20 AMP breaker/30 AMP safety switch?

[RandyPenn]

I am in the process of wiring a 60 gallon air compressor. The pressure switch has no on/off switch so I will be wiring it through a safety switch. I will be using a 20 AMP breaker. My question is I have a 30 AMP safety switch that was given to me. will this work? I see no reason why not but someone may KNOW for sure.

 

[Stuart in MN]

Yes, it will be fine. If you look around you'll discover that safety switches come in 30 amp, 60 amp, 100 amp and so on - they don't make them smaller than 30 amps.

 

[pattenp]

What is the horse power rating of the motor on your compressor? I usually see 60 gal compressors needing more than a 20A circuit.

 

[mdd1986]

If you are using the disconnect or safety switch as a local disconnecting means for the compressor you are fine.

Disconnect switches come in certain frame sizes based on typical ANSI/NEMA standards. They can be fused to just about any size. So you could use a 30A switch fused at 20 amps if you required overcurrent protection. In your case it is not required.

 

[RandyPenn]

pattenp: The compressor is rated at 3HP, the draw is stated at 13.5 AMPS

 

[pattenp]

Just to let you know, the NEC requires the circuit to be sized by the stated HP, so 3HP is 17A X 1.25 = 21.25A. Technically it should be put on a 25A breaker or 30A breaker on #10 NM wire or 25A breaker on #12 THHN. This is just an FYI. I doubt you'll have any issues with the comp tripping the 20A circuit.

Edit: If the 3HP is just on a label stuck on the tank then that's not the actual HP of the motor. If the data label on the motor itself says 3HP then that's the HP to use for sizing the circuit. If the motor doesn't state the HP and only the amp draw then the motor HP is to be assumed to be the value that corresponds in the NEC table 430.248, which means your motor is less than 3HP if it only list 13.5 amps on the motor data label.

pattenp: The compressor is rated at 3HP, the draw is stated at 13.5 AMPS

 

[RandyPenn]

pattenp: It is based on the label located on the motor itself. I would gladly put it on a 30A breaker if that's a better option. Thanks.

 

[pattenp]

If you change to a 30A breaker, you also need to use #10 wire. Does the manufacture instructions say what size circuit to use?

pattenp: It is based on the label located on the motor itself. I would gladly put it on a 30A breaker if that's a better option. Thanks.

 

[RandyPenn]

No, its an old compressor and has no manual. I do however plan on wiring it through conduit which, if i'm not mistaken, one shouldn't use NM.

 

[pattenp]

NM can be put in conduit as long as the conduit is sized correctly. It's just really hard to get NM through conduit. It's best to use individual THHN wires if doing conduit.

 

[sberry]

Why would you need a 10?

 

[laser3kw]

NM can be put in conduit as long as the conduit is sized correctly. It's just really hard to get NM through conduit. It's best to use individual THHN wires if doing conduit.

Just for my own knowledge ( I am no expert and relie on secondhand knowledge from others), I have been told for years by the best (and not so best) sparkys that it is an absolute no-no to do that. Something about double sheathing and / or potential in conduit fire (if the outer jacket smolders and wires do not arc to trip the breaker). Or is a local code thing? Illinois is pretty much on it's own when it comes to code.....
I would rather do the THHN myself anyway.

 

[pattenp]

If he puts in a 30A circuit, why wouldn't he use #10. The question is does he really need a 30A circuit. By NEC if the motor is 3HP then he does need at least a 25A circuit and that would call for either #12 THHN in conduit or #10 NM. I admit motor circuits aren't my forte, so am I seeing this wrong?

Why would you need a 10?

 

[pattenp]

It's okay by the NEC to put NM in conduit but it is not a best practice for normal runs. You may see short runs conduit used on NM in places where it's needed for protection.

Just for my own knowledge ( I am no expert and relie on secondhand knowledge from others), I have been told for years by the best (and not so best) sparkys that it is an absolute no-no to do that. Something about double sheathing and / or potential in conduit fire (if the outer jacket smolders and wires do not arc to trip the breaker). Or is a local code thing? Illinois is pretty much on it's own when it comes to code.....
I would rather do the THHN myself anyway.

 

[LX-Markham]

Bringing back this thread because I'm looking at installing a wall mounted switch for my compressor.
It's a 3HP motor running on a 220V/30A circuit. The compressor is mounted out of reach from the floor, so I would like a switch to control the receptacle. What type of switch should I be sourcing? And where is a typical place to source?

Thanks,

 

[RickP]

This is the kind I like:

It's $24 on Amazon: 30 AMP Safety Switch

You can get a pullout disconnect cheaper, but I like having the convenience of the switch. You could also try to find a 30A double pole switch that fits in a regular electrical box, but make sure it's rated for a 3hp motor -- I personally wouldn't use that type. How close is your panel -- could you use just switch the breaker?

 

[LX-Markham]

Thanks for the link! You gave me the verbiage I needed to find what I was looking for.
This is what I was thinking of:
http://www.amazon.com/Woodstock-D4157-Single-Phase-Switch/dp/B005W17GZE/ref=pd_sim_sbs_hi_5
It says it's suitable for 3HP? but it rated for 220V/20A. Guess I need to keep searching for one with 30A capacity.

This would work:
http://www.amazon.com/Leviton-3032-2R-Toggle-Double-Pole-Grounding/dp/B003BNY2RU/ref=sr_1_35?ie=UTF8&qid=1376593538&sr=8-35&keywords=30A+double+pole+switch

 

[theoldwizard1]

Leviton Industrial 3032-** is rated at 30A but only 2HP.

 

[LX-Markham]

http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=MS302-DS&section=40132&minisite=10251
Am I getting closer?

 

[theoldwizard1]

http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=MS302-DS&section=40132&minisite=10251
Am I getting closer?

Yep. Buy it from Amazon or Zoro Tools.

 

[sands35]

FYI - I picked up a new in the box 60 amp Square D disconnect switch off ebay for $40. HU362, un-fused.