Over sizing the breaker question?

[DiabolicZ]

I wanted to ask about "Over sizing the breaker". How is over sizing the breaker bad exactly? I ran a 50amp breaker and 6 gauge cable (rated at 50amp). My 225LX can draw max of 39 amps. Does that mean my 50amp breaker is too large? I figured the breaker should match the cable coming out of it. Then whatever is plugged into it has to fend for itself. Meaning my 225LX should go into protection long before my 50amp breaker trips right? How is that bad?

Now, if I had a 50 amp breaker on say 12 gauge wire, that would be bad. Then the wire would get too hot and burn before the breaker ever tripped.

[kenwhite]

I wanted to ask about "Over sizing the breaker". How is over sizing the breaker bad exactly? I ran a 50amp breaker and 6 gauge cable (rated at 50amp). My 225LX can draw max of 39 amps. Does that mean my 50amp breaker is too large? I figured the breaker should match the cable coming out of it. Then whatever is plugged into it has to fend for itself. Meaning my 225LX should go into protection long before my 50amp breaker trips right? How is that bad?

Now, if I had a 50 amp breaker on say 12 gauge wire, that would be bad. Then the wire would get too hot and burn before the breaker ever tripped.

As long as the cable insulation type, run length, and size allow for a larger amperage breaker size to be used, then there is really no issue other than the increased equipment and installation costs.

[A/C Guy]

I wanted to ask about "Over sizing the breaker". How is over sizing the breaker bad exactly? ....

There are 2 ways that people over size breakers.

1. They simple install the bigger breaker without upgrading the wiring to match. That will cause the wiring in the wall or conduit to overheat. As the equipment tries to draw the needed amperage, the wires overheat, resistance increases, then voltage drops to the machine. If you are lucky, the machine will shut down or fail. If you are not lucky, the wiring in the wall starts a fire.

2. They decide that if 50 amps (in your example) is good, then 70 amps is better. So they install #4 wire and a jumbo breaker to match. The problem that occurs is that if there is a failure in the machine, the jumbo breaker does not trip. That allows more serious damage to the machine. I see this every month in my line of work. Too large of a fuse or breaker and a $400 repair just turned into a $1400 repair. The manufacturer's engineers determined that a certain breaker is correct. That is why they list a MAX fuse / breaker size on the equipment. When something fails, the the internal components are no longer protected by the 50 amp breaker. More components fail until the 70 amp breaker trips. Sometimes, the entire unit will catch fire before the oversized breaker will trip. Now the repair bill just got very expensive.

I see more cases of scenario #1 because people are cheap. But I see scenario #2 every month.

Going back to your observation that the unit needs 39 amps. That would be the MCA. Minimum Circuit Ampacity. That means the wiring that you use must meet that minimum level of capacity. Do not use #10, it is rated for 30 amp circuits max. #8 is rated for 40 (or 50 depending on location), # 6 is required for a 50 amp breaker in many areas.

It is ok to oversize the wire as long as the breaker is not over sized. If your shop was 75 feet from the panel, then upsizing the wire to #4 combined with the 50 amp breaker would be proper. Larger wires have less voltage drop. Longer runs require larger wires to prevent excessive voltage drop.

[kenwhite]

...
2. They decide that if 50 amps (in your example) is good, then 70 amps is better. So they install #4 wire and a jumbo breaker to match. The problem that occurs is that if there is a failure in the machine, the jumbo breaker does not trip. That allows more serious damage to the machine. I see this every month in my line of work. Too large of a fuse or breaker and a $400 repair just turned into a $1400 repair. The manufacturer's engineers determined that a certain breaker is correct. That is why they list a MAX fuse / breaker size on the equipment. When something fails, the the internal components are no longer protected by the 50 amp breaker. More components fail until the 70 amp breaker trips. Sometimes, the entire unit will catch fire before the oversized breaker will trip. Now the repair bill just got very expensive...

This really should never be an issue for any item that is plugged into a socket because the equipment should be fused/breakered internally by the manuafacturer - their responsibility. Plus, not all plug and play branch circuits are dedicated to one device, so there typically needs to be extra capacity within the branch for times when there are multiple connections.

For equipment that is hard wired, then an appropriately sized disconnect and circuit breaker for the branch should be installed per the manufacturers recommendation.

[A/C Guy]

This really should never be an issue for any item that is plugged into a socket because the equipment should be fused/breakered internally by the manuafacturer - their responsibility....

There is no such requirement or legal implication of responsibility. For example, every furnace in the US is installed with a plug in cord. No furnace in the US has any built in breaker or fused protection. Same can be said for table saws, chop saws, corded drills, vacuum pumps, etc. Every welder does state a max fuse or breaker for the device. That transfers all responsibility to the operator.

