Sub Panels: Is more better? or Cheaper?

[Matt Radtke]

In the next few months, I'll probably be upgrading my main panel from 100a/24 spots to a 200a/35 spot main panel. A big part of the driver is getting the headroom to expand my basement power. Both for my shop and extra living space. I have a couple options and I'm trying to figure out the best combination of panel(s) and location(s).

What I hope to end up with in the shop: 3 20a, 110v line for routers, hand held tools, and a HF dust collector. 1 20a or 15a circuit for lighting. 1 20a 220v (future 3HP cabinet saw) and 1 30a 220v (future 5HP jointer/planer combo) for future expansion. I want to get this "pretty close to right the first time," because I (read: my wife!) want to drywall finish the ceiling along the path of the runs. So I kind of only get one shot at this.

My original plan was to put a 100a panel in one spot very close to my main panel. (Main panel is in the garage.) Total run from the main panel to propose spot (which is in the storage room) would require only about 10'-15' of cable. Quick, simple, and everything is obvious, and I don't have to fight a giant service cable or long distances. Potential downside: that spot is about as far away as possible from the entry point into my shop. I'm estimate 30 feet from the subpanel to the closest outlet location in the shop and I'd have to drill through 3 joists to keep it out of the future drywalling. With 6 circuits, I could see that getting expensive quickly. And I haven't actually wired up the shop, just brought the power to the shop.

My second thought was put a 100a panel in a more central location close to my shop. The downside is now I have that whole run (30-45 feet) from the main panel to the sub panel. And I'd still have to go through three joists. The hole I would potentially have to drill to get gauge 1 wire and make a 90 degree turn worries me. Should I be worried? On the plus side, the utility room shares a wall with my shop, so I would literally only need to run cable cable 2 feet from the panel to my first outlet.

My third thought was to put two 60 amp panels in the basement, one at each location (storage room and utility room). 6-3NM cable is cheap enough and small enough to not break any backs during installation. Seems to solve the most problems, I'd only have to run one cable to the utility room, but I'd obviously need to buy 2 panels instead of 1, which might not end up saving me money.

Option 3a was daisy chaining option 1 and 3 together: 100a sub panel in the storage room, and a 60 sub-sub-panel in the utility room. Something about that seems bush league to me, but maybe I'm worrying about nothing. I also don't know if it's any better from just 2 60a panels.

Help?

[Chris Padilla]

6/3 is quite easy to work with and I see no issues spreading around a couple 60A panels regardless if they are sub or sub sub or sub sub sub. The electricity doesn't care and as long as you isolate ground from neutral, you should be fine.

The thing I don't know is if the cost is somewhat linear as the wire gauge increases. Having long runs of 12/2 or 14/2 shouldn't break the bank. In fact, you can run it all in 12/2 (even the 15 A stuff) if you want to reduce the loss a bit.

[Buck Williams]

Matt, check out the price of #2 SER cable, 3 - #2 aluminum conductors with a #4 bare ground, O.D. is about 3/4", should be no problem to drill and pull it through 2 x 4 studs. It's done all of the time most stick built apartment buildings have their 100 amp panels fed with this cable.

[Matt Radtke]

Matt, check out the price of #2 SER cable, 3 - #2 aluminum conductors with a #4 bare ground, O.D. is about 3/4", should be no problem to drill and pull it through 2 x 4 studs. It's done all of the time most stick built apartment buildings have their 100 amp panels fed with this cable.

Anything special handling required for the aluminum cable? My exposure to aluminum wiring is pretty much "OH GOD NO," but that's just normal stuff in the wall for outlets and the like.

[Chris Padilla]

I'm not a big fan of aluminum wiring even though it feeds the house sub-panel (100A, came with the house) at my place and feeds the stove (50A). It has a lower conductivity than copper which is why it needs to be larger to carry the same amount of current as copper. It does get a bad rap but it works just fine and it is cheaper. You just need to use the goop at the connecting points to prevent the oxidation that can cause problems. Still, I wouldn't use it. I just like good old copper. :) Each to their own.

