Wiring for compressor?

[Lucid Moments]

I am having a shop built, and in the shop there is going to be a roughly 3' square closet that I am going to put an air compressor in. Purpose of the closet is to keep the noise from the compressor down.

I have seen a few comments on here about where switches need to be located for compressors. Is there any reason there can't be a switch on the outside of the closet?

At the end of the day a licensed electrician will be wiring it and I will go with what he says, but want to be reasonable when I tell him what I want.

 

[wyliesdiesels]

What do you mean by switch?

Disconnect?

What is the HP rating on the compressor?

The answer to that will affect what kind of setup you can have- either hardwired with a diwconnect on the wall or cord and plug/outlet.

BTW a motor/compressor is required to have a local disconnect if the breaker panel is further than 50’ and not within sight of the compressor. That should answer your question.

 

[Lucid Moments]

I haven't bought the compressor yet, but I am leaning towards a pretty typical Husky 60gal 3.7hp unit. Something very much like this one.

As for a switch I want to be able to turn it on and off.

 

[pattenp]

Be sure to use a switch that is horse power rated for at least 3.7Hp. You should not just use a regular light switch rated at 15 or 20 amps.

Such as ………
https://www.amazon.com/dp/B002MPQ51O/?tag=atomicindus08-20

 

[Alber ring]

I am having a shop built, and in the shop there is going to be a roughly 3' square closet that I am going to put an air compressor in. Purpose of the closet is to keep the noise from the compressor down.

I have seen a few comments on here about where switches need to be located for compressors. Is there any reason there can't be a switch on the outside of the closet?

At the end of the day a licensed electrician will be wiring it and I will go with what he says, but want to be reasonable when I tell him what I want.

In fact, if the use of a long time, resulting in hot wire, hot wardrobe board, there is a great safety risk, this is the line problem, after all, the switch has been used for a long time, easy to heat, but also prone to fire. Chest is woodiness is tasted, do not suggest you use this kind.

 

[Lucid Moments]

In fact, if the use of a long time, resulting in hot wire, hot wardrobe board, there is a great safety risk, this is the line problem, after all, the switch has been used for a long time, easy to heat, but also prone to fire. Chest is woodiness is tasted, do not suggest you use this kind.

Huh?

 

[driftpin]

In fact, if the use of a long time, resulting in hot wire, hot wardrobe board, there is a great safety risk, this is the line problem, after all, the switch has been used for a long time, easy to heat, but also prone to fire. Chest is woodiness is tasted, do not suggest you use this kind.

Huh?

It reads like some-sort of translation software, "English is not my primary language."

 

[Citation]

Be sure to use a switch that is horse power rated for at least 3.7Hp. You should not just use a regular light switch rated at 15 or 20 amps.

Such as ………
https://www.amazon.com/dp/B002MPQ51O/?tag=atomicindus08-20

For what it's worth I don't think code would consider this a 3.7 hp compressor. It's a 15A motor which I think means it's something like 2.5hp.

 

[pattenp]

For what it's worth I don't think code would consider this a 3.7 hp compressor. It's a 15A motor which I think means it's something like 2.5hp.

If the motor has a data plate that says the motor is 3.7HP then that's what you need to go by when sizing the circuit per the NEC. Doesn't matter what the amps state.

 

[grounded-b]

What do you mean by switch?

Disconnect?

What is the HP rating on the compressor?

The answer to that will affect what kind of setup you can have- either hardwired with a diwconnect on the wall or cord and plug/outlet.

BTW a motor/compressor is required to have a local disconnect if the breaker panel is further than 50’ and not within sight of the compressor. That should answer your question.

And just to be clear - a cord plugging into an outlet, IS considered a disconnect by the NEC.

 

[exranger06]

I am having a shop built, and in the shop there is going to be a roughly 3' square closet that I am going to put an air compressor in. Purpose of the closet is to keep the noise from the compressor down.

I have seen a few comments on here about where switches need to be located for compressors. Is there any reason there can't be a switch on the outside of the closet?

At the end of the day a licensed electrician will be wiring it and I will go with what he says, but want to be reasonable when I tell him what I want.

I recommend making the closet big enough so that you can walk all the way around the compressor without moving it, for when it needs maintenance and servicing, as well as heat dissipation. 3 feet doesn't sound big enough.

