Electrical mystery

[GarageEnvy]

First, a disclaimer, I'm not that good with electrical.
I've got a Dewalt metal chop saw that keeps tripping the breaker on startup. First thing I noticed was the old 1955 wiring was 14 gauge so I switched to 12 gauge and put a receptacle close to the box (about a foot from the main panel). It still trips the breaker on startup. The weird thing is that I can plug it into a cord reel (14 gauge) that is on the ceiling on the same circuit and most of the time it won't trip the breaker on startup. The problem is that on a long cut it will trip the breaker on the cord reel. This whole garage is coming down soon so it's not a crisis but I want to make sure I solve the issue in the new garage during construction.

 

[Keith_MN]

What are the power requirements for your saw? Check to see if you can find the nameplate somewhere on it, it should list the current required in amps or maybe the power required in watts.

My guess is that either your breakers are old and tripping prematurely (at too low a current) or the saw is drawing too much power which could indicate the motor is going bad.

 

[sberry]

The 14 wont deliver as much current, slows the trip. It doesn't get any better than a 12 a foot from the panel. This is a tool similar to small welders and air comps, run a wire for a dedicated outlet, a 12 is fine and use a 30 breaker. I like to label specialty circuits, find a single recept or tape off a duplex so it cant be for general use. This is a common problem.

 

[dipper]

The 14 wont deliver as much current, slows the trip. It doesn't get any better than a 12 a foot from the panel. This is a tool similar to small welders and air comps, run a wire for a dedicated outlet, a 12 is fine and use a 30 breaker. I like to label specialty circuits, find a single recept or tape off a duplex so it cant be for general use. This is a common problem.

YOUR BIGGEST PROBLEM IS HAVING A 30AMP BREAKER ON 12GAUGE WIRE.

That is a fire waiting to happen. If you want to stick with the 30amp breaker, use 10 gauge wire.

 

[sberry]

A 30 wont overheat the wire, the tool will melt down before that happens. This tool has a duty cycle to some extent and the 14 cord that comes on it is a limiting factor. Again, this circuit is designed with this tool or others similar in mind and not for general use where the items being plugged in have a max short circuit rating designed to be used on circuits limited to 20A, radios, alarm clocks, chargers, fixtures, etc.

 

[sberry]

I will add a bit to this, a reason for restricting this type of circuit to a single recept is for overheating, it keeps multiple devices such as 2 electric heaters from being plugged in to the same circuit that is over breakered for a specialty application such as a motor load.

 

[JBurgess]

YOUR BIGGEST PROBLEM IS HAVING A 30AMP BREAKER ON 12GAUGE WIRE.

That is a fire waiting to happen. If you want to stick with the 30amp breaker, use 10 gauge wire.

+1

Look at 240.4 (D) (5) before you use 12 guage on 30 amp circuit. It is limited to 20 amps.

 

[sberry]

There are exceptions for this type of circuit, several places in the code allow this for specific circuits.

 

[sberry]

There are places that allow for 12 wire to be used on circuits to 50A.

 

[FNFS2000]

not hooked to a 15amp duct taped recepticle

 

[sberry]

I agree, that piece of electric tape is not to the letter of the code, it does meet intent though of keeping anything else plugged in to that circuit. By all rights it should have single recept instead of a duplex.

 

[Aceman]

+1

Look at 240.4 (D) (5) before you use 12 guage on 30 amp circuit. It is limited to 20 amps.

I don't agree.

This is a motor driven appliance IMO, that means we start with 240.4(G). Which leads us to 422 Part II. 422.10(A) says the circuit shall not be less than the marked current rating of the appliance. In this case, I'll assume 15 amps because that's what the Dewalt site states. Round up to 16 amps x 125% and we're at #12 wire.

Since it's a motor, I'll size the OCPD using Table 430.52. 16 amps x 250% max=40 amp inverse time breaker. So put in a 30 amp breaker.

I don't have to worry about O/L protection due to 430.32(D)2.

The only potential issue I see is the receptacle rating. Since the chop saw is UL listed, you can't legally cut the cord end off and use a 30 amp cord end. I also can't see how you can use a 20 amp recep on a 30 amp circuit.

This is assuming the OP is using the correct blade in the saw, the bearings are good, etc etc and aren't causing the startup issues.

I personally wouldn't have an issue putting a 20 amp single receptacle on a 30 amp circuit if it was marked for the chop saw use only. I don't know how the inspector would take it though. Dewalt's really put you in a tough position making a saw with such a high amp draw. One possible legal way around it would be to install a subpanel that uses a different breaker with a different trip curve, allowing you to keep the 20 amp breaker and allow the chop saw to startup.

