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Old 05-13-2021, 08:46 PM   #1
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Checking voltage with a multimeter

Last summer I noticed the 30 amp plug on my pedestal was quite warm. This winter I noticed that the plug showed signs of melting - so I had it replaced.

In earlier posts folks said that low voltage could have been the cause of the plug getting warm.

So I bought myself multimeter and here are some voltage readings

1) plugged into shore power with nothing running - 121
2) with water heater set to electric - 119
3) all of the above and running microwave - 114

Can someone explain what I am seeing? Is this normal? How low can it get before I get concerned?
I always knew not to run A/C and water heater on electric at same time or else the breaker on the pedestal would blow.

Thanks
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Old 05-13-2021, 09:35 PM   #2
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You are fine. There is a voltage drop as your amperage draw increases. The plug at the pedestal might get warm but there should be no arcing signs on the prongs and it should fit tight.
Melting is bad.

You can run your A/C and your electric water heater. If the breaker is tripping there is something else going on.

Edit: More info… water heater is 1400 watts, A/C peak is about 2000 watts / about 1500 watts running. You have about 3600 total available. Don’t forget your converter at about 240 watts with lights on and your fridge if electric is selected.
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Old 05-14-2021, 01:36 PM   #3
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Originally Posted by johnlantz View Post
1) plugged into shore power with nothing running - 121
2) with water heater set to electric - 119
3) all of the above and running microwave - 114

Can someone explain what I am seeing? Is this normal? How low can it get before I get concerned?
It's perfectly normal to see some variance. I would be fine down to about 110 volts. My Progressive Industries EMS is designed to cut off at 10% less than 120v aka 108 volts.


Quote:
Originally Posted by johnlantz View Post
I always knew not to run A/C and water heater on electric at same time or else the breaker on the pedestal would blow.
That's a matter of too many amps being pulled. And I'm betting your issue is more an issue of too many amps being pulled. Breakers are designed for 80% continuous use with occasions jumps up to 100%. Which means you want to try and keep it to about 25 amps. You can use a chart like this for keeping track of approximately how many amps you're drawing:

https://www.rvtechlibrary.com/electr...eloadchart.php
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Old 05-14-2021, 08:19 PM   #4
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Just to clarify things, the receptacle is on the campsite pedestal. The plug on the end of the trailer's electrical cord plugs into that receptacle. It is the plug on the end of the power cord that is getting warm and showing signs of melting. We are assuming this is the original supplied cord and plug. If this plug is in the condition you say the internal components have been compromised and should be replaced.

I agree with most of everything previously stated, but if the pedestal has some age and the plug fits loosely into the receptacle I would ask the park management to replace the receptacle in the pedestal.

The one thing I question is the 80% continues load rating of a circuit breaker, I will have to research that one. I no longer have any NEC books, this information may be online. One thing for sure, everything is happier at 80%.

Bottom Line... With proper equipment you can pull 30amps 24/7 without equipment failures. Hopefully those attached UL label's have been rightfully earned.
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Old 05-14-2021, 09:06 PM   #5
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Quote:
Originally Posted by johnlantz View Post
Last summer I noticed the 30 amp plug on my pedestal was quite warm. This winter I noticed that the plug showed signs of melting - so I had it replaced.

In earlier posts folks said that low voltage could have been the cause of the plug getting warm.

So I bought myself multimeter and here are some voltage readings

1) plugged into shore power with nothing running - 121
2) with water heater set to electric - 119
3) all of the above and running microwave - 114

Can someone explain what I am seeing? Is this normal? How low can it get before I get concerned?
I always knew not to run A/C and water heater on electric at same time or else the breaker on the pedestal would blow.

Thanks
As mentioned a good EMS will allow you to monitor that easily and automatically act to protect your rig if the voltage sags.

Periodically you want to clean the plug connectors. The heat can just as easily be caused by increased resistance under heavy load and making poor contact. Contact cleaner, even some emery cloth to just clean off any oxidation, etc.
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Old 05-15-2021, 01:37 PM   #6
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Quote:
Originally Posted by johnlantz View Post
Last summer I noticed the 30 amp plug on my pedestal was quite warm. This winter I noticed that the plug showed signs of melting - so I had it replaced.

In earlier posts folks said that low voltage could have been the cause of the plug getting warm.

So I bought myself multimeter and here are some voltage readings

1) plugged into shore power with nothing running - 121
2) with water heater set to electric - 119
3) all of the above and running microwave - 114

Can someone explain what I am seeing? Is this normal? How low can it get before I get concerned?
I always knew not to run A/C and water heater on electric at same time or else the breaker on the pedestal would blow.

