Residential Electric Load – Which multiplier w/Tankless/EV? 0.75 or 0.4 or…?
I know how to perform a residential load calculation using either: -(a) the Standard Method, which includes a 0.75 multiplier for fixed appliances (so, a 4500W water heater would be treated as adding 3375W to the residence’s demand), or -(b) the Optional Method, which includes a 0.4 multiplier.
Which multiplier should be used with electric tankless water heaters or EV chargers? The I’ve read that some AHJs require including 100% of the nameplate wattage. One Mike Holt thread reported an AHJ treating these things as continuous loads, with a 125% multiplier. Others have arbitrary additors (in one CA county, you just add 15k… regardless of nameplate wattage!). My nearby AHJs have shrugged.
Stiebel Eltron’s electrical dept said: “A tankless load is no different than any other load. It falls into the 10k+40% category. It’s used very very occasionally.”
Is there an NEC code section on point, or a general rule here? The choice makes extreme differences in load calculations. Thanks!
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