 

[JBurgess]

I don't agree.
Since it's a motor, I'll size the OCPD using Table 430.52. 16 amps x 250% max=40 amp inverse time breaker. So put in a 30 amp breaker.

But isn't the chop saw a wound rotor motor (brushes) so only a 150% factor apply limiting you to a 25 amp breaker?

I still don't see putting a 20 amp recepticle on more than a 20 amp breaker since it is not a welder or a disharge lighting.

 

[LoneGunman]

"This is a fire waiting to happen" LOL, That is beyond ridiculous. Sberry and Aceman are getting into the reasons why it's legal so there is no reason for me to also but I will say that as an electrician I have installed numerous 30 amp circuits using 12 gauge wire and have done so while still abiding by the NEC.

What gets people in trouble with electrical work is they take one table in the code book and think it's an absolute rule while not taking into account the exceptions to that article and other sections of the code. I'm studying for my Masters Electrician license, which would entitle me to go out on my own, I am already a licensed journeyman electrician, I'm shelling out $800 to take a group of classes which will hopefully help me pass an OPEN book test. The way the NEC is laid out confuses engineers, electricians, inspectors ETC., reading one section usually does not give you an ALWAYS right answer.

 

[BackAgain]

Since the chop saw is UL listed, you can't legally cut the cord end off and use a 30 amp cord end.

Says who? Anything not permanently installed is not under the authority of the NEC. Anything you plug into a wall you can cut the cord off of and change if you wish. Appliances (tools) do not have to be UL approved. You can plug in whatever the hell you want, even if you invented it yourself. Yes, it will disable the UL rating, but who cares? It would still pass the UL testing again if somebody actually wanted to pay for that. It may not be allowed by OSHA, but I don't think we're talking about a commercial shop...

PS - the cops were in my shop last night, they didn't write me up for the 16ga hacked up extension cord haphazardly powering all the lights in my barn...

 

[sberry]

The only potential issue I see is the receptacle rating. Since the chop saw is UL listed, you can't legally cut the cord end off and use a 30 amp cord end. I also can't see how you can use a 20 amp recep on a 30 amp circuit.

Man I cant remember all the stuff so this isn't gospel but it seems somewhere there is allowance for it, also I believe for small welders I seem to recall something about limiting the wire size when doing this, something like a 12 wire, 20A recept with 30 breaker. I did run 10 to my saw, seems I put a current meter on it, at times you could load it hard enough to draw 40A, been a long time ago so don't hold me to the details.

 

[JBurgess]

Man I cant remember all the stuff so this isn't gospel but it seems somewhere there is allowance for it, also I believe for small welders I seem to recall something about limiting the wire size when doing this, something like a 12 wire, 20A recept with 30 breaker. I did run 10 to my saw, seems I put a current meter on it, at times you could load it hard enough to draw 40A, been a long time ago so don't hold me to the details.

210.21 (B) (3) exception 1 for welders

 

[Aceman]

"This is a fire waiting to happen" LOL, That is beyond ridiculous.

Ironically this is the same guy that tells people #4 copper is all you need for a 100 amp garage panel.

 

[Furious D]

I,m going to stay out of the wire size argument. Is possible you just have a weak breaker? It would be helpful to put an amp meter on the circuit if you have access to one.

I fixed a Milwaukee chop saw once that was nearly doing the exact same thing, It turned out that the blade brake was hanging up on startup and was pulling around 30 amps until it came up to speed.

 

[GarageEnvy]

Thanks for all the help. I had not considered a problem with the saw. I simply figured this was a popular tool designed to work on a typical 110 outlet. I don't have an amp meter but I think I might known someone who does. I'll give that a try.

 

[dugger10]

#10 gauge copper wire with a 30 amp breaker, problem solved. Done this many times for people.

 

[trythis]

That looks like a 15 amp receptacle. But who's counting?
I have never seen a little chop saw made by anyone that would always trip a 15 or 20 amp circuit, unless the motor is going. I have used at least 6 that I can think of made by Dewalt, Porter cable, milwaukee, and one unknown blue model. I run one daily on a 15 amp circuit that has 4 lamps on it and at least 60 feet or wire behind it on a 15 amp circuit. I have only tripped the breaker when I was also running my welding fume machine on it at the same time.
Somethings wrong with your machine. i.m.h.o. of course.