5hp 230v 80 gal compressor wiring

[LT5 John]

I need a little help. In my garage I have a small sub-panel that has a 50A breaker, and a 30A breaker...The sub-panel is fed from my main garage that's 60' away. There is a 4 prong receptacle for a welder which I don't use. So, I wanted to take the receptacle out, and wire directly into the receptacle where the welder plug was...Now, can I leave the 50A breaker there for the 5HP 230 V compressor. The amp draw as far as the specs on what I have read draws 28 amps...I was going to leave the 50A breaker and go with 10 THHN wire. Where the 4 wire in the receptacle is, just cap off the white neutral...I want to leave the existing 30A breaker there for my small compressor. Just switch that breaker off when using the 50A. Is the 50A breaker to big?, or do I change that to a 40A to feed the new compressor? Or, do leave the 50A breaker and run # 8 wire? I did a search, but there is so many contradicting opinions...

 

[pattenp]

I got lost a little with your post but I try to answer what I think you're asking. As far as the 5HP compressor goes you can use #10 THHN on a 50A breaker if the connection is hardwired (No plug/outlet connection). The #10 THHN is good to 35A and you can go higher on the breaker to account for high startup current because the motor should have its own thermal protection.

Now the smaller compressor is another story depending if it's going to use a plug. You need to make sure the outlet and plug match or exceeds the ampcapacity of the circuit. In other words you should not use a 20A plug and outlet on a 30A circuit.

 

[LS6 Tommy]

The breaker/fuse rating called for by the compressor dictates the breaker, wire and connector ratings. I'm pretty sure you can't use #10 THHN for 50A no matter what it's feeding...

Tommy

 

[LT5 John]

I got lost a little with your post but I try to answer what I think you're asking. As far as the 5HP compressor goes you can use #10 THHN on a 50A breaker if the connection is hardwired (No plug/outlet connection). The #10 THHN is good to 35A and you can go higher on the breaker to account for high startup current because the motor should have its own thermal protection.

Now the smaller compressor is another story depending if it's going to use a plug. You need to make sure the outlet and plug match or exceeds the ampcapacity of the circuit. In other words you should not use a 20A plug and outlet on a 30A circuit.

I am going to hard wire. That's what I wanted to know, just keep the 50 A breaker and use #10 THHN...The small compressor has a 20A breaker not a 30A, I re-checked. The small compressor is 230 V ...With a dedicated plug already, that works fine...I will just turn off the 50a breaker when using the small compressor, and visa versa when using the 50A

 

[pattenp]

The breaker/fuse rating called for by the compressor dictates the breaker, wire and connector ratings. I'm pretty sure you can't use #10 THHN for 50A no matter what it's feeding...

Tommy

Remember motor circuits and over current protection is different than normal general purpose plug and play circuits.

 

[larry4406]

Why not just put a matching 4-prong cord on your compressor and plug it into the existing outlet?

 

[pattenp]

Why not just put a matching 4-prong cord on your compressor and plug it into the existing outlet?

You could but the plug is not rated for 5HP. I know it's done but is not to code.

 

[wyliesdiesels]

The breaker/fuse rating called for by the compressor dictates the breaker, wire and connector ratings. I'm pretty sure you can't use #10 THHN for 50A no matter what it's feeding...

Tommy

Wrong! U post this on quite a few of the threads about compressor wiring.

U really need to stop posting this as its incorrect for motor circuits.

 

[alfredeneuman]

Wrong! U post this on quite a few of the threads about compressor wiring.

U really need to stop posting this as its incorrect for motor circuits.

...... and incorrect for welder circuits, too.

The Square D Motor Calculator has it on #10s with a 60A breaker or 40A dual-element fuses

 

[miner]

You could but the plug is not rated for 5HP. I know it's done but is not to code.

That plug rating is when used as a motor disconnect.

 

[alfredeneuman]

That plug rating is when used as a motor disconnect.

You, of course have a Code or UL listing reference for that statement?

 

[wyliesdiesels]

That plug rating is when used as a motor disconnect.

Nope

 

[miner]

You, of course have a Code or UL listing reference for that statement?

