Wiring Question

[Ed Calkins]

Hi Guys, I read other posts on this forum that informed me there are real electrical experts responding. So, I am trying to get a question answered that I can't seem to resolve looking at the books etc. I have. I am installing some 1" rigid conduit overhead in my shop from which I will hang two 220V machine outlets (and maybe a 110V outlet?). The entire length including the "hanging" runs is approximately 30'. I will probably use #10 wire for the 220 hot and ground wires, and #12 wire for the 110V wires. Question, can I use one #10 ground wire for both 220 outlets? Each 220 outlet will have separate hot wires going to two different breakers. Can I tie that same #10 ground wire to the ground connectors on the 110V outlet? Or, do I need to run separate ground wires for each outlet? Thanks, Ed

[Charlie Knauer]

Ed, if all three circuits are in the same conduit you only need 1 ground. You will be pig tailing them in each box. The ground wire should be sized for the largest circuit.

Charlie

[Ed Calkins]

Ed, if all three circuits are in the same conduit you only need 1 ground. You will be pig tailing them in each box. The ground wire should be sized for the largest circuit.

Charlie

Thanks Charlie --- that seemed logical to me but I couldn't confirm it anywhere --- good news! Ed

[Ed Calkins]

Charlie (or others),

Another question came to mind. Assuming I run the wires in the conduit to be the proper (THWN) 10 gauge from a 30 amp breaker for a 220 volt application (eg MM16 band saw, 4.x HP motor, 220V 1 ph ) do you think it would be OK to use 12 gauge wire on the cable dropping from the overhead metal box (on 1" conduit). I have some very heavy 12-3 600V insulation wire (for computer equipment) that I would like to use for the 6 to 8 foot cord dropping from the overhead to a connector to the pig tail supplied with the band saw. The manuals I have state that this length of 12 gauge wire is sufficient to limit the voltage drop to less than 2% for the 30 amp ciricuit --- but other ampacity charts I read indicate 10 gauge is needed for 30 amps. I think this bandsaw will use over 20 amps running.
Not sure what start current is. My gut feeling is that using 12 gauge wire for the last 6 to 8 feet (hanging in air) is OK, but wanted another opinion.
Thanks again, Ed

[Duncan Horner]

My gut feeling is that using 12 gauge wire for the last 6 to 8 feet (hanging in air) is OK, but wanted another opinion.
Thanks again, Ed

You shouldn't mix different size wire in a circuit, esp since you'll be overloading the wire for the last segment. If you were using a 20A breaker, I'd say go for it, but on a 30 you're pushing it. Go buy some #10 cord and strain relief and let it dangle :)

[Roger Frazee]

What plug is required on the power pigtail supplied on the machine. Just guessing they want a locking plug like a L6-30R.

Most 12/3 awg flexible cable insulations will allow 25 amps.


There are only a handful of flexible cables where 12 awg would allow 30 amps.

What is the insulation code on your flexible? ...ie.. SJOW...

[Rob Russell]

#12 is limited to 20 amps per 240.4(D) as a "small conductor". There are exceptions, but I don't think you want to get into taps or single motor rules.

[Ed Calkins]

Thanks guys, I want to do it right so I will get heavier cable for any drops that require 30 amp breakers --- I haven't purchased the machines for the two drops yet so some of this is speculation -- that is another decision about to be made. This wealth of knowledge available on the internet is somewhat of a mixxed blessing --- it is very valuable but therefore you have to access it and use it and follow it. How did I ever survive my pre-internet life?? Thanks again, I really do appreciate the help, Ed

[Roger Frazee]

I agree with Rob that 12 awg is limited to 20 amp protection not using the motor rules. However I'm not so sure you can treat this as required in 240.4 d for small conductors. Your MM16 bandsaw has a nearly 5 horsepower motor (4.8 HP) and you intend to provide it with an individual (dedicated) branch circuit. I think the first rule to follow here is you need to have the manufactuer specifications on the electrical requirements. Then we can give you accurate information on the branch circuit conductor size... as this bandsaw is a commercial machine not your lowes floor brand. I wouldn't run any wire till I have that information.

[Rob Russell]

Roger - most of the article 430 rules on motors allow for a larger circuit breaker in relation to the conductor size than a typical branch circuit would allow. If the typical homeowner sizes the conductors to the breaker size based on table 310.16, there's never going to be a worry about some future use of that circuit where the load devices pull more than the conductors were designed for.

In other words, I think we're safer by following the KISS principle and putting in standard branch circuits vs. getting into all the motor-specific stuff.

JMO - Rob

[Roger Frazee]

Roger - most of the article 430 rules on motors allow for a larger circuit breaker in relation to the conductor size than a typical branch circuit would allow. If the typical homeowner sizes the conductors to the breaker size based on table 310.16, there's never going to be a worry about some future use of that circuit where the load devices pull more than the conductors were designed for.

In other words, I think we're safer by following the KISS principle and putting in standard branch circuits vs. getting into all the motor-specific stuff.

JMO - Rob

Yeah I have to agree with you. It's just hard for me to leave my industrial roots....:)

For what it's worth I called mini max technical support and the band saw with a 4.8 hp motor 230 volts single phase requires a 30 amp breaker and 10 awg conductors. I certainly agree with the KISS principle in a home shop. However I am forced by nature to look a little deeper when commercial equipment ends up there. Ohhh and they said connecting cord and plug is fine, overload and all that motor stuff is integral to the machine.
I'd recomment a L6-30P and matching receptacle. I like locking receptacles for this type equipment.

See I'm starting to learn how to keep things simple....:D

[Rob Russell]

I agree with locking receptacles/plugs for all machinery.

If you want to talk "industrial", let's discuss my 3-phase machinery offline :) .

[Ed Calkins]

Thank You, Thank You -- your advice has been followed. I had all the wire etc. I needed other than 100' of #10 (red) so I bought it at the local building supply (nearest Home Depot is a couple of hours away). It cost $50. I didn't want to invest in the 500' bulk roll so had to buy it by the foot. Now I see why the crooks are stealing copper instead of rustling cattle. Ed

[David G Baker]

Ed,
Copper wire is cheap now compared to the last year. My local Ace Hardware was asking $135 for 250 feet of #12 two with ground. I ended up getting at Home Depot for $70 because I had a 10% discount coupon and the price was quite a bit cheaper than most other places.