Wiring and circuit breaker sizing

[Hex173t]

Hi, I’m looking for a check on my figuring.

2 or 3 questions (2 are related to each other)

I have a Lincoln 180 that I need an outlet for. It will be located where about 30 feet of wire will be needed to connect it from the CB panel to the outlet. The manual for the mig says that the standard voltage is 230v (I have about 220 measured, if it matters), input current at rated output (which is 130 amps output), is 20 amps. I’m not sure how many amps will be drawn at the advertised maximum of 180 amps out. The manual recommends a 40 amp Super Lag breaker.
I figure I need 8ga NM on the 40 amp breaker. Is this correct? Overkill?
And on the mig, if I should want to use it more than 6 or so feet away from the outlet, I would need an extension cord. A few calculators I’ve used suggest 10ga cord for up to 100 feet at rated amperage. Is this correct? Underkill?

Also, I have a compressor that I need to wire. It’s a 5HP IR, FLA 21.5, 230 volt 1 ph located about 40 feet of wiring away. NEC 430.248 says 5HP at 230V FLA is 28, but the dataplate on the motor says 21.5. I used 430.248/28 FLA. Per 430.22, multiplied 28 with 1.25 and came up with 35 amps, the minimum wiring size as 8ga NM. Breaker size 40. Is this correct? Overkill? A few other people I know ran wiring of 10ga and 30 amp breaker, but it looks to me that I need 8 and 40.
Thanks in advance.
Bill

 

[Aceman]

For your welder, it's possible #12 would work, but I couldn't tell you for sure without seeing the specs/duty cycle. I'd feel comfortable telling you #10 would definitely work on a 40 amp breaker though.

For your compressor, you have it right. #8 on a 40 amp breaker is the way to go.

 

[Dick in Wisconsin]

For your welder, it's possible #12 would work, but I couldn't tell you for sure without seeing the specs/duty cycle. I'd feel comfortable telling you #10 would definitely work on a 40 amp breaker though.

For your compressor, you have it right. #8 on a 40 amp breaker is the way to go.

Mr. Aceman: How much does the distance from the breaker come into play with the wire size?

 

[Aceman]

Mr. Aceman: How much does the distance from the breaker come into play with the wire size?

It takes a lot of distance at 240v to affect wire size. More distance than you would usually find in the typical garage.

 

[Oldbear]

I built a 35ft extension cord for my welder years ago. It's 10/3 (insulated, oil resistant) cord and I've never had any problems with it.

 

[jkeyser14]

For your welder, it's possible #12 would work, but I couldn't tell you for sure without seeing the specs/duty cycle. I'd feel comfortable telling you #10 would definitely work on a 40 amp breaker though.

For your compressor, you have it right. #8 on a 40 amp breaker is the way to go.

For your compressor, you have it right. #8 on a 40 amp breaker is the way to go.

I would disagree. Use #10 and a 30A breaker based on the motors nameplate rating. If you read 430.248 they have a disclaimer that they made assumptions about the torque curve of the motor. Per the NEC you are supposed to follow the manufacturer's information. If you were to go to a 40A breaker the circuit would be over sized and offer no protection.

I have a IR 5HP compressor (probably the same one) and it doesn't draw anything over 20A (most of the time it's closer to 16).

Side rant: the 5hp IR compressor is a piece of junk and I wish I never purchased it. IR's customer support is horrible and their warranty is a scam. For example, purchasing their maintenance kit was supposed to extend the product warranty out from one to two years. I had a problem just over 12 months from my purchase and was told that the extended warranty only covered problems with the pistons and piston rings (not stated anywhere in their advertising). They also wouldn't sell me a replacement start capacitor for the motor, they wanted to sell me a new motor for 80% of the cost of a brand new compressor. Several people have also had problems with these motors catching fire, so I always leave mine unplugged when it's unattended.

