Wiring for table saw

[woodturner]

I agree that 12 gauge on a 20amp paired breaker is a good choice.

For motor applications, NEC specifics a higher current rating, 125% of FLA as I recall, without looking it up. I'd recommend 10 guage wire, NMB is fine, run in EMT conduit if it is exposed.

[chopnhack]

For motor applications, NEC specifics a higher current rating, 125% of FLA as I recall, without looking it up. I'd recommend 10 guage wire, NMB is fine, run in EMT conduit if it is exposed.

If I am not mistaken you are quoting a part of NEC that refers to motor loads that are expected to be continuously run. That is not the case for a table saw....


As for NM we covered the section of NEC earlier that covers sleeves, however it might not be the best nor code approved method. YMMV

[cabinetman]

If I am not mistaken you are quoting a part of NEC that refers to motor loads that are expected to be continuously run. That is not the case for a table saw....

That's the problem with advice on the internet. Quoting parts from sources doesn't make it applicable to some situations. The best advice is from an electrician local to the jobsite, that is familiar with all the codes.

.

[woodturner]

If I am not mistaken you are quoting a part of NEC that refers to motor loads that are expected to be continuously run.

It's the startup surge that increases the current. Motors draw in the range of 150% of FLA on startup, and the current capability of the wire must accomodate the higher current. If the voltage drop is too high, the motor will overheat and eventually be damaged, as well as being slow to start up. NEC requires the increased current capability for motors 1/8 HP or larger.

NEC reference:
220.18 Maximum Loads.
For circuits supplying loads consisting of motor-operated utilization equipment... the total calculated load shall be based on 125 percent of the largest motor load.
430.22 Single Motor. 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 full-load current rating....

(note: "continuous duty" refers to the motor specification, not the usage. Most motors used on woodworking equipment are "continuous duty" motors)

As for NM we covered the section of NEC earlier that covers sleeves, however it might not be the best nor code approved method.

I replied before I had read all the way through the thread. "Sleeves" are one but not the only application for NM in conduit. I've never had an inspector question it, but I have had them require it. In some areas, notably Chicago, ALL residential wiring must be in conduit or AC cable, but that is a local enhancement of the NEC (local code can impose stricter requirements but cannot relax requirements of NEC).

It is a common misperception that NM is not permitted in conduit, but NEC imposes no such restriction. There is no reason not to install NM in conduit, and it is common practice. There are a number of threads on these topics on the Mike Holt forums if anyone wants to explore further.

NEC references:

334.10 Uses Permitted.
...both exposed and concealed work in normally dry locations...

334.12 Uses Not Permitted - conduit is not listed and is therefore not "not permitted"

334.15 Exposed Work
(B) Protection from Physical Damage. The cable shall be protected from physical damage where necessary by conduit, electrical metallic tubing, Schedule 80 PVC rigid nonmetallic conduit, pipe, guard strips, listed surface metal or nonmetallic raceway, or other means.
(C) In Unfinishted Basements and Crawl Spaces.....Nonmetallic-sheathed cable installed on the wall of an unfinished basement shall be permitted to be installed in a listed conduit...

[BadeMillsap]

Should have kept my virtual mouth shut! It continues to amaze me, regardless of the forum online ... if/when an electrical question arises and is answered ... a lengthy discussion (often a food fight) ensues regarding the NEC and interpretation there of ...

I am not a licensed electrician nor do I play one on TV!!

My comment about using NM in a protective sleeve was based on my personal recent solution to a problem of getting wire conveniently to a table saw located in the middle of my new shop since I decided against the effort/expense of running conduit in the slab (specifically because that would have initiated questions by the inspector about the intent and I wanted to avoid as much city scrutiny as possible since the project cost was already well over budget) .

So ... it was 12-3 NM wire for my 3hp Griz 1023SL and it seems very happy.

[chopnhack]

NEC reference:
220.18 Maximum Loads.
For circuits supplying loads consisting of motor-operated utilization equipment... the total calculated load shall be based on 125 percent of the largest motor load.
430.22 Single Motor. 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 full-load current rating....

(note: "continuous duty" refers to the motor specification, not the usage. Most motors used on woodworking equipment are "continuous duty" motors)

I'll disagree:

As you see the first title is for Max Load - a table saw only achieves max load when? When the arbor locks up! Despite that, the advice already given already exceeds this portion of the NEC with a recommendation for a 20a circuit and wiring.

Reread 430.22, it doesn't call out a continuous duty motor it actually defines the use of a motor in a continuous duty application. There is a difference that you are misunderstanding. Table saw motors are continuous duty rated versus intermittent rated because of potential duty cycle demands and thus longevity. This NEC section is referring to upsizing conductors in situations where the duty cycle maybe 100% i.e. - a motor that may run constantly.

