Powering 7.5hp Air Compressor

[Vamirr]

I'm on the tail end of a huge shop power upgrade and need some assistance on wiring my air compressor. The compressor is a 80 gallon, single phase 230v, 7.5HP North Star unit from Northern Tool. It comes with a prewired Eaton motor starter, I just need to connect it to my electrical service.

When my electrician completely reran the shop service, he ran me a direct line from the panel breaker to the starter box. He was hesitant to hook the compressor up as he'd never connected a motor starter before and wasn't too sure where to connect the power based on the directions.

From my searching, I haven't seen anyone with a setup identical to mine. I have four wires going to the box (two hots, a neutral, and a ground). It looks like I should be installing one hot wire to L1 and one hot wire to L2. I'm not sure what I should be doing with the neutral wire and the bare copper ground wire.

In similar photos I've seen on here, the neutral wire is wired into a ground bus similar to what exists in the bottom left hand side of my starter enclosure, however, most of those setups didn't have the "L3" like mine shows.


Directions:
View media item 59406
Motor Starter:
View media item 59409

 

[sld961]

The ground gets connected with the green wires. It looks like L3 is jumped from L2 in figure 12. Figure 11 looks like you just hook up both of the hots. If there is nothing that needs 120v, you shouldn't need the neutral wire.

 

[sld961]

Do you have a zoomed out pic of the box, so we can see where the wires go?

 

[Vamirr]

Here's a zoomed out pic. You can't really see where stuff is going though. I'll run out and take a few more.

View media item 59411

 

[sld961]

Looks like the wires coming in at top left are from pressure switch. Top right goes out to motor. Looks like you connect both hots to L1 and L2 on the top block.

 

[pattenp]

The 2 hots (red & black) connect to L1 & L2. The bare copper goes to the ground lug on the starter case. The white is unused and is capped off with a wirenut.

Your wire looks like Romex which is a bad choice for pulling in LFNC conduit. Should have used individual THHN conductors.

 

[wyliesdiesels]

The neutral wire is a waste/not needed and as said above u shouldve used THHN! Neutral and ground should NEVER be combined on the same bus except in the main service panel.

It looks like the manu used white instead of red for the second hot leg.

The manu. used a 3 phase starter on a single phase motor. Since u have solid state overload with phase loss protection the middle L2 leg needs to go through L3 otherwise the phase loss relay will open the coil circuit.

Heres how to wire circuits for compressors and other motor powered equipment:

Wire is sized @ 125% of NEC table FLC. This is different than motor nameplate FLA...

For 7.5HP, which has a 40a FLC, u need 50a rated wire. 125% * 40a = 50a.

This means #8 THHN or #6 NM-b(which should only go to a j box on the wall then be spliced into THHN)

A local disconnect is required if the compressor is farther than 50' from the electrical panel and not within sight.

 

[Vamirr]

Thank you all very much for your responses.

I wired the compressor as suggested with the hot wires going to L1 and L2, and the ground going to the lug on the case and removed the neutral. The compressor is operating as expected.

With regards to the cable, the electrician used 6/3 romex; the same he used for the 50A outlets for my welders. The compressor is approximately 3 feet from the service panel.

Is there something inherently wrong with using this cable for this purpose? In other words, as someone who isn't particularly knowledgeable in this area, what should I tell him with regards to having used the wrong cable? Should he have used something else for my welding outlets?

 

[sld961]

The reason you don't want to use romex in conduit is that it is essentially double insulated. Once by the wire insulation and then again by the conduit. This can lead to overheating in the wires. I'm not an electrician, but if it's only 3ft ft, I wouldn't be worried. THHN should have been used in the conduit, which is individual wires, not "bundled" together like romex.

 

[Astro-t]

Bring your romex to a jb on the wall and from there to the compressor. You can than strip the jacket off.

 

[pattenp]

Bring your romex to a jb on the wall and from there to the compressor. You can than strip the jacket off.

That's a NEC violation. If using NM the sheath is to extend through the conduit and a minimum of 1/4" into the device box. 314.17(C)

 

[Astro-t]

He has to enter the JB with a connector! He can strip the jacket off inside the JB enter the lfnc via the JB. I dont know what the violation is?

 

[wyliesdiesels]

He has to enter the JB with a connector! He can strip the jacket off inside the JB enter the lfnc via the JB. I dont know what the violation is?

U cant use the individual conductors in NM-b wire in conduit because the conductors are not individually marked.

 

[Astro-t]

U cant use the individual conductors in NM-b wire in conduit because the conductors are not individually marked.

He is using black and red? Marked with what?

 

[pattenp]

You are not to strip off the jacket of NM when placing it in conduit. You are to strip it only within boxes at connection points.

 

[sberry]

While that is accurate it's not something to lose sleep over in this case.

 

[sberry]

He is using black and red? Marked with what?

The wire needs to be marked every couple feet. They don't want someone picking up auto wire or to date it for code changes etc.

 

[Astro-t]

The wire needs to be marked every couple feet. They don't want someone picking up auto wire or to date it for code changes etc.

Ok! I must have be done this a million times in the last 28 years wrong! LOL!

 

[sberry]

I am not sure what the mark system is for individuals is, I am sure someone here knows details but as example with cable there is a color/label system tells when it was made, pretty much tells what code it was installed under.

 

[Astro-t]

Hopefully this is a residential garage not a commercial garage.The wiring methods change. He should have a disconnecting means if its not with in site of the breaker.

 

[pattenp]

Just trying to educate here and not nitpick, but if the liquid tight conduit is 3/4 inch it may be too small because of fill limits for the 6/3 Romex. You use the widest dimension of Romex to determine the fill area.

 

[wyliesdiesels]

He is using black and red? Marked with what?

