# Breaker and wire size help



## WronGun (Oct 18, 2013)

What would you guys run for thhn and breaker for this air compressor? 










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## WronGun (Oct 18, 2013)

It’s been replaced with the same exact rating compressor and it’s been running with 208v on a 30A Double pole breaker..... now it trips after running for a bit 


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## Switched (Dec 23, 2012)

A 50a breaker


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## J F Go (Mar 1, 2014)

Looks to me like 33 A @208 so I would say you need a 45 A 2pole breaker. Isn't 80% of 40=32 ? So the wire size needs to increase also if it's #10.


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## WronGun (Oct 18, 2013)

J F Go said:


> Looks to me like 33 A @208 so I would say you need a 45 A 2pole breaker. Isn't 80% of 40=32 ? So the wire size needs to increase also if it's #10.




10awg thhn is good for 40A 


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## gpop (May 14, 2018)

Can not remember with out looking. Something like 130% of np for a 1.15 and 140% for a 1.25 sf for overloads so breaker should be a lot larger than 30

Its 33 amp before 1.15sf 

what size is the wire?


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## WronGun (Oct 18, 2013)

gpop said:


> Can not remember with out looking. Something like 130% of np for a 1.15 and 140% for a 1.25 sf for overloads so breaker should be a lot larger than 30
> 
> Its 33 amp before 1.15sf
> 
> what size is the wire?




Wire is #10 thhn, it does change over to 10awg Mc for about 10’ 


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## 847Videos (Dec 8, 2014)

Look at article 430... lazy ass 

Wire:
125% over full load
#8 thhn
You have to derrate a #10 btw won’t work.


Breaker: 
175% over full load for a time delay breaker
300% over full load for instantaneous trip breaker

Motor is single phase so I assume this is going in a residential load center, those breakers are instantaneous trip....

You “WILL” need a motor starter with over loads btw

I suggest you hire a licensed Electrican before torching your house or getting electrocuted 


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## WronGun (Oct 18, 2013)

847Videos said:


> Look at article 430... lazy ass
> 
> Wire:
> 125% over full load
> ...




I am a licensed electrician. Didn’t know that the electrical license means you know every possible thing in the trade. 

This is in an industrial setting as I stated 208V

I haven’t installed anything yet just checking before i do anything. 

I don’t have much experience hooking up compressors. The owner who is my client just took the old compressor feeds and popped them into the new compressor which has all the same specs on name plate and now called me in because it’s tripping. 

Both the old and new compressor have built in motor staters with a terminal for L1, L2, and ground. 




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## 847Videos (Dec 8, 2014)

No worries,

Look at the distribution panel, call the manufacturer and see about getting a time delay breaker part number.

Sounds like you have 3 phase power available, 
I would recommend they use a 3 phase motor as it will be easier to turn the compressor under load.

Verify the heater “overload” size as well..... motor either has 1.10 or 1.25 which means your using that percentage over full load...

Look over article 430. 
If you have questions, list the article number...
Make sure you have the whole layout designed and verified, grounding etc... 
Your code book is your bible, get to know it. 
Minimal requirements 




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## frenchelectrican (Mar 15, 2007)

Wrongun .,

You need 50 amp breaker with #8 THHN then you are good to go but the question is which type of overload protection do the motor have interal OL or have a contractor with OL elements in there?

Edit.,, I noted you mention starter in there and did you check the setting on the starter OL to make sure it work on 208 V 33 amps ? and do expect the current reading go higher when the tank get near cutoff pressure point so that is typical. 

When it restart it should start unloaded if started loaded a good chance it will trip the OL or CB one of the two.


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## WronGun (Oct 18, 2013)

frenchelectrican said:


> Wrongun .,
> 
> You need 50 amp breaker with #8 THHN then you are good to go but the question is which type of overload protection do the motor have interal OL or have a contractor with OL elements in there?
> 
> ...













