7.5HP Air Compressor 208V Ground-fault/Short Circuit protection and motor circuit conductors.

[jklr]

Hello,

I've got another motor calc that I have done and just want to make sure I am interpreting the code correctly.

We are going to be swapping out a old compressor for a new one. Details below.

Old compressor and circuitry.

5HP
23FLA
40c
RPM 1750
Ser Fac 1.15

#8 thhn on a 40amp qo standard trip beaker.


New compressor
7.5HP
FLA 33
40c
Rpm 1750
SF 1.15

According to 430.248
7.5HP = 44amps @ 208v
430.22 44 x 1.25 = 55Amps
Table 310.16 75c. 6 awg thhn

430.52.... Using Standard trip QO breaker.

Do we use the nameplate for the FLA or 430.248 FLC for the breaker?
If we use FLA then 33 x 300(non time delay)= 99 MAX (100) and 33x1.25 41.25 MIN (45) (per table 240.6)

Or if FLC 44 X 300 = 132 amp MAX
44 x 1.25 = 55 amp min

About a 200 ft run, VD 33amps at 208v 3.08% VD.

Plan on coming out of panel with 3/4 emt then switching over to 6/2 MC above grid ceiling then go up to the roof perlins and strap MC for about 130ft inside the garage then set a box and then go down the wall to disco, then flex over to compressor. I had planned on using a 45 amp breaker if we use fla or a 55amp breaker if we use flc for 430.52.

The motor has its own thermal overload.

Thanks!

 

[don_resqcapt19]

Motor conductor size and branch circuit short-circuit and ground-fault protection are based on the values found in the Article 430 Tables.

Also the code only uses the term Full Load Current (FLC) and does not use the term Full Load Amps (FLA). However it uses two different FLCs...the one from that table for the sizing of the conductors and branch circuit protection and the one from the nameplate for sizing the overload protection.

 

[LarryFine]

However it uses two different FLCs...the one from that table for the sizing of the conductors and branch circuit protection and the one from the nameplate for sizing the overload protection.

Nameplates aren't used for circuit sizing because replacements may have different current requirements.

 

[jklr]

Motor conductor size and branch circuit short-circuit and ground-fault protection are based on the values found in the Article 430 Tables.

Also the code only uses the term Full Load Current (FLC) and does not use the term Full Load Amps (FLA). However it uses two different FLCs...the one from that table for the sizing of the conductors and branch circuit protection and the one from the nameplate for sizing the overload protection.

Thank you for the clarification!

 

[jklr]

Nameplates aren't used for circuit sizing because replacements may have different current requirements.

Thanks for the reply!

 

[jklr]

Ok now the kicker. They want to put the new compressor down in the oil change pit. The pit has multiple tanks for holding new and used oil. The only work performed in the pit is oil changes and there is no mechanical ventilation. I am going to start looking into Article 500s, but at first glance it is somewhat confusing determining whether the area is classified class1 div 1 or class 1 div 2 or if any areas are unclassified.

 

[retirede]

Ok now the kicker. They want to put the new compressor down in the oil change pit.

 

[ptonsparky]

Ok now the kicker. They want to put the new compressor down in the oil change pit. The pit has multiple tanks for holding new and used oil. The only work performed in the pit is oil changes and there is no mechanical ventilation. I am going to start looking into Article 500s, but at first glance it is somewhat confusing determining whether the area is classified class1 div 1 or class 1 div 2 or if any areas are unclassified.

See post 7.

You don't classify the area. Go up the food chain. An AHJ... Anyone but you.

 

[Jraef]

430.52.... Using Standard trip QO breaker.

Just for your edification:
You say you are using a BREAKER, then you are referring to percentages (300%) which is for FUSES (non-time delay). There is a different column in 430.52 for breakers (Inverse Time are standard thermal-mag breakers), calling for 250% max., not 300%.

So 250% of 44A FLC = 110A as the MAXIMUM breaker size, not 132A.

Also note that for the conductor size (125% of Table FLC), that is the MINIMUM, you can go larger (and may need to if there is distance).
But for the breaker size, 250% of Table FLC is the MAXIMUM. You can go smaller if you want to, but going smaller does raise the possibility of nuisance tripping, so I always try to go as large as allowable.