Unbalanced water heater

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hhsting

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Have storage type water heater 50 gal unbalanced with T1 at 41.6A and T2 and T3 at 24.0A all at 208V. So the question I have is if I take 41.6x1.25=52A then I get 60A as breaker size. However engineer provided 50A breaker??

Which would it be 50A or 60A?
 
hhsting said:
Have storage type water heater 50 gal unbalanced with T1 at 41.6A and T2 and T3 at 24.0A all at 208V. So the question I have is if I take 41.6x1.25=52A then I get 60A as breaker size. However engineer provided 50A breaker??

Which would it be 50A or 60A?
Click to expand...
Do you have manufacturer's specifications? Did you ask the engineer why they choose 50A?
 
Rock86 said:
Do you have manufacturer's specifications? Did you ask the engineer why they choose 50A?
Click to expand...

Its AO smith DEL-50 model. Manufacturer data sheet only gives full load amps no breaker sizes. Engineer says 41.6x1.25=52A so manufacturer says 50A. I dont see that in their datasheet
 
Looked up the model.... not much to go on. This seems like something the engineer should confirm with the Manufacturer and provide evidence to their decision if you require it.
 
I looked up the model and the 3 phase 208 volt unit is 12kw. 12 kw/ 208 * 3^2 = 33.33

Section 422.13(E) allows 150% for the overcurrent protective device.

33 x 1.5 = 50 amps
 
Dennis Alwon said:
I looked up the model and the 3 phase 208 volt unit is 12kw. 12 kw/ 208 * 3^2 = 33.33
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I don't grok your computation. I think you mean 12,000/(208 * 3^0.5) = 33.33. Which would apply if the tank heater is rated 12 kW via (3) 4 kW elements connected L-L as a delta.

The spec sheet I saw says the unit has only two elements. Per the OP, the elements are 24.0 A * 208V = 5 kW each, and based on the current adding in one phase (which gives a factor of sqrt(3), not 2), both elements can operate simultaneously. So if the maximum one leg can draw is 41.6A, surely that is the basis for any further computations?

Cheers, Wayne
 
wwhitney said:
I don't grok your computation. I think you mean 12,000/(208 * 3^0.5) = 33.33. Which would apply if the tank heater is rated 12 kW via (3) 4 kW elements connected L-L as a delta.

The spec sheet I saw says the unit has only two elements. Per the OP, the elements are 24.0 A * 208V = 5 kW each, and based on the current adding in one phase (which gives a factor of sqrt(3), not 2), both elements can operate simultaneously. So if the maximum one leg can draw is 41.6A, surely that is the basis for any further computations?

Cheers, Wayne
Click to expand...

Yes it should be 208 * sq. rt 3 = 360

I didn't see the info on the elements so I just went by what they stated. You are correct if they show 41.6 amp then that's a done deal.
 
wwhitney said:
I don't grok your computation. I think you mean 12,000/(208 * 3^0.5) = 33.33. Which would apply if the tank heater is rated 12 kW via (3) 4 kW elements connected L-L as a delta.

The spec sheet I saw says the unit has only two elements. Per the OP, the elements are 24.0 A * 208V = 5 kW each, and based on the current adding in one phase (which gives a factor of sqrt(3), not 2), both elements can operate simultaneously. So if the maximum one leg can draw is 41.6A, surely that is the basis for any further computations?

Cheers, Wayne
Click to expand...


The one I saw, I went back to see, has 2- 6kw elements
 
May be wrong, but I think to get his numbers you would have (2) 5kw on 3 phase.
 
Yes, the spec sheet I saw says it can have a variety element configurations, up to 6 kW each, and either allowed to run simultaneously or interlocked. The max would 12 kW with simultaneous 6 kW elements, per Dennis's info. But as augie notes, the OP's numbers correspond to simultaneous 5 kW elements.

Cheers, Wayne
 
With no other input I would think it would be on a circuit with a 52 amp rating and a 60 amp breaker,. If the manufacturer or the design engineer specified a 50 amp breaker and it was installed as such I would not doubt it will operate successfully.
 
GoldDigger said:
Does the manufacturer really suggest this unit for a three phase source? It seems to be more properly intended for single (split) phase.
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I believe it's designed for either, with the elements wired in parallel for 1ph or in open-delta for 3ph.
 
My take is, don't worry about it. The manufacturer works under different rules, and my first guess was, the 42A element may not stay on for 3 hours at a time, so under their rules, it doesn't have to be 125%
 
Strathead said:
My take is, don't worry about it. The manufacturer works under different rules, and my first guess was, the 42A element may not stay on for 3 hours at a time, so under their rules, it doesn't have to be 125%
Click to expand...
A storable water heater as specified is continuous per nec which requires you to use 125%

422.13 Storage-Type Water Heaters. A fixed storage-type
water heater that has a capacity of 450 L (120 gal) or less shall
be considered a continuous load for the purposes of sizing
branch circuits.
Click to expand...
 
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