Thanks
If the contacts on the campground's pedestal receptacle are corroded or have weak tension the contacts will heat up the receptacle and plug. The contacts can get weak tension from many hours of maximum amperage load. In that case the receptacle should be replaced.

However, it is not unusual for the plug to feel a little warm when you have a full amperage load on it. Warm is okay, but melted as you had is not.
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Old 05-15-2021, 02:05 PM   #7
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Originally Posted by RamblerGuy View Post
If the contacts on the campground's pedestal receptacle are corroded or have weak tension the contacts will heat up the receptacle and plug. The contacts can get weak tension from many hours of maximum amperage load. In that case the receptacle should be replaced.

However, it is not unusual for the plug to feel a little warm when you have a full amperage load on it. Warm is okay, but melted as you had is not.
Going along with RamblerGuy's comments and to inform those new to rv's.
Plugging in or unplugging your rv into a live pedestal places unnecessary arcing on the pedestal outlet and your rv's plug. Over time, this arcing no matter how slight, wears out the contacts.
Never plug your rv into a pedestal without turning off the pedestal breaker first. The same applies when disconnecting from a pedestal, turn off the pedestal breaker first then unplug.
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Old 05-15-2021, 03:37 PM   #8
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Going along with RamblerGuy's comments and to inform those new to rv's.
Plugging in or unplugging your rv into a live pedestal places unnecessary arcing on the pedestal outlet and your rv's plug. Over time, this arcing no matter how slight, wears out the contacts.
Never plug your rv into a pedestal without turning off the pedestal breaker first. The same applies when disconnecting from a pedestal, turn off the pedestal breaker first then unplug.
I fully agree with the above, this SHOULD be standard practice for everyone.

FWIW, I carry a can of contact cleaner and always spray the pedestal before I plug in. I also have a 30->15 amp adapter with a three way plugged into it. The three way has a digital volt meter and one of the wiring testers. I always check the pedestal to insure proper wiring before connecting my trailer.
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Old 05-15-2021, 04:49 PM   #9
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There are a number of reasons that cause a receptacle or cord cap to heat up. The most likely for it to start melting is a loose connection on the receptacle or not a solid contact of the wire on the receptacle or a failure on the male cord cap. 80 percent continuous load on a breaker is correct per code. In other words the breaker is designed as such. Yes the breaker will carry over 24 amps but if you are pulling 28 amps for ten hours the breaker will heat up. Worse case the 30 amp breaker will trip. Take it as a sign to lighten you power consumption. Breaker do fail and will start tripping before their rating. So if you touch the face of a breaker and it is hot or the male cord cap is warm and you know you are not using more than normal electricity report it to the office of the campground. Voltage drop is another issue. Normal voltage should not fall below 105 volts. Yes that is a bit low for long periods of use. You are good to go if the voltage range is between 110 volts and 135 volts.
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Old 05-15-2021, 05:25 PM   #10
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X2 Look for loose or corroded connections on the pedestal outlet.
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Old 05-15-2021, 07:07 PM   #11
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More than 80%

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Originally Posted by ependydad View Post
That's a matter of too many amps being pulled. And I'm betting your issue is more an issue of too many amps being pulled. Breakers are designed for 80% continuous use with occasions jumps up to 100%. Which means you want to try and keep it to about 25 amps. You can use a chart like this for keeping track of approximately how many amps you're drawing:
Doug, it's been a while since I did building design--summer of 1967 as a coop (now called intern), but I specced my share of breakers then.

As I'm sure you know, residential breakers have two trip mechanisms:
--The magnetic trip handles short and severe overloads with 1/2 cycle or 1 cycle of 60Hz, equal to 0.017 seconds.
--The thermal trip is designed to break on overloads but not have nuisance tripping from motors starting, or current inrush to capacitors in the converter.

The Square D QQ and QQB series breakers are said to be the fastest tripping breakers in the industry, with magnetic tripping within 1/2 or 1 cycle of 60 Hz. Their trip curves are shown on page 20 of this specification. Per the trip curves, these breakers can run indefinitely at 100% rated current (single-pole breaker, 25 C ambient temperature). They will trip after 10-40 seconds at double the rated current.
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Old 05-16-2021, 01:32 PM   #12
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Thanks

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Originally Posted by Larry-NC View Post
Doug, it's been a while since I did building design--summer of 1967 as a coop (now called intern), but I specced my share of breakers then.

As I'm sure you know, residential breakers have two trip mechanisms:
--The magnetic trip handles short and severe overloads with 1/2 cycle or 1 cycle of 60Hz, equal to 0.017 seconds.
--The thermal trip is designed to break on overloads but not have nuisance tripping from motors starting, or current inrush to capacitors in the converter.

