Is 30 amps enough for a 3hp cabinet saw?

[bluzcat]

I will have my new Jet saw by Thursday (thanks again Jeffery). I have a 24'x32' woodshop connected to a 30'x40' three bay garage. The woodshop already has a 30 amp 220v circuit for my compressor. I'd like to use this circuit for the comp. and TS. The compressor is almost always turned off and the two pieces of equipment would not run at the same time.

Question: Is a 30 amp circuit enough for a 3hp saw? I have access to a 60 amp circuit powering a heater in the main garage. That just seems like overkill.

[LCHIEN]

yes.......

[BrazosJake]

Yes. Assuming the motor produces a true 3HP of output, even it's only 60% efficienct, it shouldn't pull more than about 17 amps.

[LarryG]

Question: Is a 30 amp circuit enough for a 3hp saw?

Actually, even that is overkill. My PM2000's 3HP motor draws, if memory serves, a maximum of 17A. I have it on a 20A (double) breaker.

[Jeffrey Schronce]

The saw calls for 220V Double Pole 20A breaker. 30A will be fine, but you will not have same level of protection from heat on your interior wiring.

BTW, that is a heck of space for a woodshop!

[bluzcat]

Thanks for the fast reply. Yes it is a nice space for a shop, but its size has presented it's own issues. For so long I have wanted my own dedicated woodshop. Now that I have it, I want it set-up just right. I was reading in another thread about over-analyzing where everything should go, staying in the planning stage too long. It hit a little too close to home. Time is my worst enemy: never enough (wife, 3 kids, 50+ hour-a-week day job).
If I know I can't finish something, I have trouble getting started.
The knowledge gained from this sight has motivated me like nothing else. Everytime I see a picture of Kirby's shop, however, it reminds me how far I have to go.

[ssmith1627]

If I know I can't finish something, I have trouble getting started.

That's a great way to put that -- I think I'm very similar. I want to be able to at least envision how I'm going to do each step along the way before I get started in something. Once I can do that, I'll work on it every day. But until then I can't even get started on it.

Don't worry about the shop layout though....you'll have to tweak it over time as you use it. I've gone through about 3 rounds with mine in a year trying to get the right balance of being able to use each tool in the space I have and still getting the right performance on the dust collection side of things. You have to find what works and what works for you.

Send us some pictures of that huge space so we can drool.

Steve

[GaryA]

The saw calls for 220V Double Pole 20A breaker. 30A will be fine, but you will not have same level of protection from heat on your interior wiring.

BTW, that is a heck of space for a woodshop!

Thanks...I had the same question.

"Jeffrey Schronce -Fishing The Amazon" I like it....you are definitely the king!

[scorrpio]

If the saw spec says '20A' breaker, having it on a 30 would be dangerous. Even if your wires are sized for 30, you could burn your saw motor.

[jackellis]

The data plate on the motor for that Jet saw says it will draw about 14.5 amps.

[DaveStL]

The saw calls for 220V Double Pole 20A breaker. 30A will be fine, but you will not have same level of protection from heat on your interior wiring.

I missed that-- is 20A spec'd in the manual?

I put in 30A which really seems like overkill, because code seems to say you assume 17A for a 3 hp motor regardless of the motor nameplate, and the permissible load of any single plug-in device on a 20 A branch circuit is only 16A.

So either--
1) code changed since 1996 (starting to suspect this, since the nameplate doesn't have a time rating)
2) I'm missing something (most likely)--
3) code hasn't kept up w/ technology

Any experts out there?

[scorrpio]

I don't have access to Jet manuals, but this is from Grizzly G1023SL (which also has 3hp motor):

The model G1023SL/G1023SLX Left-Tilting 10" Table Saw has a 3HP, 3450RPM motor which requires a 220V single-phase circuit. ... The motor will safely draw about 18 amps at 220V under load.

