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Compressor outlet? box?

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ynned

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I'm getting ready to (finally) close up walls in my garage, and I'm going to drop a 30A 240V line for future compressor. My question is what is a good way to terminate it? I have a regular plastic outlet box at the location, and it will be a dedicated service, but the small box sure seems in adequate. maybe a 2 gang? it will be a PITA to replace the box when I get the compressor, but not impossible.

Edit: This switch looks like it will fit in a regular box.
 
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Angelfire

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I went with a 4" square metal box for all of my 240V circuits (9 in total) and then used mud rings that left the opening like a single gang. Something like this:

https://www.homedepot.com/p/4-in-Square-Single-Device-Mud-Ring-Raised-1-1-4-in-8775/100686459

They have different heights of the mud ring to accommodate whatever material you are covering them up with (in my case, 1/2" drywall so used a 1/2" raised ring).

This will give you more room to stuff the wires in plus I like the added rigidity offered by the metal boxes vs. plastic.
Cheers
 
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ynned

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Bert_ said:
A lot of guys are after 5hp or so compressors. That takes 8 romex
Click to expand...

Ah. I looked at some compressors which I'd like, and their ratings ranged from about 17 to 22 amps. I know I had a Craftsman which called itself 5 HP, and it ran on 110v 15a. HP is lied about a lot, especially with compressors. I didn't even pay attention to rated hp when I looked. I also had for a while a huge 3
phase 120 gal or so, which had two pumps each driven by a 3/4 HP motor. So I see no correlation.
 
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rpcraft

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My builder used a single gang on my compressor outlet. Right now it has a 110 outlet on out and only running one of the legs on it but when it comes time to convert it I'm definitely going to rip it off and replace it with a 2 gang. The thought of trying to stuff a 240 plug in there with the wire... Yeesh, it was a huge PITA on my welder circuit. I really do not want to repeat that, I only managed to shave off half of one finger nail, lol.
 
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Angelfire

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alfredeneuman said:
The proper ring for 1/2" drywall is 5/8". The 8-32 screw heads in the corners of the box, because they're exposed after installation, spaces the box back another 1/8" from the drywall.
Click to expand...

I'd have to go look to see exactly what I used to be honest.....it's been awhile. Didn't have anything standing proud and no gaps below the surface so I must have used the proper size.
 
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wyliesdiesels

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ynned said:
I'm getting ready to (finally) close up walls in my garage, and I'm going to drop a 30A 240V line for future compressor. My question is what is a good way to terminate it? I have a regular plastic outlet box at the location, and it will be a dedicated service, but the small box sure seems in adequate. maybe a 2 gang? it will be a PITA to replace the box when I get the compressor, but not impossible.

Edit: This switch looks like it will fit in a regular box.
Click to expand...

Before you get too far into planning, you need to know the HP rating on the comp. If rated more than 3HP then it needs to be hardwired. cannot use an outlet

ynned said:
Why #8? 30a calls for 10 ga.
Click to expand...

depends on HP.

jproaster said:
Oops. I ran 10 wire for my quincy qt 54; it's not hooked up yet. Do I need 8?
Click to expand...

Is it 5HP? if so then yes.

bochnak said:
Wire size should be 125% of the motor FLA. Since you don't have the compressor yet, you don't know the FLA.

My 5hp is about 22-23 FLA, so 30A / #10 wire works just fine.

I used this Bryant 30002D switch:
https://www.automationdirect.com/ad...ntrollers_-z-_disconnects_(30-60_amps)/30002d
Click to expand...

wire is sized based on HP and FLC table in NEC NOT FLA on nameplate.
 
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matt_i

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IIRC there are two 4" square boxes, either a 2-1/8" deep or a 1-1/2" deep. I always opt for the deeper one.
 
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ynned

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Just to close the thread, I ended up with a 10 wire ending in a 4" sq box. Compressor choice will obviously depend on that. Thanks for the input.
Edit: Sorry, on a 30 a breaker.
 
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Bert_

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I wonder if the Full Load Current tables will ever get updated. I don't think you can buy a 5hp motor that pulls 28A anymore. 90% of them are around 22-24A, lowest I've seen is some new Baldors that list 19A for a 5hp "industrial duty" motor.
 
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shaggyant

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wyliesdiesels said:
wire is sized based on HP and FLC table in NEC NOT FLA on nameplate.
Click to expand...

Horsepower ratings these days are mostly marketing ****. When cruising Home Depot I saw this shop vac and I wondered how this could possibly work. The NEC tables would have me running 8 gauge for a vacuum cleaner.

https://www.homedepot.com/p/Ridgid-4-Gal-5-0-Peak-HP-Portable-Wet-Dry-Vacuum-WD4070/202077241

Bert_ said:
I wonder if the Full Load Current tables will ever get updated. I don't think you can buy a 5hp motor that pulls 28A anymore. 90% of them are around 22-24A, lowest I've seen is some new Baldors that list 19A for a 5hp "industrial duty" motor.
Click to expand...

