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Old 08-05-2022, 02:28 PM   #15
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Bigb56: I did answer your question. Current capacity depends on cable design and not wire gauge only.

The manufactures rating includes intended usage. It it intended to be put in a wall with restricted air flow? Is it is intended to be thrown loose on the floor or ground with free air flow around it. How is it rated when arranged in a cable tray? Again, current capacity is more than just wire gauge.
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Old 08-05-2022, 03:21 PM   #16
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If 10 gauge wire, used in 30 amp service, is safe to use, at what amperage is it actually going to fail.

Let's say you plunge an axe thru your 30 amp cable, which is plugged into a 50 amp service thru an adaptor.

Will the cable handle the 50 amps of dead short and trip the breaker OR will the cable overheat and burst into flames.

I would think if it can handle 30 amps all day, it can handle 50 amps for as long as it takes to trip the 50 amp breaker.
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Old 08-05-2022, 06:04 PM   #17
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Originally Posted by twinboat View Post
If 10 gauge wire, used in 30 amp service, is safe to use, at what amperage is it actually going to fail.

Let's say you plunge an axe thru your 30 amp cable, which is plugged into a 50 amp service thru an adaptor.

Will the cable handle the 50 amps of dead short and trip the breaker OR will the cable overheat and burst into flames.

I would think if it can handle 30 amps all day, it can handle 50 amps for as long as it takes to trip the 50 amp breaker.
Of course it can, and that's why NEC allows short circuit protection to be rated higher than overload protection.
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Old 08-06-2022, 06:45 AM   #18
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Originally Posted by MichaelBarb View Post
Bigb56: I did answer your question. Current capacity depends on cable design and not wire gauge only.

The manufactures rating includes intended usage. It it intended to be put in a wall with restricted air flow? Is it is intended to be thrown loose on the floor or ground with free air flow around it. How is it rated when arranged in a cable tray? Again, current capacity is more than just wire gauge.
The reason we are allowed to plug smaller and lower ampacity rated cords, and connect smaller and lower ampacity conductors to higher ampacity circuits is because those loads are self limiting in current by design, or there is overcurrent protection provided at the load for things like motors which can't be self limiting. As far as the adapter and the trailer cord, the 30 amp main breaker in the trailer serves as the overcurrent protection for both and the 50 amp breaker serves as the short circuit protection.
One only has to look at 250.122 to see that the #10 grounding conductor in the adapter and in the trailer cord is rated to safely carry enough fault current to open an OCPD up to 60 amps without suffering damage.
I can feed a clothes dryer and an air conditioner both with the same #10 NM and for the clothes dryer I am limited to a 30 amp OCPD but with an air conditioner I can breaker it at 50 amps on the supply side and fuse it at 30 amps at the load per NEC and per the manufacturer's name plate instructions.
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Old 08-06-2022, 12:28 PM   #19
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I have worked in cable manufacturing. A grounding conductor can be smaller than the hot and neutral conductors because it is uninsulated. An uninsulated conductor allows for more cooling than an insulated one. There is more to it than just wire gauge.

There are also all kinds of special exceptions that have been grandfathered in. When you do railroad work there are some things you can do that seem in violation of NEC code. These were covered by codes before NEC and are grandfathered in. Same when doing in work in the city of Chicago, Los Angelous, and other odd places. In general, the local codes are more stringent than NEC, but some odd things get grandfathered in.

Over time the grandfathered exceptions are being eliminated. Some will never be. The plugs we use in RV's are a good example. By rights they are not switch rated. In other words, they cannot be used to break power under load. There is no way to contain the arc flash. Twist locks are not switch rated but the older spade connectors we use are grandfathered in as switch rated. It is a topic of ongoing debate. Personally, I have found it almost humous over the years. The anti-arc flash movement has gotten radical in some ways but justified in most.

There is a fundamental law of safety rules and codes, "There will be no changes unless there is blood." A macabre statement but unfortunately it is true.
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Old 08-06-2022, 04:58 PM   #20
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It is simple. The RV is rated for 30 amps, and the cord is rated for 30 amps. The RV has a 30-amp breaker in the inlet panel and it will trip if the amperage exceeds wo amps. You are protected.

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Old 08-06-2022, 06:12 PM   #21
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I Agree
Have tripped the RV camper breaker but very rare trip the campground service
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