Ok! I must have be done this a million times in the last 28 years wrong! LOL!

I am not sure what the mark system is for individuals is, I am sure someone here knows details but as example with cable there is a color/label system tells when it was made, pretty much tells what code it was installed under.

Individual conductors have a marking that identifies, among other things, the gauge, voltage rating, insulation type and manufacturer. See the examples below.

The individual conductors in NM-b aka Romex are NOT marked in this regard. Only the outer jacket is marked.

 

[CNGsaves]

For 3 ft, I'd rip it out and Do It Right !!

WyliesDiesel and PattenP will set you straight OP if you want step-by-step.

Nice compressor by the way. Do you have airline system all setup ?? Pics ??

 

[sberry]

I realize that are marked, what changes do they make when they upgrade?

 

[Astro-t]

Individual conductors have a marking that identifies, among other things, the gauge, voltage rating, insulation type and manufacturer. See the examples below.

The individual conductors in NM-b aka Romex are NOT marked in this regard. Only the outer jacket is marked.

If the jacket is marked whats inside they dont have to mark the wire. Your are nut case I`m out!!!!!!

 

[monkeyman1]

Several accurate NEC statements made. None of which I would be concerned with.


Sent from my iPhone 6 Plus purchased selling eggs.

 

[Norcal]

Several accurate NEC statements made. None of which I would be concerned with.


Sent from my iPhone 6 Plus purchased selling eggs.

Then I hope your electrical work does not go beyond operating light switches & inserting attachment plugs into receptacles.

 

[wyliesdiesels]

If the jacket is marked whats inside they dont have to mark the wire. Your are nut case I`m out!!!!!!

Nice ad-hominem.

I could care less what u think of me. Youre obviously a hack.

Using NM-b conductors that are unmarked, without the jacket is a clear NEC violation!

But continue right along with your crappy work!

 

[monkeyman1]

Then I hope your electrical work does not go beyond operating light switches & inserting attachment plugs into receptacles.

My electrical work is an engineering company department manager for IE&A design and I've been in the business for over 25 years.

Go back to Kalifornia where they can't pass gas without a license to do so.


Sent from my iPhone 6 Plus purchased selling eggs.

 

[LS6 Tommy]

Black to L1. Red to L2. Copper to ground lug. No need for N. Cap it off.
I politely suggest getting a different electrician if he runs the wrong type of cable with more conductors than you need and says he has never fed a starter before...


The NEC is nation wide. It doesn't change from one state to another.


Tommy

 

[Norcal]

Black to L1. Red to L2. Copper to ground lug. No need for N. Cap it off.
I politely suggest getting a different electrician if he runs the wrong type of cable with more conductors than you need and says he has never fed a starter before...


The NEC is nation wide. It doesn't change from one state to another.


Tommy

Some people have only done residential & other then the shops like here on GJ, starters are rare, but if they can't figure it out with the provided documentation it does raise a huge red flag.

 

[sberry]

The code is all there for very good reason, some minor violations here and minor being the word, compared to other stuff we see like the same comp running 18 years on a 12 wire.
My guess would be a maintenance electrician moonlighting, many have a good general concept but are a long ways from knowing all the details to residential installs. Nothing in this is going to burn the place down.

 

[sberry]

My question and I spose I would have to look but in the pic above we see a green wire with black letter,,,,,, would the letter color be different with a change? Or add a suffix to the rating?
I was in a building the other day, had about 5 flavors of NM thru nm-b

 

[LS6 Tommy]

Some people have only done residential & other then the shops like here on GJ, starters are rare, but if they can't figure it out with the provided documentation it does raise a huge red flag.

Well said. That's basically what I meant.

Tommy

 

[wyliesdiesels]

My electrical work is an engineering company department manager for IE&A design and I've been in the business for over 25 years.

Go back to Kalifornia where they can't pass gas without a license to do so.


Sent from my iPhone 6 Plus purchased selling eggs.

Engineers!

Well that explains it all!

 

[Norcal]

Engineers!

Well that explains it all!

I typed a reply but chose not to post it.

 

[sberry]

I got a lot of respect for engineers, most of them are way sharper than I am. It may have got more complicated than it needed to be but look at all of the over current methods and design that wouldn't even occur to most people that didn't study it.
Look how many smart people jump when they see a breaker larger than a 30 on a 10.
I elude to this in other threads where so much is a judgement/economics call and while it seems we study and research more are confused than when started.
This was where I got my **** in a ringer in another thread, we assume cause we study if for a bit till our eyes bleed we are being effective and not always so. Most love confusion as it makes it easier to up sell.
We forget about working on the principle and are always starting out with,,, whats the best usually followed by,,, I didn't want to spend that much. We assume because we did work it has a benefit, because we spent we got for it.
It isn't the question is poor but often the answers are opinions based on opinion and not on fact. We want validation we made the right choice.
Its technically correct there are a couple issues with this, none of them in this 3 ft chunk of wire going to create a danger in this installation. It would be similar to needing a cable staple every 18 inches in an old basement, should one go back and do it all over because a couple of them are 20 or 24 inches.

 

[sberry]

As far as I see this looks pretty fair. They used a big wire, got connectors and where there was a real issue they stopped and got advice. Showed some pics. There would have only been minor losses and a spike in safety numbers with a cable 3 sizes smaller, a lot to do with duty cycle.

 

[LS6 Tommy]

I typed a reply but chose not to post it.

I did the same thing. I don't wish to inadvertently start flaming people...

Tommy

 

[monkeyman1]

Engineers!



Well that explains it all!

Flame away. I was a licensed electrician for 12 years before my current job. DCS to 138KV protective relaying to fiber optics. Been there done that. I've forgotten more than some of you guys will ever know.


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