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Electrical question.
- Thread starter NDallyn
- Start date
- Joined
- Feb 17, 2007
- Messages
- 3,375
If you damage the cord and only break some strands, but, don't short it out it will not carry the rated load properly and could overheat and burn even with the 20 amp cord and breaker. The only problem with an adapter and a 50 amp breaker is of course the cord between the adapter and the 15 amp fuses.
I like the idea of making a small box with a 50 amp cord input a 20 amp breaker set up and 20 amp plug. You are covered then. That is exactly the purpose of a breaker panel.
I am not an electrician. I did get straight As in electronics and electrical theory in College. I did spend 7 years of my early youth repairing electrical/electronic devices.
I like the idea of making a small box with a 50 amp cord input a 20 amp breaker set up and 20 amp plug. You are covered then. That is exactly the purpose of a breaker panel.
I am not an electrician. I did get straight As in electronics and electrical theory in College. I did spend 7 years of my early youth repairing electrical/electronic devices.
NDallyn
If as you say "this oven will be going on a bench in a shop - not in a house, not on the floor where the cord could be crushed" and "the controller has a 15amp fuse to the power supply", a properly made adapter plug should be acceptable. It is not very different from the adapters used for connecting RV's to AC pannels with no 15A receptacle. A subsidiary panel with a 20A breaker would be the best in the long run.
I have been on the other side from CDH, designing electrical equipment that is connected to a power system for the last 20 years. We have never put in protection for the connection between the mains and the equipment and none of the safety agencies (UL, CSA etc.) require it. The reality is that the equipment is far more likely to have a fault than the power cable. The only time I have heard of a setup where the mains cable is protected is the mains cables used in the nanny-state of the UK that have a fuse in the (big-assed) plug.
Phil
If as you say "this oven will be going on a bench in a shop - not in a house, not on the floor where the cord could be crushed" and "the controller has a 15amp fuse to the power supply", a properly made adapter plug should be acceptable. It is not very different from the adapters used for connecting RV's to AC pannels with no 15A receptacle. A subsidiary panel with a 20A breaker would be the best in the long run.
I have been on the other side from CDH, designing electrical equipment that is connected to a power system for the last 20 years. We have never put in protection for the connection between the mains and the equipment and none of the safety agencies (UL, CSA etc.) require it. The reality is that the equipment is far more likely to have a fault than the power cable. The only time I have heard of a setup where the mains cable is protected is the mains cables used in the nanny-state of the UK that have a fuse in the (big-assed) plug.
Phil
PSO, you are correct that the agencies do not require secondary cord protection in the US for most appliances (neglecting tinsel cord like your Xmas light strings). What you are forgetting is that the conductor size (AWG) of those cords has a minimum value matched to the plug. The plug is specified and matched to the amperage of the outlet. Hence we have the NEMA 20 amp, 30 amp, 50 amp, etc. plugs, and each has a specified minimum conductor size. No device will get a UL listing if it has a 50 amp plug and 14 AWG cord, for example. The UL inspection would reject it as unsafe. In practice cords are allowed to be 1 or 2 sizes smaller (depending on ampacity) than the distribution wire (hence 16 AWG cords on lamps and coffeemakers plugged into 20 amp circuits which requires a 12 AWG wiring) but the question here was about 50 amp (6 AWG) breakers with 14 AWG cords...much too large of a difference to reliably trip a breaker in the case of a direct short in the cord.
While that one situation may seem trivial or minor to some, it is a real hazard and IMO needed to be called out. Cutting power cords is not that uncommon in a workshop. Been there, seen the sparks...
So in the end the cord is matched to the amperage of the outlet, but in a roundabout manner, and the readers of this thread know far more than most care about matching wire sizes to circuit breakers.
While that one situation may seem trivial or minor to some, it is a real hazard and IMO needed to be called out. Cutting power cords is not that uncommon in a workshop. Been there, seen the sparks...
So in the end the cord is matched to the amperage of the outlet, but in a roundabout manner, and the readers of this thread know far more than most care about matching wire sizes to circuit breakers.