 

[Aceman]

I would disagree. Use #10 and a 30A breaker based on the motors nameplate rating. If you read 430.248 they have a disclaimer that they made assumptions about the torque curve of the motor. Per the NEC you are supposed to follow the manufacturer's information. If you were to go to a 40A breaker the circuit would be over sized and offer no protection.

NEC articles aside, please show me some manufacturer documentation stating a 40 amp breaker is oversized for this motor.

 

[hidollartoys]

I would disagree. Use #10 and a 30A breaker based on the motors nameplate rating. If you read 430.248 they have a disclaimer that they made assumptions about the torque curve of the motor. Per the NEC you are supposed to follow the manufacturer's information. If you were to go to a 40A breaker the circuit would be over sized and offer no protection.

I dont understand why so many code spewing card carrying electricians continually disregard the NEC motor circuit sizing requirements.

 

[sberry]

Get some 10, use a 30 for the welder a 30 for the comp unless it tripped, I have one the same class,,, never an issue..
The guys at Lincoln were sniffing the circuit board glue when they came up with that for that machine. Its competitors allow a 14 wire @ 35 and if it is 12 or better can be breakered at 50. They must have just copied and paste that brain fart for last 20+ years. A 250 class by same mfg allows for a 10 min wire,,ha

As for the comp seems I read it as,,,, if the name plate is not available then you need to use that formula,, in this case you know its 21A, no mystery. 1000's of these wired this way, pass inspections every day.

 

[hammerandhand]

-Use #8 wire for 40 amp circuits. Use a #8 extension cord, and only as long as needed. Avoid extra length whenever possible.
-If the data plate on the motor says 21.5 amps, then use #10 wire and a 30 amp circuit

 

[sberry]

This machine will run on 100 ft of 12 and the operator will not be able to tell the difference. No need to worry about distance and V drop,,, in this case it is a great learning tool but in practice mental ************. An 8 would run 2 of these at the same time.

 

[sparky36000]

I would disagree. Use #10 and a 30A breaker based on the motors nameplate rating. If you read 430.248 they have a disclaimer that they made assumptions about the torque curve of the motor. Per the NEC you are supposed to follow the manufacturer's information. If you were to go to a 40A breaker the circuit would be over sized and offer no protection.

I dont understand why so many code spewing card carrying electricians continually disregard the NEC motor circuit sizing requirements.

NEC 403.6(A)(1) requires that motor circuit conductors are to be based on NEC table values based on motor nameplate HP. BUT, exception #3 states that motor operated appliances be sized according to nameplate values, which would be the case here.

Conductors for individual motors are never sized based on nameplate values. Code table values take into account worse case, if the motor is ever changed for a motor with same HP rating but slightly different running characteristics. Nameplate current is only used to size overload protection if external overloads need to be used (overload heaters in a motor starter).

 

[sberry]

Good explanation.

 

[hidollartoys]

Sparky, I was using the first part of my post from jkeyser's post, which I believe is wrong advice. I agree with you .

The last statement in my post was my take on how NEC motor circuit sizing is SO misunderstood, even by most "electricians".

 

[sparky36000]

Sparky, I was using the first part of my post from jkeyser's post, which I believe is wrong advice. I agree with you .

The last statement in my post was my take on how NEC motor circuit sizing is SO misunderstood, even by most "electricians".

I wasn't trying to correct you, just trying to clarify. I agree that motor circuit sizing is very misunderstood. I'm an electrician and an IBEW apprentice instructor, and I get a lot of "deer in the headlights" stares from my apprentices when we start going over motor calculations. By the time we get through it, most of them are better at it than I am though

 

[hidollartoys]

Sparky, As an apprentice instructor you probably have a better understanding of the code than most.

I was not jumping on, but wanted to clarify my position. I am an IBEW electrician (master license) who works in a heavy industrial enviroment where we deal with this sort of thing all the time. Our facility is over 75 years old and we are constantly upgrading equipment and assoicated wiring daily.

