Electrical Safety

There was an earlier post that someone replaced a breaker on a motor because it was tripping.

After much discussion, I do not believe the OP understands, or admits, what they did wrong.

Breakers are sized to protect wiring and devices, they should be sized correctly from the start and NEVER replaced with a larger one if it starts tripping. Just because it has not started a fire yet is not an excuse for it being OK. Older homes had a small quantity of large fuses, so things just got added to the fuses and it was common practice to put in larger fuses or pennies. This led to many fires. and the advent of the NEC or national electrical code. There is a very good base of electrical engineers and electricians here, so please post if you have questions.

There is no shame in being wrong, unless you do not correct the issues and be safe.

I will add, most motors have internal overloads, so should self protect.

Breakers do not have an infinite life. As they age they get weaker.
If a breaker is tripping often, at least replace it with a new one of the same amperage, if it was the correct size to begin with.

Had a 16 HP motor tripping a breaker erratically- Sometimes minutes, sometimes hours. Had an electrician come check the motor draw. We put in a new breaker same size- problem solved.

Motor circuits can be treated different. Can use time delay protection to avoid nuisance tripping, can't recall exact numbers but can size to let something like 225% of nominal rated through. Wiring is still sized at 125% of FLA or something like that.

Just to note, time delay protection is not just a bigger breaker. It will trip at the same rating for long loads to protect the conductors. It just lets short over loads occur for motor starting.

A few years ago several breakers kept "tripping" in the basement on a 200 amp panel, so I called an Electrician. There was condensation and rust on several of the breakers. Needless to say the panel and all the breakers were replaced. We think water had found it's way down the drop pipe into the panel. Electrician said it was a fire waiting to happen. Insurance covered the cost, and it was a learning experience for me not to ignore or override what safety equipment is designed for.

David,
You are right about internal protection. However starting a submersiable pump under hundreds of feet of water pressure needs a special pump. Having hundreds of feet of wire you'll need smaller guage wire than most think is needed to handle the LRA.

Locked Rotor Amps, sometimes abbreviated LRA, is exactly what the name implies. If the rotor is locked and can't move while electrical power is applied, the motor will draw this many amps. Locked Rotor Amps are much higher than running amps, generally around five times max running amps.

Doing the same thing over again and expecting a different result isn't working. Learn from the past and fixed it the right way.

geo.

That's a common problem where trades overlap, plumbing and electrical, carpentry and electrical, etc.

More common in rural areas with no permits or inspection, very costly to bring out an electrician to complete the job.

Still no excuse for the person doing the job to not know or care enough to learn the correct way to do the electrical.

In this case the OP at least knew enough to catch it. Think how many jobs get done wrong and the home owner never checks or doesn't know what to look for!

To me, it was fairly simple. Buss, Cutler-Hammer, etc. all provide handy little slide-rule devices that will tell you the recommended breaker size, wire size, conduit size, FLA, etc., for whatever motor you have, whatever phase. These are based on the NEC. Go by those slide rules, available at most electrical shops, and you will be OK. And DON'T upsize. Then you will NOT be OK.

I believe there are a few cases where you can use a smaller wire size such as free air or possibly underground. Knob and tube may have been rated differently too but dont quote me on these.
In a few cases I have used larger wire than I needed because that is what I had in the van or for voltage drop. In these cases it was tied into a smaller wire down the line. I put labels on the wire near the breaker hoping that if it does trip the person working on it wont put a larger breaker on it. At the time I dont think anything in he code book said it had to be labeled? If any of you are ever in a panel upsizing a breaker because of wire size better make good and well the wire stays the same size through out. Tap rules also come into play here. If the wires are under a certain length the can be smaller.

Correct me if I am wrong but a 30 amp breaker on a 1 hp motor running on 220 volts is already to big of a breaker to start with and he changed it to a 40 amp.

You are correct.

I had a customer do the same thing, was smaller customer that did not understand.

40 amp breaker was tripping, so moved it to 70 amp, burned up some stuff.

David, great post, AS USUAL when any electrical or legal question is posed:

A) There is "some" (NOT saying all mind you don't anyone have a calf) misinformation and misunderstanding out there.

B) There are a TON of opinions, some lay some professional, some ignorant some educated, some right some wrong.

