25 Amp Motor, 20 Amp Circuit

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  #1  
Old 07-25-05, 09:52 AM
lostinthejungle
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Question 25 Amp Motor, 20 Amp Circuit

OK, so let's live and learn. I just bought a table saw that has a 110 v. 25 Amp motor, and well you may have guessed it, the garage is wired 20 Amp. Oh the motor will run a minute or two, but now that the breaker has activated a couple of times, theres not enough run time to even cut a 1 by 2 pine furring strip.

I've got plenty of room in our breaker box, so the questions are:

Can I put a 30 Amp breaker in the box, run a single outlet to it, and are there 110 outlets that can handle 25 amps - didn't find any at Lowes - oh yea, what size wire would I need for that one outlet?

(I may actually have an electrician hook up, but would like to run everything short of the breaker box myself.)
 

Last edited by lostinthejungle; 07-25-05 at 10:15 AM. Reason: Clarification
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  #2  
Old 07-25-05, 10:21 AM
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The motor amps doesnt help us. We need to know the horse power of this single phase motor. Then we will be able to tell you wire size and maximum circuit breaker.
 
  #3  
Old 07-25-05, 10:27 AM
lostinthejungle
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2 Horses

It's a 2 HP, 110 single phase
 
  #4  
Old 07-25-05, 12:54 PM
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Sorry couldnt get back to you....at work...hope you understand

Generally you just dont up the breaker size on cord and plug equipment. Motors are treated differently but mostly when hard wired.

Can you supply the make and model # of the saw?

If you have the owners manual what does it say for breaker size or fuse size and wire size?

Did this motor come with a factory cord and plug or is it hard wired with a customer supplied pigtail?

Reason I'm asking is cord and plug motors generally are limited to the plug that is attached to them (if factory installed). Look at this chart........ specifically the 125 volt 2 pole 3 wire grounding row.

http://www.leviton.com/sections/techsupp/nema.htm

It sounds like you have a nema 5-20p and are already using a 20 amp breaker.

Can you tell us what plug is on the saw?

Also most tablesaws of this size horse power can be wired low voltage or high voltage. Look on the name plate in the voltage block and see if it can be wired at the higher voltage.....it will show 110/220.

If it can be wired at the higher voltage that will reduce the amp draw to 12.5 motor amps (FLA). Can you tell us what the electrical requirements are in the owners manual?
 

Last edited by Roger; 07-25-05 at 01:25 PM.
  #5  
Old 07-25-05, 01:12 PM
lostinthejungle
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It came with a regular 3 prong 110 v wire, all I had to do was attach it to the motor housing after I installed the motor.

The saw is a LOBO (Machinery) 12 inch Contractor type (TS-0012) and it says it can be wired for 110, or 220, which I understand 220 would be preferable, but since it's a contractor type and I'd like to have that flexibility (move to a "job" site), I'd like to keep it at the 110 v setup.

(And thanks for taking the time to respond!)
 
  #6  
Old 07-25-05, 04:38 PM
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Well I was doing pretty good till you told me they supplied a 15 amp cord with a saw that has a 25 amp FLA at 110V. This would suggest that there is no overload internal to the motor.

Best I can get out of 1999 code is Article 430.42(c) allows if overload protection is present internal to the motor the the rating of the attachment plug and receptacle will determine the rating of the circuit for which the motor can be connected. The intent is towards a factory supplied cord.

If it doesnt have overload internal then it cannot be connected to anything over 15 amp branch circuit rated [article 430.42(c)]

So without covering this reply up with more code qoutes can you see if there is a T designation on the nameplate or a red reset button on the motor so we can determine if the motor has thermal protection.

I have no idea how you could ever use a 15 amp cord that plugs into a 15 or 20 amp circuit with this motor.

If I make the calculations for branch circuit conductors based on the information you have given I get for 2 hp 110volt FLC 24 amps table 430.148 I get

Minimum #10 awg copper conductors (30 amp minimum conductor ampacity)

This would mean you would need a 5-30P plug and 5-30R receptacle using number #10 awg flexible cord.

You would then run 10/2G from a 30 amp breaker to the receptacle.

This all hinges as I see things on whether or not you have overload protection internal in the motor ( should be 33.6 amps) which I would think you would. I have never seen a 2 hp tablesaw that doesnt have it internally.

At any rate you probably should wait for others to reply as this is a little differrent than I am familiar with.

Also this doesnt help you move it around to job sites.
 

Last edited by Roger; 07-25-05 at 08:09 PM.
  #7  
Old 07-25-05, 06:33 PM
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Hello,

I figured I would dable in this a bit. yep sad to say I just am not much into the Industrial part of the electrical field.