 

[pattenp]

And just to be clear - a cord plugging into an outlet, IS considered a disconnect by the NEC.

And to be more clear. If a plug is used as a disconnect for a motor the plug and outlet need to have the proper HP rating as to the motor HP.

 

[Lonnies Performance]

Also keep in mind you should not be using a corded plug on this compressor. A 14-60R 60A plug is only rated for 3.5HP maximum regardless of the motor amperage.

 

[wyliesdiesels]

In fact, if the use of a long time, resulting in hot wire, hot wardrobe board, there is a great safety risk, this is the line problem, after all, the switch has been used for a long time, easy to heat, but also prone to fire. Chest is woodiness is tasted, do not suggest you use this kind.

wait what?

And just to be clear - a cord plugging into an outlet, IS considered a disconnect by the NEC.

yup. thanks forgot to add that

And to be more clear. If a plug is used as a disconnect for a motor the plug and outlet need to have the proper HP rating as to the motor HP.

Also keep in mind you should not be using a corded plug on this compressor. A 14-60R 60A plug is only rated for 3.5HP maximum regardless of the motor amperage.

 

[Citation]

If the motor has a data plate that says the motor is 3.7HP then that's what you need to go by when sizing the circuit per the NEC. Doesn't matter what the amps state.

That's kind of the point. Most don't. They say SPL for the hp.

 

[Citation]

Also keep in mind you should not be using a corded plug on this compressor. A 14-60R 60A plug is only rated for 3.5HP maximum regardless of the motor amperage.

Before telling the OP they need to size for a 3.7hp motor we should verify the motor plate says 3.7 vs SPL. Earlier today I took a look at a 3.7 hp CH compressor at Lowe's. It's motor actually said 3.7 and was rated at just over 17A. Most of these are 15A, motors with no HP rating on the motor (regardless of the marketing claims on the stickers on the tank).

OP, the question about closet size was a good one. If larger isn't a good option you might consider partition walls that you could bolt in place and remove as needed. You would still need to address getting air into the closest to cool the compressor but that can be done with fans and vents.

 

[pattenp]

That's kind of the point. Most don't. They say SPL for the hp.

The issue is not how many motors give the HP or just say SPL. I'm just saying if the HP is listed then that's what you use instead of the Amps.

The 3.7HP was based on the example compressor the OP linked to. It's a given that the actual compressor that the OP gets may be different.

 

[Lucid Moments]

Since there was some question about the actual HP rating of the motor I found a picture of the data plate. It appears as if it is a true 3.7HP motor. If you look closely you can see it on the motor data plate.

 

[wyliesdiesels]

Since it is indeed 3.7HP, then it will need to be hardwired unless you want to spend big bucks for pin and sleeve connectors...

 

[Lucid Moments]

I like the idea of it being hardwired better for some reason anyway. I also talked to the electrician that will be wiring the shop and from what he said he thinks it will be best to just use the circuit breaker to turn the compressor on and off. I am not sure I love that, but will talk further with him to decide when the time gets closer to actually putting stuff in place.

 

[wyliesdiesels]

I like the idea of it being hardwired better for some reason anyway. I also talked to the electrician that will be wiring the shop and from what he said he thinks it will be best to just use the circuit breaker to turn the compressor on and off. I am not sure I love that, but will talk further with him to decide when the time gets closer to actually putting stuff in place.

if the circuit breaker is further than 50' from and not within sight of the compressor then it cannot be used as the disconnect.

 

[Bert_]

You can't follow NEC for a 3.7 HP motor anyway. It's a BS rating. Standardized motor sizes go from 3hp straight to 5hp. 17.2A is a 3HP motor...

 

[Lucid Moments]

The circuit breaker will be within 50' of the compressor, and when the door is open it will be within sight of the compressor as well.

 

[Citation]

You can't follow NEC for a 3.7 HP motor anyway. It's a BS rating. Standardized motor sizes go from 3hp straight to 5hp. 17.2A is a 3HP motor...

