How far is too far?

How much voltage drop occurs when you add an extension cord to your shore power cord? Please take this survey!

Dear Readers,

I just saw this picture on another forum which got me thinking about voltage drop due to extending your shore power cord to reach a distant pedestal. Once the voltage at your RV gets down below 105 volts, damage to your Air Conditioner and residential refrigerator can occur.

Here’s the numbers

So what happens to the voltage at your RV when you add 25, 50, 75, 100 or even 200 ft of 10-gauge extension cord to a 30-amp outlet? Let’s assume the pedestal can maintain a full 120-volts at 30-amps which is probably optimistic.

Let’s try 25 ft

How about 50 ft

Now let’s add 75 ft

What happens with 100 ft

Let’s go nuts with 200 ft

Why does this happen?

Voltage drop over a conductor only occurs when current is flowing. So with zero amperes of current there will be zero loss of volts. That means if the pedestal has 120-volts, then your RV would have 120-volts. But if the pedestal only has 110-volts to begin with, then the max voltage at your RV will be 110 volts.

But when your air conditioner and electric water come on at the same time, that’s probably 20-amperes of current. And that current can create a significant voltage drop over a long shore power cord. The result is that you could lose 5 or 10 volts (or more) over a long extension cord if your RV is drawing a lot of current.

Shorter and bigger is better!

If you have to hook up to a distant pedestal outlet, then use the shortest and heaviest extension cord available. And always clean the connectors with contact cleaner before plugging in. Both CRC and DeoxIT make great contact cleaning products.

Please take this survey

So what’s the longest you’ve had to run your shore power cord to plug into a pedestal outlet? Please add your normal shore power cord (usually 25 feet) plus whatever extension cord you needed. For example, if you had to add a 25 ft extension cord to your 25 ft shore power cord, then that would be 50 ft. If you only use your RV’s 25 ft shore power cord, please enter 25 ft. And add info on any special hookups in the comments below.

Let’s play safe out there - Mike