[kenwhite]

There is no such requirement or legal implication of responsibility. For example, every furnace in the US is installed with a plug in cord. No furnace in the US has any built in breaker or fused protection. Same can be said for table saws, chop saws, corded drills, vacuum pumps, etc. Every welder does state a max fuse or breaker for the device. That transfers all responsibility to the operator.

Like I said, every branch that has a socket has its breaker sized for the cable insulation type, cable run length, # of cables bundle togther, load duty cycle, and cable AWG size to protect the wiring. It is the manufacturers responsibility to fuse/breaker if they want to protect the end user equipment from excessive damage or fire hazards.

The breaker protects the wiring between the socket(s) and panel, it is not sized or designed to protect the equipment that is plugged into the socket.

Oh, and my furnace is hard wired into a fused disconnect and not plugged into a 120 V wall socket - this is per the manufacturers recommendation, so be careful when you use the word every...

Typically the minumum fuse/breaker size is recommended for proper operation so the circuit is not being interrupted often when trying to use the device.

[ASE_MasterTech]

2. They decide that if 50 amps (in your example) is good, then 70 amps is better. So they install #4 wire and a jumbo breaker to match. The problem that occurs is that if there is a failure in the machine, the jumbo breaker does not trip. That allows more serious damage to the machine. I see this every month in my line of work. Too large of a fuse or breaker and a $400 repair just turned into a $1400 repair. The manufacturer's engineers determined that a certain breaker is correct. That is why they list a MAX fuse / breaker size on the equipment. When something fails, the the internal components are no longer protected by the 50 amp breaker. More components fail until the 70 amp breaker trips. Sometimes, the entire unit will catch fire before the oversized breaker will trip. Now the repair bill just got very expensive.

Sorry, but this statement simply isn't true.
Breakers/fuses are sized to protect the circuit run (ie-correct wire gauge size), not the appliance in use.
If the above statement were correct, you should never plug your television/stereo/phone charger/etc.. into that 20amp receptacle in your wall as none of these items are 'load protected' by a 20amp breaker.

[performance]

There is a section in the NEC dedicated to welders. They fall into a category all their own. I believe its section 630. I can't believe the number of calls I get from electricians with all sorts of bad information. I always point them to the NEC, rather than give them advice. It concerns me that a large number of the electricians never heard of it. But suffice it to say, there are very specific guidelines that should be followed, though they are more forgiving because they fall under a duty cycle limited category. Normal rules don't apply....

[ASE_MasterTech]

There is a section in the NEC dedicated to welders. They fall into a category all their own. I believe its section 630. I can't believe the number of calls I get from electricians with all sorts of bad information. I always point them to the NEC, rather than give them advice. It concerns me that a large number of the electricians never heard of it. But suffice it to say, there are very specific guidelines that should be followed, though they are more forgiving because they fall under a duty cycle limited category. Normal rules don't apply....

I beg to differ, but 'normal rules' do apply.
The simple fact is that wire gauges are determined by voltage/amperage load in ALL applications, AC or DC, this is due to 'heat/conductivity' considerations.
I built the home I am in & put additions (add-a-level) on 2 previous homes, & on rough & final electrical inspections I have never been told to provide an 'appliance' for circuit approval.
If the breaker/fuse is 50amp then the wire from the f/b to the outlet should be at least 6awg.
What you do after the outlet (ie-extension cords, etc..) really depends on heat dissipation (#8 wire may be ok for 50amp extension because it's not in a wall or conduit), distance is also a factor to consider.

[performance]

I hate to disagree, but No, normal rules are not applied. I've discussed this not only with electrical engineers, but also with 40 year industrial electricians. There is a reduction for duty cycle limited machines, and a formula that they use that is different than the standard for appliances. And I believe a different requirement for breakers. Again, Section 630 discusses this in detail. If your inspectors didn't know this, then they weren't on top of their game, as it is spelled out in black and white. Run length is considered, of course, but different gauges are allowed according to maximum duty cycle. In my research, I even found a dedicated class offered for wiring welders and similar components.

[ASE_MasterTech]

I hate to disagree, but No, normal rules are not applied. I've discussed this not only with electrical engineers, but also with 40 year industrial electricians. There is a reduction for duty cycle limited machines, and a formula that they use that is different than the standard for appliances. And I believe a different requirement for breakers. Again, Section 630 discusses this in detail. If your inspectors didn't know this, then they weren't on top of their game, as it is spelled out in black and white. Run length is considered, of course, but different gauges are allowed according to maximum duty cycle. In my research, I even found a dedicated class offered for wiring welders and similar components.

Perhaps I wasn't clear, so again I will state;
Appliance considerations are not part of 'hard wiring' regarding wire gauge vs breaker/fuse sizing, rather it is the other way around.
You wouldn't/shouldn't ever put a 50amp device on a 40amp circuit (regardless of 'duty cycle'), but you may put a 40amp device on a 50amp circuit
BTW, good luck explaining the under-gauged wire 'duty cycle' thing to a fire inspector sent out by your Homeowners Insurance company.
I'm just sayin...