I know. I keep seeing the “5hp SPL” spec on these compressor nameplates followed by a 15 FLA. it just doesn’t compute based on a watts to horsepower conversion.

https://www.amazon.com/dp/B0009WET9M/?tag=atomicindus08-20
 
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wyliesdiesels

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shaggyant said:
Horsepower ratings these days are mostly marketing ****. When cruising Home Depot I saw this shop vac and I wondered how this could possibly work. The NEC tables would have me running 8 gauge for a vacuum cleaner.

https://www.homedepot.com/p/Ridgid-4-Gal-5-0-Peak-HP-Portable-Wet-Dry-Vacuum-WD4070/202077241



I know. I keep seeing the “5hp SPL” spec on these compressor nameplates followed by a 15 FLA. it just doesn’t compute based on a watts to horsepower conversion.

https://www.amazon.com/dp/B0009WET9M/?tag=atomicindus08-20
Click to expand...

regardless of inflated HP numbers, that is the code permissible way of sizing wire for motor circuit.
 
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Bert_

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shaggyant said:
Horsepower ratings these days are mostly marketing ****. When cruising Home Depot I saw this shop vac and I wondered how this could possibly work. The NEC tables would have me running 8 gauge for a vacuum cleaner.

https://www.homedepot.com/p/Ridgid-...mazon.com/dp/B0009WET9M/?tag=atomicindus08-20
Click to expand...

Not what I'm talking about. Even real 5hp motors don't draw what the nec table says. Most of the 5 hp motors I've seen made in the last 30 years are 24a or less. Baldor is now making REAL 5 hp single phase motors that draw 19A.

I understand the tables are supposed to be a worst case scenario so that the wiring will be large enough for any 5hp motor installed. The tables seem to be based off motors that haven't been produced in decades.
 
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sberry

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My steamer has 5 that is heavy duty, pulls 22 and comes factory cord 10;30 and simply calls for a 30A circuit I believe. As I recall Sears had a comp, 2 stage, vertical, the biggest cheap one they made at the time,,,, as I recall it may have had a 28 Marathon motor on it.
 
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sberry

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Bert_ said:
Not what I'm talking about. Even real 5hp motors don't draw what the nec table says. Most of the 5 hp motors I've seen made in the last 30 years are 24a or less. Baldor is now making REAL 5 hp single phase motors that draw 19A.

I understand the tables are supposed to be a worst case scenario so that the wiring will be large enough for any 5hp motor installed. The tables seem to be based off motors that haven't been produced in decades.
Click to expand...

I don't panic when I see these wired on a 10 cable 30 circuit. Code was written when voltage was 220 and motors pulled near 6 amps per hp. I got a 3 rated 18 I think.
 
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wyliesdiesels

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Bert_ said:
Not what I'm talking about. Even real 5hp motors don't draw what the nec table says. Most of the 5 hp motors I've seen made in the last 30 years are 24a or less. Baldor is now making REAL 5 hp single phase motors that draw 19A.

I understand the tables are supposed to be a worst case scenario so that the wiring will be large enough for any 5hp motor installed. The tables seem to be based off motors that haven't been produced in decades.
Click to expand...

yes ive often wondered about that.

Seems motors have gotten more and more efficient but NEC code on FLC tables have not been updated.
 
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bochnak

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wyliesdiesels said:
Before you get too far into planning, you need to know the HP rating on the comp. If rated more than 3HP then it needs to be hardwired. cannot use an outlet



depends on HP.



Is it 5HP? if so then yes.



wire is sized based on HP and FLC table in NEC NOT FLA on nameplate.
Click to expand...

I must have misread/interpreted the NEC book, then. I thought it was namplate OR table. So I ended up with #10 and 30A breaker and it is running fine.
 
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sberry

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I had a couple buds were big city fire investigators and had a chance to ask at a convention class about undersized wire. No one could remember attributing fires to small comp or welder wire, all kinds of other stuff using them and it was mostly small electric heaters and such and people fooling with fuses.
We had one on here where the guy asked if the 12 that had been on their 7.5 for 18 years was right. Evidently the Dad had the "electrician" from work wire it up. One has to wonder how many of these are out there?
I see 10/30 and don't hear much about tripped breakers either. I have a 5 on 30 I installed way back in the day, has ran fine. The only trips I have ever had have been a 30 on a walk in cooler and a 20 on my 3 hp well I changed out to 30
 
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ynned

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ynned said:
Just to close the thread, I ended up with a 10 wire ending in a 4" sq box. Compressor choice will obviously depend on that. Thanks for the input.
Edit: Sorry, on a 30 a breaker.
Click to expand...

Bought this compressor. It comes equipped with a NEMA 6-20 plug on a 14 ga cord. This plug has only 3 prongs, and the corresponding outlet (which I've already bought and have on hand) has 3 connections, 2 gold and a green. I've been led to believe that the proper way to connect the outlet is to connect both hot legs (red and black) to the gold screws, and the bare (ground) to green, leaving the neutral (white) unconnected. Is this correct?

Also, as I said, the supplied cord is 14 ga, even though the owner's manual says the draw is 15.7 A. I think a 20 A breaker should be used, but if memory serves, 14ga wire is only supposed to carry 15A. Should I install the 20 A breaker?

attached is a pic of the motor plate, and the spec table from the owner's manual.

TIA
 

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sberry

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The motor has its own thermal on it. The kicker here is the plug. In this case cant put too small a wire on the recept and a breaker has to match. Its factory approved. If it didn't come plug it may be able to be wired to a 30 circuit.
 
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