30 amp breaker on 20 amp receptacle?

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iwire

Moderator
Staff member
Location
Massachusetts
I assume if it is a compressor it will not be on all the time so 18 amps is fine on a 20 amp breaker. 80% is not necessary unless it is continuous.

If I recall you do not have to add a 'second' 125% to a motor that is continuous as all motors get a 125% bump just for being motors. I may be mistaken.
 

davedottcom

Senior Member
If I recall you do not have to add a 'second' 125% to a motor that is continuous as all motors get a 125% bump just for being motors. I may be mistaken.

A second 125% ?

What was the first?

or is this (1st) 125% already calculated into the amperage on the motor nameplate?
 

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Here is an interesting event. Suppose you have a 25 amp ocpd on a #12 wire. Could you use a 30 amp cord and plug? T. 210.21(B)(2) states maximum load but no mention of 25 amps.
 

sgunsel

Senior Member
Some compressors run continuously, sometimes by design, sometimes not. Some industrial compressors are intended to run continuiously and use an unloader valve to reduce load when demand is low. Depending on the load and compressor capacity, they may never run at reduced load. In large facilities, there may be banks of large compressors, and many full time HP just to keep up with leakage.

When dealing with motors, use article 430. Some of the requirements are a bit different from ordinary wiring.
 

growler

Senior Member
Location
Atlanta,GA
Finally spoke to him.

He claims they use different motors for different applications & they build the machine accordingly if the customerer can provide the voltage they need. He said as long as we order a 208V motor it will only draw 18 Amps & the 20 amp circuit will be ok.

I'm not used to sizing motor circuits but 18 Amps sounds high for a 20 amp circuit!?


If they list 18 amps as the minimum circuit ampacity then a 20 amp circuit should be fine.

Does this machine come from the factory with a cord and male plug, if so ask what size and type. If it comes with a 20 amp twist lock then install a 20 amp twist lock receptacle. I don't remove cords and plugs that come from the factory, if they don' know what they are doing when the build it then it's not my responsibility. I don't get paid that kind of money.

If it's to be hard wired ask for a model number for the machine and see if the installation instuctions are available at the manufacturers web site. They have to buy the motor some place and there is name plate information out there. If the will give a brand name and number you can find it.
 

davedottcom

Senior Member
Continued!

Continued!

as you may or may not remember...I was told as long as the service voltage is 208, then a 208 V motor will work fine on a 20 amp circuit.

so...

A 20 amp circuit was permitted, installed, inspected, passed, paid for...done...right?....Wrong!

I get a call/email from the tobacco store owner saying the RYO machine now needs something "New"!?!?

Here is the email he forwarded to me...

As per our telephone conversation, we were being held up by the company that manufactures the 208 motors for the compressors.
The 208 V motors will no longer be available, so from now on all compressors will be 240 V.
If you have 208 V you must install this boost capacitor first so the 240 V compressor works properly.
Grainger part #4LEF9 and make sure that the electrician uses the #4 wiring diagram.
If you have any questions have your electrician call me so I can explain.

Grainger part #4LEF9 is a transformer that has 240 Primary & 24V secondary!?

I called the guy, no answer... so, I sent an email asking for:
* Motor specs. (A Clear picture of the Nameplate on the motor)
* Name of Motor Manufacturer
* Motor Model Number
* UL listing # for the RYO machine
 

growler

Senior Member
Location
Atlanta,GA
A 20 amp circuit was permitted, installed, inspected, passed, paid for...done...right?....Wrong!


If the job was paid for then it's done as far as I'm conserned.

That's the great thing about installing a receptacle they can plug whatever they want into said receptacle, it's not my problem.

If the equipment shows up and needs a buck-boost tranformer well that's another job and has nothing to do with the receptacle install.

And Graigner probably isn't the cheapest place to buy a transformer.
 
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