[performance]

Nothing to explain. I'd just point them to section 630.

[performance]

There is also a lot written about it on the web. Its not to say a wire can't be oversized. Breaker size is regulated though, I believe to no more than 200% if I remember right.

However, a sharp welding inspector would recognize a proper welding receptacle such as a NEMA 6-30 and know its purpose.

[DiabolicZ]

I see more cases of scenario #1 because people are cheap. But I see scenario #2 every month.

I could see that happening. Just for my general pacific 50 amp breaker and 8' of #6 wire, it cost me $80.

[kenwhite]

Duty cycle is an important consideration when designing a branch/circuit, I even listed it in post 6 above. The thing about the NEC is that it is full of exceptions under various conditions which is true for section 630 residential vs commercial/industrial. Below is a brief overview of 630 copied from another site.

"Article 630. Electric Welders
Welding equipment does its job either by creating an electric arc between two surfaces or by heating a rod that melts from overcurrent. Either way results in a hefty momentary current draw. Welding machines come in many shapes and sizes. On the smaller end of the scale are portable welding units used for manual welding, such as in a fabrication shop. At the larger end of the scale are robotic welding machines the size of a house, used for making everything from automobile bodies to refrigerator panels. All of these must comply with Article 630.
The primary concern of Article 630 is adequately sizing the conductors and circuit protection to handle this type of load. Fortunately for the power distribution engineer and the field electrician, Article 630 requires certain information to be provided on the nameplate of the equipment. Article 630 explains how to use this information for proper sizing of conductors and circuit protection.
Welding cable has requirements other conductors don't have. For example, it must be supported at not less than 6-inch intervals. Also, the insulation on these cables must be flame-retardant."

[ASE_MasterTech]

Ok then, let me put this another way.
From my understanding, NEC article 630 deals with the use of undersized wire based on the duty cycle of 'self-protecting' equipment (ie-welding) in certain circumstances (ie-equipment is dedicated to that circuit).
So if you put a 50amp receptacle/breaker in a structure (home or business) with 10/2 or 8/2 wire & upon sale of structure it is discovered by any inspector, in most states, you WILL NOT recieve a 'certificate of occupancy' for the prospective purchasers. So until corrected, say goodbye to that sale.
However, if fortune is on your side & nothing is discovered, pray every night that the new owners do not decide to plug in their motorhome, or some other 'appliance' that actually requires 50amps at greater then 10% 'duty cycle', into that 50amp 'NEC 630 compliant' receptacle/breaker. I think you (or your attorney) will have a difficult time explaining the nuances of NEC article 630 to a Judge & jury of peers, as you sit accused of 'gross negligence' regarding property loss, or God forbid, loss of life.
So for crying out loud, & piece of mind, use 6awg for a 50amp breaker/receptacle run.

[performance]

There isn't a certificate of occupancy permit for private residences after a structure is built in many states...At least not in this one. IF the correct plug is used, then it will be obvious, since the 6-50 is the only standard plug for single phase 220V welders and cutting equipment. The camper won't plug in.

[kenwhite]

The thing you have to consider when looking at the duty cycle, is that while the continuous current limit may be exceeded for short periods of time, the average current based on the duty cycle load is typically much less than rated continuous current.

If the branch has multiple loads, the breaker would still trip trip if severly overloaded when multiple loads are being used - normally a thermal breaker is specified for this type of circuit.

Article 630 is really written for commercial/light industrial use with exceptions for residential/home use of a welder.

[kenwhite]

Oh, and one other thing.

Just because a certain welder draws X# of amps, this does not mean that a certain AWG wire needs to be installed.

There are many factors that I listed in post #6 above that actually determine the size and type of cable that must be used.

Insulation type is also very, very, important when determining where the run can be placed and how much of the cable's ampacity will have to be derated...

EDIT: As Mark stated in his first post, if your are not comfortable doing all or part of the wiring upgrade, hire a competent electrician to either do it for you, or help you do it...

[ASE_MasterTech]

OK, I'll rephrase..
Here in the northeast most states I know require a 'Certificate of Occupancy' (& the accompanying inspections) be issued for any incoming occupant, be it renters-leasers-owners, commercial or residential. Structures/buildings are required to meet or exceed the code requirements in force at time of construction or most recent renovation, excluding 'fire code' issues which must be up to date.
Here in NJ, after owning 4 homes, 2 Amoco Service Stations, & currently working for Government, I can tell you that 6awg has been required on any 50amp outlet circuit I installed or had installed. This is 'code' here regardless of NEC recommendations, & IMHO just good common sense for wire buried in a wall or conduit whose future use may or may not involve a 'protected' or 'limited duty' device..