Is this compressor plug acceptable?

[bullnerd]

I hate to ask another compressor wiring question because they usually don't end well, but...I just bought a used compressor and would like to hook it up temporarily right next to the breaker panel.

This is the plug it was run on for the last ten years.

Can I just install a nema l6-20 receptacle and plug it in?

Breaker size and wire size recommendations?

Thanks guys.

 

[pattenp]

Yes. 20A 2pole breaker on #12 Cu wire.

 

[brewchief]

I'll say no, 2.98 KW is 3.99 horse power, that would require a plug that's horsepower rated that high which will be pin and sleeve style and$$$, the alternative is to hardwire it.

Sent from my SM-G965U using Tapatalk

 

[mattblast]

The plug will work fine for running the compressor but it is not up to code. The reason it fails code is because a plug is technically a disconnect and unplugging this type of plug while the motor is running will cause an arc an the plug may not separate from the receptacle.

So though it would not pass an electrical inspection, it is not necessarily unsafe. It can take the current with the motor running just don’t use it as a disconnect.

 

[bullnerd]

OK, thanks guys. Like I said, it will be temporary until I move it to its permanent location.

I can hard wire/shut off it when I do.

 

[mike93lx]

I'll say no, 2.98 KW is 3.99 horse power, that would require a plug that's horsepower rated that high which will be pin and sleeve style and$$$, the alternative is to hardwire it.

Sent from my SM-G965U using Tapatalk

Yes, year 11 is when it burns down

 

[American Locomotive]

Most 6L-20 plugs are rated for 2HP, but it's a little unclear what you actually have. Tag says 5HP. Motor nameplate says 4HP, amps suggest more like ~3 HP.

What an odd compressor.

Based on the 3HP rating, a 6L-20 would not be appropriate to meet NEC guidelines. But, many people do exactly what you plan to do without issue. The plug will handle the power just fine, but should not be used to disconnect the motor while running.

 

[bullnerd]

Yes, year 11 is when it burns down

I had to buy this one because my shop burned down with my compressor in it.

Most 6L-20 plugs are rated for 2HP, but it's a little unclear what you actually have. Tag says 5HP. Motor nameplate says 4HP, amps suggest more like ~3 HP.

What an odd compressor.

Based on the 3HP rating, a 6L-20 would not be appropriate to meet NEC guidelines. But, many people do exactly what you plan to do without issue. The plug will handle the power just fine, but should not be used to disconnect the motor while running.

Stock Speed-aire .

BTW, is it common to unplug a compressor while its running?

 

[American Locomotive]

BTW, is it common to unplug a compressor while its running?

The idea is that since plugs are removable, they should be rated to be disconnected and connected under full load. Motors have very high inrush currents that making connecting them live tricky. A lot of magnetic/electric shenanigans occurs when you suddenly cut the power to an electromagnet (which a motor is), which makes disconnecting them under load tricky.

Basically manufacturers won't rate a 6L-20 as being "safe and reliable" for connecting/disconnecting a 3+ HP motor under load.

 

[pattenp]

Sorry I misread the data on the motor. I thought it was around 2hp. Was using my cell phone.

 

[wyliesdiesels]

Most 6L-20 plugs are rated for 2HP, but it's a little unclear what you actually have. Tag says 5HP. Motor nameplate says 4HP, amps suggest more like ~3 HP.

What an odd compressor.

Based on the 3HP rating, a 6L-20 would not be appropriate to meet NEC guidelines. But, many people do exactly what you plan to do without issue. The plug will handle the power just fine, but should not be used to disconnect the motor while running.

agreed. its got at least 3 different ratings for HP based on the dataplates

 

[bullnerd]

The idea is that since plugs are removable, they should be rated to be disconnected and connected under full load. Motors have very high inrush currents that making connecting them live tricky. A lot of magnetic/electric shenanigans occurs when you suddenly cut the power to an electromagnet (which a motor is), which makes disconnecting them under load tricky.

