Max # Conductors in EMT

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mgknitt01

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I have 3 woodshop machines that need power. Each machine requires a
30amp 3/phase 208 recep with an overall length of 190'. Am I allowed to pull all #10awg conductors in one raceway without derating or voltage drop calculations?
 
mgknitt01 said:
I have 3 woodshop machines that need power. Each machine requires a
30amp 3/phase 208 recep with an overall length of 190'. Am I allowed to pull all #10awg conductors in one raceway without derating or voltage drop calculations?
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Not more than 3 current carrying conductors in a raceway then you don't have to derate,sounds like you do, edit (however) also you need to check you load and calculate the VD. Here is a site http://www.elec-toolbox.com/calculators/voltdrop.htm
 
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mgknitt01 said:
I have 3 woodshop machines that need power. Each machine requires a
30amp 3/phase 208 recep with an overall length of 190'. Am I allowed to pull all #10awg conductors in one raceway without derating or voltage drop calculations?
Click to expand...
Look at Table 310.15(B)(2)(a)
 
Thanks for your previous advice, apparently voltage drop requires #6 awg, so
is it better to run seperate conduits for each machine and pull separate grounds or can I run one conduit for all 3 machines and pull one ground and what is #8awg the reqired size ground for #6awg
 
mgknitt01 said:
Thanks for your previous advice, apparently voltage drop requires #6 awg, so
is it better to run seperate conduits for each machine and pull separate grounds or can I run one conduit for all 3 machines and pull one ground and what is #8awg the reqired size ground for #6awg
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Yes you can use one conduit with one ground. Look at Table 250.122-- It has to do with overcurrent protection not the size of the current carrying conductors but you will have to derate.
 
Am I reading this Table 250.122 right, It says the rating or setting of automatic overcurrent device in circuit ahead of equipment, conduit, ect. Not exceeding (amperes),
which would be a 3pole 30 amp breaker. The grounding conductor would be
#10awg?
 
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MG, I'd seriously consider running a single feeder to a sub-panel near the equipment. The description you gave indicates the three loads are grouped, and this would be cheaper than 3 circuits.

Unless all three machines will run simultaneously, a single set of #6 cu conductors should be plenty. A 12-space 3ph panel would allow a fourth 3-ph load (or 1 or 2 1-ph loads) to be added in the future.
 
LarryFine said:
MG, I'd seriously consider running a single feeder to a sub-panel near the equipment. The description you gave indicates the three loads are grouped, and this would be cheaper than 3 circuits.
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I agree.

Unless all three machines will run simultaneously, a single set of #6 cu conductors should be plenty. A 12-space 3ph panel would allow a fourth 3-ph load (or 1 or 2 1-ph loads) to be added in the future.
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I disagree, the feeder will have to be large enough for the connected load.
 
1793 said:
You might want to look at Article 250.122(B) for equipment grounding conductor size.
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thanks norb I neglected that info.

mgknitt01 said:
When you say 3 circuits you mean 3 conduit runs right?
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No, run one conduit with 3 phase and a ground that is sufficient to carry the load of all three motors. Set a subpanel and then wire the 3 machines from the subpanel.
 
mgknitt01 said:
Thanks for your previous advice, apparently voltage drop requires #6 awg, so
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MG--- you better try that voltage drop calculation again. I think you plugged in 30 amps. You need to plug in the load of the motors not the circuit size-- I am asssuming it is less than 30 amp.
 
iwire said:
I disagree, the feeder will have to be large enough for the connected load.
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Okay, I agree with that, but I did qualify my faux pas with not running machines simultaneoulsy, but of course an exclusionary interlock would be necessary. However, the feeder OCPD would protect the feeder conductors from real damage. 30a receptacles should not be subject to 30 amps.

mgknitt01 said:
When you say 3 circuits you mean 3 conduit runs with required conductors in each right?
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Yes. Whether you consider running 3 separate conduits, each with a set of #10's; or a single conduit with three sets of oversized conductors which you'll still have to distribute; it's gotta be less expensive, labor and materials both, to run a single set of conductors in a single conduit to a panel near the machinery.

From there, you'd use a separate 3-pole breaker and #10 wire in whatever wiring method suits the location, from the panel to each machine. With load diversification, you'll experience improved machine performance and cooler running due to a larger conductor for the majority of the 190-foot run.
 
Dennis Alwon said:
No, run one conduit with 3 phase and a ground that is sufficient to carry the load of all three motors. Set a subpanel and then wire the 3 machines from the subpanel.
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You may want to pull a neutral for possible 110 volt circuits.
 
LarryFine said:
Okay, I agree with that, but I did qualify my faux pas with not running machines simultaneoulsy, but of course an exclusionary interlock would be necessary.
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IMO to much unneeded complexity. cont actors and pilot relays.

I like the "KISS" method (Keep It Simple Stupid)

However, the feeder OCPD would protect the feeder conductors from real damage. 30a receptacles should not be subject to 30 amps.
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What works is not always what meets code.

Yes. Whether you consider running 3 separate conduits, each with a set of #10's; or a single conduit with three sets of oversized conductors which you'll still have to distribute; it's gotta be less expensive, labor and materials both, to run a single set of conductors in a single conduit to a panel near the machinery.
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Actually after thinking on this some more to meet the NEC all that needs to be done is run nine 10 AWGs in the same conduit.

Assuming 90 C conductors the 10s could still be protected at 30 amps after derating.

However 190' feet is a long way on 10s for a 30 amp circuit. To overcome voltage drop he would need nine 8 AWGs and if in the same conduit it would have to be an 1.25"

That being the case it might make more sense to run one set of 4 AWGs (24 amps x 3 = 72 amps) to a panel as Larry has suggested.
 
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