Hey Sparkies: Circuit sizing help -

[William McCormick]

Did you try a new 15 amp breaker ?

So if there was 20 amp feeding it that worked perfectly then you installed the 15(max overcurrent ??) only to have it trip.

Your next step would be

pull out #10's and replace with number 12's so you could use a 15 amp MAYBE ?

or

put the 20 amp back on the #10's ?



Yes I realize what you are saying is true about the smaller wire fixing that but it was possibly never really the problem. It was the fast acting breaker kicking it out. But irrelevant if the #12 was plenty fine for load and with only a 15 amp breaker I will give you that it was a fix. A situation such as this is 99.9 % of the time fixed by another method. More than likely the breaker was actually defective. Too fast acting or out of spec.

So it had 10's so it wasn't suffering voltage drop and you say 15 was max and it had a 15 and it was tripping.
Problem. Yes.
Needed the #10's pulled out and smaller wire run instead. Unlikely is all I am saying.

What did a amprobe say it was pulling at startup and running ? Did you try a new breaker ?


If it is sized at max allowed ampacity breaker you should have had PLENTY of amps to start no matter if it had #6's from the breaker to the A/C unit. If it is taking more than the max over current allowed then there is a equipment or voltage issue or they put the wrong overcurrent on the nameplate.
Never realized a wall a/c has a overcurrent max especially at 15 amp.

Sounds like about a 24,500 They draw about 12 amps running but should start with a 15 amp.

The max over should be enough that is required to start that it should not have been happening. Rather than pull out the wire and since the 15 was just too fast acting and tripping you should have just put it on a 20 amp. Wall units are cord and plug connected usually. The overcurrent protection on the wire feeding one is not really where they normally get there protection from. Nice to have the least it requires for better protection but a good 15 amp or if it even took a 20 so be it. Just for start up and wire size is more than there and you know the load. No danger.

I am guessing something more was going on and not working 100%. Like the breaker just wore out from supplying power to the previous unit for last 25 years.


Of course if the volts go down the amps go up and if if are going up the volts are going down some more. Lol.
Long cord going to pull more amps with same load. It is lost to heat from too small of a wire. It is what expected voltage loss is based on and why we must tolerate some amoubt of losses.

Must have needed to be CODE compliant. Lol.

Just not normally how tripping breakers are rectified by reducing wire size is my point. I do understand it allowed you situation to work but similar situation few and FAR between. Betting it just needed a GOOD breaker.

They are +- 10% often so 10% under when you need it all can be a problem I suppose. Usually when a breaker trips that fast during startup it is actually a defective one.

And yes I think you are going to need the right start or run capacitor on anything you work on or they would only sell one. Just changed out the main board in a big Miller engine drive and it had some big ole' cans on that sucker. Had to take them off the old board and bolt on the new one. You would not wanna get bit by one that size. It might leave a mark. Lol.

Yes wire has capacitance.

It is like the magnetic field that is produced when you energize a circuit and hear the wire slap around inside the EMT.

Yes, we did get a new breaker, it worked on another breaker that fed a standard wall outlet run with 14AWG that I had also connected the number 10 AWG wire to in the panel before we got another new breaker. This was a single phase 120 volt unit tiny thing I just did not want to rip apart the cathedral ceiling to get a wire to it. We could not start it through number 10 AWG wire from a 15 amp breaker. I said some of the exact same things as some guys here were saying. But I had seen something similar but I still did not think that is what it was on something so small. I was going through the different testing and then we plugged it into another outlet run with 14AWG and I was impressed. I checked the wiring and it was all good. It just could not start a little AC unit through the 10AWG wire. It was a brand new unit.

Sincerely,

William McCormick

[danielplace]

Yes, we did get a new breaker, it worked on another breaker that fed a standard wall outlet run with 14AWG that I had also connected the number 10 AWG wire to in the panel before we got another new breaker. This was a single phase 120 volt unit tiny thing I just did not want to rip apart the cathedral ceiling to get a wire to it. We could not start it through number 10 AWG wire from a 15 amp breaker. I said some of the exact same things as some guys here were saying. But I had seen something similar but I still did not think that is what it was on something so small. I was going through the different testing and then we plugged it into another outlet run with 14AWG and I was impressed. I checked the wiring and it was all good. It just could not start a little AC unit through the 10AWG wire. It was a brand new unit.

Sincerely,

William McCormick

I respect your fix and I get it. On a #10 that breaker was getting a harder hit which no doubt it would than with something smaller. Smaller wire was your surge protector. Cool.

You the man. Fixed.

Maybe you should have used #14 and fixed it even better. Lol.

I think I would have had to see if a 20 amp on that #10 wire would do the trick and walk away knowing you are not just a wire size change in resistance away from a tripping issue. Only for surge. Those small units do not really rely on upstream overcurrent for any real protection it requires.

It should have just had a 20 amp on it to begin with if it was tripping a 15 amp with #10 wire don't you think. If reducing the wire from 10 to 12 stopped the tripping then the breaker was too small, eh ?