[Jeff Duncan]

Personally I'd put the shop panel in the shop and run the cable to that. I would think you could get by with #2, but obviously you need to use whatever code requires. I just ran 3 gauge 4 wire for a sander and it's not that big. Probably fit through a 1-1/4" hole. 2 gauge would be larger but, your only running 2 wires and a ground so??? I will say it's a bit tough with bends, but you only have to do it once!

good luck,
JeffD

[Matt Radtke]

Personally I'd put the shop panel in the shop and run the cable to that. I would think you could get by with #2, but obviously you need to use whatever code requires. I just ran 3 gauge 4 wire for a sander and it's not that big. Probably fit through a 1-1/4" hole. 2 gauge would be larger but, your only running 2 wires and a ground so??? I will say it's a bit tough with bends, but you only have to do it once!

good luck,
JeffD

Well, 4 wires for a sub panel. Hot, Hot, Neutral, and Ground. Isolated ground at the sub panel and that jazz.

[Rollie Meyers]

Matt, check out the price of #2 SER cable, 3 - #2 aluminum conductors with a #4 bare ground, O.D. is about 3/4", should be no problem to drill and pull it through 2 x 4 studs. It's done all of the time most stick built apartment buildings have their 100 amp panels fed with this cable.


2 AWG aluminum is NOT suitable for 100A when used for a subfeed, for that purpose 90 ampere breaker has to be used.

[Matt Radtke]

2 AWG aluminum is NOT suitable for 100A when used for a subfeed, for that purpose 90 ampere breaker has to be used.

I was coming to the same conclusion, though 90a would probably be more than fine for my uses. Of course, 4/0 SER is cheap enough I could do that and be over built.

[Rod Sheridan]

Hi, I'm a big fan of multiwire branch circuits for home shops.

If you put in a 2 pole 20 ampere breaker with 12/3 wire it will supply all your 20A 240V receptacles and all your 120V 20A receptacles in your shop.

I have 4" square boxes every 5 feet along the wall with a 240V duplex and a 120V duplex. Covers all my shop machinery and portable power tools with one breaker.

I also have a separate 240V circuit for the cyclone.

There's no point running a bunch of circuits for a home shop................Regards, Rod.

[Matt Radtke]

Hi, I'm a big fan of multiwire branch circuits for home shops.

If you put in a 2 pole 20 ampere breaker with 12/3 wire it will supply all your 20A 240V receptacles and all your 120V 20A receptacles in your shop.

I have 4" square boxes every 5 feet along the wall with a 240V duplex and a 120V duplex. Covers all my shop machinery and portable power tools with one breaker.

I also have a separate 240V circuit for the cyclone.

There's no point running a bunch of circuits for a home shop................Regards, Rod.

While I I like the idea of use 12/3 for 110, I feel like a single circuit will come back to haunt me. And I have ambitions of a couple larger machines. The last thing I want to do is under-power, get that larger machine, and then have to tear out my ceiling to get more power run.

What big things? 3HP cabinet saw, 5HP Griz J/P Combo, and likely someday my father's vertical mill.

If I never upgrade past a HF dust collector, it seems possible that it plus a 3HP cabinet saw would draw more than 20amp on one circuit. By all means, convince me I'm wrong there and I'll scale back slightly.

[Chris Padilla]

Several years ago when copper was a lot cheaper, I just redid my entire garage with stranded #10 everywhere. I put in flex conduit and pulled the wires. I did the multiwire (Edison) for all my branch circuits as well. All my 30A were individually run back to the panel.

If you REALLY want to future-proof your circuits, run 10/3 everywhere or put in flex conduit so you can pull bigger wires later if needed. Cry once with a lighter wallet and sore fingers dealing with #10 but sleep well over the years knowing you can run any piece of equipment you want at any location you want.

Think about the items that will need their own circuits. You've listed a few: Dust Collector and Air Compressor are the two main ones as these are likely to run when you are running other items. Perhaps an air conditioner, heater, or secondary air filter might need its own circuit. Lights will be on their own for sure (or should...some suggest two separate circuits!). Things like a table saw, jointer, planer, jointer/planer combo, bandsaw, lathe (metal and/or wood) or a mill can technically be shared on a single 240V/30A or 240V/20A circuit.

[Rod Sheridan]

While I I like the idea of use 12/3 for 110, I feel like a single circuit will come back to haunt me. And I have ambitions of a couple larger machines. The last thing I want to do is under-power, get that larger machine, and then have to tear out my ceiling to get more power run.

What big things? 3HP cabinet saw, 5HP Griz J/P Combo, and likely someday my father's vertical mill.

