Branch ckt. quest.

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Copperclad

Copperclad

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Merritt Island, FL USA
Howdy Fellas!
I had a question regarding an insta hot type water heater. According to the cut sheet it is rated 3500w@120 volts and requires a min, ckt ampacity of 30 amps. Seems pretty cut and dry to me, so off to the van I go for a fresh roll of 10/2 MC (this a commercial build out by the way) A co-worker starts flappin' his chops about needing 8 wire on a 40 amp breaker.... I thought a branch ckt. could be loaded to 100% capacity if its not considered a continuous load. Am I mistaken, or missing something here?

Many Thanks,
Ted
 
What was his argument for a 40 amp circuit? 210.23 would allow the 30 amp circuit if the load is not continuous.
 
Copperclad said:
Howdy Fellas!
I had a question regarding an insta hot type water heater. According to the cut sheet it is rated 3500w@120 volts and requires a min, ckt ampacity of 30 amps. Seems pretty cut and dry to me, so off to the van I go for a fresh roll of 10/2 MC (this a commercial build out by the way) A co-worker starts flappin' his chops about needing 8 wire on a 40 amp breaker.... I thought a branch ckt. could be loaded to 100% capacity if its not considered a continuous load. Am I mistaken, or missing something here?

Many Thanks,
Ted
Click to expand...
210.19(A)(1)
 
Ampacity of MC is stated in 330.80.

This leads you to 310.15, which leads you to T310.16.

T310.16 shows the ampacity of #10, even under the 60?C column as directed by 110.14(C), as 30 amps.

If the minimum circuit ampacity listed on the heater is 30 amps, I'd say you've got a 30a circuit with your 10 MC.

You co-worker may say you need 8 if there's a spec somewhere on the job that requires it. But a 40a breaker may exceed what the heater is listed for.
 
infinity said:
Do you think that this is a continuous load?
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According to my understanding as to how the water heaters work, I would say no. I mentioned 210.19(A)(1)
because it states that the circuit shall have an ampacity of not less than the noncontinuous load + 125% of the continuous load. There is no continuous load.
 
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His argument ( my coworker) is that all branch ckts should be sized @ 125% in a commercial application. I say phooey! I don't believe insta hot type heaters fall under the fixed storage-type water heater as in 422.13 so as be considered continuous.
 
Copperclad said:
His argument ( my coworker) is that all branch ckts should be sized @ 125% in a commercial application. I say phooey! I don't believe insta hot type heaters fall under the fixed storage-type water heater as in 422.13 so as be considered continuous.
Click to expand...

If this is to provide hot water to a sink, who runs hot water for more than three hours?
 
480sparky said:
If this is to provide hot water to a sink, who runs hot water for more than three hours?
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You mean on purpose? What if a washing machine hose bursts, or someone passes out in a shower, or . . .

It seems to me that a tankless water heater has more chance of running continuously than a storage water heater does.
 
LarryFine said:
You mean on purpose? What if a washing machine hose bursts, or someone passes out in a shower, or . . .

It seems to me that a tankless water heater has more chance of running continuously than a storage water heater does.
Click to expand...

Then I guess I would call into the equation the word 'expected' in the definition of continuous load.
 
LarryFine said:
You mean on purpose? What if a washing machine hose bursts, or someone passes out in a shower, or . . .

It seems to me that a tankless water heater has more chance of running continuously than a storage water heater does.
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It does supply hot water to one bathroom sink in a small commercial unit. Im thinking if the pipe did burst, or for whatever reason the heater has to run on continuous duty then I would just assume the thing trip the 30amp breaker as opposed to the it just sizzling away at my power bill on the 40 amp breaker.
 
480sparky said:
If this is to provide hot water to a sink, who runs hot water for more than three hours?
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Now a shower that would be different. If you we're around my house in the evening. Them girls just keep that hot water going, If the tank didn't run out they would stay in thier for three hours..
 
Yep.
HoltBlueDot.jpg
 
Copperclad said:
I agree that it is not a continuous load. So it would be considered ok to load a branch ckt at 100% if not a continuous load, right?
Click to expand...

Yes, you can find that info in 210.23.
 
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