Best Practices for Sub Panel Install

[JHZR2]

I'm curious if anyone can comment on the best practices or NEC for a subpanel I want to install. I have an eaton 100A panel avilable free, so Id like to use it as the sub panel. It has a 100A main breaker on it.

I plan to pull service from my main 200A panel, to the eaton panel on the other side of the house. I plan to put most of the home's 240V loads on that new panel, as well as a few 15A lighting circuits. My calculated load under any condition is less than 100A by a long shot. 60A would be more than fine, only issue being that I have this other 100A panel already, free, and it's got a lot of spaces for breakers which I like.

The two panels are in the basement, the wire between them will be exposed, or conduit if I decide to run individual wires.

My main question is if I don't need 100A of service, but the sub panel has a 100A breaker, must I feed it with a 100A breaker and wire of sufficient ampacity from my main? I assume I could feed it with a 60 or 75A breaker on the main panel, then sufficiently sized Cu wire, and just have the 100A breaker on the main panel as a disconnect. Is this wrong/bad/dumb to do?

Some of the space I want to run the wire is tight, so given wire bend radius, etc., it would be desirable to use the right sized (for ampacity) cu wire which is readily available, vs a much larger Al wire sized for the 100A.

Thoughts?

Thank you!

 

[AandPDan]

Originally Posted By: JHZR2
My main question is if I don't need 100A of service, but the sub panel has a 100A breaker, must I feed it with a 100A breaker and wire of sufficient ampacity from my main? I assume I could feed it with a 60 or 75A breaker on the main panel, then sufficiently sized Cu wire, and just have the 100A breaker on the main panel as a disconnect. Is this wrong/bad/dumb to do?


If you meant that you want to use the 100a breaker on the SUB panel as a disconnect that's fine. The breaker on the MAIN panel must be appropriate for the gauge wire you run.

You could, as an example, run #10 with a 30 amp breaker in the main and still keep the 100 amp in the subpanel, as a disconnect.

 

[bepperb]

Being you have no control over the quality of the home inspector your future buyers hire and the likelyhood that a bad inspector will note the "oversized" breaker in the sub I would have them match when you go to sell. And if you're going to replace it then you might as well do it now. It's not a lot of money. I would use your larger panel, though.

 

[Thermo1223]

Nothing wrong with running a 100A breaker as long as the line is designed to carry that load. You could also run a smaller breaker on that same line but if the line can do 100A keep it as that.

We all have 200A mains but do we ever actually pull 200A? No, but the wire is sized correctly so we could if we needed too.

Plus 100A lets you plan for the future.

One more edit:

I would definitely use conduit, use the flexible stuff to make it easier to snake through those tough areas.

 

[Volvohead]

Unless you need a 100A subpanel capacity, I would just use a 60A subpanel and do it right.

This is a 220 job. Running primary feed wire at 100A is a PITA. Pulling 6/3 cable is much easier.

With a 100A panel supplied at 60A, a subpanel overload will rely on the service panel breaker and not the subpanel's. Most code inspectors around here don't like to see that. The subpanel fault should end at the subpanel.

Definitely get an inspector's sticker on the job, to keep your homeowner's coverage happy.

 

[JHZR2]

Thing is the 60A sub panels aren't big enough for my liking. And, the appropriate cu wire for 100A isn't readily available, easily. I need less than 35 feet of it, but it's still a big cost, and if I don't need to feed 100A, what's the point.

Wonder if I can find the equivalent panel sku and return/exchange it for another panel with as many open slots but no main breaker.... Then the service breaker is the only safety and sized to the ampacity of the conductor.

 

[eljefino]

There's a "rule of six" rule where a panel with more than six breakers needs a main disconnect so you can flip everything off in a hurry.

So if you find a sub without a main, it'll be very small.

 

[rjundi]

A long time ago everyone though 60amp panels or even 100amp panels would suffice for an entire home. However things change up over time and folks need far more.

I would suggest wiring it appropriately. As a guess is this in a barn or something? In near future electric charging vehicle will be here and my guess is 60amp won't supply.

 

[JHZR2]

Originally Posted By: rjundi
A long time ago everyone though 60amp panels or even 100amp panels would suffice for an entire home. However things change up over time and folks need far more.

I would suggest wiring it appropriately. As a guess is this in a barn or something? In near future electric charging vehicle will be here and my guess is 60amp won't supply.


To some extent codes require more circuits and people want more for convenience.

But this is in my home, entirely. I just find adding new circuits off a breaker to be easier for a backfit than to make a rats nest of wires all spliced. Back in the days of knob and tube, electricians did a beautiful job of splicing all kinds of circuits off the knob and tube. They would do beautiful wound splices that were really neat and compact. With romex and wire nuts, things are easier but also somewhat bulkier and uglier, plus code makes it all done in junction boxes (the old knob and tube splices would be done in the open). Easier often to just run a wire up through the joists and then to where we want it.

