BREAEKER SIZING

[pierre]

Re: BREAEKER SIZING

Why not call the manufacturer and ask the tech what is required? Then use 110.3(B). I would bet that 30 amp breaker is recommended by the manufacturer.

Pierre

 

[iwire]

Re: BREAEKER SIZING

Originally posted by bphgravity:
The logic that we can use the rating at which something is tested is ridiculous.

Bryan really? I am ridiculous?

UL has listed the units internal wiring for protection up 150% of the rated current at the higher voltage and current.

If that wiring will be safely protected by a 30 amp OCPD at 240 volts it is still safely protected with 30 OCPD at 208 volts.

Please explain why that is not the case?

 

[bphgravity]

Re: BREAEKER SIZING

Originally posted by iwire:
Bryan really? I am ridiculous?

I said the logic is ridiculus, not you. Nothing I ever write is personal.

UL has listed the units internal wiring for protection up 150% of the rated current at the higher voltage and current.

If that wiring will be safely protected by a 30 amp OCPD at 240 volts it is still safely protected with 30 OCPD at 208 volts.

Please explain why that is not the case?

In this specific example, I agree the use of a 30-ampere branch circuit or 25-ampere branch cirucit can both be argued. My only point is that many appliances and equipment will have ratings well above their intended use. I just feel that when it comes to wire sizing and protection, calculations should be based of the nominal voltage of the system used.

 

[pierre]

Re: BREAEKER SIZING

220.2 Computations.
(A) Voltages. Unless other voltages are specified, for purposes of computing branch-circuit and feeder loads, nominal system voltages of 120, 120/240 , 208Y/120, 240, 347, 480Y/277, 480, 600/347, and 600 volts shall be used.

Pierre

 

[shocker3218]

Re: BREAEKER SIZING

I definately overlooked the obvious. The resistance of the element is the only constant. The name plate (and the element itself) only has the rating of 4500 watts at 240 volt. Running a reduced voltage in this case causes a lower power output.

Guess I work with too many motors, and am use to the output being the same.

Thanks for all the input, it was definately appreciated. Sometimes I get too set in my ways and totaly loose track of the obvious.

As a side comment, the mechanical engineer and electrical work for different companies and a lot of mis-communication happened on this job.

 

[bennie]

Re: BREAEKER SIZING

Ask the inspector where he can get a domestic water heater that runs 3 hours continously. They are illegal for a residential use.

 

[apauling]

Re: BREAEKER SIZING

bennie, explain. water heaters "run" by turning on hot faucet and temp control says heat. user determines run time???

paul

 

[iwire]

Re: BREAEKER SIZING

Bryan & Pierre I am well aware of 220.2 Computations and would use the applied voltage for computations of the minimum circuit ampacity.

That is not what we are talking about when we talk about the maximum allowed OCPD in this case.

The heater in the question is rated for 30 amp OCP at 240, run at 208 the components are still rated 30 amps.

This is the same as having a piece of 10 AWG wire, it is rated for 30 amp OCP if it is loaded to 29 amps or 9 amps, the wires rating remains unchanged.

For this installation a 25 or 30 is acceptable and I do not think the inspector was correct in asking for the change.

 

[springtownspark]

Re: BREAEKER SIZING

I have been watching this thread since it started and find it interesting it's still running. Ever note the cost of a 25a breaker compared to a 30 or was it just my location ?

 

[shocker3218]

Re: BREAEKER SIZING

not sure of difference in cost of breakers. Supply house swapped at no cost to us.

I thought at first this was a simple question, but it sure did stir up some good conversation. What a great tool this web site is!

 

[thunder15j]

Re: BREAEKER SIZING

I would like to add some input on water heater elements from a service perspective. On a service call to check a failed smallish electric water heater, I found that the 1500 watt @120V element had failed. Since I didn't have immediate access to that exact element, I decided to utilize basic ohm's law by replacing the failed element with a 3KW element/240 volt, one that I just happened to have with me. My logic of applying half the voltage to a fixed resistance resulted in a quickly repaired WH and the elimination of a 2nd trip to the job. I did clamp on with my meter to double check the load and found that the amperage was a little lower than expected. I don't recall the exact load, however in theory it would be around 9.4 amps.

 

[caosesvida]

Re: BREAEKER SIZING

without doing the math I will stick my head out and say its closer to 1/3 the wattage, going with 240 on a 120 circuit.

 

[don_resqcapt19]

Re: BREAEKER SIZING

The wattage changes with the square of the voltage change. You cut the voltage 1/2 so the wattage will be 1/4 of the rated 3000 watts or 750 watts.
Don