Can not get the right answer for this question. Need a specific code reference.

[mggriffin93]

A 120/240 volt single phase, 3wire feeder supplies 150 general purpose recepticals in an office building with 3200 square feet. When sizing this feeder, what will be the minimum calculated amperage load to be used?
Answer: 77 amperes.

The reference i was given is table 220.44 and 220.14(k). Can anyone please help explain this? I have calculated it many different ways and can not get 77 amperes. Sorry if I didn’t post this right. I am new to the forum.

 

[augie47]

What answer did you get ?

 

[mggriffin93]

3200sqft x 3va/sqft=9600va

9600va divided by 120V= 80 amperes.
Table 220.44 demand factor says first 10kva at 100%

But 220.14 (h) and (I) says to use 180va for each outlet.
180va x 150=27000va
27000 divided by 120v =225 amperes.

 

[david luchini]

3200sqft x 3va/sqft=9600va

9600va divided by 120V= 80 amperes.
Table 220.44 demand factor says first 10kva at 100%

But 220.14 (h) and (I) says to use 180va for each outlet.
180va x 150=27000va
27000 divided by 120v =225 amperes.

Try using 240V for starters.

 

[Ingenieur]

150 x 180 = 27000 va
first 10000 at 100%
balance at 50% = ?
total = 10000 + ? = ? / 240 = ?

 

[mggriffin93]

Try using 240V for starters.

. General purpose recepticals are not 240v

 

[Ingenieur]

. General purpose recepticals are not 240v

the load is distributed over 2 legs
the guy likely has forgotten more than you know lol

 

[david luchini]

. General purpose recepticals are not 240v

The feeder is 120/240V single phase, 3 wire. Use 240V.

 

[ActionDave]

. General purpose recepticals are not 240v

No, but the supply voltage to the building is.

 

[augie47]

I think the key may be they are asking you to calculate the receptacle load only.
220.4(K) + 220.44 gives you the 77 amps I believe.

 

[topgone]

3200sqft x 3va/sqft=9600va

9600va divided by 120V= 80 amperes.
Table 220.44 demand factor says first 10kva at 100%

But 220.14 (h) and (I) says to use 180va for each outlet.
180va x 150=27000va
27000 divided by 120v =225 amperes.

Why do you use 3 VA/sq, ft.? Receptacles will be given 180 VA/strap.

 

[mggriffin93]

The feeder is 120/240V single phase, 3 wire. Use 240V.

Got it now thanks.

 

[mggriffin93]

Why do you use 3 VA/sq, ft.? Receptacles will be given 180 VA/strap.

Sorry I meant to do it with 3.5. Table 220.12 office buildings 3.5 va / sqft.

 

[mggriffin93]

150 x 180 = 27000 va
first 10000 at 100%
balance at 50% = ?
total = 10000 + ? = ? / 240 = ?

Got it ! Thanks for the help

 

[packersparky]

Sorry I meant to do it with 3.5. Table 220.12 office buildings 3.5 va / sqft.

For office buildings, that table is for lighting loads only. You do not use it for receptacle loads.

 

[topgone]

For office buildings, that table is for lighting loads only. You do not use it for receptacle loads.

Correct. Anyway, he got the answer already.

 

[Ingenieur]

Got it ! Thanks for the help

friendly word of advice since you are a newby
when a member gives advice (eg use 240)
think about it before dismissing it out of hand
look who's giving it
post count
he's a moderator for one, meaning they trust him technically
two, look at their profile
he's an EE and a PE likely with decades of experience
good chance he knows what he is talking about if he took time to answer/help

enjoy the forum
lots of knowledge base here