Confused about Square-D 90A Breaker
- Thread starter b-boy
- Start date
3's would have been too light. 2's got you to 3.5% vd. This assumes you ever get to that level of loading. More important, someone recognized the need to adjust the feeder size and did so b/c of the distance.
You said that like it was a Code Requirement.
Nope. I said it as a smart design requirement based upon the existing stated distance. Too many previous replies were oblivious of this system impact.
Maybe one day NEC will finally provide enforceable tables/correction factors to adjust for the impact of vd. For now, "Informational Notes" are just a way of sneaking up on the topic.
rlitman
Well-known member
How so? The code enforces smart design requirements that are scientifically based on safety. There is nothing inherently unsafe about the voltage drop of the circuit at 100A. And tripping the breaker is not a good cure to the voltage drop issue. The right answer is to plan out your wire for the intended loads.
You need to read 90.1B. The boys at nfpa don’t give themselves as much credit as you give them.
Code provisions for safety do not imply good design considerations for efficiency, convenience, adequacy for good service or future expansion. Their words.
As to the right answer……
The OP did plan for a 90a feeder. Read his first post. I'll assume he did a load calc and allowed for some future expansion since he was operating with a 60a cb for sometime. Regardless, 90a was his basis of design. So why shouldn't it trip above the design value?
If he were to have neglected vd, he could have blindly used #4 Cu’s good for 85A and ocp’d it with a 90a cb (next cb size up from 85a).
Since he smartly considered vd up to and including 90a, he ran #2 Cu THWN’s. Keeping within recommended limits of vd, the ckt should carry only a max of 90a. And how do you do that? Ocp it at 90a.
Allowing any larger cb than 90a will permit the feeder to deliver lower than recommended voltage to the loads. You don’t know what the supply voltage is and can’t assume it is always 120/240v. What if it is 110/220v at the pole? A 5% loss between pole and loads provides for 104/209v at the loads. Low voltage conditions do nothing to promote equipment life or adequate performance.
When the conductor is upsized to minimize vd, you do not upsize the cb. Doing so defeats the entire purpose.
rlitman
Well-known member
A circuit breaker is not a magical device that holds the load below 90A. You're saying that if the voltage drops, without actually encountering a dangerous situation, it is preferable to shut off the power. I'm saying that that's a nuisance trip.
The code allows you to plug a 100' 16 gauge extension cord into a 20A outlet. And there's nothing to stop you from running a heat gun or 18A miter saw on that cord. Should outlets that might have extension cords plugged in have lower rated breakers in them?
Breakers are simple safety devices that protect the wiring. They are NOT control devices that protect the devices plugged into them. That control must be done at the load-calc and device level.
Aceman
Well-known member
You're putting words in the NEC that aren't there, mm08822.
VD isn't enforceable.
You know that, and used poor word choice saying it isn't "permitted." Then your argument morphed into saying "the code is a minimum, this is actually just good design using a 90."
Your posts are misleading.
Everyone makes mistakes, including myself, but it appears not everyone can admit when they make them.
VD isn't enforceable.
You know that, and used poor word choice saying it isn't "permitted." Then your argument morphed into saying "the code is a minimum, this is actually just good design using a 90."
Your posts are misleading.
Everyone makes mistakes, including myself, but it appears not everyone can admit when they make them.
sberry
Banned
just to add.
I need to figure out how to cut on my phone,, but the breaker only protects the wire on a general circuit (with a couple of exceptions) it also can/does protect against fault within connected equipment.
sberry
Banned
How many times can a guy use you and your in a post?
sberry
Banned
I know is tempting to police the internet on several forums but do we straighten out the rest of the crew in the real world? I shouls have snapped a pic of a couple jobs this last week by a couple genius types with licences in their pockets.
Proper terminology is minor.
Proper terminology is minor.
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rlitman
Well-known member
Yes, to a degree. The plug on equipment allows an appliance manufacturer to make some assumptions about available fault currents.
But that the only “connected equipment” relevant to this thread would be the sub-panel directly fed by the breaker in question itself. In this situation, the high impedance of the wire supplying the sub, could potentially allow for using lower interrupt rated breakers in the panel. However, residential breakers already have the lowest interrupt ratings available, so it it’s a moot point here.
alfredeneuman
Well-known member
How minor is it? Just what you personally decide it is?
Using 220 or 110 is minor, but not to some people.
They're all judgement calls.
sberry
Banned
I agree it should be corrected. But is pales in some gems. I know this guy holds a journeymans, doubt a master's but cant make it out of the panel without a couple of basic vode violations and nefore we even make it to the second building where the devices didnt work, about 20 issues in 2 square feet but cant even bury the right wire, put on a box connector, or put a single wore under a screw where there were a dozen open spots, not mention a convoluted box install yjat wasnt needed, wasny grounded, wasnt wiref right and haf 30 on a general circuit .
We should send him over and feel free to yake jis tools away and beat his azz.
We should send him over and feel free to yake jis tools away and beat his azz.
sberry
Banned
These guys aint even remotely dangerous in comparison. 8000 hours experience, testing, cant even run a simple 120v circuit without at least a dozen code violations.
alfredeneuman
Well-known member
Using 220 or 110 instead of 240 and 120 can really mess up an Electrical Engineer's figures.
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Aceman,
I didn’t put words into the NEC at all. For that matter, I explained it in Post 36 where I said vd is not enforceable but why it should be considered and compensated for.
Since you and others interpreted my use of the word “permitted” as meaning “permitted by code” without fully understanding the intent of me adding the following 2 sentences in the same post, it apparently was not the best choice of words or the overall statement should have been more explicit. In the time I had when I made that post it was good enough.
Any run over 100ft triggers me to check for the impact of vd and possibly correcting for it. In this case it is exactly what I did and replied so. The voltage drop calculation for 3% drop at 250 ft of #2 Cu only “permits” 90A as the max load. That is the consistent theme in all of my posts in this thread. It’s your choice if you care to ignore vd or how you size ocp using up-sized conductors.
So agreed poor choice of a word/initial explanation, but you’re way off telling me I pivoted on my initial position.
This is not a question of protecting the wiring from o/l, sc. It’s about delivering the proper voltage range under increasing load. If you install a cb sized for the up-sized conductor that was up-sized to eliminate vd, you are providing the false impression of available headroom on that ckt and have lost any control of minimizing vd/delivering the intended voltage range in the future after everyone involved in the installation is long gone.
alfredeneuman
Well-known member
sberry
Banned
A guy told me that a poco engineer said there was no such thing as number 2 alum wire,,, only 4 and 1 which was really 1/0.
I am not sure what types of electrical engineers there are, probably lots but I have met a couple that made it thru school without ever opening a code book.
But,,, I never opened a welding code book either, only vaguely know there are codes that pertain to various tests I have taken over the years.
I am not sure what types of electrical engineers there are, probably lots but I have met a couple that made it thru school without ever opening a code book.
But,,, I never opened a welding code book either, only vaguely know there are codes that pertain to various tests I have taken over the years.
alfredeneuman
Well-known member
Well, a guy told me that his uncle's friend is related to a guy that knows a man who told him the Moon was actually made of Green Cheese, but I didn't believe him.
sberry
Banned
I had designed a system all for number 2. A week later he xomes with some wire he "got", said it came from a neighbor, a poco engineer who told him there was no such thing as 2. While that is 2 step hearsay I believe him.