Wiring up a subpanel in attached workshop

Question

I need to wire up my attached workshop, which is about 50' from the main panel. I don't want to make a bunch of homeruns and would rather install a workshop-specific panel for this task. I will be running the following:

1. 5HP Planer - 30A 240V
2. 5HP Shaper - 30A 240V
3. 1HP Power feeder - 15A 240V
4. 2x 1.5HP Shapers - 15A 240V

Down the line I will also be adding an air compressor and a dust collection system. Obviously I will not be running all of the equipment at once, but it's very likely that I might run my 5HP shaper, 1HP power feeder, and my dust collection system at the same time in the very near future.

Having said that, I'm trying to figure out how to make my life easiest. My main panel is located outside on the opposite side of the house, so the plan is to run in conduit down to my crawl space and then once inside, run through the joists without protection. Here are my questions:

1. I will feed my subpanel with 4 wire cable. 2 hots, a neutral, and a ground. Right?
2. In my subpanel, I will NOT bond my neutral and grounding blocks. Ground and neutral will be independent. Right?
3. What size subpanel should I get for these needs? I was thinking a 60A. Right?
4. What size wire? For 60A at that distance, my calculations say 6 gauge copper. Is that correct?
5. I don't intend on placing a ground rod anywhere, as this subpanel is attached to my main structure (And the subpanel is inside, it'd be very difficult to drive a ground rod anywhere near it). Is this OK?
6. I don't quite understand why I need to separate the ground and neutral at the subpanel. My main panel has the two bonded, so my neutral at my subpanel will still be grounded since it's grounded at the main panel. Can someone explain why this is necessary, just to satisfy my curiosity?
7. How many different circuits should I be considering for these needs? I was thinking 1 for the 5HP planer, 1 for the 5HP shaper, 1 for the power feeder (And future power feeders), and 1 15A for the 2 1.5HP shapers, as they will never run at the same time.
8. Is there anything else I'm missing or overlooking?

I'd like to start working on this expansion by the weekend, so your advice is very much appreciated.

UPDATE: I purchased https://www.lowes.com/pd/Eaton-40-Circuit-20-Space-100-Amp-Main-Breaker-Load-Center-Value-Pack/3027588 which comes with two neutral bars bonded together with a strap. Am I allowed to simply remove the strap and use one of the bus bars as a ground bar, or do I need to purchase a ground bar kit separately? Additionally, the panel came with a small piece of bent metal that attaches one of the bars to the panel. Should this be connected so that the panel is grounded?

Answer 1

1. Right
2. Right. At the subpanel, the neutral and grounding blocks should remain separate.
3. Now is not the time to skimp. 60A looks OK for now, but if you add a 30A dust collector, you've run out of capacity. If you add any lights, 120V receptacles, etc to that subpanel, you're limiting yourself even more. 100A panels are not much more expensive than 60A. Related to this, get a physically bigger panel than you think you need, too. Your plan calls for 8 spaces, but I'd go with at least 16, maybe 20 or 21 or 22, depending on what's available from the manufacturer. Again, bigger panels are cheap now, and they give you a lot more flexibility in the future.
4. As this answer indicates, you'll want #1 Cu or #1/0 Al for 100A, unless everything is temperature rated for 75C in which case #3 Cu or #1 Al would work.
5. This is not only OK, this is the correct and safe way to do it. See this answer or this question and its answers or this one for an explanation of why. The gist is that, with the neutral and ground bonded together at both the main panel and subpanel, any ground fault would energize anything that is grounded.
6. Same as above.
7. Sounds reasonable.

Answer 2

I don't quite understand why I need to separate the ground and neutral at the subpanel. My main panel has the two bonded, so my neutral at my subpanel will still be grounded since it's grounded at the main panel. Can someone explain why this is necessary, just to satisfy my curiosity?

By keeping the neutrals and grounds separate you ensure there will be no neutral current on the feeder ground (the wire feeding the sub-panel) and there will be no ground fault current on the feeder neutral.

Normally, a ground wire is safe to touch and if it has neutral current flowing on it will no longer be safe.

This is simplistic explanation but easier to understand.

Good luck!

Answer 3

Getting this right

Given your choice of subpanel, you'll need to do three things when connecting it to make it safe for your application:

1. You'll need to fit a separate ground bar -- you can get a pair of GBK21s for somewhere between $20 and $40. Your ground wires will all land on these, which simply screw into the back of the cabinet.
2. You'll need to pull the bonding strap out -- this is the small piece of bent metal that connects the neutral bar to the cabinet. It should just pivot down once you've loosened the neutral bar screw and popped it out of the neutral bar though.
3. You'll want to keep the inter-neutral-bar strap in there and make sure all your neutrals land on the neutral bars.

This makes sure you won't mix up neutral and ground (as having current flow on the grounding system can be a serious shock hazard, say due to a failing neutral somewhere), while providing maximum flexibility when landing wires into the panel.

Answer 4

Why bond neutral-ground in a single location, at the service entrance?

Imagine the neutral wire from the sub panel to the main is cut. If the ground is bonded to the neutral at the sub panel, then the ground will carry a load and become energized. And you wouldn't know about the wiring issue. That's a safety hazard.

If the ground is not bonded to neutral at the sub panel, then a cut neutral would result in appliances not working in your workshop. The ground should only carry ground fault currents (short time current to trip a breaker) but should not carry load currents.

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Statistically, the risk of that happening at the main panel is much lower. But if the neutral is cut from the main panel, then the ground can become energized. That's the drawback of tying the neutral to earth.