Thanks for your input and trust we will exchange view points again.

Mike

 

[Hex173t]

Thanks to all who replied.

I’ve been looking into this for some time, I thought I had it covered. But it’s been bothering me, that everyone else that has a similar sized motor wired with 10ga and that the hook up terminals in the switch box (terminology correct?) looked too small for 8ga. And that the motor said what the FLA is, and using that number would allow me use of 10ga, where I’d match what I’ve seen on other’s installation.

I missed exception 3.

430.6 (A)(1) Exception No. 3: For a listed motor-operated appliance that is marked with both motor horsepower and full-load current, the motor full-load current marked on the nameplate of the appliance shall be used instead of the horsepower rating on the appliance nameplate to determine the ampacity or rating of the disconnecting means, the branch-circuit conductors, the controller, the branch-circuit short-circuit and ground-fault protection, and any separate overload protection.

There is a ‘listed’ mark on the motor, RU, where the R is backwards. It seems this is used on components of larger assemblies per UL.com. So, the motor is listed, exception 3 applies, I’m to use the lower 21.5 FLA, and 125% puts me under 30 amps, 10ga wire, 30 amp breaker.

Thanks again for all the advice,

Bill

 

[hidollartoys]

Bill, you should check Article 100 "Definitions" for the description on an "appliance". I do not believe, nor would I consider an air compressor as being an appliance no more than I would consider a welder an appliance.

 

[sberry]

Id does say feeder rating,,, but at any rate this is a place a little common sense may be sufficient.. the thing pulls 21A, dont lose sleep over it.

 

[sberry]

Heck, the thing would run on a 12 and one would never know it.

 

[Aceman]

Sberry, there's a difference between doing it right and good enough. And a difference between what you do at your own place versus what advice you give others. You're fine with good enough, that's obvious. But, you shouldn't be surprised the professional electricians on here are recommending the code compliant way.

Since he's doing this from scratch, there isn't wire already in the walls, why shouldn't a guy do it the right way to begin with?

On a sidenote, I disagree with using Exc. 3 for an air compressor. I don't think the codes definition of an appliance was intended to be used on air compressors, so I stand by my original post of #8 and a 40 amp breaker.

I have yet to see any documentation on a 40 amp breaker being oversized by Jkeyser14......

 

[pattenp]

Hex173t, does the motor data plate have 5HP on it, or does the compressor branding label have 5HP on it. My opinion is if it's just the compressor brand label that has 5HP on, I'd use the FLA of 21.5 off the motor and go with a 30A circuit.

I agree with Aceman on the 40A if the motor is actually marked as a 5HP. In any case the 40A is not over sized because the breaker is sized to protect the circuit not the device. The compressor motor should have its own thermal overload protection. Okay... I'm ready. Pile on.

 

[Hex173t]

Pattenp,

The motor dataplate says 5HP, and also 21.5 FLA. Solution: 1 leg with 8, the other with 10. Kidding only

Bill

 

[madosta]

1 leg with 8...

I read that as 1 keg with 8 guys...

Work *****.

 

[Highbeam]

I've also been taught that the breaker protects the wire. If you oversize to a 40 amp for the compressor then no problem and you are ready for an even larger compressor someday.

 

[hidollartoys]

I've also been taught that the breaker protects the wire. If you oversize to a 40 amp for the compressor then no problem and you are ready for an even larger compressor someday.

Article 240 does not apply when sizing OCP for motor circuits.

Here is the correct NEC way to size a motor circuit:
1. Determine fullload current.. Taken from Table Amps tables (not nameplate)
2. Determine overload heaters.. Taken from Nameplate X % from 430.32(a)(1)
3. Determine branch circuit wire size.. 125% X Table amps
4. Determine branch circuit ocp.. table amps X % from 430.52 (next size up)

There are some variances but this the correct NEC way to size and wire a motor branch circuit.