The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Calling all Non-US members!! (Non-US only)
by aussie240
12/07/16 02:39 AM
Photo Upload Tutorial
by DanK
12/06/16 11:35 PM
Sprinklered equipment 26-008
by bigpapa
12/02/16 04:24 PM
On Delay Relay with Auto Reset
by Potseal
12/01/16 09:59 AM
Wow, that was close!
by jraef
11/28/16 07:06 PM
New in the Gallery:
12.5A through 0.75mm▓ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 13
HotLine1 9
Texas_Ranger 8
sparkyinak 7
Potseal 6
Who's Online
0 registered (), 92 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#130754 - 12/06/06 09:10 AM i think im gettin it...
JLC Offline
Member

Registered: 10/06/06
Posts: 12
Loc: pelham manor,NY,usa
OK this one is a 240V/3Ph/60Hz

1 - Blower Motor============1200.VA(5A)
4 - single valve Solenoids====40.39VA(10.1W)ea
1 - Dual valve solenoid=======60.VA
2 - drive motors @ 5VA ea=====10.VA
2 - Temp. cntrlrs @ 1A ea====240.VA
2 - Flame Monitors @ 1A ea===240.VA
10 - Lights @.025A ea(7const)==21.VA
1 - Motor Starter==============8.VA
______________________________________
System Total=================1819.39VA
1819.39VA / 240V================7.58A
______________________________________
Trans. Total==================619.39VA
619.39VA / 240V=================2.58A

So I hope i have this stuff down now so i can size these systems on my own. For this system i would use a 240VPri. - 120VSec. Trans. with 750VA? with a 3A fuse, and (3)10A fuses in my disconnect switch, is this right?

Top
#130755 - 12/06/06 12:36 PM Re: i think im gettin it...
jraef Offline
Member

Registered: 07/21/04
Posts: 91
Loc: San francisco, CA, USA
Not if your blower motor is running off of this transformer.
_________________________
JRaef

Top
#130756 - 12/06/06 12:47 PM Re: i think im gettin it...
ITO Offline
Member

Registered: 11/26/06
Posts: 341
Loc: Texas
240V/3PH?

(E*1.72)/P = I for 3phase.


[This message has been edited by ITO (edited 12-06-2006).]
_________________________
101┬░ Rx = + /_\

Top
#130757 - 12/06/06 01:54 PM Re: i think im gettin it...
JLC Offline
Member

Registered: 10/06/06
Posts: 12
Loc: pelham manor,NY,usa
no the blower motor is running off of the 240V/3PH/60Hz line. the trans is for all the other components.

Top
#130758 - 12/07/06 03:44 AM Re: i think im gettin it...
rws Offline
Member

Registered: 12/06/06
Posts: 14
Loc: Texas
I = P/(E*1.732)

In 3 ph, the supply voltage would be 208V.

In practicality, we would find on the motor decal the FLA and multiply by 1.25 and if that includes enough current to match the LRA, fine, if not, then use the LRA. Otherwise, we would look in the table in the NEC with the motor's hp, voltage, and motor type.

Example: induction type motor, 208V 3 ph, 5 hp. Whatever the amp draw in the table is, that would get multiplied by at least 1.25 to ensure enough current to accomodate LRA or LRC (same difference. Got to have enough current to meet locked rotor, or complete standstill of the motor.) Usually, if you take the full load amperage and do the 125 % on that, it will be enough to meet LRA.

But those size fuses would still work, especially if they are standard trade sizes.

[This message has been edited by rws (edited 12-07-2006).]

Top
#130759 - 12/07/06 05:50 AM Re: i think im gettin it...
ITO Offline
Member

Registered: 11/26/06
Posts: 341
Loc: Texas
http://electrical-contractor.net/ubb/Forum7/HTML/000543.html

[This message has been edited by ITO (edited 12-07-2006).]
_________________________
101┬░ Rx = + /_\

Top
#130760 - 12/07/06 10:07 AM Re: i think im gettin it...
BugMan Offline
Member

Registered: 08/24/06
Posts: 10
Careful, you could have 240 3-phase for a delta fed service.

Top



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals