Dryers Water Heaters

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No calculation for a dryer is needed in a single family dwelling. The service load is either 5000kVA or nameplate, which ever is larger.

When it comes to multi family dwellings there is a calculation. Here is the formula:

Single Phase - Total nameplate times demand % based on number of dryers. Use 5kVA for any that are less than 5kVA.

Three Phase - Twice the maximum number connected between any two legs. Technique of solution is as follows:

Take the total number of actual appliances and divide by three. If this results in a decimal (.33 or .66) round up to the next whole number. Multiply this number times two. Multiply the result times the nameplate or 5kVA for each dryer, which ever is larger. Then multiply by the demand factor from the table in 220 for the total number of actual dryers (not twice the number connected between any two legs). When the number of dryers is over fifty, this factor will always be 25%. The result is the service demand for dryers connected to a three phase service.


Here is a chart which can be used to find dryer load for single and three phase services. It is of my own design. It is reproduced here as it appears in Reference Formulas Appendix.

Find practice problems HERE.

Find audio support HERE.

Water Heaters

There is no special calculation for a water heater connected to a service except that if there are 4 or more fixed appliances, the demand can be calculated at 75% for a water heater.



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