Here is one kind of reference:

http://www.cooperindustries.com/content/dam/public/crousehinds/resources/catalog-sections/p_section.pdf

The tables on page 14 ("Arktite Horsepower Ratings" etc.)show hp ratings for Arktite plugs and receptacles (I have it handy because I just bought this style plug for my welder).

The table on the left shows locked rotor interrupt ratings for plugs by ampacity. These are low hp values (like 5 hp at 30 amps 240 V 3 phase) although they are a bit higher than the comparable hp ratings for NEMA plugs.

However, the table on the right shows max hp ratings which are much higher (15 hp at 30 amps 240 V 3 phase) and there is an accompanying note that at these ratings you cannot use the plug and receptacle as a disconnect under load.

So it seems that hp ratings on this style of plug are explicitly taking into account breaking the circuit when the motor is under load. I believe the same is true for NEMA style plugs, though I have not found this kind of detailed info on them.

Anyway, if you do not use the plug as a disconnect (because you have a snap switch that is rated to interrupt the motor load, for example) then there does not appear to be an issue having a plug/receptacle in the circuit provided it is rated for the ampacity of the circuit.

 

[miner]

Nope

Maybe you can answer a question I asked in another thread that pertains to this. How do so many machinery manufacturers get away with selling 5 hp machines with NEMA plugs that are rated at 2 hp?

 

[wyliesdiesels]

Here is one kind of reference:

http://www.cooperindustries.com/content/dam/public/crousehinds/resources/catalog-sections/p_section.pdf

The tables on page 14 ("Arktite Horsepower Ratings" etc.)show hp ratings for Arktite plugs and receptacles (I have it handy because I just bought this style plug for my welder).

The table on the left shows locked rotor interrupt ratings for plugs by ampacity. These are low hp values (like 5 hp at 30 amps 240 V 3 phase) although they are a bit higher than the comparable hp ratings for NEMA plugs.

However, the table on the right shows max hp ratings which are much higher (15 hp at 30 amps 240 V 3 phase) and there is an accompanying note that at these ratings you cannot use the plug and receptacle as a disconnect under load.

So it seems that hp ratings on this style of plug are explicitly taking into account breaking the circuit when the motor is under load. I believe the same is true for NEMA style plugs, though I have not found this kind of detailed info on them.

Anyway, if you do not use the plug as a disconnect (because you have a snap switch that is rated to interrupt the motor load, for example) then there does not appear to be an issue having a plug/receptacle in the circuit provided it is rated for the ampacity of the circuit.

Those are pin and sleeve plugs and receptacles which DO have a higher HP rating.

Standard NEMA plugs and receptacles arent rated for more than 3-3.5HP...

Maybe you can answer a question I asked in another thread that pertains to this. How do so many machinery manufacturers get away with selling 5 hp machines with NEMA plugs that are rated at 2 hp?

I cant answer about those machines specifically other than maybe the machines arent UL listed...

Have u thought of asking them directly?

 

[miner]

Those are pin and sleeve plugs and receptacles which DO have a higher HP rating.

Standard NEMA plugs and receptacles arent rated for more than 3-3.5HP...

Yes, as I said, the hp rating for the arktite plugs is a bit higher than NEMA plugs. But my point is that this rating pertains specifically to when the plug is used as a motor disconnect. Hence the *much higher* hp ratings for the arktite plugs in situations where they are NOT to be used as a disconnect.

I cant answer about those machines specifically other than maybe the machines arent UL listed...

Have u thought of asking them directly?

The machines I have in mind are things like table saws and planers that use UL listed components. E.g., a machine that uses a NEMA L6-30 on a 5 hp 240 V single phase motor. Would you call that a code violation?

 

[wyliesdiesels]

Yes, as I said, the hp rating for the arktite plugs is a bit higher than NEMA plugs. But my point is that this rating pertains specifically to when the plug is used as a motor disconnect. Hence the *much higher* hp ratings for the arktite plugs in situations where they are NOT to be used as a disconnect.

The machines I have in mind are things like table saws and planers that use UL listed components. E.g., a machine that uses a NEMA L6-30 on a 5 hp 240 V single phase motor. Would you call that a code violation?