That being said FWIW here's my rusty recall based on the NEC as it was way back when I practiced power distribution but no warranty, things change and my memory cells are fading lol. I was also an electrical engineer for Century Electric Motor Company but that was like 50 years ago

1) When you design a branch circuit you FIRST compute the "maximum continuous current"
2) You size the conductors to have a MINIMUM ampacity of 125% of the MCC
3) You provide and size overcurrent protection TO PROTECT THE WIRE which was sized per the above !!!!!!!!!
4) The Motor (wire already protected per the above) itself is protected by internal thermal overload protection or external thermal overload devices such as found in motor starters or combination starters etc aka "heaters" or "thermals" properly sized to avoid excess current and overheating and motor damage.

OVERCURRENT PROTECTION

When a motor starts there's an initial high surge current that may be 3 to 6 times as much as full load current and a typical general purpose Thermal Magnetic circuit breaker might therefore trip SOOOOOOOOOOOO when I practiced the code allowed the use of a circuit breaker as much as 175% above the value as computed above to allow the motor to start. Their reasoning as I recall was based on the fact if a dead short were present the "magnetic" portion of the thermal magnetic breaker would still cause it to trip PLUS the motors thermal protection device (as above) would still protect the motor.

HOWEVER other methods were available such as instead of using circuit breakers use Dual Element Time Delay Fuses orrrrrrrrrrr I think they made HACR circuit breakers which served a similar purpose as Dual Element Time delay Fuses to allow the motor to start and not trip.

Sooo you compute the maximum continuous current,,,,,,,,,,size the conductors to have a minimum ampacity of 125%,,,,,,,,,size the overcurrent protection to protect THE WIRE,,,,,,,,,,,Make exception to allow motor to start (Time delay fuses or bigger or specialized breakers) ,,,,,,,,,provide motor thermal overload protection,,,,,,,,,,

DISCLAIMER Im long retired n rusty so if any professional electrical engineers or electricians can add to this or correct it PLEASE DO SO so we might all learn.

NOTE Anytime fire or life safety is concerned consult local authority or trained professional electricians or engineers and DO NOT risk your home or life on opinions (lay or professional mine included) posted here, too much is at risk !!!!

John T BSEE,JD Long retired n rusty power distribution design engineer so noooooooo warranty don't bet your life or home on it

I haven't followed all this, but my Cutler-Hammer slip-stick reads; 1 HP, single phase, 230 volt, motor full load amps = 8 amps, THHN metallic conduit size = 1 inch, ampacity of copper conductor should be = 115 amps, voltage drop = 0.0370 volts/ amp per 100 ft., instantaneous trip GMCP / HMCP circuit breaker rating = 15 amps, ordinary circuit breaker trip rating = 15 amps, time delay fuse = 10 amps.
Get a slip stick, makes it very simple.

In fact, what I have done, very successfully, is follow the above Cutler-Hammer slip stick recommendations, and if the motor starts up and runs just fine, I step it DOWN one circuit breaker size, and see if it still works OK. For the most protection.

Well, some of this safety mess has gone overboard at the same time people are getting more stupid. It's sometimes hard to find a middle ground. I was raised in a house where there was no electricity in the house when it was built. When electricity was added the wiring was feed through the walls and the receptacles were just screwed to the plaster lath without being in a box. I know on occasion pennies were used in the fuses temporarily until an actual fuse could be obtained. Then nobody cheeped out and used 14 gauge wire on anything either like they do today. The service wires were run through the attic as just bare copper wires on glass insulators. The wires were still 4' apart but sometimes people went in the attic. As of last July I know the house was still there and I know prior to 2014 nobody was ever hurt on the wiring. People just used to be more careful with things like that.

There is short circuit protection and there is thermal protection . Two separate topics but sadly 99.9%of the general population and 95% of electricians do not know the difference .

Good job guys. A lot of good advice from actual professionals. Interesting information can be found at the SQ. D website. Take a look at the time to trip rate for various breakers at various amps. Then look up how quickly the breaker must open to save your life. I believe a 20 amp breaker must see 70 amps to open quick enough. That's why bonding is important.

Dang, visited site to see what was new. Seems to be same OLD story. Hope everyone had a good holiday

I don?t see how a licensed electrician wouldn?t know the
difference. That?s one of the first things they taught us in trade
school. It?s ok to replace the breaker with a new one the same
size but NEVER with a higher amp rated breaker unless your
running bigger conductors and higher ampacity recepticals
that all have the same rating.

Exactly there are overload ( we call them
heaters) and breakers for wire protection.