If I never upgrade past a HF dust collector, it seems possible that it plus a 3HP cabinet saw would draw more than 20amp on one circuit. By all means, convince me I'm wrong there and I'll scale back slightly.

My major machines are 4 HP (saw/shaper, Jointer/planer), perfect for a 20 ampere branch circuit.

You'll need a separate circuit for the dust collector.

Regards, Rod.

[Matt Radtke]

Using 10/3 everywhere is not a bad plan and I'll have to think about that one.

And yes, I didn't even mention lighting because yes, it'll get its own circuit.

[Julie Moriarty]

In the next few months, I'll probably be upgrading my main panel from 100a/24 spots to a 200a/35 spot main panel.

I'd upgrade to a 200A, 40 space panel instead of a 36 space. The extra space will be there when you need it.


What I hope to end up with in the shop: 3 20a, 110v line for routers, hand held tools, and a HF dust collector. 1 20a or 15a circuit for lighting. 1 20a 220v (future 3HP cabinet saw) and 1 30a 220v (future 5HP jointer/planer combo) for future expansion. I want to get this "pretty close to right the first time," because I (read: my wife!) want to drywall finish the ceiling along the path of the runs. So I kind of only get one shot at this.

If I counted right, right now you need (4) single pole breakers and (2) 2-pole breakers. That's 8 spaces so you probably want a panel with 12-16 breaker spaces, or more. Since you're planning on drywalling the ceiling, run some feeders out to junction boxes you can access later, in a wall or ceiling that isn't drywalled. You'll have to do some looking into the crystal ball to decide what and where you might need the power in the future. At the very least, run two circuits to each location. You don't have to land them on breakers until you need them.


My original plan was to put a 100a panel in one spot very close to my main panel. (Main panel is in the garage.) Total run from the main panel to propose spot (which is in the storage room) would require only about 10'-15' of cable. Quick, simple, and everything is obvious, and I don't have to fight a giant service cable or long distances. Potential downside: that spot is about as far away as possible from the entry point into my shop. I'm estimate 30 feet from the subpanel to the closest outlet location in the shop and I'd have to drill through 3 joists to keep it out of the future drywalling. With 6 circuits, I could see that getting expensive quickly. And I haven't actually wired up the shop, just brought the power to the shop.

My second thought was put a 100a panel in a more central location close to my shop. The downside is now I have that whole run (30-45 feet) from the main panel to the sub panel. And I'd still have to go through three joists. The hole I would potentially have to drill to get gauge 1 wire and make a 90 degree turn worries me. Should I be worried? On the plus side, the utility room shares a wall with my shop, so I would literally only need to run cable cable 2 feet from the panel to my first outlet.

My third thought was to put two 60 amp panels in the basement, one at each location (storage room and utility room). 6-3NM cable is cheap enough and small enough to not break any backs during installation. Seems to solve the most problems, I'd only have to run one cable to the utility room, but I'd obviously need to buy 2 panels instead of 1, which might not end up saving me money.

Option 3a was daisy chaining option 1 and 3 together: 100a sub panel in the storage room, and a 60 sub-sub-panel in the utility room. Something about that seems bush league to me, but maybe I'm worrying about nothing. I also don't know if it's any better from just 2 60a panels.

Help?

Option 1 seems the worst. Get the panel closest to where you will be tapping it for power. It's also nice to have the panel in your shop in the event you trip a breaker, then it's a short trip to reset it.

Option 2 is what I'd go with. I don't know why you'd be worried drilling the joists unless you have something like 2x6 joists. I've drilled through 2x10s for 2" pipe with no problem. You just have to be towards the center of the joist. Inspectors around here will fail the job if holes are drilled too close to the bottom of the joist but allow for drilling very close to the top. I've never heard of any joist failing because of a hole drilled for electrical distribution. If you go with this option, get the largest 100A panel you can find.

Option 3 isn't unheard of but it can tax the first sub panel, depending on the loads distributed from there. On big jobs, we start with very large switchgear and distribute to subsequently smaller and smaller distribution panels until we finally get to something like a 200A, 120/208v panel. But all the wiring and breakers are sized properly. While Option 3 may not be bush league, it is a bit unusual in a residential application and you'd have to figure for the loads to make sure the sub panels, wire and breakers are properly sized.

Hope this helps.