This is what It has except only the L1/L2 version 



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## WronGun (Oct 18, 2013)

We tested it today and it only trips as it get closer to full fill 


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## Cow (Jan 16, 2008)

#6 on a 60 amp breaker to start with. If it still has issues tripping at startup, then the breaker size can go up.


Just an FYI, for motors:


Look up the full load amps based on HP, voltage, phase in the art 430.248 motor tables.


Multiply that by 125% for a continuous load.


Use that amperage to select your wire size from the art 310 wire table.


Done.


Here we go:


208v 7.5HP 1 phase = Table 430.248= 44 amps.


44 amps x 125%= 55 amps min conductor size=#6 THHN


44 amps x 250%=110 amp inverse breaker size max. 430.52



So to recap, you would run #6 thhn and use a 55-->60-110 amp breaker.


And yes, it is legal to use a #6 thhn on a 110 amp breaker for a motor application. Just be aware your ground wire size follows your OCPD size.


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## 847Videos (Dec 8, 2014)

WronGun said:


>



115% over full load current.
Don’t forget your ground wire, article 250.122
We can feed you, but you need to learn how to fish...




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## frenchelectrican (Mar 15, 2007)

WronGun said:


> We tested it today and it only trips as it get closer to full fill
> 
> 
> Sent from my iPhone using Tapatalk


Gotcha .,,

Check the OL relay dail pointer to make sure you are at 33 or 35 amp setting then you should be good to go. if reading too low turn it clockwise to increase the amp setting on OL relay. 

That why I mention before the current drawage will rise before it cut off on the pressure switch setting


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## 847Videos (Dec 8, 2014)

Cow said:


> #6 on a 60 amp breaker to start with. If it still has issues tripping at startup, then the breaker size can go up.
> 
> 
> Just an FYI, for motors:
> ...





Love it... 
That’s how you get it done
Now you walk in with facts based on the national code.


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## WronGun (Oct 18, 2013)

847Videos said:


> Love it...
> That’s how you get it done
> Now you walk in with facts based on the national code.
> 
> ...




It amazes me they has the same spec unit running for a very longggg time on the same exact circuit 


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## 847Videos (Dec 8, 2014)

Cow said:


> Look up the full load amps based on HP, voltage, phase in the art 430.248 motor tables.
> 
> 208v 7.5HP 1 phase = Table 430.248= 44 amps.



He has the nameplate info available 
I agree with everything else 



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## 847Videos (Dec 8, 2014)

WronGun said:


> It amazes me they has the same spec unit running for a very longggg time on the same exact circuit
> 
> 
> Sent from my iPhone using Tapatalk




In the end, EVERYTHING electrical is required to be designed with minimal standards based on all the studies all the engineers at UL, national fire protection etc...

If someone designed the circuit and installed it and it hasn’t burnt, shouldn’t be the standard to go buy... 

I see all kinds of stupid stuff out there...


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## Mulder (Sep 11, 2010)

847Videos said:


> He has the nameplate info available
> I agree with everything else [emoji1316][emoji817][emoji851]
> 
> 
> ...


The nameplate amps is only used for sizing overloads. Use the tables for wire size and overcurrent protection.


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## 847Videos (Dec 8, 2014)

[emoji848] I would design the circuit for the specified load looking at the nameplate. Because that’s the load I’m trying to serve.
But common sense says, design the circuit with whatever won’t cause it to burn and have us looking like a holes...

Maybe design it off the charts and pick the better of the two.... The NEC is meant to be minimal standards... Therefore I agree with you.

#8 or #6
I’d go with a #6 for better heat dissipation
Overload values off the name plate, because the goal/interest here is to protect the motor.

Breaker is short ckt protection for the feeders, and able to take the lock rotor amps at start up...

Grounding is very important on motors as well as the unit vibrates and if anything gets wacky, we want the breaker to trip.

Still think, compressors should be 3 phase if the property has it


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## Cow (Jan 16, 2008)

Read 430.6(A)1 in regards to wire and breaker sizing.


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## WronGun (Oct 18, 2013)

After reading the article and other posts on this subject I’ve found a dozen different answers....[emoji1749]


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## 847Videos (Dec 8, 2014)

Cow said:


> Read 430.6(A)1 in regards to wire and breaker sizing.



Respect where respect is due...
1,000% Correct.:vs_shake:
Exactly how this is done.
And just for that, I'm going to revisit Article 430 myself as it never hurts to invest in our trade.
"Other than for motors built for low speeds (less than 1200 RPM) or high torques, and for mul- tispeed motors, the values given in Table 430.247, *Table 430.248, Table 430.249, and Table 430.250 shall be used to determine the ampacity of conductors or ampere ratings of switches, branch-circuit short-circuit and ground-fault pro- tection, instead of the actual current rating marked on the motor nameplate."*


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## Switched (Dec 23, 2012)

WronGun said:


> After reading the article and other posts on this subject I’ve found a dozen different answers....[emoji1749]
> 
> 
> Sent from my iPhone using Tapatalk


This is a confusing section for those of us that don't work with it everyday. I don't quite understand all of it either, but the explanations here make sense.


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## 847Videos (Dec 8, 2014)

WronGun said:


> After reading the article and other posts on this subject I’ve found a dozen different answers....[emoji1749]



Read the code, everything else is just an opinion...
Back it up your design with article numbers


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## cabletie (Feb 12, 2011)

Nope only one answer. Cow’s is correct.


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## 847Videos (Dec 8, 2014)

cabletie said:


> Nope only one answer. Cow’s is correct.





I second that, Cow is correct.
Verify with the article numbers he provided


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## Switched (Dec 23, 2012)

So... Can I go back and edit my incorrect post? lol


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## WronGun (Oct 18, 2013)

847Videos said:


> Read the code, everything else is just an opinion...
> Back it up your design with article numbers




Sure #6 on a 60 would work , but it seems #8 on a 50 would Also be acceptable. 

Yes it’s true I don’t work on this Everyday , the nameplates I’ve used for installations in the past offered more information. Min and max breaker size , fla, etc.etc. I’ve never had to dig very deep.


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## 847Videos (Dec 8, 2014)

WronGun said:


> Sure #6 on a 60 would work , but it seems #8 on a 50 would Also be acceptable.
> 
> Yes it’s true I don’t work on this Everyday , the nameplates I’ve used for installations in the past offered more information. Min and max breaker size , fla, etc.etc. I’ve never had to dig very deep.
> 
> ...



I've always used Name Plate
I have a digital copy of the code book
And from now on, I'll bring it up on my phone and design the everything except the heaters off the charts just like the code specifies....


Good time we bust out and knock the dust off our code books hu... lol
:biggrin:


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## Switched (Dec 23, 2012)

WronGun said:


> Sure #6 on a 60 would work , but it seems #8 on a 50 would Also be acceptable.
> 
> Yes it’s true I don’t work on this Everyday , the nameplates I’ve used for installations in the past offered more information. Min and max breaker size , fla, etc.etc. I’ve never had to dig very deep.
> 
> ...


I thought 8 on a 50 would work, because I incorrectly thought we could use the nameplate FLA to size the breaker. The section @Cow mentioned though shows I was wrong.


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## cabletie (Feb 12, 2011)

I’m glad I wasn’t the first one in. I didn’t have the time to respond when I first read it. When I did the math on a calculator I came up with #8 on a 100amp breaker. But I used 230 volts. You can’t see the tables when your using an app like ElectriCalc 

When I saw Cow’s response I opened up the table to see the different columns. I though 230v covered it down to 208v.


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## WronGun (Oct 18, 2013)

Well this has been a great lesson on motors...

Good news is I can use the existing 3/4” emt 

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## frenchelectrican (Mar 15, 2007)

WronGun said:


> Well this has been a great lesson on motors...
> 
> Good news is I can use the existing 3/4” emt
> 
> Sent from my iPhone using Tapatalk


It is and you will run into central air conditing system ., same way with motors as you will review art 430 and art 440 from time to time to remind yourself on the numbers.


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## WronGun (Oct 18, 2013)

frenchelectrican said:


> It is and you will run into central air conditing system ., same way with motors as you will review art 430 and art 440 from time to time to remind yourself on the numbers.




Im sure i will. 

The last few rtu’s i did had everything laid out the on plate including conductor sizes. 


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## splatz (May 23, 2015)

Correct me if I am wrong, here is how I figure... 

The HP field is 7.5, simple enough. The AMPS field on this nameplate is 31, that's the FLA, but that's not the FLC. Already confusing. 

FLC is not found on the nameplate, you find the FLC for the HP in the table. (In this case, 430.28 for single phase AC motors.) The tables account for power factor and efficiency. 

Wire size for CCC's is based on the FLC. (If the load is continuous, the 80% rule / 1.25 multiplier applies as usual.) 

The OCPD size can exceed the usual max, the max OCPD allowed is calculated from FLC and a multiplier from 430.52. The lookup in 430.52 depends on the type of motor. _(I am not clear other than consulting the manufacturer how you walk up to a motor and know which type it is.)_

Overloads may be built into the starter or dual element fuses in the disconnect. Overloads are sized from FLA and a multiplier per 430.32. For motors > 1hp, the multiplier is 

* 1.25 for motors with SF > 1.15, OR, temperature rise 40°C or less
* 1.15 otherwise 

SF is clearly marked on the nameplate, not sure about temperature rise. 

To NEMA and NEC, it would be super, super helpful if you f***ing f***s could use the EXACT SAME TERMS AND LABELS.


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## HackWork (Oct 2, 2009)

I am glad that some of you got it, because I don't have a clue what is going on. :sad:


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## WronGun (Oct 18, 2013)

Ok ... I feel a little better now knowing my head isn’t the only one that is spinning. 


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## Dennis Alwon (May 9, 2009)

You do not use the nameplate but rather T. 430.248. You need to use the table value for 7.5 hp and it is 44 amps x 1.25 means you need a conductor rated 55 amps. The overcurrent protective device can be 250% of the fla which means 33 amps x 2.5 = 82.5 amps for an inverse time breaker. T.430.52 You can use the next higher size breaker.


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## cabletie (Feb 12, 2011)

33 ???? x 250%

Should be 44 x 250% = 110 amp breaker.


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## Dennis Alwon (May 9, 2009)

cabletie said:


> 33 ???? x 250%
> 
> Should be 44 x 250% = 110 amp breaker.


Look at the table.. It is 250% of the fla or full load current (amps). That is 33 amps not 44.


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## splatz (May 23, 2015)

I'm putting $10 on FLC = 44


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## splatz (May 23, 2015)

For an inverse time breaker, multiplier is 250%, so 

44 * 250% = 44 * 2.5 = 110


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## cabletie (Feb 12, 2011)

I was also taught to go to the smaller size if it’s not a common size fuse or breaker. If starting is a problem then you go next size higher (exception 1) if it still a problem then you go to exception 2. Sorry about the pic.


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## Dennis Alwon (May 9, 2009)

splatz said:


> I'm putting $10 on FLC = 44


I'll take the $10. Table 250.52 does not speak of table 250.248 etc. The conductor size is based on the Table not the overcurrent protective device. The reason being is that the table is based on the worse case scenario (inefficient motor) and they want the conductor to be able to carry the load in case someone install an inefficient motor. The overcurrent protective device is simpler to change but in general it probably would not need changing in most instances.


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## Cow (Jan 16, 2008)

Dennis, before you confuse anyone else:



Cow said:


> Read 430.6(A)1 in regards to wire and breaker sizing.


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## Dennis Alwon (May 9, 2009)

I will concede that you would use the table if the fla wasn't given but if it is there I am pretty sure you would use the nameplate


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## Cow (Jan 16, 2008)

Dennis Alwon said:


> I will concede that you would use the table if the fla wasn't given but if it is there I am pretty sure you would use the nameplate



I disagree, that's not what the article I posted says.


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## Dennis Alwon (May 9, 2009)

I stand corrected... I always thought the fla would be used for the particular motor which makes more sense to me.

Thank you


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## Dennis Alwon (May 9, 2009)

Cow said:


> I disagree, that's not what the article I posted says.


I responded before I saw your post


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## Mulder (Sep 11, 2010)

Dennis Alwon said:


> I will concede that you would use the table if the fla wasn't given but if it is there I am pretty sure you would use the nameplate


430.6(A)(1) does not mention nameplate at all. You have to use the tables or wire size and overcurrent protection.


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## 847Videos (Dec 8, 2014)

Use the tables to size breaker, Wire and starter....
Overload settings, use the service factor value on the name plate.

Terminology....

S.F: service factor 

FLA: Full load amps
FLC: Full load current
LRA: Lock Rotor amps 



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## WronGun (Oct 18, 2013)

Not to change the subject , but If we were to add a VFD to a motor would all the same calculations be applied to feed the VFD ? 


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## 847Videos (Dec 8, 2014)

Same motor, VFD would just be a means to control the speed.

You’d need a disconnect no starter


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## WronGun (Oct 18, 2013)

847Videos said:


> Same motor, VFD would just be a means to control the speed.
> 
> You’d need a disconnect no starter
> 
> ...



Just in general not this motor , but say HVAC

I’m saying a VFD needs to be fed first then continues to the motor. 

To get conductor sizing and OCPD protection for VFD would we fall back to the motor it is supplying. 

I’ve been faced with more and more of this work lately and I’m just trying to understand it better.

Back when I was an employee I installed tons of them but never had to think. I was given the equipment and materials and had at it.

Now all I’m given is a VFD , and the rest is on me. 


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## frenchelectrican (Mar 15, 2007)

WronGun said:


> Not to change the subject , but If we were to add a VFD to a motor would all the same calculations be applied to feed the VFD ?
> 
> 
> Sent from my iPhone using Tapatalk


Yuh in most case the VSD do follow the same requirement as conventail motor system is ., 

unless specifically noted by VSD manufacter for OCPD that is the one of few extra step you have to be aware of it.

But for conductor or main OCPD just follow the table as few guys posted.


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## 847Videos (Dec 8, 2014)

WronGun said:


> Back when I was an employee I installed tons of them but never had to think. I was given the equipment and materials and had at it.
> 
> Now all I’m given is a VFD , and the rest is on me.



How did that work out? [emoji23]
You where trained from the neck down,
NEVER EVER.... Neglect the brain [emoji3447][emoji851]

Don’t use it you lose it, worked with “30yr” electricians that couldn’t wire up a ballast....lol
If I was paying those wages they’d be fired, the neck down guys are great for the production work in large projects, but they end up short changing themselves in the long run...

My opinion [emoji1373]



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## WronGun (Oct 18, 2013)

847Videos said:


> How did that work out? [emoji23]
> You where trained from the neck down,
> NEVER EVER.... Neglect the brain [emoji3447][emoji851]
> 
> ...




Your absolutely right , but the companies want us to just install what has been figured out by the offices. It makes sense from a company standpoint. They have full time guys to figure this stuff out and double and triple check their work, so the field guys can get right into it. 

I’ve only worked for companies with 300+ employees , 1 company where I spent 70% of my time had 1000+ employees 

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## emtnut (Mar 1, 2015)

Cow said:


> I disagree, that's not what the article I posted says.


Interesting. Under CEC, motor data trumps the tables.

For your NEC, would exception #3 not apply here (under 430.6) ?