The model G1023SL/G1023SLX should be fused at 20 amps. Fusing at amperage ratings higher than 20 amps will not adequately protect the circuit. Also be sure that the wiring in your circuit is rated to handle 20 amps.

[ssmith1627]

Fusing at amperage ratings higher than 20 amps will not adequately protect the circuit.[/b] Also be sure that the wiring in your circuit is rated to handle 20 amps.

That makes sense to me. The same for using 12 gauge wire rated for 20 amps and then wiring it to a 30 amp breaker in the box. The breaker would not protect the wire because it would not trip at say 25 amps. The breaker has to match what you're trying to protect or it won't do its job.

You could go the opposite way and be ok -- 15 amp breaker for 12 gauge (20 amp) wire. The breaker would trip before you'd have a problem with the wire and that's fine. But you can't have it the other way around.

Steve

[DaveStL]

I don't have access to Jet manuals, but this is from Grizzly G1023SL (which also has 3hp motor):

The model G1023SL/G1023SLX Left-Tilting 10" Table Saw has a 3HP, 3450RPM motor which requires a 220V single-phase circuit. ... The motor will safely draw about 18 amps at 220V under load.

The model G1023SL/G1023SLX should be fused at 20 amps. Fusing at amperage ratings higher than 20 amps will not adequately protect the circuit. Also be sure that the wiring in your circuit is rated to handle 20 amps.

Sounds like the Griz has a fuse, and they're telling you not to replace it w/ one above 20A? The Jet has a thermal device to protect the saw, so I'm not worried about using the breaker for that purpose.

Looking at code, it seems to me that you have to use at least 10-ga wire for a 3 hp or a 5 hp saw, because you're not allowed to plug in a device on a (15A or) 20A circuit that's more than 80% of the circuit rating. In sizing a circuit to supply a 5 hp motor you assume 27A (IIRC; not looking at the table) but it's not subject to the 80% rule.

Maybe the code guys assume that drivers are pretty interchangeable, so you have to use an amperage for sizing that is on the low end of efficiency of available motors. But 10-ga wire for a 14.5A saw seems like an awful waste.

On the bright side, the shop is ready for an upgrade to 5 hp!

[scorrpio]

The quote is from Grizzly 'circuit requirements' page. But if you want code, here is code. (NEC 2005)

II. Motor Circuit Conductors
430.22 Single Motor
(A) General, Conductors that supply a single motor used in a continuous duty application shall have an ampacity of not less than 125 percent of the motor's full-load current as determined by 430.6(A)(1).

Note, this is for conductors, meaning a motor that draws 18A needs wires sized for at least 22.5A.

III. Motor and Branch-Circuit Overload Protection
430.32 Continuous-Duty Motors
(A) More Than 1 Horsepower. Each motor used in a continuous duty application and rated more than 1 hp shall be protected against overload by one of the means in 430.32(A)(1) through (A)(4).
(1) Separate Overload Device. A separate overload device that is responsive to motor current. This device shall be selected to trip at no more than the following percent of the motor nameplate full-load current rating:
Motors with a marked service factor of 1.15 or greater 125%
Motors with a marked temperature rise 40C or less 125%
All other motors 115%
(2) Thermal Protector. A thermal protector integral with the motor...
(3) Integral with Motor. A protective device integral with a motor...
(4) Larger Than 1500 Horsepower...
(2-4 do not apply here, specified for reference only).
Note: Any motor application shall be considered as continuous duty unless the nature of the apparatus it drives is such that the motor will not oprtate continuously with load under any condition of use

The 80% rule, you might be confusing from non-motor household appliance tables. In particular, table 220.55 specifying that no fixed kitchen appliaance (i.e electric range) should present more than 80% load on the circuit it is on.

So basically, an external motor overload protector cannot exceed 125% of motor amp rating, and in case of a 3hp (about 18A) motor, that's 22-23 amps tops. I maintain - that 30 amp breaker can cost OP his saw.