I do however have to touch on some things. I question this 2 HP motor that is supplied with a 15 AMP plug and cord layout. Sure it is known that some SO and SJ have a higher rating in some cases but this seems to be extreme if you ask me and has nothing to do with the required protection and operation of the actual saw as it pertains to the motor which is why many larger on site models that are 220V only draw 12 AMPS.....as have a dedicated circuit for them.

I have put together a few Articles that explain each requirement in the chain of events.

Let's review three very important principles:

1. You must size the conductors at 125% of the motor FLC [430.22(A)].

2. You must size the overloads from 115% to 125% of the motor nameplate current rating [430.32(A)(1)].

3. You must size the short-circuit ground-fault protection device from 150% to 300% of the motor FLC [Table 430.52].

Cord and plug or hard wired.....motors are motors and the above applies to figuring the size of circuit and protection for them.


Just to clear up the old " next size up rule " refer to Section 430-52(c)(1) ,Exception 1

I have to ask you this.......this unit has to have a nameplate on it, can you post the nameplate information please.


My issue here is I do not believe they would supply a 15 AMP cord ( 14 AWG stranded no doubt ) to a 2 hp motor....just does not add up as you have seen a 20A circuit will not hold the draw so this has to be dedicated equipment and find it strange they would supply this.
 

Last edited by ElectricalMan; 07-25-05 at 06:46 PM.
  #8  
Old 07-25-05, 07:05 PM
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OK,

The question of this type appliance got me thinking and when you get an electrician thinking " AFTER HOURS " it means he is either sleeping on the couch tonight or he is AMPED up from a long day....ok....both of which may be true ( wife is upset again )....anyway....

1.) from what I can gather these units have a magnetic switch with thermal overload protection built in.

2.) in all cases I have run into in my research they all suggest a 10 AWG supply cord.

3.) The also all recommend a 30AMP breaker supplying the circuit which again would cover the 115% FLC ( which is 27.6 in case anyone was wondering )

AS for the cord....code says it can be used as the disconnect in this case as well so clear on that......

I find that most suggest direct wiring to the circuit via a junction box and so on but they do not rule out a 30A plug and cord assembly which I would recommend if you wish to make it portable.

So I decided to go to the source...I went to the LOBO website to see their models specs on the unit you are refering to....now they say the model is PRE-WIRED.......

So are you saying the wire that came already in the unit is 14 AWG SO or SJ wire.....this is important because every other one I have looked at tonight recommend 10 AWG cord........

So to clear it up...which is quite confusing I sent them an e-mail and will post their reply......

FYI- if it were me I would suggest using a NEMA-5-30R receptable flush mount and a NEMA 5-30P plug assembly......fix ya right up....
 

Last edited by ElectricalMan; 07-25-05 at 07:41 PM.
  #9  
Old 07-25-05, 08:04 PM
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I also wanted to mention I do get asked alot how come it seems like cords can be smaller and carry a larger AMP rating than lets say normal THHN in some cases......well that depends on the type of cord being used....

Well take a gander at Art 400-5(A) and that should explain it for most people as some cords have their own ratings. For example note that HSO cord for a 14 AWG has a AMP rating of 20 AMPS......and 12 AWG SJ if a (2) wires are current caring only....can be 25 AMPS rated.

Do not get this confused with ANYTHING else where 310-16 applies....this is only for specfic cords.

This sometimes can confuse people and since cords are only allowed in specific applications and lenghts the confussion swells....
 
  #10  
Old 07-26-05, 12:01 PM
lostinthejungle
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Whoa - you guys are good!

Well, in response to your reponses, I think I need to take a closer look at the motor badge, as it does have a bunch of info that you guys understand (that is also to say, that I don't understand), which I will do when I get home this afternoon and will add to the message.

As I think I mentioned, all I had to do when I got the saw was to run the wire from the on/off switch to the motor, so the saw was prewired for 110. As an observation, before I get home, the motor has two small boxes hanging off of it; the one that I wired to the switch, and a small box (semi tubular) or cover that has some wired electronic component(s) under it (I don't know what it/they are - maybe the thermal overload stuff???).

Will write back after I check it out this evening - AGAIN - THANKS FOR ALL YOUR INPUT!!!
 
  #11  
Old 07-26-05, 03:32 PM
lostinthejungle
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Hey Roger and ElectricalMan - Here's the Badge Info

OK the Motor badget says: Ko Ting Ltd (mfg.)

Output: 2 HP KW 1.5
HZ 60 Pole 2
Volt 110/220 Heat 60 C
AMP 25/12.5 Class E
RPM (I know this) 3450 Date 2000/2
Phase 1

So, it was hot the day I was using the saw, and the day I did some other work it was not so hot and I did not have a problem with the breaker. Also, I was using a 50 ft extention cord (don't know the amp's but probably smaller than I should be using - so, if I used an air conditioning cord at 9' instead, would that make a difference?

