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 > How long can you go on a 50 amp extension cord?

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theoldwizard1

SE MI

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Posted: 10/01/20 03:16am Link  |  Quote  |  Print  |  Notify Moderator

FYI - 100' of 6/4 SOOW would weigh close to 70 lbs and the cord alone (no ends) would cost about $275.

valhalla360

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Posted: 10/01/20 05:15am Link  |  Quote  |  Print  |  Notify Moderator

Old-Biscuit wrote:

100' with 50A #6 power cord 40A load will have roughly a 3-4 Volt drop from source to RV
120VAC....116/117VAC


You are assuming the house has good strong voltage and it won't sag under heavy load (and you are thinking 120v when a 50amp is 240v)

If the outlet is 50am, it should be 240V but don't be surprised to see 220v at the outlet.

At 220v, 20amp per leg jumps to around 22amps per leg (assuming the air/con units are on separate legs). So each leg sees 22amp @ 110v at the outlet and with voltage drop around 108v at the RV.

That's marginal for me where I start considering if should deploy the voltage booster or break out the generator.

If for some reason both air/con units are on the same leg, the amps doubles on that leg and voltage drop results in around 106v.

This ignores bad connections or issues with the wiring in the house, so you could easily lose another 2-3 volts in real life.


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wa8yxm

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Posted: 10/01/20 06:09am Link  |  Quote  |  Print  |  Notify Moderator

With most things electrical it is like the Senior answer to the question "Boxers or Briefs"
The youngsters said "Briefs"
The middle aged said "Boxers"
The seniors "Depends".

Now the 50 amp cord is designed to carry 50 amps for, based on the wire size, about 100 feet if I'm not mistaken.

But not many motor homes pull the full 50 amps on either leg. Usually around 30 is peak load

50 amps round trip on one leg 100' takes 4ga wire
but 30 amps takes 6

This calculator may be a bit confusing espically at 50 amps because you use every amp in the less loaded leg twice. (IE if one leg is 30 amp and one is 20 the effect is to reduce voltage drop.


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BB_TX

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Posted: 10/01/20 08:29am Link  |  Quote  |  Print  |  Notify Moderator

supercub wrote:

.......
I'm trying to plug into a house with 50 amp plug. Thanks

I hope this is a 50 amp plug wired for an RV and not a 50 amp dryer plug.

joelc

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Posted: 10/01/20 08:44am Link  |  Quote  |  Print  |  Notify Moderator

I have gone with the cord that came with my unit and an extension. ?? 50'. I do not remember the formula for voltage drop, but you should be okay. Do you have a surge/EMS protector? This might assist.

DrewE

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Posted: 10/01/20 09:22am Link  |  Quote  |  Print  |  Notify Moderator

BB_TX wrote:

supercub wrote:

.......
I'm trying to plug into a house with 50 amp plug. Thanks

I hope this is a 50 amp plug wired for an RV and not a 50 amp dryer plug.


A 50A four wire range socket is exactly the same as a 50A RV socket. They're both standard NEMA 14-50 connectors. If it's an older three wire socket, they're physically incompatible since the socket has fewer connections than the plug.

Electric dryer circuits are usually 30A circuits. The main problem for RV sockets being mistaken/miswired are with 30A RV connections, which are superficially similar to the older 3 wire 30A dryer connections but wired quite differently, with 120V rather than 240V service.





Old-Biscuit

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Posted: 10/01/20 09:57am Link  |  Quote  |  Print  |  Notify Moderator

valhalla360 wrote:

Old-Biscuit wrote:

100' with 50A #6 power cord 40A load will have roughly a 3-4 Volt drop from source to RV
120VAC....116/117VAC


You are assuming the house has good strong voltage and it won't sag under heavy load (and you are thinking 120v when a 50amp is 240v)

If the outlet is 50am, it should be 240V but don't be surprised to see 220v at the outlet.

At 220v, 20amp per leg jumps to around 22amps per leg (assuming the air/con units are on separate legs). So each leg sees 22amp @ 110v at the outlet and with voltage drop around 108v at the RV.

That's marginal for me where I start considering if should deploy the voltage booster or break out the generator.

If for some reason both air/con units are on the same leg, the amps doubles on that leg and voltage drop results in around 106v.

This ignores bad connections or issues with the wiring in the house, so you could easily lose another 2-3 volts in real life.


It's only 240VAC if you measure voltage across BOTH Hot Legs
Each Leg is 120VAC rated for 50 amps
Each leg feeds 1/2 of RV Main AC Panel Buss
40A on one leg will drop 120VAC down to roughly 116/117 VAC
Each leg can handle that amp load w/o issue

240VAC only comes into play IF the RV has a 240VAC appliance which very few have such appliances


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time2roll

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Posted: 10/01/20 10:18am Link  |  Quote  |  Print  |  Notify Moderator

If you only see 220 at the outlet with no load in a single family home it is time to call the power company.

Real continuous load is probably closer to 20 or 25 amps max for those voltage drop calculations.


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Posted: 10/01/20 11:11am Link  |  Quote  |  Print  |  Notify Moderator

1. You should be ok with 50amps at 100'.
2. Since the trailer is already hooked up, it's safe to assume the receptacle is correct.
3. 100' will weigh a bunch but I would assume you're not going to be lugging it around much.
4. Depending on your situation and how long you'll be using the cord, I'd protect it by slicing a few pieces of 1 1/4 pvc for it to lay on to protect it from rodents and gravel etc.
5. When you're finished with it, you can always cut it up into smaller pieces which are more manageable. My cord is 45' on a reel. I carry another two pieces. One is 25' and the other 15'. Plugs at both ends allow me to plug in almost anywhere....Dennis


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rgatijnet1

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Posted: 10/01/20 01:21pm Link  |  Quote  |  Print  |  Notify Moderator

Also you need to take in to consideration the wiring going to the 50A plug that you will be connecting to. If it is a long run from the source to the 50A pedestal you may already be marginal as far as voltage drop goes. Not all 50A plugs are wired to provide 100 amps of power.

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