HP ratings are specific to the UL listed device. So your point is moot...

Its no more a code violation than it is a listing violation...the components are being used outside their listing...

But are u sure that the plugs are rated for only 3HP?

 

[miner]

HP ratings are specific to the UL listed device. So your point is moot...

Its not a code violation but more so a listing violation...the components are being used outside their listing...

So using a device outside the specifics of their UL listing is not a code violation? OK.

 

[miner]

Here is something interesting: you can buy mechanical disconnects that incorporate standard NEMA plugs and receptacles, but which have higher hp ratings. For example, a switch rated at 5 hp that uses a standard L15-20 (3 hp rating). Or a switch rated at 10 hp that uses a standard L16-20 (5 hp rating). Presumably this is due to the fact that the switch is being used as the disconnect, not the plug. Or are these devices are using components outside their UL listing?

http://www.hubbellcatalog.com/wiring/catalogpages/section-b.pdf (see page B-65)

 

[pattenp]

You are looking at 3 phase use. If you noticed single phase goes up to 3hp.

 

[LS6 Tommy]

Wrong! U post this on quite a few of the threads about compressor wiring.

U really need to stop posting this as its incorrect for motor circuits.

1. You need to chill out.
2. Show me the other posts where I said this.
3. I said I was pretty sure, not that I was positive. Pattenp pointed out my mistake. I'm always the first one to admit when I'm wrong. Why do feel you need to be so nasty about it when someone is incorrect? I don't recall anyone jumping down your throat if you've been wrong. And I'm relatively sure it has happened at least once.

We're all here to learn from each other. Leave the chastising for the other websites...

Tommy

 

[miner]

You are looking at 3 phase use. If you noticed single phase goes up to 3hp.

Even if you look at single phase the hp rating of the switch (in that brochure) is *more* than the rating of the plug/receptacles it uses.

 

[pattenp]

Even if you look at single phase the hp rating of the switch (in that brochure) is *more* than the rating of the plug/receptacles it uses.

The HP rating for the switch unit enclosure is determined by the receptacle that is chosen. So even though the switch may have a higher HP rating than the outlet or plug, the outlet or plug chosen sets the HP limit. Read the "Ratings" at the top of 63B or 65B.

 

[miner]

The HP rating for the switch unit enclosure is determined by the receptacle that is chosen. So even though the switch may have a higher HP rating than the outlet or plug, the outlet or plug chosen sets the HP limit. Read the "Ratings" at the top of 63B or 65B.

The switch body is the same (HBLMITL), but the hp rating changes based on what receptacle is installed in the switch. So yes, the hp rating is "determined" but not necessarily "equal" to the receptacle rating. That is why they can have a switch/receptacle combination that has a higher HP rating than the receptacle/plug.

My point is very simple: hp ratings for plugs are based, at least in part, on being able to break the the motor full load current. But when not used as a disconnect they MAY be able to power motors at hp higher than their rating. In fact, they commonly DO power motors at higher hp since there are many many machines sold in this country with plugs that are supposedly under rated for their motors. I also gave a couple of explicit counter-examples (the arktite plugs and the Hubble switch).

I am not telling anyone what to do, BTW. It just seems clear to me that there is a more interesting story behind this issue than:

Nope

 

[pattenp]

The switch body is the same (HBLMITL), but the hp rating changes based on what receptacle is installed in the switch. So yes, the hp rating is "determined" but not necessarily "equal" to the receptacle rating. That is why they can have a switch/receptacle combination that has a higher HP rating than the receptacle/plug.

My point is very simple: hp ratings for plugs are based, at least in part, on being able to break the the motor full load current. But when not used as a disconnect they MAY be able to power motors at hp higher than their rating. In fact, they commonly DO power motors at higher hp since there are many many machines sold in this country with plugs that are supposedly under rated for their motors. I also gave a couple of explicit counter-examples (the arktite plugs and the Hubble switch).