All help is appreciated - and ElectricalMan, you wouldn't be close to Mechanicsville, would you?
 
  #12  
Old 07-26-05, 04:26 PM
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Using the extension cord was the cause of the breaker tripping quickly.

No manufactured extension cord will satisfy this saw. I'd bet there is a warning in the manual against extension cords.

It seems that most imported power tools come with inadequate cord/switch/plug assemblies.

If you must have a longer cord, I would suggest replacing the cord that came with the saw with a longer cord made of 10/3 SO cable.

P.S. - the semi-tubular cover on the motor is a capacitor.
 
  #13  
Old 07-26-05, 06:26 PM
lostinthejungle
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Hey Bob - Thanks

I'll try your recommendation - beats rewiring the house. And I do not believe that LOBO actually paid a technical writer to write their manuals - after installing the motor, and without mentioning how to wire it, the manual says, Now you are ready to use your saw!

Thanks everybody - also just a question - will a breaker break more often in hot weather than in cold?
 
  #14  
Old 07-26-05, 06:57 PM
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I agree in that in the end since you are planning on making this unit portable I would change over to 10/3 SO and use the plug and cord design I had posted earlier as your best option.

Like I said from all that I can see it should not be a 15 AMP cord and plug on this unit regardless....just using the example from the other manufacturers who all recommend 10/3 and 30 amp breakers....

So if it were Me....I would upgrade all that.

As for being near mechanicsville.....sorry....about 2 1/2 to 3 hours away.
 
  #15  
Old 07-26-05, 07:49 PM
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As a final note to E-Mans comments....This saw draws more current than a 20 amp circuit can deliver. At full load it draws 25 amps. You would size the branch circuit for this saw on 110v from Table 430.148 using the listed FLC of 24 amp then adding 25% to get the minimum size ampacity for the wire. This motor requires #10 awg based on that calculation.
Also the 20 amp circuit #12 awg would be allowed to carry 25 amps in a motor branch circuit article 110.14(c)and(d). verified by the motor carrying a design code E on the name plate.
This is still 5 amps below the minimum wire ampacity for this motor.
This motor should have a 5-30P plug on a flexible cord rated for 30 amps and plugged into a 30 amp circuit with a 5-30R receptacle..
There also does not appear to me thermal overload protection internal to this motor. However this motor being made in china is subject to IEC designations not NEMA as in the states. Could be why it was supplied with an inadequate cord for our requirements here.
At anyrate my opinion is this saw isnt going to be a very portable saw for construction site use. I would suggest wiring it 220 volt. then you could operate it on the 220 volt 20 amp circuit using a cord with a 6-20P and matching receptacle.
Either 110 volt or 220 volt this saw also requires a dedicated circuit as it is over the 50% rule on either voltage and right at the 80% rule on 110 Volt branch circuit using cord and plug equipment article 210.23(a). No other loads can share the branch circuit with this saw.
 

Last edited by Roger; 07-27-05 at 12:50 AM.
  #16  
Old 07-26-05, 08:45 PM
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I agree with Rodger here,, it isnt going to be very portable anyway, wire it to a 240V circuit and call it good. As for portable any place that has 120V has 240 nearby or from a decent genset.
 
  #17  
Old 11-25-13, 05:47 PM
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Step Down

If the motor can handle 220 V then that will work well. If it requires 110 V I would recommend running a 220 V line up there, then use a step down transformer between the wall and the motor TC-4000A 4000 Watt Step Down Voltage Transformer
This particular step down is designed for 220 V to 110 V. The maximum allowance on this particular transformer is designed for 4000 W or 4kW.
The motor if rated at 25A peak, and will peak at (25A)(110V) = 2750W or 2.75kW I am assuming there is a negligible power factor involved, so likely you will be under 3kVA. This does NOT mean you will want to buy the 3kW transformer, NEVER run your lines at peak. That is asking for a fire.
Since you would be running the lines at 220V you will transmit at 2750W/220V = 12.5A, this will result in (1/2)^2 = (0.25) the line loss, which means 1/4 the heat generated in the line, i.e. very low risk of fire. Still use larger gauged wire for ultimate protection, and you will be fine with a 20A breaker for the application, that is if it is rated for 220V.
I know this may be a bit foreign, but this will ensure less line loss(heat) and satisfy the demand, if 110V is needed.
 
  #18  
Old 11-25-13, 06:05 PM
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Luke, thanks for contributing but this thread is over 7 years old.

There is no need for any transformers 240 and 120 are standard voltages in the US.
 
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