follow up admin test

[rainski]

hello all

i am not used to navigating the threads well yet, so started this new thread...

the motor controls class was really basic, which is where i am anyway! i did get a great look ahead at my school homework lessons.

back to load calcs, i hope you can help me with multifamily premises laundry load.

the 2002 henrey's says:

if the multifamily dwelling has laundry facilities on premises available to all tenants the the 1500va would not be applied in the general lighting load. the laundry load would become "house load", 1500va x the number of units added to the total service load. house load is at nameplate, no demand factors are applied to house load.

bold type is henrey's

i have searched diligently thru my study texts; 2008 code calcs by jatc, miller 2008. stallcup 2008 and the above referenced 2002 henrey's. i cannot find any justification in the code for the 1500va per unit, (no demand factor applied). henrey is the only book that addresses it. my reading of 220.84.b house loads - optional of the 2008 leads me back to part III. i would take this to mean that i would refer to table 220.54 for multiple dryers demand factors, but i have found nothing to support that. premises laundry load is a part of one of the test questions, so i want to be clear on this.

also:

in my practice problems i came across a resi calc that did not give the house voltage. it did give the ac as 230. when i went to check my work, the voltage used for the total va breakdown was 240. was i wrong to assume 230 because of the ac when it comes to testing?

thank you much,
rainski

[suemarkp]

I don't know enough to answer the test type questions. Never taken one and don't want too -- the code is too wishy washy to have good answers to a lot of situations (and it seems many authors have differing opinions about how things should be handled). If you're off a few amps I don't see why it really matters, I'd like to see range based answers (e.g. you need a 140-150A service, or a 190-200A service, etc). But this could complicate picking the correct size wire if you've crossed an ampacity boundary in 310.16.

But for your last question, see 220.5(A) Voltages. Unless other voltages are specified, for purposes of calculating branch-circuit and feeder loads, nominal
system voltages of 120, 120/240, 208Y/120, 240, 347, 480Y/277, 480, 600Y/347, and 600 volts shall be used.

Where you'd typically deviate from 120V or 240V would be in the motor and HVAC section where many times you use 115 or 230V (the tables there also use those values). When calculating a total service or feeder though, with a mix of motors, HVAC units, lighting, etc, I'd have those HVAC and motors converted to VA based on their table values or nameplate provided (and using the 115 or 230V voltages). But when calculating the total general service or feeder, divide by 240V since that is what you need to use for a mixed or otherwise general calculation.

If you were calculating an HVAC specific branch circuit or feeder, and everything on it was specified as 230V, then I think you'd be OK at using 230V.

[Wgoodrich]

Try looking in Article 100 definitions. Each apartment is considered and meets the definition of a dwelling unit. Dwelling units are required to include a laundry load of 1500 va for each dwelling unit. An exception for this is found for multidwelling units being 3 or more if the property owner furnishes a laundry room available to all tenants.

The question 240 versus 230 SueMarkup pretty well answered. When calculating apperant voltage is used being 230 volts when finding amps applied voltage is used. Difference between the two is normally found using .707 concerning the sine wave.

[rainski]

hello again

i really am making progress, even if it doesn't show.:proud:

Try looking in Article 100 definitions. Each apartment is considered and meets the definition of a dwelling unit. Dwelling units are required to include a laundry load of 1500 va for each dwelling unit. An exception for this is found for multidwelling units being 3 or more if the property owner furnishes a laundry room available to all tenants.

i do understand that a laundry circuit is required for each dwelling unit. it would appear that the laundry load for apartments with laundry facilities is not completely omitted, but instead differed to the house load. house loads do not allow demand factors, hence the value is removed from the individual units. that would explain the "1500 x #units" as a calculation separate from the general loads in the practice problems. then the actual dryer load is not a concern when we are not given any values for premises dryers. i am going to keep looking for information that specifically addresses house load calcs.

The question 240 versus 230 SueMarkup yes, i should know to use the standard voltage of 240 unless told otherwise. given your answer i think that it may be that only henrey's even uses 230 as the given house voltage, (but it was not in the discussed problem). i will look for that more closely. pretty well answered. When calculating apperant voltage is used being 230 volts when finding amps applied voltage is used. Difference between the two is normally found using .707 concerning the sine wave.

thank you again

out of curiosity: i wanted to work on the parking lot problem, but i don't know what program to use that can be saved in a jpeg format to paste into the post.... my .dwg type program that i use cannot be saved under anything but the proprietary format. is there something else that can be used for designing that is free?

rainski