50 amp sore cord question

[Kpackpackkelley]

I want to make my 50 amp shore cord out of 6/4 soow or stw cord. When I look at the amp ratings on these two cords its 45 amps.
When I looked at a 50 amp shore cord with moulded plugs at the rv supply its 6/3 + 8-1 its stw cord but it's rated for 50 amps. Does anyone know why it's rated 5 more amps ?
Thanks

[Kpackpackkelley]

Big Katuna wrote:
You don't need 4 #6. The 4th green wire can be #10 and they DO make a product like that.

I have amp meters on my RV and you could really get by on an extension cord with 4 #8s. I have rarely seen a 30a draw on the front leg and the second leg just runs the rear AC.

If this is for your primary cord then by all means use the 3-#6, 1-#10 wire.

I'm just learning all these amp ratings.
I understand you would very rarely have even 25 amps a leg but you have the neutral being shared so it would have to be able to carry both 25 amps which would be 50 amps since its 120 volt only from a generator that's what I'm working on . I believe the soow cord is alright on shore power but from a 7 k gen you have 2 legs of 120 volt not 120/240. I'm just trying to figure all these amp ratings for different size and number of conductors plus which voltage it is rated for.

[Golden_HVAC]

The cord might overheat due to the extra layer of plastic over the 4 conductors, this is why they offer a lower rating than THHN #6 wire is rated at.

By the way, if you stuff several #6 wires in a 2" conduit, the amp rating is de-rated from what #6 wire with only 2 conductors in a single conduit is rated at. I don't have a chart in front of me, so I can not give you an example, but it is much lower when 9 conductors are in the same conduit, the reason is that all those conductors are constantly giving off heat, and will overheat the conduit over time.

There is a exception to code regulations that allows you to use the next higher overcurrent protective device if they do not make the size that you need. So a 45 amp wire can be protected at the next up circuit breaker, or 50 amps.

Also if you have ever taken apart a electric stove, you might notice a lot of high nickle wire inside, all fused at the same 50 amps as the range, and #12 wire! It probably will have less than 20 amps going through a given wire under normal use, so it is OK. And #12 wire "Can" handle 40 amps if it has the correct high temperature insulation, and is in free air! Voltage drop might be a problem over a distance more than a couple of feet.

You will be fine with the #6 wire at 50 amps. Even #8 wire at 50 amps will work for short durations. For what it is worth, most homes in the United States have #4 wire as a service conductor for a typical 100 amp home service. Normally rated at only 70 - 90 amps, there is a exception for a home service where #4 is good for 100 amps max overcurrent protection. In a business, they would require #2 wire at 100 amp service. The exception is for homes, not apartment buildings or businesses.

And the wire going to your #4 in your home might be #8 wire from the electric company pole. Just two copper wires wrapped around a steel conductor to hold up the other wires.

Fred.

[Big_Katuna]

You don't need 4 #6. The 4th green wire can be #10 and they DO make a product like that.

I have amp meters on my RV and you could really get by on an extension cord with 4 #8s. I have rarely seen a 30a draw on the front leg and the second leg just runs the rear AC.

If this is for your primary cord then by all means use the 3-#6, 1-#10 wire.

[ken_white]

Kpackpackkelley wrote:
I want to make my 50 amp shore cord out of 6/4 soow or stw cord. When I look at the amp ratings on these two cords its 45 amps.
When I looked at a 50 amp shore cord with moulded plugs at the rv supply its 6/3 + 8-1 its stw cord but it's rated for 50 amps. Does anyone know why it's rated 5 more amps ?
Thanks

The current rating of a cable is a function of the AWG and insulation material type.

The same sized AWG cable can have varying current rating depending on insulation class - i.e. temperature rating.

EDIT: I forgot, the size and number of bundled cables affects ampacity too.