker for a load at over 31 amperes

3,000 watt / 120 E = 25 i

Your math is incorrect. You need to find the resistance using 240 volts and then find the current using 120 volts and the resistance.

 

[LarryFine]

Your math is incorrect. You need to find the resistance using 240 volts and then find the current using 120 volts and the resistance.

Not if it's designed for 120v.

 

[infinity]

Not if it's designed for 120v.

Of course but that's not the question.

 

[LarryFine]

If you google what the size breaker and wire should be for a water heater 120 gallon or less at 3,000 watts at 120 volts

We’re getting online advise to install either a 12 AWG or 10 AWG wire with a 30 ampere breaker for this 3,000 watt 120 volt water heater

 

[infinity]

Click on the attachment in the OP.

 

[kwired]

With the questions being asked and a little unclarity in OP, the first question I have is this a heater rated 3000 watts @ 120 volts or is it a 3000 watt heater @ 240 volts but being run @ 120?

If 3000 watt 240 volt heater running @ 120 then the actual draw will only be 25% of 3000 which would be 750 watts. Pretty small for a 120 gallon tank and would have a long recovery time.

Or maybe this is actually a 12 kW heater but operating at 120 volts? that would end up being 3000 watts output.

But if the current drawn regardless of what the voltage is were 25 amps, then you are correct in OP that minimum ampacity of conductor is going to be 125% of that which is 31.25 A which because of small conductor rule will need to be at least 8 AWG here and the minimum overcurrent device would be 35 A.

 

[kwired]

Click on the attachment in the OP.

Information in that attachment is not code compliant, for the 120 volt scenario @ 25 amps.

 

[Jpflex]

With the questions being asked and a little unclarity in OP, the first question I have is this a heater rated 3000 watts @ 120 volts or is it a 3000 watt heater @ 240 volts but being run @ 120?

If 3000 watt 240 volt heater running @ 120 then the actual draw will only be 25% of 3000 which would be 750 watts. Pretty small for a 120 gallon tank and would have a long recovery time.

Or maybe this is actually a 12 kW heater but operating at 120 volts? that would end up being 3000 watts output.

But if the current drawn regardless of what the voltage is were 25 amps, then you are correct in OP that minimum ampacity of conductor is going to be 125% of that which is 31.25 A which because of small conductor rule will need to be at least 8 AWG here and the minimum overcurrent device would be 35 A.

Yes the example was for a 3,000 watt water heater at 120 volts. Internet searches seem to give invalid answers

 

[infinity]

Yes the example was for a 3,000 watt water heater at 120 volts. Internet searches seem to give invalid answers

Internet searches can just give you the result of what it finds on the internet. There is more wrong information on the internet than correct information. YouTube has the same problem.

 

[tortuga]

There is more wrong information on the internet than correct information. YouTube has the same problem.

see post#4

 

[LarryFine]

Click on the attachment in the OP.

I did. The first comment should include the heater being designed for the given voltage, not merely being run on it. This comes up often when people apply the math presuming a constant load power, which requires different equipment, rather than a constant load impedance

 

[LarryFine]

With the questions being asked and a little unclarity in OP, the first question I have is this a heater rated 3000 watts @ 120 volts or is it a 3000 watt heater @ 240 volts but being run @ 120?

The former.

 

[tortuga]

This is probably the unit:

ATMOR HotTap 3kW 0.5 GPM 2-in-1 Electric Tankless Water Heater / Faucet AT-3TAP-HD - The Home Depot

Have plenty of hot water with this Atmor HotTap electric tankless water heater/faucet. For saving water, it activates only with water flow. It includes an adjustable swivel spout, a handle and a temperature

www.homedepot.com

 

[tortuga]

Not confusing at all, just run your red wire to your neutral breaker and make sure both breakers are grounded LOL

 

[roger]

Well if that is the unit I wouldn't consider it to be a continuous (more than three hours) load.

 

[infinity]

With the questions being asked and a little unclarity in OP, the first question I have is this a heater rated 3000 watts @ 120 volts or is it a 3000 watt heater @ 240 volts but being run @ 120?

The bold is the way I read it but after reading it again maybe I read it incorrectly. Maybe jbflex will come back and clarify.