[Steve Meliza]

You cannot bore a hole in a joist within 2" of the outer edges of the width and it cannot exceed 1/3 of the width of a joist. So a 2x6 joist being 5 1/2" wide would allow for a 1 1/2" hole exactly in the middle of the width. You can also notch the edge of a joist, but only in the outer 1/3 of the span and not deeper than 25% of the width of the joist. I'd say you probably can run your cable for option #2.

For some reason multiwire branch circuits are popular on SMC despite their shortcomings (cost and electrical hazards). Price out 12/3 and 10/3 and you'll find they are made of gold. Then compound the fact that you have multiple types and sizes of wire to run. What you really want to do is use a common size such as 12/2 everywhere than you can so that you can buy it in a large spool. Compare the price of 100' of 12/2 to 250' of 12/2 and you'll see what I mean. In my garage they would be even less practical in that all 120VAC circuits must be GFCI protected. If I ran 12/3 to all my outlets then every single outlet would have to be a GFCI outlet and that gets expensive in a hurry and discourages regular testing of the GFCI capability. Instead my two 120VAC general purpose outlet circuits are from GFCI breakers that cost me $35 each. Time to test GFCI? Walk over to the sub-panel and knock it out. But if you decide to run 12/3 or 10/3 because you feel it has advantages too good to pass up then so be it, it isn't wrong to do so.

[Chris Padilla]

One nice thing about X/3 wiring, including multiwire branch circuits, is that you can make the red a switched hot. Now in a shop this might not be a big deal but as I've renovated my house, I've replaced most of the branch wiring with X/3 so that I can have a switched hot anywhere I want it. VERY HANDY. Is it possible that running two x/2 is cheaper than running one X/3? I've never priced it out but I'll take a look next time I'm at the borg.

Multiwire branch circuits are acceptable by NEC, Steve, so what is so hazardous about them? Cost I won't argue with and GFCI is another good point but hazardous??

And as far as boring holes in studs closer than 2", isn't that what plate protectors are for? Also, this must only be true for load-bearing walls. What about non load-bearing walls and chewing up the studs? I recently gutted my master bathroom and let me tell you, the 2x6 plumbing wall in there had 2x4 studs and 2x6 studs chopped quite severely. I was shocked but I also realized it wasn't a load-bearing wall, either.

[Tom M King]

Use No-Ox, or some such anticorrosion coating on all aluminum wire junctions, and tighten the lug really tight. I keep a 1/4" breaker bar, short extension, and Allen sockets in the Electrical box to tighten all such lugs tight enough that the inspector can't come behind me and tighten them any more.

http://www.sanchem.com/electrical-contact-lubricant.html

[Ole Anderson]

And leave a dedicated circuit for a future 3 hp 220 v dust collector, you may take the plunge sooner than later. I vote for running the fat cable to your shop and keep the #12 runs shorter. Less voltage drop that way. Plus the breakers will be close when you need them, no running to the garage. And you will likely have to upgrade your service drop from the pole.

[Rollie Meyers]

Use No-Ox, or some such anticorrosion coating on all aluminum wire junctions, and tighten the lug really tight. I keep a 1/4" breaker bar, short extension, and Allen sockets in the Electrical box to tighten all such lugs tight enough that the inspector can't come behind me and tighten them any more.

http://www.sanchem.com/electrical-contact-lubricant.html

Code requires that they be torqued with proper tools to manuf. specs, & too tight is just as bad as too loose, & No-alox is not required unless manufacturers instructions require it's use, proper use of the anti-oxidant compound means working it in between the strands.

[Julie Moriarty]

FWIW, when I was a first year apprentice, a representative from the aluminum wire industry came to one of our classes to educate us on the wonders of aluminum wire. At the time, aluminum was just beginning to show up in our area and the rep wanted to get us on board with using their products. I saw aluminum wire being used on the jobsite for about the next 8-10 years or so but gradually it disappeared, even the larger stuff.

Most know the problem with smaller aluminum wire but many felt larger size wire was okay, as long as you did everything right. What we found over the years is the wire in the lugs tended to become loose and had to be re-tightened periodically or arcing would occur. Products like Noalox would reduce arcing problems but it did nothing to prevent the loosening effect that occurred with aluminum wire. I did a few jobs where we had to go back into the switchgear years later and re-tighten all the lugs. I was surprised how loose they had become. Also, while aluminum wire is lighter and cheaper, it doesn't like to make tight bends and if you score it, it can easily break where scored.

