CONDUIT FILL

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ohmhead said:
What is the the max amount of no# 2 copper thwn-2 wires I can get in a 1 inch flex metal conduit ? I see 3 total can I run the ground on the out side of the flex which would be a number 8 thwn-2 and if so can it be bare copper wire .
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FYI,With an increase of phase conductor size to a # 2awg, the increased EGC size would be a # 6 awg. Should still fit in the 60% fill x 24" nipple.
 
Dennis Alwon said:
Why do you need #2 wire? Can't you use #6 from the disconnect to the unit?
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The wire size is designed by engineer its always over kill but when the units hit the job the wire size never changes unless its too small .
So this is not a voltage drop issue . We cant change the wire size its just not that easy if fact it would cost us more money and months to RFI it wait for a answer and them give them credit back for twice the money it cost us to just leave it . On a large project one thing you never give credit back is costly .
 
ohmhead said:
Can you explain this how did you pick 6 wire for the number 2 awg phase conductor ?
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Sure, 250.122(B) requirement. " where ungrounded conductors are increased in size from the minimum size that has sufficient ampacity for the intended installation, wire-type equipment grounding conductors, where installed, shall be increased in size proportionately according to the circular mil area of the ungrounded conductors."

A 60 amp breaker would use a # 6 awg cu. and a # 10 awg cu. EGC. An increase phase conductor to # 2awg would result in needing a # 6 awg cu. EGC.

new phase conductor circular mil (66360)/ old phase conductor circular mil (26240) = ratio(2.5)x original EGC circular mil(10380) = new EGC circular mil(25950).Next higher is 26240 (#6 awg).
 
RUWired said:
Sure, 250.122(B) requirement. " where ungrounded conductors are increased in size from the minimum size that has sufficient ampacity for the intended installation, wire-type equipment grounding conductors, where installed, shall be increased in size proportionately according to the circular mil area of the ungrounded conductors."

A 60 amp breaker would use a # 6 awg cu. and a # 10 awg cu. EGC. An increase phase conductor to # 2awg would result in needing a # 6 awg cu. EGC.

new phase conductor circular mil (66360)/ old phase conductor circular mil (26240) = ratio(2.5)x original EGC circular mil(10380) = new EGC circular mil(25950).Next higher is 26240 (#6 awg).
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Ok so in any case that you increase the wire size larger then the wire size actually needed per 310 .16 you must do this . So voltage drop or any reason we divide larger wire by the smaller so if I increase the breaker size closer to the wire ampacity we should be able to go back towards 8 awg lets say 80 amp breaker I use 4 wire
(41740) cm 2 wire (66360) =1.5 so I multiply 1.5 x 8 wire which all I need normally per 250.122 16510 x 1.5 = 24765 which is less than 26240 number 6 # what do I do use 8 or 6 ?
 
Will #2 wire even fit in the terminals of the VFD, assuming it's designed for #6 wire?


SceneryDriver
 
ohmhead said:
lets say 80 amp breaker I use 4 wire
(41740) cm 2 wire (66360) =1.5 so I multiply 1.5 x 8 wire which all I need normally per 250.122 16510 x 1.5 = 24765 which is less than 26240 number 6 # what do I do use 8 or 6 ?
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Will the VFD allows the use of an 80 amp breaker. In your scenario, a # 6 awg cu. EGC will be needed. You would always use the next closest higher circular mill.
 
RUWired said:
Will the VFD allows the use of an 80 amp breaker. In your scenario, a # 6 awg cu. EGC will be needed. You would always use the next closest higher circular mill.
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The AHU unit is a factory wired unit with a name plate which states crt -( 59 FLA) &( 60 amp OCP max) it has three fans we were to make a one point connection but the unit from the factory just installed the three VFD,s which now we must connect each individually .

What were trying to do is save the mechanical contractor the cost and still be code smart .

I see your point and thank you for your input I guess will have to change the ECG due to this rule on up sizing I cant change the design of engineer for reasons that cost more so were trying our best to help him and still meet code .

So 60 amp max breaker and we use number 2#awg phase wire and the engineer calls out 8 # ground will up size the ground or ECG that's in our best interest can you make the ground larger in size or is there a rule on that . LOL

We were thinking maybe there was a exception to the rule on motors as far as starting in rush in this case a larger breaker was say needed so that would correct the issue even if the name plate says 60 max if we used a 100 amp breaker in panel and leave the wire EGC at 8 #awg
 
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ohmhead said:
We were thinking maybe there was a exception to the rule on motors as far as starting in rush in this case a larger breaker was say needed so that would correct the issue even if the name plate says 60 max if we used a 100 amp breaker in panel and leave the wire EGC at 8 #awg
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IMO that rule does need some tweaking and there are situations that come up from time to time that the determined EGC size doesn't really make any sense.

In your case a #8 EGC is good for a 100 amp breaker according to T250.122, but you have still increased the size of the ungrounded conductors beyond the minimum required size so the EGC still needs increased proportionally.
 
You only need to consider the inrush for VFD's if they have bypass contactors that allow you to start accross-the-line when the inverter craps out. If this is a retrofit, I seriously doubt that feature is included, mainly because it takes up 2wice the space, but you should check.

Many VFD catalogs will give you a recommended breaker size that is way below 250% of FLA.
 
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