[woodturner]

As you see the first title is for Max Load

Yes - the maximum current load permitted for the wire, not the motor loading.

430.22, it doesn't call out a continuous duty motor it actually defines the use of a motor in a continuous duty application.

I can understand how some could infer that interpretation, but NEC 430.22 does specify a "continuous duty" motor, a designation assigned by the motor manufacturer, rather than continuous loading, which is what you described. 210.19 is the section that derates conductors based on continuous loading.

More detailed explanations are available in the Mike Holt forums if you want further explanation or information. That's probably a better place to discuss the nuances of NEC, given that there are other licensed electricians and PEs there, while I think there are only a couple of us here. A membership (which is limited to licensed individuals) is not required to read the Mike Holt forums.

[woodturner]

it was 12-3 NM wire for my 3hp Griz 1023SL and it seems very happy.

Sounds like you have a short run of wire and it should be fine. One "quick and dirty" check is to watch nearby incandescent lights when you start the saw. If the lights don't dim visibly, it's likely fine.

Motor efficiency and type also comes into play. As another reference point, I have a 2 HP Leeson motor on my General TS. Although it's only a 20' wire run from the panel, even with 10 gauge NMB it dims the lights a little on startup, but voltage drop is still within NEC spec

[Tom Slick]

The "NMB in conduit" argument can be avoided by using MC of the correct size.

[chopnhack]

Yes - the maximum current load permitted for the wire, not the motor loading..

NEC reference:
220.18 Maximum Loads.
For circuits supplying loads consisting of motor-operated utilization equipment... the total calculated load shall be based on 125 percent of the largest motor load.

The conductors are sized to support the motor load, that is the entire purpose of this section.

I can understand how some could infer that interpretation, but NEC 403.22 does specify a "continuous duty" motor, a designation assigned by the motor manufacturer, rather than continuous loading, which is what you described. 210.19 is the section that derates conductors based on continuous loading.
.

NEC 430.22 is also known to some as Duty Cycle Service when designing branch conductors for motor service. And that part of the code does not specify a continuous duty motor rather it gives the guidelines to design for whatever motor needs to be used, whether intermittent or continuous duty. The OP got what he needed, the rest of this discussion is too esoteric.

[chopnhack]

The "NMB in conduit" argument can be avoided by using MC of the correct size.

True, and this is the safest and probably best use of MC in a shop environment where its subject to damage. MC also allows for flexing to some extent so if a machine is hardwired but has some vibration, the MC can handle it where EMT would not work.

[chopnhack]

Sounds like you have a short run of wire and it should be fine. One "quick and dirty" check is to watch nearby incandescent lights when you start the saw. If the lights don't dim visibly, it's likely fine.

Motor efficiency and type also comes into play. As another reference point, I have a 2 HP Leeson motor on my General TS. Although it's only a 20" wire run from the panel, even with 10 gauge NMB it dims the lights a little on startup.

Wow, 20" to your panel... how do you work like that?

Seriously though, if you have a 10g wiring feeding a 2hp motor and your lights are dimming don't you think you should address it?

Are you running 120v? That would be nearly a 20a draw if not more on startup....

[woodturner]

if you have a 10g wiring feeding a 2hp motor and your lights are dimming don't you think you should address it?

Are you running 120v? That would be nearly a 20a draw if not more on startup....

No need to "address it", it's normal and not a problem, voltage drop is still within NEC limits.

The TS is wired for 240 VAC, but as mentioned has an actual continuous duty 2 HP synchronous motor. Motors draw large current surges on startup than can be signficantly greater than the nameplate rating (The 125% derating specified by NEC is an averaged value to protect the wiring).

[chopnhack]

No need to "address it", it's normal and not a problem, voltage drop is still within NEC limits.

The TS is wired for 240 VAC, but as mentioned has an actual continuous duty 2 HP synchronous motor. Motors draw large current surges on startup than can be signficantly greater than the nameplate rating (The 125% derating specified by NEC is an averaged value to protect the wiring).

That's cool, so long as you stay safe while working. But seriously, how did you get your t.s. so close to your breaker box

[Tom Slick]

True, and this is the safest and probably best use of MC in a shop environment where its subject to damage. MC also allows for flexing to some extent so if a machine is hardwired but has some vibration, the MC can handle it where EMT would not work.

In what garage or small shop application would any shop equipment be hardwired? Maybe an overhead dust collector? Every tool is going to have a cord and plug, even the 240v stuff.

Dimming lights can also indicate a loose (floating) neutral