You can plug any 120 volt appliance into 20 amp outlet and not worry about over current being 20 instead of a 15 so you make it a 20 and use 20 amp outlet on the dedicated circuit if you need it a legal install.

[William McCormick]

I respect your fix and I get it. On a #10 that breaker was getting a harder hit which no doubt it would than with something smaller. Smaller wire was your surge protector. Cool.

You the man. Fixed.

Maybe you should have used #14 and fixed it even better. Lol.

I think I would have had to see if a 20 amp on that #10 wire would do the trick and walk away knowing you are not just a wire size change in resistance away from a tripping issue. Only for surge. Those small units do not really rely on upstream overcurrent for any real protection it requires.

It should have just had a 20 amp on it to begin with if it was tripping a 15 amp with #10 wire don't you think. If reducing the wire from 10 to 12 stopped the tripping then the breaker was too small, eh ?

You can plug any 120 volt appliance into 20 amp outlet and not worry about over current being 20 instead of a 15 so you make it a 20 and use 20 amp outlet on the dedicated circuit if you need it a legal install.

A twenty amp breaker with 10AWG would be no problem that we do all the time. The only thing that saved me was that I had never done 10AWG on a 15 amp breaker before not even in the shop to test something, or I would still be there figuring. When I got to something I did not know or never saw work, I had to stop and consider that as a strong possibility, because as I said I was part of something similar with heavier equipment years before so I knew it was possible but I really never thought it could do that with such a little difference in wire size. I also had a good friend who wired up the Shoreham nuclear plant and he told us that it would never be turned on without ripping it down and starting again because they had design flaws in the plant's electrical layout that would never pass. Well anyway, he had explained the breakers function in the panel, as he was installing a panel in a shop, I was setting up my welder in. And he explained the branch circuit to me. It is really called that because you have to have larger breakers feeding circuits that feed smaller breakers and circuits. You cannot feed a twenty amp breaker with a twenty amp breaker it will not work and will not supply the same voltage and amperage as a 40 amp breaker supplying a twenty amp breaker will. I had another friend who learned from a lineman that the main breaker or fuse in a building is also a current limiting device that keeps large induction motors or transformers from detonating power company transformers upon start. He had detonated a power company pole transformer and damaged his body somewhat, equipment in his shop, and others when he bypassed the main breaker to get more amps to test a motor for the Navy that had to have a minimum amperage on start to pass the test. So I had a really good head start on all this.

Some guys and young kids got killed in Queens when they went up the pole on a ladder or stood on a box truck and put cheaters on the secondary from the transformer without current limiting devices, to power their electric transformer type welder with no current limiting device.


Sincerely,

William McCommick

[danielplace]

Do you have any idea just how many breakers come in line before the power gets from the transformer vault in a typical condo building to a branch circuit on a EM sub panel ?

Main breaker feeding the 277/480 main distribution panel then the breaker in that panel feeding the power company line into the Emergency transfer switch breaker then to a main breaker feeding the high voltage EM panel then a breaker feeding a step down transformer then a breaker feeding the 120/240 low voltage EM panel with a breaker in it feeding the EM subpanel with a breaker in it finally feeding a single 120 volt branch circuit.

That is a lot of breakers being run in and out of but yet we get perfect voltage 400 feet up on the roof of a 40 story building.

The taller buildings may have more than a single transformer vault on the main floor.

Lots of stuff on the roof of a modern condo. All the elevator is up there, all the power for the cellular base transmitters and all the power to run multiple swing stages all at once.

Wired all the equipment for the DEA and Homeland security on top of a condo that is right on the inlet in Fort Lauderdale. They have all kinds of high tech surveillance on these buildings. This building is setup. It has a huge diesel genset on the first floor. A second huge natural gas and propane genset on a building outside we constructed just for the generator. The transformer vault has dual main transmission lines being fed into the building from two completely different sources so it is basically outage free already.

[MetalMan23]

I'm pretty sure the OP is gone

[wb4rt]

Nope, just overwhelmed at the depth of discussion. As originally asked, this is a 8x10 lawnmower shed. Will never have air conditioning and welders because it is too small. If the future needs grow, that person can deal with it.

I appreciate all the knowledge, experience, and advice offered but kind of overkill.

Thanks guys, I believe I have my answer. Feel free to carry on the discussion!

[danielplace]

Nope, just overwhelmed at the depth of discussion. As originally asked, this is a 8x10 lawnmower shed. Will never have air conditioning and welders because it is too small. If the future needs grow, that person can deal with it.

I appreciate all the knowledge, experience, and advice offered but kind of overkill.

Thanks guys, I believe I have my answer. Feel free to carry on the discussion!

Then you only need to extend a branch circuit from the house with a single set of #12's and it will run 3 led lights and a battery charger. Anything more for that is a waste of money. No breakers no disconnects no nothing. Tap into existing and be done.

I was just trying to say if you going through all that for 30 you might as well go 60 is all.