But this also drives proliferation of spaces though there are only small overall loads.

 

[zzyzzx]

I would run the lines to the sub panel big enough to carry 100A anyway, just in case it's ever needed. 60A breaker in main panel to feed it should be just fine.

 

[Volvohead]

Originally Posted By: JHZR2
Thing is the 60A sub panels aren't big enough for my liking. . .


How big is your service panel? Perhaps an upgraded service panel and just pulling the extra circuits you need from that. Because a new service panel typically involves a meter pull, it often requires an electrician.

While we have a basement 60A subpanel, our service panel is a 40 breaker 200A QO box in the garage.

A subpanel is not really meant to replace a service panel.

If you're running most of your circuits to the subpanel, you might be better off moving the service panel to that location. That requires an entry shutoff, a serious conduit run, and an electrician.

I presume this is non-Richie Rich residential, so I don't think you would need more than one service panel/drop to accomodate multiple big boxes.

 

[il_signore97]

Originally Posted By: JHZR2
Thing is the 60A sub panels aren't big enough for my liking. And, the appropriate cu wire for 100A isn't readily available, easily. I need less than 35 feet of it, but it's still a big cost, and if I don't need to feed 100A, what's the point.

Wonder if I can find the equivalent panel sku and return/exchange it for another panel with as many open slots but no main breaker.... Then the service breaker is the only safety and sized to the ampacity of the conductor.


My wife and I purchased our first house together in 2012, and as it was old and was wired incorrectly, I re-wired the house myself. I also put a sub panel in the attached garage at the same time. I found a 12-slot sub panel (or 24-slot if using space saver breakers) with no main breaker, but both my main and sub panels are Simmens. The panel cost me 65 bucks at Home Depot, so no big deal price wise in my case. I ran 6/3 wire with ground out to the sub panel and protected it with a 60A breaker in the main panel.

In your case, I assume you want to do something similar to my setup, but with the existing main panel that you have sitting around. My first question is, would it be possible to buy a 60A main breaker for the sub panel to replace the 100A breaker that is in it now? That would certainly avert some of the possible future issues with potential buyers or home inspectors seeing a 60A breaker in your main panel, but a 100A breaker as the main shut-off in the sub panel.

Also, one other very important point... If you use a main panel as a sub panel, make sure you do not forget to remove the bonding screw or strap that bonds the ground and the neutral conductors together. Most main panels come like this by default, but a sub panel must not have a bonded neutral and ground (only at the service entrance).

 

[GMFan]

Originally Posted By: JHZR2
I'm curious if anyone can comment on the best practices or NEC for a subpanel I want to install. I have an eaton 100A panel avilable free, so Id like to use it as the sub panel. It has a 100A main breaker on it.

I plan to pull service from my main 200A panel, to the eaton panel on the other side of the house. I plan to put most of the home's 240V loads on that new panel, as well as a few 15A lighting circuits. My calculated load under any condition is less than 100A by a long shot. 60A would be more than fine, only issue being that I have this other 100A panel already, free, and it's got a lot of spaces for breakers which I like.



Just be aware that even though the panel may be 100A the continuous load is always 80% of the rating meaning a 100A panel is rated 80A continuous load.

Originally Posted By: JHZR2


The two panels are in the basement, the wire between them will be exposed, or conduit if I decide to run individual wires.

My main question is if I don't need 100A of service, but the sub panel has a 100A breaker, must I feed it with a 100A breaker and wire of sufficient ampacity from my main? I assume I could feed it with a 60 or 75A breaker on the main panel, then sufficiently sized Cu wire, and just have the 100A breaker on the main panel as a disconnect. Is this wrong/bad/dumb to do?




This is allowed by code but isn't ideal. Essentially your 100A panel main breaker would be a disconnect. An alternative to running larger wire is to run two parallel conductors. For example, you could run 2 sets of #6 AWG to achieve 100A ampacity than #1 AWG. Having a 60A breaker in your main panel feeding your 100A panel with 100A main breaker simply means your ampacity is limited by your 60A feeder breaker.

Per the NEC all wiring must be installed so that it is not susceptible to damage. I would conceal the wire within a ceiling. If you are installed exposed I would use EMT conduit along the ceiling and pull the wires within. #1 AWG isn't hard to pull as long as your conduit is sized properly. Unlike smaller gages of wire, #1 is stranded, not solid Cu.

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[Anduril]

It is allowed by code, unless your municipality has a specific amendment prohibiting it. Personally, who cares what a home inspector may or may not say some time in the future. My response to them would be it was legal at the time and (presumably) passed inspection. Take it or leave it. A sub panel is not really a "value-adding" piece of the property.

I have been finding out, over time, that the house we bough a year ago is full of violations, yet the home inspector caught none of them. He basically just made sure the outlets worked.