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## WronGun (Oct 18, 2013)

Today I went to the building where I got to enter the neighbors adjacent unit who has the same identical compressor unit. (Which is the reason he bought his) 

Installed with 10awg thhn on a 40A breaker, it’s been running now for a year. Not sure if the installer was the same. 

This now becomes hard for me to explain if I need to run all new pipe , wires , etc. 

Pipework in these units are about 16’-18’ high , 80’ from panel, so its a bit of work.

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## 847Videos (Dec 8, 2014)

I’d design and install it based on the national electrical code, the Chicago code says you take ownership of what you install, so if something happens, and you find yourself in court having to justify what you did, the “Nieghbor” hired an untrained handy man so I copied his design won’t fly 




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## joebanana (Dec 21, 2010)

WronGun said:


> After reading the article and other posts on this subject I’ve found a dozen different answers....
> 
> 
> Sent from my iPhone using Tapatalk


That seems to be the standard in this trade. Get 10 electricians together, and get 10 different ways to do the exact same thing.


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## 847Videos (Dec 8, 2014)

joebanana said:


> That seems to be the standard in this trade. Get 10 electricians together, and get 10 different ways to do the exact same thing.


:vs_laugh::vs_laugh::vs_laugh:


Look at the thread, @Cow laid it out correctly


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## joebanana (Dec 21, 2010)

WronGun said:


> Today I went to the building where I got to enter the neighbors adjacent unit who has the same identical compressor unit. (Which is the reason he bought his)
> 
> Installed with 10awg thhn on a 40A breaker, it’s been running now for a year. Not sure if the installer was the same.
> 
> ...


So just for my own curiosity, did you put an amprobe on the circuit? How about a voltage reading at the load? My point being, you've got approx. 112' from the panel, what's the V/D?


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## micromind (Aug 11, 2007)

WronGun said:


> Today I went to the building where I got to enter the neighbors adjacent unit who has the same identical compressor unit. (Which is the reason he bought his)
> 
> Installed with 10awg thhn on a 40A breaker, it’s been running now for a year. Not sure if the installer was the same.
> 
> ...


Just because it works doesn't mean it's code compliant. 

On the other hand, because this installation works, it casts serious doubt on the validity of the code.......


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## splatz (May 23, 2015)

micromind said:


> Just because it works doesn't mean it's code compliant.


Very true. I also don't assume because it worked for someone, sometime, it will work for me, today. Motors are not perfect, it might work for that one but not another. 

If you do it to the letter / by the numbers, then if there's an issue it's not on you.


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## WronGun (Oct 18, 2013)

I agree, and that’s what I’m going to price it out for , but technically what can happen?

At the panel it’s Protected by a 30a breaker and right before the starter it’s Protected by a 30a fused disco. 

The worst that can happen? it trips...2 points of protection would need to fail..... just sayin.... 


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## jelhill (Nov 11, 2018)

WronGun said:


> We tested it today and it only trips as it get closer to full fill
> 
> 
> Sent from my iPhone using Tapatalk


I’m curious... did you have an amp meter on the #10 feeder (line side) when you were doing you start-up tests? What actual readings were you getting? Use the stop button on the meter and record 2 or 3 tries. In addition to you being under-sized with the #10 and 30/2 breaker.... you may have a weak breaker.


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## gpop (May 14, 2018)

just adjust the pressure switch down by 20 psi and call it good to go. 

Less psi = less load = less amps


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## jelhill (Nov 11, 2018)

gpop said:


> just adjust the pressure switch down by 20 psi and call it good to go.
> 
> Less psi = less load = less amps


Good point... I wonder if the customer even has a specific PSI requirement.


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## WronGun (Oct 18, 2013)

jelhill said:


> Good point... I wonder if the customer even has a specific PSI requirement.




It’s a very small excavation company , they are just using this to maintain the fleet 


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## jelhill (Nov 11, 2018)

WronGun said:


> It’s a very small excavation company , they are just using this to maintain the fleet
> 
> 
> Sent from my iPhone using Tapatalk


Then @gpop is right... try adjusting the pressure regulator.