[Chris Padilla]

For fun, I took some pics of the prices of the various x/2 and x/3 and for 250' of it from the orange box, we had the following prices:

10/2 - 133.00
10/3 - 191.00
12/2 - 66.74
12/3 - 122.00
14/2 - 43.57
14/3 - 72.24

For #14, you are paying an extra 28.67 for that red wire over /2. For /2, each wire is 21.79 each (black and white only).
For #12, you are paying an extra 55.26 for that red wire over /2. For /2, each wire is 33.37 each (black and white only).
For #10, you are paying an extra 58.00 for that red wire over /2. For /2, each wire is 66.50 each (black and white only).

For #14, the red wire is 6.88 higher in /3 versus the black and white in /2.
For #12, the red wire is 21.89 higher in /3 versus the black and white in /2. Quite a jump from #14.
For #10, the red wire is 8.50 LOWER in /3 versus the black and white in /2.

Interesting stuff.

[Chris Padilla]

...and I think I'll check the breakers that have Al wire on them...make sure they aren't loose.

[Rod Sheridan]

Agree Julie, however annual maintenance along with an infra-red survey is basic maintenance for switchgear, prevents most failures...........Rod.

[Steve Meliza]

Multiwire branch circuits are acceptable by NEC, Steve, so what is so hazardous about them? Cost I won't argue with and GFCI is another good point but hazardous??

Most of the electrocution and fire hazards are resolved by using a double pull breaker as now required by the NEC, but we all know why DIY homeowner's have a bad reputation; they're not always known to follow code or get a permit and inspection. How many "clever" homeowners would save a buck by replacing a defective double pull breaker with two single pulls or clear up some room by replacing it with a 1" tandem? There used to be a website with lots of pretty drawings and clear explanations how a fault in a piece of equipment could result in an over-voltage condition on the other side of the circuit, but I'm having trouble locating it, but what I did find was a real life example of what can happen when the neutral comes loose: http://mattgreensmith.wordpress.com/2012/07/24/irrelevant-aside-household-electrical-problem/ Note that in this story and in the comment at the end neither had a double pull breaker.

The MWBC doesn't really save much money, especially if you have to use GFCI. It requires that you use a double pull breaker spanning both phases which may or may not happen depending on the installer and if a good inspection is performed. If your neutral comes loose in operation kiss your equipment electrical goodbye. If a load shorts out then all or part of the 240VAC appears across the other leg. About the only true advantage is the ability to have 120VAC and 240VAC available from one run of wiring, but I've never found myself needing such an arrangement as my 240VAC equipment are few in number and get a home run dedicated circuit.

In summary, the MWBC is not safe unless installed and maintained properly while the traditional branch circuit with dedicated neutral can be abused pretty badly before becoming unsafe. A good design fails into a safe mode, not a dangerous one.


And as far as boring holes in studs closer than 2", isn't that what plate protectors are for? Also, this must only be true for load-bearing walls. What about non load-bearing walls and chewing up the studs? I recently gutted my master bathroom and let me tell you, the 2x6 plumbing wall in there had 2x4 studs and 2x6 studs chopped quite severely. I was shocked but I also realized it wasn't a load-bearing wall, either.
The question and answer were specifically relating to ceiling joists, not walls. The issue is joist strength, not protection from nails. Load bearing or not, I'd never assume that what a plumber (or DIY homeowner) did to a stud was prudent or to code.

[Rod Sheridan]

Steve, the multi-wire branch circuit is used to supply every residential customer in Canada and the USA, as you're aware.

It must be a terrible safety hazaard.

I presume you're also against 3 phase 4 wire circuits as well?

The MWB circuit is safe, and is a great way to power your shop from one circuit................Regards, Rod.

[Julie Moriarty]

Most of the electrocution and fire hazards are resolved by using a double pull breaker...

In the three and a half decades I worked as an electrician, practically all the circuitry I worked on was multi-wire branch circuits fed from single pole breakers. Not once did I ever get a shock from feedback through the dead leg of of a MWBC nor did I ever hear any of my fellow electricians claim they did either.

As for MWBC being the source of a fire, I can only say I've never heard any fire inspector make that claim, and in my position, I had to deal with many fire inspectors. The primary concern fire inspectors had was making sure the fire safety protections were in place and installed properly. Nor did I personally see or hear of any instance where there may be a fire hazard due to the application of MWBC.