Basically manufacturers won't rate a 6L-20 as being "safe and reliable" for connecting/disconnecting a 3+ HP motor under load.

Ok, thanks. I never even considered pulling a plug on a running tool. Maybe if its on fire I guess I would, or to prevent harm, but at that point...

Sorry I misread the data on the motor. I thought it was around 2hp. Was using my cell phone.

Now what am I going to do, I was going with your first suggestion because I have 12 wire.lol!

agreed. its got at least 3 different ratings for HP based on the dataplates

I don't know, its a stock SPeed-aire and the company I bought it from never changed anything and it was serviced by a compressor company.

How about if you just go by the motor tag?

Do electricians ever agree on anything? lol! What if you guys are on a job and there are five different electricians, what do you do?

 

[American Locomotive]

I don't know, its a stock SPeed-aire and the company I bought it from never changed anything and it was serviced by a compressor company.

How about if you just go by the motor tag?

The problem is the motor tag still doesn't make sense. The HP listing says 2.98KW, which is 4HP, but tag also says 15A, which is a little low for an old 4HP motor. I would be expecting closer to 18-19A at 4HP.

If it were a brand new NEMA Premium high efficiency motor, it may be possible for it to be 4HP @ 15A.

Either way, since the nameplate says 4HP, you technically have to size everything as a 4HP motor.

 

[KenC]

I'm no expert but have owned several of those 'fake hp rated' compressors. They all used the same 56frame motor with a 15A rating. The motor tags usually say 'SPL' in the HP area. The motor maker would not mis-rate the motor, but the compressor maker would label the unit as a 5HP. Looks to me like this motor supplier use wattage in the HP area and likely used a current figure that is probably start current, which is what the compressor makers used to do. That has now been banned.

All the '5hp' units I saw in the past came with a 15a, 250v plug. This one has been changed to a twistlock by the end user I'll bet.

 

[mm08822]

I'm no expert but have owned several of those 'fake hp rated' compressors. They all used the same 56frame motor with a 15A rating. The motor tags usually say 'SPL' in the HP area. The motor maker would not mis-rate the motor, but the compressor maker would label the unit as a 5HP. Looks to me like this motor supplier use wattage in the HP area and likely used a current figure that is probably start current, which is what the compressor makers used to do. That has now been banned.

All the '5hp' units I saw in the past came with a 15a, 250v plug. This one has been changed to a twistlock by the end user I'll bet.

Since FLA’s and a KW value were provided on the motor nameplate, I see it as the motor is 86% efficient = 2980 watts/(230VAC x 15A).

Starting current would be much higher - typically 5-7x FLA’s.

Mfr’s reportedly used available starting torque to come up with the inflated HP values (or HP when in full SF mode) which are intermittent values and not continuous hp ratings that general purpose motors commonly use.

Seeing the SF @ 1.0 and Insulation @ Class B, the 230x 15 = 3450/746 w/hp = 4.6Hp input (not output). The compressor mfr darlings probably also rounded 4.6 up to 5 HP to help all consumers not think so hard.

Seems like this is still the practice today.

 

[pattenp]

With all this back and forth about what size motor it is, if it's been on a 20A circuit for the last ten years with no issues obviously the amp load is not too much for the 20A circuit. One of the safety problems in the eyes of the NEC is the plug is the disconnect and should be rated for the HP of the motor so when disconnected under load it won't shoot sparks in your face. Just based on a judgement call I'd have no problem running it on a 20A circuit using the L6-20 plug in your first post.

 

[mm08822]

Agreed, if this compressor came with a factory cord and plug and the instructions required it be plugged into a 20A 120VAC ckt that would be the end of it. Never looked at again – no concern for HP (real or otherwise).

 

[bullnerd]

Thanks guys.

This compressor was a backup for a small eyeglass grinding company that had a screw type for the main air supply. This only ran when the screw was under maintenance.

They bought a new screw compressor and it came with a new version of this same compressor.