30 amp breaker on 20 amp receptacle?

Status
Not open for further replies.
davedottcom

davedottcom

Senior Member
Customer wants a 20 amp / 240V single receptacle for a Cigarette rolling machine! (Compressor)

The machine manufacturer asks for a 2-pole 30 amp breaker to be installed on the 20 amp/ 240V receptacle!?

The service is 3-phase 208V/120V.

Is this permitted, as long as the wire is rated for 30 amps? (#10)
 
davedottcom

davedottcom

Senior Member
RobbieR said:
Unless I'm reading it wrong....
Customer wants a 20A receptacle (Assuming 20A breaker)
The manufacturer is asking for a 30A breaker.

But it is early, so who knows? :lol:
Click to expand...


Nope, they want a 20 amp receptacle with a 30 amp breaker!

I don't understand why they just dont want a 30 amp receptacle!!!
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
davedottcom said:
Nope, they want a 20 amp receptacle with a 30 amp breaker!

I don't understand why they just dont want a 30 amp receptacle!!!
Click to expand...


That wouldn't be permitted. A 30 amp receptacle and a 20 amp OCPD is just fine.

I've have seen this done before. An air compressor with a 15 amp cord and plug on a 20 amp circuit and 20 amp receptacle would trip the 20 amp CB on start up. Just popped in a 30 amp breaker and all is good. My 30 amp CB hasn't tripped yet. :roll:
 
davedottcom

davedottcom

Senior Member
I made a call to the installer today... He said he "thinks" the motor draws about 8 amps @ 208.

"We put a 30 amp breaker on it so it doesn't trip! That's how we always do it!" he says... :roll:

I'm waiting to hear back from the project manager with the motor specs...

I still don't understand why they think they need to do this!?
 
davedottcom

davedottcom

Senior Member
...missed his call last night... he left a message saying the motor draws 18 amps if the voltage is 240, but if the voltage is 208 (which it is) it will trip a 20 amp breaker.

ok...so...

18*240=4320

4320 / 208= 20.8

So, if it draws more than 20 amps @ 208 this motor is not allowed to be plugged in...
It needs to be hard wired on a 30 amp circuit... correct?
 
S

sgunsel

Senior Member
The service is 208Y/120. Is the motor 1 phase or 3 phase? If it is a 3 HP motor at 208v, we would allow for 17 amps at 230 and 18.7 amps at 208v per table 430.248. For a 5 P 3 phase motor, table 430.250 shows 15.2 amps at 230v and 16.7 at 208v; 7 HP would be 22 amps at 230 and 24.2 at 208. Regardless, a 40 amp breaker would be acceptable provided the wiring is good for at least 125% x FLA. Presumably, thermal overload protection is provided by the motor starter.
 
jaylectricity

jaylectricity

Senior Member
Location
Massachusetts
Occupation
licensed journeyman electrician
The first thing I notice is that a machine that draws more than 20A would not be permitted to have a 20A plug on it. So it's not going to draw more than the receptacle can handle anyway.

Possibly a 30A circuit breaker is required for start-up intensity.
 
jaylectricity

jaylectricity

Senior Member
Location
Massachusetts
Occupation
licensed journeyman electrician
davedottcom said:
...missed his call last night... he left a message saying the motor draws 18 amps if the voltage is 240, but if the voltage is 208 (which it is) it will trip a 20 amp breaker.

ok...so...

18*240=4320

4320 / 208= 20.8

So, if it draws more than 20 amps @ 208 this motor is not allowed to be plugged in...
It needs to be hard wired on a 30 amp circuit... correct?
Click to expand...

Oops, didn't read this comment thoroughly. You can probably disregard my previous comment.
 
davedottcom

davedottcom

Senior Member
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!?
 
stevebea

stevebea

Senior Member
Location
Southeastern PA
davedottcom said:
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!?
Click to expand...

80% = 16A
 
growler

growler

Senior Member
Location
Atlanta,GA
davedottcom said:
Nope, they want a 20 amp receptacle with a 30 amp breaker!

I don't understand why they just dont want a 30 amp receptacle!!!
Click to expand...


I have had this problem when the machines were being manufactured in China.

I don't really care what the manufacturer says all I look for is the name plate on the machine.

This will tell you what you need to do.

Make sure the machine installation matches name plate rating and any "written" installation instructions. That's only if they meet code. Make sure you don't void any warranty given.
 
davedottcom

davedottcom

Senior Member
I wish I had the motor to look at the nameplate!

The company won't send the equipment until the electrical wiring is completed! They have a set-up & training thing they do & they dont want to make 2 trips I guess.

So, all I have to go on is what this guy tells me over the phone... he says it draws 18 amps @ 208... where he got this information, I have no idea. Is it accurate? Who knows!?!?

I'm frustrated with the whole thing... I've already spent more time on this than it's worth!

At this point, the way I see it is, they are hiring me to install a 20 amp receptacle on a 20 amp circuit... so that's what I'm going to do. It will be permitted that way & inspected as such & that will be that.

As for 210.21(B)(2) Maximum Cord & PLug-Connected Load ...it doesn't apply since the circuit is supplying only (1) receptacle. 210.21(B)(2) is for two or more receptacles...

I think I read that right!?
 
Dennis Alwon

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
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.
 
Status
Not open for further replies.
Top