Air compressor draw question

[brickG-man]

I have been in construction all of my life but have to admit that my weakness in the industry is electrical.
I have a good sized workshop in my garage with 100 amp service. Lots of woodworking machinery, many outlets and lights. I also like to tinker with cars so a compressor comes in handy. The only thing that I may use the compressor for as far as woodworking is a nail gun or an air nozzle for blowing dust out of motors. My 20 gallon 3HP Sanborn takes care of that just fine as well as for tire inflation. My 1/2" impact is not a problem, however the compressor wont handle my die grinder and my little gravity flow sandblaster without long rests to catch up.

I have decided to upgrade to a Quincy two stage 5HP 60 gal tank. The compressor draws 24 amps and they recommend a 30 amp breaker. So finally, my electrical question is: Am I pushing the limits of my 100 amp service with the 5HP compressor and a 30 amp breaker? To me it seems fine since I never run more than one of my woodworking machines at a time. And I highly doubt that I would be running any of my machines and using the compressor at the same time.

Thanks
Hank

 

[dave89iroc]

You will be fine with the 100a

 

[sberry]

Its been done on 60

 

[wyliesdiesels]

You will be fine.

When wiring it up keep these things in mind:

Must be hardwired since its 5HP(no receptacle!)

Needs a disconnect if more than 50' from panel and not within sight.

Wire needs to be sized @ 125% of NEC FLC- this translates to #10 THHN in conduit or #8 NM-b

Breaker can be sized max 250% of NEC FLC(28a) which would be 70a.

Need a motor starter if pressure switch isnt HP rated and rated for FLC of motor(this should already be taken care of on a package unit)

 

[brickG-man]

You will be fine.

When wiring it up keep these things in mind:

Must be hardwired since its 5HP(no receptacle!)

Needs a disconnect if more than 50' from panel and not within sight.

Wire needs to be sized @ 125% of NEC FLC- this translates to #10 THHN in conduit or #8 NM-b

Breaker can be sized max 250% of NEC FLC(28a) which would be 70a.

Need a motor starter if pressure switch isnt HP rated and rated for FLC of motor(this should already be taken care of on a package unit)

Thanks for that. I will make sure that my electrician is aware of all of this, except for the distance. The compressor will be right next to the panel. Also, isnt it advisable for there there be a flex connection between the compressor and the power souce (or is that what the NM-b is?)?

 

[justsam]

NM-b is what I suspect you know as Romex. It is not what should be used directly connecting to the compressor. Wylie is talking about the piece that goes from the panel to the box that will serve the compressor.

You are correct that it is a good idea to use flexible conduit such as Sealtite, and stranded conductors within the conduit to better deal with the vibration. This would be from the compressor to the local hardwired box that feeds it.

Great choice of compressor, you should have no issues running out of air!

 

[wyliesdiesels]

Thanks for that. I will make sure that my electrician is aware of all of this, except for the distance. The compressor will be right next to the panel. Also, isnt it advisable for there there be a flex connection between the compressor and the power souce (or is that what the NM-b is?)?

Your electrician(if hes any good) should know ALL of this already. Its the NEC code.

For the flex connection I would use FMC/greenfield and pull 3 #10 stranded THHNs through it- either black, black and green or black, red and green...

 

[alfredeneuman]

You will be fine.
Needs a disconnect if more than 50' from panel and not within sight.

The Code changed to "within sight from and readily accessible" from the 50' rule a while back.

 

[wyliesdiesels]

The Code changed to "within sight from and readily accessible" from the 50' rule a while back.

So no more 50' rule? When was the code change? 2014? If so that explains why i hadnt known about it since im still on 2011!

 

[Charles (in GA)]

From the 2011 NEC.

In Sight From (Within Sight From, Within Sight).
Where this Code specifies that one equipment shall be “in sight from,” “within sight from,” or “within sight of,” and so forth, another equipment, the specified equipment is to be visible and not more than 15 m (50 ft) distant from the other.

By this def, if the equipment is 51 ft, it is not considered "in sight" even if it is plainly in sight.

Did the wording of the 2014 code change from this?

Charles

 

[alfredeneuman]

I didn't read the definition

I think I deserve one of these, so I'll give it to myself before anybody else does> wned:

 

[Charles (in GA)]

From the 2011 NEC.

In Sight From (Within Sight From, Within Sight).
Where this Code specifies that one equipment shall be “in sight from,” “within sight from,” or “within sight of,” and so forth, another equipment, the specified equipment is to be visible and not more than 15 m (50 ft) distant from the other.

Charles

2011 NEC, 2008 NEC, 2005 NEC, 2002 NEC

430.102(B)(1) Location

Separate Motor Disconnect.
A disconnecting means for the motor shall be located in sight from the motor location and the driven machinery location.

EDIT: (The readily accessible part is only for air conditioning equipment)

This is a case where you have to tie one part of the code, with the definition specified in article 100 for it to make sense.

Substitute what I put in bold with the "in sight from" found in 430.102, and one can see what they really mean.

 

[MTW]

References Please

Must be hardwired since its 5HP(no receptacle!)
Breaker can be sized max 250% of NEC FLC(28a) which would be 70a.

Must be hardwired since its 5HP(no receptacle!)

Can you provide a reference for this? I've seen you state this many times before. All I see is that the code requires the connector to be HP rated.