I am not telling anyone what to do, BTW. It just seems clear to me that there is a more interesting story behind this issue than:

Your point is simple but wrong from a safety stand point. A plug by its very nature is a disconnect whether or not it's unplugged. The switch plug unit you linked to is not to be used on motor loads that exceed the HP rating of the receptacle used. There is nothing to prevent the unplugging of the motor load regardless of having a switch. I see no where in the specs that a switch unit that has a switch with a higher HP rating than the receptacle can be used at the higher switch rated HP. The HP rating on plugs is not based on the fact of being regularly plugged or unplugged under load, but if by necessity the plug is used as a safety disconnect when under load.

 

[miner]

Your point is simple but wrong from a safety stand point. A plug by its very nature is a disconnect whether or not it's unplugged. The switch plug unit you linked to is not to be used on motor loads that exceed the HP rating of the receptacle used. There is nothing to prevent the unplugging of the motor load regardless of having a switch. I see no where in the specs that a switch unit that has a switch with a higher HP rating than the receptacle can be used at the higher switch rated HP. The HP rating on plugs is not based on the fact of being regularly plugged or unplugged under load, but if by necessity the plug is used as a safety disconnect when under load.

Fair enough. I do think you are misinterpreting the specs of the switch, but it is not really a big deal. I find it interesting you call it a code issue and Wylie says otherwise. In any case, cheers.

 

[larry4406]

Right or wrong I used a 50A range cord on my 7.5 HP compressor with matching receptacle, 50A breaker, and #6 4 conductor wire (line, line, neutral, ground).

 

[pattenp]

Fair enough. I do think you are misinterpreting the specs of the switch, but it is not really a big deal. I find it interesting you call it a code issue and Wylie says otherwise. In any case, cheers.

I'm going on the bases of the NEC so I see no misinterpretation of the allowed use of the switch encloser when paired with a lesser HP rated outlet. I see where Wylie said it's not a code violation but I have to disagree. The NEC follows that devices are to be used as stated by the manufacturer or within their approved use rating. The NEC and UL are all about fire and personal safety when it comes to the distribution and use of electricity. So if you are using an electrical device such as a switch or outlet in a circuit beyond its listed rating you are not in compliance with the NEC.

Oh, Larry4460, the setup you have will work just fine and with great odds will not burn down your garage. I'll get off my NEC soapbox Now.

 

[wyliesdiesels]

So using a device outside the specifics of their UL listing is not a code violation? OK.

Fair enough. I do think you are misinterpreting the specs of the switch, but it is not really a big deal. I find it interesting you call it a code issue and Wylie says otherwise. In any case, cheers.

I'm going on the bases of the NEC so I see no misinterpretation of the allowed use of the switch encloser when paired with a lesser HP rated outlet. I see where Wylie said it's not a code violation but I have to disagree. The NEC follows that devices are to be used as stated by the manufacturer or within their approved use rating. The NEC and UL are all about fire and personal safety when it comes to the distribution and use of electricity. So if you are using an electrical device such as a switch or outlet in a circuit beyond its listed rating you are not in compliance with the NEC.

Oh, Larry4460, the setup you have will work just fine and with great odds will not burn down your garage. I'll get off my NEC soapbox Now.

Of course it is a code violation. What i typed was not what i meant to say. Damn phone Thats what i get for being in a hurry and not proof reading. And I havent had time to get back on here since then. Been dealing with all the wildfire catastrophe out here...I have edited my post...

Because the device is being used outside its U/L listing, it most definitely is a code violation.

But miner: how do u know that the specific plugs the manufacturer is using are only rated for 3 HP?

Right or wrong I used a 50A range cord on my 7.5 HP compressor with matching receptacle, 50A breaker, and #6 4 conductor wire (line, line, neutral, ground).

The neutral wasnt need so that was a bit of a waste. But obviously if u already had it then nevermind...

 

[Charles (in GA)]

Its a code issue because the code requires that all products used be appropriately listed, and used in accordance with the listing (and code).

 

[Norcal]

Its a code issue because the code requires that all products used be appropriately listed, and used in accordance with the listing (and code).

Just to add, instructions supplied by the manufacturer are usually part of the listing and must be followed to comply with code requirements.