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#98355 - 04/21/06 05:55 AM Dwelling unit service or feeder calculation
mweaver Offline
Junior Member
Registered: 11/16/04
Posts: 6
Loc: Salina Ks, 67401
I am having confusion regarding the proper calculation of a storage-type (120 gal or less) water heater within a dwelling calculation acomplished by the general method of calculaiton in the 2005 NEC.

By the general method, it is permissible to apply a demand of 75% when four or more dwelling unit appliances become part of the dwelling service or feeder calculation (Article 220.53). This I understand and with four or more appliances the 120 gal or less storage-type water heater would be subject to the demand. but ...

New to the 2005 NEC, A water heater is a continuous load (Article 422.13) .

The continuous load requirements for a feeder or service dictate that the portion of the feeder or service be sized 125% of any continuous load connected to the service or feeder (Articles 215.2(A)(1) for feeders and 230.42(A) for services.

With this in mind, would a storage-type water heater be: water heater load X 125% = water heater contonuous load X 75% for four or more appliances?

[This message has been edited by mweaver (edited 04-21-2006).]
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