FLC for 800 Hp 460VAC Motor
- Thread starter texasmike
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- San Francisco Bay Area, CA, USA
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1.2A/HP
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- Illinois
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- retired electrician
While the 1.2 is a good rule of thumb, what code section actually addresses the current for motors larger than 500 hp?. 430.6 addresses some cases outside the table values, but does not address motors larger than 500 hp.
If the code does not define it I would back calculate off the 500 hp
Fla = 590
i = (746 x hp) / (1.732 x eff x pf x 460)
solve for eff x pf call it k
k = (746 x 500) / (1.732 x 590 x 460) = 0.794
for 800 hp
i = (746 x 800) / (1.732 x 0.794 x 460) = 944 A
short version
800/500 x 590 = 944
Fla = 590
i = (746 x hp) / (1.732 x eff x pf x 460)
solve for eff x pf call it k
k = (746 x 500) / (1.732 x 590 x 460) = 0.794
for 800 hp
i = (746 x 800) / (1.732 x 0.794 x 460) = 944 A
short version
800/500 x 590 = 944
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
It's not addressed in the NEC anywhere that I am aware of. As a generality, AHJs that I have encountered use the following statement out of 430.6.A.1 as justification for going ahead and using nameplate values:
But that doesn't help when you have to design the circuit and components long before the motor arrives and often before the motor is even ordered. The 1.2A/HP comes from an EASA (Electrical Apparatus Service Assoc.) guidebook I still have that has a reproduction of the 1996 NEC Table 430.150 (which is now 250) and at the bottom of that chart, there is one more row of values entitled "Over 200HP" and labeled;
[Approximate Amps / HP] [200V = 2.72] [208V = 2.64] [230V = 2.4] [460V = 1.2] [575V = .96] [2300V = .24] [4000V = .14]
I don't know if that is actually printed in the 1996 NEC, I no longer have a copy that old (it's not in the 2002 however). But even if it was, it no longer is. I have found that just like the values in 430.250, the number comes out a little conservatively higher than what I see on motors, so for sure don't use that for setting OL relays. But I find it's a good value to use for sizing conductors, OCPDs etc.
But that doesn't help when you have to design the circuit and components long before the motor arrives and often before the motor is even ordered. The 1.2A/HP comes from an EASA (Electrical Apparatus Service Assoc.) guidebook I still have that has a reproduction of the 1996 NEC Table 430.150 (which is now 250) and at the bottom of that chart, there is one more row of values entitled "Over 200HP" and labeled;
[Approximate Amps / HP] [200V = 2.72] [208V = 2.64] [230V = 2.4] [460V = 1.2] [575V = .96] [2300V = .24] [4000V = .14]
I don't know if that is actually printed in the 1996 NEC, I no longer have a copy that old (it's not in the 2002 however). But even if it was, it no longer is. I have found that just like the values in 430.250, the number comes out a little conservatively higher than what I see on motors, so for sure don't use that for setting OL relays. But I find it's a good value to use for sizing conductors, OCPDs etc.
- Location
- San Francisco Bay Area, CA, USA
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- Electrical Engineer
Took a picture of it...
You can extrapolate off the table
seems fairly linear
200 hp = 240 A
assume 400 hp = 2 x 240 = 480 A
From table 400 hp = 477 A
0.6% lower
250 hp = 302
2 x 302 = 604 A
table 500 hp = 590 A
2% lower
and so on
most are ~2-3% lower than table values
400 hp = 477 A
2 x 477 = 954 A
my calc 944 A
my calc is 1% lower than 2 x 400 hp fla
944/800 = 1.18 A/hp
seems fairly linear
200 hp = 240 A
assume 400 hp = 2 x 240 = 480 A
From table 400 hp = 477 A
0.6% lower
250 hp = 302
2 x 302 = 604 A
table 500 hp = 590 A
2% lower
and so on
most are ~2-3% lower than table values
400 hp = 477 A
2 x 477 = 954 A
my calc 944 A
my calc is 1% lower than 2 x 400 hp fla
944/800 = 1.18 A/hp
I think the table is a good guide, perhaps a very good guide. But it has to based on assumptions about power factor and efficiency.
There has been a push for higher efficiencies in recent years so IE1 is standard, IE2 is high efficiency, and IE3 is premium. Not sure that the same table would apply to all.
FWIW, my stab at the 800HP (~600kW) made it 960A.
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Is it FLC or FLA?
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There's a difference?Is it FLC or FLA?
The 960A from my calculation is full load current.
But you can call it what you want.....................
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Yes. NEC assigns motor full load current FLC which may not be same as motor name plate current FLA.There's a difference?
The 960A from my calculation is full load current.
But you can call it what you want.....................
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See my post #9.
My calculation was for full load motor current.
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But without a code reference.
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
But only up to 500HP. So the distinction becomes moot for this discussion.
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I think that's a reply to Sahib's comment. I screwed up the quotation brackets.
It wouldn't be a distinction for me you see. I don't think we use FLA, just FLC.
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Beyond 500hp, it is the other way around.
jumper
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I fixed all the quotes in posts.
Not for me nor for most Brits. In fact we use kW, not HP anyway. It's one step fewer in the calculation............Beyond 500hp, it is the other way around.
Thank you,sir!
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