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## jelhill (Nov 11, 2018)

WronGun said:


> I am a licensed electrician. *Didn’t know that the electrical license means you know every possible thing in the trade.* ...
> 
> This is in an industrial setting as I stated 208V
> 
> ...





:clap: :rockon:


You asked a very legitimate question, just look at all the (Positive) responses you got.


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## Wiresmith (Feb 9, 2013)

i don't have my code book with me but vfds require i think 125% wire ampacity of the vfd rating, and often you use a larger vfd than the motor for several reasons. i think in the code book in motor section it is under something like motor controlling equipment or something like that.

also the new motor may be tripping because its a different efficiency motor than the last. sounds like it had wrong wiring before though, just offering of why same spec motor and now it trips. ratings only mean so much, take current readings on the similar compressor that's running. it says right on it 31 amps.


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## sbrn33 (Mar 15, 2007)

This is a #8 on a 60 amp breaker all day long. I know you like to run with it on this site but just do it right and be done. 
I know you know what you are doing, but in this thread you definitely do not sound like it. You sound like a mechanic that just keeps replacing parts until it works. Hard to make money that way.


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## frenchelectrican (Mar 15, 2007)

sbrn33 said:


> This is a #8 on a 60 amp breaker all day long. I know you like to run with it on this site but just do it right and be done.
> I know you know what you are doing, but in this thread you definitely do not sound like it. You sound like a mechanic that just keeps replacing parts until it works. Hard to make money that way.


I agree with Sbrn and he did bring up couple very good points reguarding of the set up.
If I were you .,, I would rip the #10 chit out and run in correct size conductor and correct breaker size and be done with it and not have to worry about callback or other issue.

#10 on 208 with 30ish amp and ya are pushing the limit on voltage drop those compressor motor dont like too low a voltage so be aware of it.


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## 460 Delta (May 9, 2018)

If they have 208 VAC, I wonder why they didn't order a 3 phase motor? Is this by chance the same place that had the issue with smoking the Siemens starters?


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## WronGun (Oct 18, 2013)

460 Delta said:


> If they have 208 VAC, I wonder why they didn't order a 3 phase motor? Is this by chance the same place that had the issue with smoking the Siemens starters?




If they had reached out to me first , I would’ve advised them to go with 3-phase...

Same industrial building , different tenant. 

We replaced the starter on that job and also a new 3-phase compressor, all good. 

I dont know why people insist on keeping these pieces of equipment that date back to the 40’s 

we’ve been replacing some of the tenants really old compressors, all have been 3-phase. 

All the 3-phase units were installed correctly. These couple of single phase units are cutting it too close. 



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## WronGun (Oct 18, 2013)

Testing today shows the unit runs 22A -38A

Most of the running amperage is 22A-28A and rises up to 38A as it gets closer to full capacity. 

The startup when empty was 22A 

Fill is 200psi , after releasing down to 150psi the startup was 130Amps for approx 1/2 second. 

We cycled this 3 times with all the same readings and no trips. 

We did upsize the breaker to 40A to run the tests. 

The 30A dual element fuses on the disco right before the starter never blew. 

I reported my findings to the tenant with my recommendations. 

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## gpop (May 14, 2018)

200 psi for shop tools. snap-on man is going to be happy replacing seals. 

Most tools are rated at 90psi so everyone runs about 150 psi (will be about 90 while tool is running due to the restriction in the lines).


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## Jack Legg (Mar 12, 2014)

Tom Henry has a good format for overloads, branch ckt wire size, branch ckt overcurrent device, feeder wire size, feeder overcurrent device


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## Norcal (Mar 22, 2007)

WronGun said:


> Not to change the subject , but If we were to add a VFD to a motor would all the same calculations be applied to feed the VFD ?
> 
> 
> Sent from my iPhone using Tapatalk





The OP's motor is single phase.


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