Shop Service Comments?


Old 03-28-02, 08:01 AM
Tom Carter
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Thumbs up Shop Service Comments?

First post here on this great forum. I really appreciate having the expert advice available on these DIY forums.
I have a plan to add power to the new workshop I'm building, and I'd like to run it by here for your concurrence.
1800-sq ft high-bay detached workshop will have both woodworking and metal/engine tools, climate control (possibly heat pump) and several 3-5 hp single and 3-phase motors (rotary phase converter).
I plan to add a 240V/100A breaker to my 200A service entrance panel at the house. Will run #2AWG THWN (2 black, 1 white, plus #6AWG equipment ground conductors) underground in 1-1/2 inch PVC conduit buried 18" for 125 ft. At shop, will install a 200A SEP I already have, with a 200A service disconnect/breaker. Will isolate the neutral buss from ground and will install two grounding electrodes 6-ft apart at shop to ground the EGC buss there. Will add 20A and 30A circuits as needed in shop using NMC and quad receptacles.

See anything (A) unsafe, (B) non-NEC compliant, or (C) wasteful? I'd appreciate your comments. Thanks again for being there.
Tom C
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Old 03-28-02, 11:04 AM
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Table 430-148 of the NEC lists 28 amps as the full-load current of a 5 HP single-phase 230 volt motor. The starting surge may be 300% of this value or approx 100 amps.If you add this to a 5HP motor already running, which is 130 amps. you may trip the 100 amp breaker at the service.On motor-feeders the NEC permits a circuit-breaker with a rating that exceeds the rating of the feeder conductors,ex., a 150 amp breaker protecting conductors rated at 100 amps.I believe a motor-feeder calculation is needed.I suggest you submit a detailed list of the loads you plan on connecting to the feeder. Another question is the maximum load (compared to the total connected load) that will be in operation at a given time. This depends upon how you will utilize the motor-driven equiptments. Please reply-thanks.
Old 03-28-02, 12:22 PM
Tom Carter
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Worst case might be:

lights on plus maybe fan, radio-2KW;
dust collector running-3hp, 230V;
start 3-phase rotary convertor, then start 5 hp 3-phase radial arm saw.

One unknown might be the 5 hp compressor with a mind of its own kicking in.

Clearly, if I decide on a heat pump, that would be too much.

Think I should revisit Plan A for dedicated 200A service from the electric co-op?

Trying the pic again--see attachment.
Old 03-28-02, 05:50 PM
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Because of the length of the run. I would suggest copper conductors sized as you mention, not aluminum.
Service size is a question. Practically adding the loads you will have on continuously, may be a concern because of starting current of the larger motors. 5HP, 3ph radial arm saw seems pretty big!
Old 03-28-02, 06:29 PM
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Aside from the service questions, one minor issue:
Why are you running NMC to you recepticles? In VA can you not run EMT? I would recommend EMT conduit in a shop environment. sounds like you are doing some serious fabricating in there. Cost difference is slight but well worth it.
Old 03-28-02, 08:01 PM
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If interior will be finished with panelling or wall board, NM cable is fine and much easier to install.
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