The Square D QQ and QQB series breakers are said to be the fastest tripping breakers in the industry, with magnetic tripping within 1/2 or 1 cycle of 60 Hz. Their trip curves are shown on page 20 of this specification. Per the trip curves, these breakers can run indefinitely at 100% rated current (single-pole breaker, 25 C ambient temperature). They will trip after 10-40 seconds at double the rated current.

Been wanting to thank you for a while now. Your answers are always well thought out and accurate.
Seriously, not like some on here that post opinions or beliefs. Yours are based in facts and research. Took a while for me to realize you have a wide range of knowledge. Good work!!!

FYI I live about 30 miles south of Raleigh, just off I-95. Happy Trails.
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Old 05-17-2021, 02:44 PM   #13
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Originally Posted by Larry-NC View Post
Doug, it's been a while since I did building design--summer of 1967 as a coop (now called intern), but I specced my share of breakers then.

As I'm sure you know, residential breakers have two trip mechanisms:
--The magnetic trip handles short and severe overloads with 1/2 cycle or 1 cycle of 60Hz, equal to 0.017 seconds.
--The thermal trip is designed to break on overloads but not have nuisance tripping from motors starting, or current inrush to capacitors in the converter.

The Square D QQ and QQB series breakers are said to be the fastest tripping breakers in the industry, with magnetic tripping within 1/2 or 1 cycle of 60 Hz. Their trip curves are shown on page 20 of this specification. Per the trip curves, these breakers can run indefinitely at 100% rated current (single-pole breaker, 25 C ambient temperature). They will trip after 10-40 seconds at double the rated current.
Appreciate the link. I'll admit, I got the 80% rule from a buddy who is a master electrician in a crazy number of states. I never actually looked it up.

Thanks for the info and I'll read the link and will stop quoting that.
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Old 05-18-2021, 08:46 AM   #14
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Appreciate the link. I'll admit, I got the 80% rule from a buddy who is a master electrician in a crazy number of states. I never actually looked it up.

Thanks for the info and I'll read the link and will stop quoting that.
The 80% comes from a rule in the NEC (National Electrical Code) on circuit loading. Also depending how well the RV Park's electrical system was designed will effect the voltage drop issues some people may find.
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Old 05-18-2021, 03:29 PM   #15
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The 80% comes from a rule in the NEC (National Electrical Code) on circuit loading. Also depending how well the RV Park's electrical system was designed will effect the voltage drop issues some people may find.
Any chance you know the specific rule of the NEC that mentions this?
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Old 05-18-2021, 07:18 PM   #16
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Any chance you know the specific rule of the NEC that mentions this?
I hope I got it, but I think it's 384-16(c). You'll have to forgive me as I'm a Canuck Electrician. Both codes are very similar though, just laid out differently.
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Old 05-19-2021, 06:31 AM   #17
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Originally Posted by johnlantz View Post
Last summer I noticed the 30 amp plug on my pedestal was quite warm. This winter I noticed that the plug showed signs of melting - so I had it replaced.

In earlier posts folks said that low voltage could have been the cause of the plug getting warm.

So I bought myself multimeter and here are some voltage readings

1) plugged into shore power with nothing running - 121
2) with water heater set to electric - 119
3) all of the above and running microwave - 114

Can someone explain what I am seeing? Is this normal? How low can it get before I get concerned?
I always knew not to run A/C and water heater on electric at same time or else the breaker on the pedestal would blow.

Thanks
I am a little late to the conversation, but according to Mike Sokol,one of the prime reasons for cord plug melting is a worn cord or a cord not plugged in properly. If it isn't a tight fit there can be arcing." (Mike Sokol)
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Old 05-19-2021, 07:44 AM   #18
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I hope I got it, but I think it's 384-16(c). You'll have to forgive me as I'm a Canuck Electrician. Both codes are very similar though, just laid out differently.
Yep same place just the sub paragraph continuous loads moves around mine was 384-16(D)
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Old 05-19-2021, 07:48 AM   #19
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The 80% comes from a rule in the NEC (National Electrical Code) on circuit loading. Also depending how well the RV Park's electrical system was designed will effect the voltage drop issues some people may find.
As a follow-up to that if you camp close to the power source you'll have few issues with voltage drop. Last guy at the far end, full campground on a hot night with everyone's AC on you'll have voltage drop issues.
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Old 05-19-2021, 10:39 AM   #20
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I hope I got it, but I think it's 384-16(c). You'll have to forgive me as I'm a Canuck Electrician. Both codes are very similar though, just laid out differently.
Appreciate the info.
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