single-phase loads off 3-phase 4-wire

[TimWA]

I want to understand the calcs associated with this. 220.54 & 220.55 discuss calculating on the basis twice the maximum number of ranges/dryers between any two phases.

Ok so that sounds like twice times a third of the total ranges/dryers (or the phase with the maximum number) demanded through Tables 220.54/220.55 gives the total of...what, each phase? All phases? Amps out of the bug?
-Tim

[ November 06, 2005, 02:42 AM: Message edited by: TimWA ]

 

[bphgravity]

Re: single-phase loads off 3-phase 4-wire

Look at it this way. Lets say you have 9 single phase ranges served from a 208Y/120 Volt service. Maximum number on any two phases is 3 ranges x 2 = 6 ranges.

Per 220.55, 6 ranges equal 24,000 VA.
Per phase demand = 24 kVA / 2 = 12 kVA
Equivalent 3? load = 12,000 x 3 = 36,000 VA


See Annex D for more examples of this calculation.

 

[TimWA]

Re: single-phase loads off 3-phase 4-wire

Well yes I see that if your ranges were individually rated 15kW, six of them amount to 24kW demand per Table 220.55.

At first it seemed nonsense to double a quantity and then halve it, but after working your example back and forth (and those in Annex D) the light finally went on with the effect this method produces, a finely-adjusted demand factor in addressing these types of load.

Thanks Bryan, you so often reply to my varied queries in a way that hits the mark for me, I greatly appreciate it.
-Tim Brain

[ November 07, 2005, 02:19 AM: Message edited by: TimWA ]