tank less Electric water heater load

[flatlander]

Is this correct load for a feeder supplying 10 thankless water heaters in a residential apartment building.

Each unit is 50 amps 240.

50×10 = 500
Less demand 75%
375 amps. ?

 

[Ingenieur]

50 A ckt or actual load?
those things suck power

 

[flatlander]

Spec sheet calls for 12kw or 50a @240

 

[kwired]

Is this correct load for a feeder supplying 10 thankless water heaters in a residential apartment building.

Each unit is 50 amps 240.

50×10 = 500
Less demand 75%
375 amps. ?

220.53 allows that and is likely where you came up with that.

 

[JFletcher]

Is this correct load for a feeder supplying 10 thankless water heaters in a residential apartment building.

Each unit is 50 amps 240.

50×10 = 500
Less demand 75%
375 amps. ?

Can we not use 220.84(C)(3)(d) here and get 43% x 500A = 215A?

 

[kwired]

Can we not use 220.84(C)(3)(d) here and get 43% x 500A = 215A?

Yes, but you can't pick and choose which sections of part III and part IV you wish to use, you must use all of standard calculation or all of optional calculation. You can pick whichever end result you want to go with.

 

[JFletcher]

Yes, but you can't pick and choose which sections of part III and part IV you wish to use, you must use all of standard calculation or all of optional calculation. You can pick whichever end result you want to go with.

If you were just adding the heaters to an existing building, do you have to go by how everything else was calculated?

10 units gives the 43% demand factor from table 220.84

 

[kwired]

If you were just adding the heaters to an existing building, do you have to go by how everything else was calculated?

10 units gives the 43% demand factor from table 220.84

There is 220.83 for determining if existing is sufficient to add some load. But again you follow what is all mentioned in that section and can't pick and choose things from other sections to come up with your end result

 

[jumper]

If you were just adding the heaters to an existing building, do you have to go by how everything else was calculated?

10 units gives the 43% demand factor from table 220.84

Yes, that is a demand factor for the total calculated load for the dwelling units. You cannot apply it to just one item.

 

[flatlander]

I also see a note that if you use that service demand of 43% then you cannot take the other 75%.