Is there a resource for this? Bit of an aside but having read a number of discussions here I think this is an area of confusion, not the least of which, mine.
First, it would make sense to me that this should be based on motor current draw, not HP (I mean this as a question as to why, not a statement that I know better than the NEC). Was HP picked because it was easier to deal with vs reading motor current?
Second, in the cases of the SPL motors I have seen others say we should follow the current rating vs what ever HP claim is made. Certainly that would make sense when looking at the "6hp" 15A compressors. However, with a "3.7 hp" rating on the motor plate I would assume that needs to be treated as the actual value vs the marketing, inflated value. Still, 3.7 vs 3.5 reminds me of the 9.9hp outboard boat motors. The law say 10hp and above had different rules so 9.9 it was.
Anyway, is there an actual rule that says a 3.7 is treated as a 3?

To illustrate why I'm curious, here are a selection of 3hp motors from Grainger
Lower cost motor claims 12.5 FLA
https://www.grainger.com/product/DAYTON-3-HP-General-Purpose-Motor-5JE13

Also lower cost but claims 14.7 FLA
https://www.grainger.com/product/MARATHON-MOTORS-3-HP-General-Purpose-Motor-19YU36

Somewhat more expensive, 16 FLA
https://www.grainger.com/product/DAYTON-3-HP-General-Purpose-Motor-6K632

Lower RPM motor, 17.8 FLA
https://www.grainger.com/product/DAYTON-3-HP-General-Purpose-Motor-5K483

All of these are "3hp" per the motor plate. The last one draws slightly more current than the 3.7hp in question yet it seems it would be OK with a plug while the lower current compressor motor would not. What's the thinking here?

 

[pattenp]

You can't follow NEC for a 3.7 HP motor anyway. It's a BS rating. Standardized motor sizes go from 3hp straight to 5hp. 17.2A is a 3HP motor...

Sure you can. You interpolate the HP table to get the amps.

 

[Citation]

Sure you can. You interpolate the HP table to get the amps.

That seem problematic given the 12.5-17.8 A range on the motors I just cited.

 

[Bert_]

You size wire and equipment based on the HP so that any motor of the same size can run on the wiring. Example would be if some equipment comes with a premium efficiency motor but someone swaps a standard efficiency motor when it fails. Changing motors is a pretty common thing.

 

[Notgrownup]

I wired mine with a plus and receptacle. This way I can move it..It’s also plumbed with a cut off valve and quick connect ...

 

[TRWham]

Sure you can. You interpolate the HP table to get the amps.

It (meaning 430.6) really only says the reverse- that you can use nameplate amperage to interpolate HP if HP is not marked. The problem is that it doesn't tell you what you can do with that information. I agree it seems reasonable to infer you could then use that HP number to interpolate an NEC accepted FLA, but it does not say that in black and white so I have always interpreted that we should just jump to the next size feed. In this case I would provision for a 5 hp motor with either 8 AWG NM cable or 10 AWG wire in conduit and drive on down the road.

 

[pattenp]

That seem problematic given the 12.5-17.8 A range on the motors I just cited.

What's problematic? The NEC 430.248 table says to use 17A for 3HP for sizing supply conductors. To follow NEC requirements your argument over the range of amps you find on 3HP motors is mute if the motors are listed as 3HP.

 

[Rubiconcruiser]

If it’s cord connected. That’s your disconnect. No switch is necessary. Outside of room not. Must be visible from comp location

 

[pattenp]

It (meaning 430.6) really only says the reverse- that you can use nameplate amperage to interpolate HP if HP is not marked. The problem is that it doesn't tell you what you can do with that information. I agree it seems reasonable to infer you could then use that HP number to interpolate an NEC accepted FLA, but it does not say that in black and white so I have always interpreted that we should just jump to the next size feed. In this case I would provision for a 5 hp motor with either 8 AWG NM cable or 10 AWG wire in conduit and drive on down the road.

I know what you're saying but to interpolate the Amps column to the HP column or HP column to Amps column from that table gives the same answer. This is one of those code interpretation issues. It's not written in black and white to use the next higher HP on the table when a HP is not listed. I'll stick with interpolating the table since that's what I was taught in class and plus it just makes sense to me.

 

[bowtieboy77]

I would not put a switch on the outside for one main reason. If you have to turn compressor on with the switch at the compressor it allows you to check oil level, drain tank, and inspect belts. If the switch is on the outside of the closet you will tend to forget to do these inspections and if compressor develops a oil leak its very easy to seize up a expensive compressor.