This is not to say the code changes requiring MWBC to be fed from two-pole breakers were unwarranted, only that if there are claims being made stating most of the electrocution and fire hazards are resolved through the application of the new code, those claims may be a bit exaggerated.

[Steve Meliza]

Like I said before, there is nothing wrong about choosing to use a multiwire branch circuit if the advantages outweigh the disadvantages for the woodworker wiring up their home workshop. We are rarely discussing 3 phase or commercial settings where MWBC are common and never worked on by the same guy that flipped the burger you had for lunch. All I did was inform of the risks to the DIY homeowner that are widely recognized outside of SMC.

Perform a search for "multiwire branch circuit" on your favorite Internet search tool then filter out those hits which are simply explaining what it is. I get the following results on the first page:
"improper multi wire branch circuits are a common yet easily overlooked defect in ... "
"Understanding the Dangers of Multiwire Branch Circuits. By Mike Holt"
"The savings from multiwire branch circuits can come at a high cost."
"Beware; the Multiwire Branch Circuit"

Move on deeper into the search results and confusion abounds about the ability to add AFCI and GFCI protection to multiwire branch circuits.

Keep moving on and look for a credible advocate of MWBC's in a residential application (other than here at SMC). I'll wait.

For fun switch your search string to "advantages of multiwire branch circuits". In the first page of results I found not one of them listed any advantages of MWBC without also describing the hazards, and one of the most common cited is fire - "A misfed multiwire branch circuit will silently heat the neutral until it either burns clear inside an enclosure or ignites flammable building material resulting in property loss or worse."

I repeat, use a multiwire branch circuit if you want to.

[Chris Padilla]

Steve,

Electricity in general is dangerous if things are done incorrectly. Perhaps MWBC are "more" prone to being wired improperly or handled improperly? I did the search and found a link describing how IF THE NEUTRAL was disconnected and how long would a TV with 240 V across it burn up? I guess I can see that. Perhaps someone is working on a receptacle on a MWB and removes it temporarily or something. If that receptacle wasn't wired pigtailed, I guess that neutral could be disconnected. I can see in 3-phase that if the wrong neutral is picked to add a circuit too and if the circuit isn't fully shut down that an over-voltage condition can exist.

But again, if things are done wrong, then sure, things could go awry quickly. An open/disconnected neutral is an extremely dangerous condition and I can see how it would be more so in a MWBC. I can see how things in MWBC can go awry more easily than in other situations.

[Steve Meliza]

Perhaps someone is working on a receptacle on a MWB and removes it temporarily or something. If that receptacle wasn't wired pigtailed, I guess that neutral could be disconnected.
I once had a good friend proudly announce that she had replaced several receptacles in the house without having to shut the breaker off.

[Julie Moriarty]

Steve,

Electricity in general is dangerous if things are done incorrectly. Perhaps MWBC are "more" prone to being wired improperly or handled improperly? I did the search and found a link describing how IF THE NEUTRAL was disconnected and how long would a TV with 240 V across it burn up? I guess I can see that. Perhaps someone is working on a receptacle on a MWB and removes it temporarily or something. If that receptacle wasn't wired pigtailed, I guess that neutral could be disconnected. I can see in 3-phase that if the wrong neutral is picked to add a circuit too and if the circuit isn't fully shut down that an over-voltage condition can exist.

But again, if things are done wrong, then sure, things could go awry quickly. An open/disconnected neutral is an extremely dangerous condition and I can see how it would be more so in a MWBC. I can see how things in MWBC can go awry more easily than in other situations.

You've got it right with the neutral issues, Chris. An open neutral can create all kinds of dangers as electricity is seeking the easiest path to ground. Of all the stories I heard and of all the things I personally experienced, the open neutral got the most attention. If you have 2 hots sharing 1 neutral and the hot wires are landed on single pole breakers, you have to know to turn off both breakers before tampering with the wiring. Usually the breakers would be one on top of the other and easy to identify, but I've seen many instances where they are separated and even being on opposite sides (though not directly across from one another, I hope). Every time I trimmed a panel, I would tape the hots and their neutral (single phase or 3 phase) together where the conduit entered the panel, just in case someone later came back and moved the breakers around. Most of the electricians I worked with did the same thing because we all knew how much potential havoc and danger there is with open or crossed neutrals.