NEC 2011 430.109 (F)
(F) Cord-and-Plug-Connected Motors. For a cord-and plug-connected motor, a horsepower-rated attachment plug and receptacle, flanged surface inlet and cord connector, or attachment plug and cord connector having ratings no less than the motor ratings shall be permitted to serve as the disconnecting means. Horsepower-rated attachment plugs, flanged surface inlets, receptacles, or cord connectors shall not be required for cord-and-plug-connected appliances in accordance with 422.33, room air conditioners in accordance with 440.63, or portable motors rated 1⁄3 hp or less.

Breaker can be sized max 250% of NEC FLC(28a) which would be 70a.

The above statement can also be misleading. The rating of the overload assembly must be considered, when using this rating (250%). In today's world many overload devices (IEC) are not robust enough to use this rating, especially equipment designed with a price point for consumer use. The reality is that your only allowed to go as large as the rating marked on the overload assembly that is in use.

2011 NEC 430-52 (C) (2)
(2) Overload Relay Table. Where maximum branch-circuit short-circuit and ground-fault protective device ratings are shown in the manufacturer’s overload relay table for use with a motor controller or are otherwise marked on the equipment, they shall not be exceeded even if higher values are allowed as shown above.

For those NEC code bookworms interested, a copy of the NEC can be obtained from here:
https://law.resource.org/pub/us/code/ibr/

Scroll down the list to nfpa.nec section to download the reference you desire.

The 2011 edition has a working index with the supplied file, the 2014 version is un-indexed but a complete scanned version.

MTW Ω

 

[Charles (in GA)]

The issue with the hp rated plugs and receptacles, is that you won't find a blade type that is rated for greater than 3 hp. Its not an absolute that it be hardwired, but for all practical purposes, for virtually all GJ members, it is way beyond their price point, to purchase and install (even from Ebay) a pin and sleeve connector, which is all you are going to find that has hp ratings above 3 hp.

Charles

 

[brickG-man]

Even though the thread wandered just a tad off-topic, I believe that I received my answer. Looks like things are a go for the 5hp compressor, wired direct with a flexable conduit.
Looks like I pay a visit to Northern tool this weekend.
Thanks everyone.
Hank

 

[alfredeneuman]

Congratulations to you!

The issue with the hp rated plugs and receptacles, is that you won't find a blade type that is rated for greater than 3 hp. ............ a pin and sleeve connector, which is all you are going to find that has hp ratings above 3 hp. Charles

That may not be quite true.

A NEMA 14-60 is rated at 3.5 hp. according to Leviton, which is a household voltage.

http://www.leviton.com/OA_HTML/ProductDetail.jsp?partnumber=9460&section=42418&minisite=10251

"Other than household voltage" straight blade receptacles are available up to 10 hp..

 

[MTW]

Let it be known that I'm not trying to beat up on Charles for offering his valued assistance to participants of the forum. I fully understand his points and agree with most of it. However it bothers me when some thing are repeatedly stated as fact and include no reference or explanation.

The statement "Must be hardwired since its 5HP" just doesn't sit well, when I see it multiple times, and know it not to be technically correct. I can relate to it may be more costly to implement, but not impossible to achieve. I just think that the wording of it should be different to reflect the reality. Judging by some of the Garage build-outs showcased on this forum, I don't even think that the budget is always the issue. Offer up the facts of the situation or code and let the installer decide what they can afford.

As to the issue of sizing a short circuit/ground fault rating of a breaker to be used with motor controls I offer the following example of the OP. 5HP 230V 1Φ.

For the example let me use a Schneider TeSys product as an example. NEC Tables call for 28FLA for this motor, and require that a minimum of 25% be added to that for branch circuit rating. Personally I like to add 50% for some headroom when possible, to make the installation more reliable. Code allows 175% for fuses and 250% for breakers as a maximum, when using the table values.

For the Tele overload listing, with a setting range of 23-32A it list 40A as the maximum overcurrent device for standard fuses and magnetic breakers, 63A for the current limiting type. Typical residential breakers are not listed as current limiting, and therefore would be restricted to 40A in this case. Way less than the 70A (250%) maximum allowed in the code.

Comparisons:
NEC Min Value 28x1.25= 35A
My preference 28x1.5= 42A
NEC Max Value 28x2.5= 70A

So the homework example shows that even my preference of x1.5 is not acceptable in this instance. 40A breaker would be the correct choice in this case example. If the compressor was labeled and listed with something else, then that would be the correct choice.

MTW Ω

 

[ron in sc]

I have 50 amp breaker, then two 30 amp fast acting fuses.

Baldor motor with magnetic starter. Motor says it runs on 20.6 amps.

Measured start up amps and it was 91 amps, a few times a little more a few times a little less. This is for a very short period of time. Never blew a fast acting fuse.

Measured startup amps with Fluke 376

 

[TAMPAGT07]

I have 50 amp breaker, then two 30 amp fast acting fuses.

Baldor motor with magnetic starter. Motor says it runs on 20.6 amps.

Measured start up amps and it was 91 amps, a few times a little more a few times a little less. This is for a very short period of time. Never blew a fast acting fuse.

Measured startup amps with Fluke 376

Is this possible?

 

[DenisG]

Is this possible?

It's like the first passion between amorous wires.

 

[wyliesdiesels]

Is this possible?

Yup!

In-rush current can be 4x-6x FLC...