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Old 06-23-2019, 01:08 AM   #1
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Default Does 1+1=1 For Extension Cords?

Sitting here on a Saturday when a question popped into my head that I have wondered about before, but never seen addressed.

I have a 25ft/30amp shore cord plus a 25ft/30amp extension cord (made from the old shore cord after the female plug was damaged). My question is, does 1 - 25' cord plugged into 1- 25' cord equal 1 - 50' cord (1+1=1)?

If not, how much voltage drop do I loose at the plug connection joining the two cords vs. using one continuous length of cord? Besides my rv, I wonder if it is something worth taking into account when calculating voltage drop should a Hurricane or other emergency require multiple cords in series.
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Old 06-23-2019, 01:22 AM   #2
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Sitting here on a Saturday when a question popped into my head that I have wondered about before, but never seen addressed.

I have a 25ft/30amp shore cord plus a 25ft/30amp extension cord (made from the old shore cord after the female plug was damaged). My question is, does 1 - 25' cord plugged into 1- 25' cord equal 1 - 50' cord (1+1=1)?

If not, how much voltage drop do I loose at the plug connection joining the two cords vs. using one continuous length of cord? Besides my rv, I wonder if it is something worth taking into account when calculating voltage drop should a Hurricane or other emergency require multiple cords in series.

It all depends on the quality and age of the connectors. You will have 6 connections of resistance in the extra connector, so it can be significant. You can try to measure with an ohmmeter, but probably better to hook up the cord and run near max amps through it and check the voltage drop with one cord and two and compare to a voltage drop chart. If the extra connectors get quite hot, you know you have an issue.
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Old 06-23-2019, 03:47 AM   #3
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It all depends on the quality and age of the connectors. You will have 6 connections of resistance in the extra connector, so it can be significant. You can try to measure with an ohmmeter, but probably better to hook up the cord and run near max amps through it and check the voltage drop with one cord and two and compare to a voltage drop chart. If the extra connectors get quite hot, you know you have an issue.
Cords are in new condition with new Progressive Industries end to replace the end on the prior cord (now used as an extension cord). So they should be as good as it gets. But as you've noted, using two cords instead of one doubles the connections. So I was just curious.

While in my driveway, I've been able to run the roof air on a 50 ft. 10 gauge extension from a 20A outlet at home using an adapter at the coach with only a 4-5 volt drop (still 118 volts) noted on my Progressive Industries EMS-PT30X plugged into a coach outlet (again using an adapter). I'll do some testing to find out if the two 30 amp cords perform the same. But without 30 amp service at home and a comparable 50 ft. 30 amp cord, I can't do any comparisons that don't involve adapters.

However, I can test that whatever I'm using delivers enough current and doesn't get hot doing it, which is all that really matters.
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Old 06-24-2019, 01:42 AM   #4
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The advice that Booster gave you is right on but I will add 1 more point it you are starting out with low voltage it will be worse. But also looking at reality most time you will not be running max amps. You even said you ran it on a 20A circuit. As a general rule the only thing you will run continually that draws a substantial amount of power is the AC. The microwave may pull the same but only for a short period of time. The more amps you pull the warmer the cords and connections get the more resistance will cause a larger voltage drop increasing the amp draw. I'll also mention that I have the same setup with 2 cords using the second only when needed. There was even a couple times when I had to plug into a 12 gauge cord. Once in about 12 years i did blow a fuse with the AC and microwave but there was also a about 100" of 12 gauge cord involved plugged into a 15 or 20A circuit
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Old 06-24-2019, 03:52 AM   #5
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The advice that Booster gave you is right on but I will add 1 more point it you are starting out with low voltage it will be worse. But also looking at reality most time you will not be running max amps. You even said you ran it on a 20A circuit. As a general rule the only thing you will run continually that draws a substantial amount of power is the AC. The microwave may pull the same but only for a short period of time. The more amps you pull the warmer the cords and connections get the more resistance will cause a larger voltage drop increasing the amp draw. I'll also mention that I have the same setup with 2 cords using the second only when needed. There was even a couple times when I had to plug into a 12 gauge cord. Once in about 12 years i did blow a fuse with the AC and microwave but there was also a about 100" of 12 gauge cord involved plugged into a 15 or 20A circuit
I too only plan to use my second 30A cord only when needed. So far, I've never needed it, but the minute I decide to leave it at home, I'm sure I will.

I had a double motive for my inquiry. Prior to buying my "b", I stocked up on Hurricane preparations as I live on the Texas Gulf Coast only about 4 miles inland. My emergency generator is small and only has two 120v outlets. To minimize current loss I purchased 10 ga. extension cords. My options at the time were to buy one 100' ft., two 50 ft., or my actual choice was to buy two 25 ft. and one 50 ft. because I felt it afforded me the most flexibility. Ever since then, however, I've wondered if ever needed the full 100 ft., would I loose significant capacity by connecting multiple cords together.

For instance, would I be just a well off with a single 100 ft. 12 ga. cord that does not have all the additional connections? It's always been a nagging question of mine that I've wondered about.
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Old 06-30-2019, 08:28 PM   #6
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Here is a link to a chart and an interactive calculator where you can enter cable gage, length, voltage and current parameters and see the results. https://www.powerstream.com/Wire_Size.htm
For what its worth, I have a 50 foot 10 gauge extension with 20/30 amp adapters at each end connected to a surge protector mounted in the cable storage compartment (theft protection) for a total of 75 feet. With A/C on the protector display shows 120 volts at 7 amps when plugged in at the house. Works fine for me.
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Old 06-30-2019, 08:46 PM   #7
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Default Voltage drop adds up.

What you have is often better than one long cord. With two shorter cords, you can use just one cord when the distance only requires one, and then you only have the voltage drop from one length of wire.

