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jeffhood

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a central electric heater has a 15 kw rating and a 3/4 horsepower motor. What size subfeed cable would be required to feed a subpanel that would be used to disseminate the loads?
 
Re: heating

Originally posted by jeffhood:
a central electric heater has a 15 kw rating and a 3/4 horsepower motor. What size subfeed cable would be required to feed a subpanel that would be used to disseminate the loads?
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Okay, I'll take a stab: #6 cu.
 
Re: heating

What's the supply system?

Roger
 
Re: heating

there are few thing i will like to know before i can give you the answer here

1] what is the power supply is ?

2] is that wired on single or three phase ?

3] what is the distance from subfeed or main panel ??

those question it will make the diffrence when selecting a correct wire size that will be determed and also the final location some area might have to derated in case unuseal area like attic area or high temp area

Merci, marc
 
Re: heating

ok i came up with this if this unit is straght electric heating device here

15KW 240 v single phase 62.5 amps
3/4 Hp motor [ on 240 v ] 6.9 amps

total load 69.4 amps

i add 25 percent over because this will be a " contouis running device if so.

the adjustment amp factor is 86.75 amp

the wire size i will use is #3 THHN/THWN wire but if other size wire please watch the derating this figures is based on 75C cables but if use SE or other cable you may have to use the 60C table which it will bump up to #2 size but alum always bump up one size anyway

i will let other chime in here too see if the answer come up the same with me or not


Merci , Marc
 
Re: heating

i add 25 percent over because this will be a " contouis running device if so.

the adjustment amp factor is 86.75 amp
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Would electric heat be a continuos load?
 
Re: heating

yes if it is running more than 3 hours cycle then it will be contouis but if ran in interment cycle i still leave some leeway there because i leave extra room for starting surge on the motor and inrush current for electric heating element


kinda off point here for a min but if i rember right [ of course please do correct me if i barking up on wrong rubber tree ] most electric heating device have current more than 42 or 45 amp have to be subdivied to two or more .

Merci , Marc
 
Re: heating

you can't use the data plate on motors when sizing the load right? you use 430 tables

[ January 13, 2006, 06:10 AM: Message edited by: wyatt ]
 
Re: heating

Originally posted by wyatt:
you can't use the data plate on motors when sizing the load right? you use 430 tables
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Correct.

Roger
 
Re: heating

thanks for the replies, got a question?Since the #2 xxhw will be coming from the main pnl feeding a subpanel with two 60 amp breakers in that inturn feed the heating unit do we calculate the subfeed as a branch circuit or a feeder?Also if the loads of heating have to be divided into loads not exceeding 48 amps then is it permissible to install like described above or would yuou have to install 2 seperate parrall 60 amp circuits from heating unit to main pnl.???????????????
 
Re: heating

Originally posted by jeffhood:
thanks for the replies, got a question?Since the #2 xxhw will be coming from the main pnl feeding a subpanel with two 60 amp breakers in that inturn feed the heating unit do we calculate the subfeed as a branch circuit or a feeder?
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According to definition, it's a feeder:
Feeder. All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.
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Also if the loads of heating have to be divided into loads not exceeding 48 amps then is it permissible to install like described above or would yuou have to install 2 seperate parrall 60 amp circuits from heating unit to main pnl.???????????????
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The former.
 
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