- Joined
- Feb 17, 2007
- Messages
- 3,375
If you cut the cord it won't matter if you have a 10, 20 or 50 amp plug it also wouldn't matter if you have a 15, 20 or 50 amp breaker. If the cut makes a dead short it will be over 50 amps and pop the breaker. Maybe a split second latter with the 50 than the 15. If you are standing in a puddle of water and do it a 15 amp breaker will not help you out much either. It isn't the amperage that will kill you it will be the voltage. To save you in this type of exposure you need ground fault protection. The only way a 20 amp device plugged into a 50 amp plug and breaker will cause harm is if something happens to cause the cord or device to cause draw considerably more than the 20 amps it was designed to carry for a period of time and remain less than the 50 amps that the breaker will trip at. In this instance the device itself is fused so that leaves only the cord to some how create a draw over 20 amps and under 50. An very unlikely occurrence. If you damage the 20 amp cord and it is not completely severed but incapable of carrying its load it will get hot and be dangerous no matter if it has a 20 amp plug or a 50 amp plug.
Once again if you are worried have the 50 amp plug with heavy wire to a sub box with 20 amp breaker and 20 amp outlet made up.
Once again if you are worried have the 50 amp plug with heavy wire to a sub box with 20 amp breaker and 20 amp outlet made up.
Geek alert: EE trying to clear an electrical misconception!
Hopefully this link will take you to a chart for the time/current trip curve for a typical GE circuit breaker used today for residential panels. It is your standard 'snap in' type breaker found in panels and home improvement stores everywhere, but the idea is typical for all standard CB's. When I cut&paste it into my browser it works...
http://www.geindustrial.com/publibrary/checkout/Time%20Current%20Curves|GES-6202A|generic
Note that the top/bottom scale is rated in multiples of the rating. For example, at 2x, the acceptable time to "clear" (the term for tripping the breaker, technically 'clearing the fault') a 2x overload is 15-100 seconds. At 10x (that is 500 amps in our 50 amp example) the range is 0.3-2.0 seconds. I have the formula at my desk at work to calculate short circuit current based on wire size, transformer capacity, etc. and I could throw out all kinds of numbers...but I'll just say that 500 amps for even 0.3 seconds will fry a lot of 14 AWG wire. Due to typical QC practices the normal response is probably near the middle of the curve. Anyone who has experienced a hard short will recall that it hummed/buzzed for an instant or two before the breaker trips...this is why. The breakers are made to do that...hence the term "time delay breaker".
This time delay is eliminated in a GFCI breaker, and that plus the fact that they actively clear in milliseconds and they clear on a 25 milliamps of short circuit current should clearly illustrate why they save lives...
Now where's the beating a dead horse icon...???
Hopefully this link will take you to a chart for the time/current trip curve for a typical GE circuit breaker used today for residential panels. It is your standard 'snap in' type breaker found in panels and home improvement stores everywhere, but the idea is typical for all standard CB's. When I cut&paste it into my browser it works...
http://www.geindustrial.com/publibrary/checkout/Time%20Current%20Curves|GES-6202A|generic
Note that the top/bottom scale is rated in multiples of the rating. For example, at 2x, the acceptable time to "clear" (the term for tripping the breaker, technically 'clearing the fault') a 2x overload is 15-100 seconds. At 10x (that is 500 amps in our 50 amp example) the range is 0.3-2.0 seconds. I have the formula at my desk at work to calculate short circuit current based on wire size, transformer capacity, etc. and I could throw out all kinds of numbers...but I'll just say that 500 amps for even 0.3 seconds will fry a lot of 14 AWG wire. Due to typical QC practices the normal response is probably near the middle of the curve. Anyone who has experienced a hard short will recall that it hummed/buzzed for an instant or two before the breaker trips...this is why. The breakers are made to do that...hence the term "time delay breaker".
This time delay is eliminated in a GFCI breaker, and that plus the fact that they actively clear in milliseconds and they clear on a 25 milliamps of short circuit current should clearly illustrate why they save lives...
Now where's the beating a dead horse icon...???
- Joined
- Nov 9, 2006
- Messages
- 1,072
AHAA! That'll make your decision for you. As has been noted previously, your 15A breaker and 20A cord are your weaksister links in the system. It'll work to cobble together an extension-cord type converter and you could even put a 20A breaker box inline if it'll make you sleep better. Good system for a temp fix.
J-