With two cords of the same size in series, you will get twice the voltage drop. That becomes a problem when you are drawing a large current, such as running air conditioning. If you didn't need a longer cord, there's less voltage drop with a shorter cord (if the same gauge wire). The connectors do add a small amount of resistance, but they are designed to minimize their voltage drop so they don't get hot, and as long as they are in good condition they don't have a major influence on the total loss. If they do get hot, it's time to replace them.

There is a situation where two cords in series can have a safety issue. If a person touches the connectors when they are wet, there can be a shock hazard. But this applies to any high voltage electrical connection; you have to be careful if it's been raining.

I recommend any electrical cord used outside to have a GFCI at the source. This will save your life. If your power panel or electrical outlet doesn't have one, you can get a GFCI on a short "pig-tail" cable and add to the front of your shore power cable.
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Old 06-30-2019, 11:15 PM   #8
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The connectors do add a small amount of resistance, but they are designed to minimize their voltage drop so they don't get hot, and as long as they are in good condition they don't have a major influence on the total loss. If they do get hot, it's time to replace them.

This relates directly to my original question. Thanks.

I recommend any electrical cord used outside to have a GFCI at the source. This will save your life. If your power panel or electrical outlet doesn't have one, you can get a GFCI on a short "pig-tail" cable and add to the front of your shore power cable.
Good suggestion.
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Old 07-01-2019, 01:45 AM   #9
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Default Portable GFCI devices

The portable "pigtail" GFCI devices I referred to are shown here:

https://www.homedepot.com/s/gfci%2520cord?NCNI-5

Those are for 15 or 20 Amp (120 volt AC) outlets only, and I have yet to see a portable GFCI device made for 30 or 50 Amp circuits. Unless you wired a 30 or 50 Amp RV electrical pedestal in your home, most of us are plugging into a 20 Amp circuit at home anyway.
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Old 07-01-2019, 01:58 AM   #10
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30 Amp Inline GFCI
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Old 07-01-2019, 02:18 AM   #11
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I actually plug in to a GFI outlet in my garage so I have that protection and agree it is important.
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Old 07-01-2019, 04:26 AM   #12
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Default 30A GFCI pigtail

Wow, that's nice. thanks for that! At $134, it's not out of line. They even have a 240 volt version for a few dollars more.

It turns out Home Despot does sell a 240 volt GFCI pigtail, but the 240 volt twistlock socket isn't protected, just the two individual 120 volt socket outputs.

https://www.homedepot.com/p/DEK-10-4...8510/204356742
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Old 07-01-2019, 03:22 PM   #13
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What you have is often better than one long cord. With two shorter cords, you can use just one cord when the distance only requires one, and then you only have the voltage drop from one length of wire.

With two cords of the same size in series, you will get twice the voltage drop. That becomes a problem when you are drawing a large current, such as running air conditioning. If you didn't need a longer cord, there's less voltage drop with a shorter cord (if the same gauge wire). The connectors do add a small amount of resistance, but they are designed to minimize their voltage drop so they don't get hot, and as long as they are in good condition they don't have a major influence on the total loss. If they do get hot, it's time to replace them.

There is a situation where two cords in series can have a safety issue. If a person touches the connectors when they are wet, there can be a shock hazard. But this applies to any high voltage electrical connection; you have to be careful if it's been raining.

I recommend any electrical cord used outside to have a GFCI at the source. This will save your life. If your power panel or electrical outlet doesn't have one, you can get a GFCI on a short "pig-tail" cable and add to the front of your shore power cable.
Sorry but a second GFCI will blow the GFCI in the van. You can't have two GFCI on one circuit.
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Old 07-01-2019, 04:02 PM   #14
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Sorry but a second GFCI will blow the GFCI in the van. You can't have two GFCI on one circuit.

Not always true. Our Roadtrek sits plugged into a GFCI in our garage all the time, and for a while it had GFCI breakers in the van and GFCI outlets(since swapped to standard ones). That was 3 GFCIs in a row and never tripped any of them. A lot of Roadtreks with Tripplite inverter/chargers had issues, but it was very likely the Tripplite in most of them. Pre 2007 Tripplites seem to be less prone to tripping GFCI circuits.
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Old 07-01-2019, 06:33 PM   #15
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Not always true. Our Roadtrek sits plugged into a GFCI in our garage all the time, and for a while it had GFCI breakers in the van and GFCI outlets(since swapped to standard ones). That was 3 GFCIs in a row and never tripped any of them. A lot of Roadtreks with Tripplite inverter/chargers had issues, but it was very likely the Tripplite in most of them. Pre 2007 Tripplites seem to be less prone to tripping GFCI circuits.
Well it could very well be my model RT ( 2005/190/Popular ) but it will trip if double GFCI occurs. Maybe it is because of the type of inverter.
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Old 07-02-2019, 08:40 PM   #16
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I plugged into a GFCI protected outlet box on the outside of my garage wall with all three of my Class Bs. Never tripped.
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Old 07-03-2019, 10:04 PM   #17
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Default GFCI tripping

The reasons GFCI trip can sometimes be a little complicated. GFCI devices measure the the current in the hot wire and subtract it from the current in the neutral using with a small toroid tranformer. If these two are not equal, something is drawing current down a different path and that can potentially be a human being touching a live circuit.

And this works very well at 60 cycle AC. The problem is when the devices powered by the AC circuit create higher frequencies. Like an antenna, these high frequencies will travel down whatever path they can find; the hot wire, the neutral wire, or the ground -- or even travel through the air. And that makes GFCIs think there's a fault.

So don't blame the GFCI, it's usually the loads telling them to trip. What equipment manufacturers need to do, is design better high-frequency filtering so this doesn't happen.
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