Plugging in to shore power

RF_Burns

RF_Burns

Super Moderator
Staff member
Sep 7, 2008
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Rich,
A 50Amp service is 240 VAC (two 120VAC legs to neutral). A 50Amp to 30 Amp adapter connects the 30 Amp cable to one of the 120V legs.

You could actually draw 50 Amps from this, but you are limited to 30 Amps in your panel by the main breaker.

The post 30 Amp outlet is 120VAC with a 30 Amp breaker at the post.

My opinion is the fewer connections the better, so if you have a 30 amp cord and there is a 30 amp outlet at the post, use the 30 Amp outlet. The
other consideration is the 50 Amp adapter is usually a dog-bone cable which leaves the 30 Amp cable connector hanging outside in the weather. When
plugged directly into a 30 amp outlet your cable connector is usually protected from weather under a hood.

Just mt 2 cents.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
Same same. The pedestal will supply up to 30 amps at 120 volts maximum no matter what you plug into it.

I prefer 240 volt at 50 amp because most places have this service these days and the cable will have 1/2 of the total current draw across any of the
conductors for the same load. If I am forced to use a 30 amp pedestal then I simply add an adapter to the cable.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Technically the 50 to 30A adaptor is not code. (14-50 to TT-30)
The post breaker is over sized for protecting the 30A cord set.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
If you want to get very technical about it, the GMC is nowhere close to
being "up to the code". There is a hodge podge of different cord sets,
generators, internal circuit protection, and the list goes on as the
coaches age and well intentioned users change stuff, add inverters, solar,
etc., etc. You ought to feel lucky that they don't "light you up" when you
approach one and touch some metal parts while you are standing on a good
ground. It has happened to me more than once.
Let's see, is this green wire supposed to be grounded, or is it
supposed to be bonded? They are both one and the same, right? Shouldn't
make much of a difference, should it? Nahhhh!
Jim Hupy
Salem, Oregon

On Tue, Jan 14, 2020, 6:29 AM John R. Lebetski via Gmclist <

> Technically the 50 to 30A adaptor is not code. (14-50 to TT-30)
> The post breaker is over sized for protecting the 30A cord set.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
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>
 
Just to be clear, the White wire and the Green wire are NOT the same.
The Green safety ground wire should be connected to the ground bar and in turn to the motorhome chassis only.
The White wire, the Neutral, should be connected to the neutral bar only in your coach.
The 120V electric panel in your coach is a sub panel, not a main panel. Have a paper written about this very subject if anyone is interested.

>
>
> If you want to get very technical about it, the GMC is nowhere close to
> being "up to the code". There is a hodge podge of different cord sets,
> generators, internal circuit protection, and the list goes on as the
> coaches age and well intentioned users change stuff, add inverters, solar,
> etc., etc. You ought to feel lucky that they don't "light you up" when you
> approach one and touch some metal parts while you are standing on a good
> ground. It has happened to me more than once.
> Let's see, is this green wire supposed to be grounded, or is it
> supposed to be bonded? They are both one and the same, right? Shouldn't
> make much of a difference, should it? Nahhhh!
> Jim Hupy
> Salem, Oregon
>
> On Tue, Jan 14, 2020, 6:29 AM John R. Lebetski via Gmclist <

>
> > Technically the 50 to 30A adaptor is not code. (14-50 to TT-30)
> > The post breaker is over sized for protecting the 30A cord set.
> > --
> > John Lebetski
> > Woodstock, IL
> > 77 Eleganza II
> >
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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I’m interested in the white paper.

I understand “star grounding” in professional audio and video.

But most of the electrical panels I’ve seen has the “technical earth” bonded to the neutral.

Hell yes it’s confusing.

In the interim…. no ground loops are good.

Dolph

DE AD0LF

Wheeling, West Virginia

1977 26’ ex-PalmBeach
Howell EFI & EBL, Reaction Arms, Manny Transmission

“The Aluminum and Fiberglass Mistress"

>
> Just to be clear, the White wire and the Green wire are NOT the same.
> The Green safety ground wire should be connected to the ground bar and in turn to the motorhome chassis only.
> The White wire, the Neutral, should be connected to the neutral bar only in your coach.
> The 120V electric panel in your coach is a sub panel, not a main panel. Have a paper written about this very subject if anyone is interested.
>

>>
>>
>> If you want to get very technical about it, the GMC is nowhere close to
>> being "up to the code". There is a hodge podge of different cord sets,
>> generators, internal circuit protection, and the list goes on as the
>> coaches age and well intentioned users change stuff, add inverters, solar,
>> etc., etc. You ought to feel lucky that they don't "light you up" when you
>> approach one and touch some metal parts while you are standing on a good
>> ground. It has happened to me more than once.
>> Let's see, is this green wire supposed to be grounded, or is it
>> supposed to be bonded? They are both one and the same, right? Shouldn't
>> make much of a difference, should it? Nahhhh!
>> Jim Hupy
>> Salem, Oregon
>>
>> On Tue, Jan 14, 2020, 6:29 AM John R. Lebetski via Gmclist <

>>
>>> Technically the 50 to 30A adaptor is not code. (14-50 to TT-30)
>>> The post breaker is over sized for protecting the 30A cord set.
>>> --
>>> John Lebetski
>>> Woodstock, IL
>>> 77 Eleganza II
>>>
>>>
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
No 100 amps from the 50 amp circuit...25 amps on each power leg to neutral at 120 volts and 50 amps between both power legs at 240 volts.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
> No 100 amps from the 50 amp circuit...25 amps on each power leg to
neutral at 120 volts and 50 amps between both power legs at 240 volts.

>

Uh no, I don't think so.

A 50 A 240 V service can provide up to 50x240 or 12,000 watts.

But connecting a 50A 240 V circuit through a dogbone adapter to a 120V
pigtail uses only one of the 50A legs, meaning you still get half the
power or 6,000 watts from the remaining leg and the neutral..

6000 watts / 120V is still 50A, but it's at 120 volts.

The coach 30A breaker limits downstream current to coach circuits, the
connection between the pedestal and the coach main breaker is protected
(sorta) by the pedestal breaker. If there is a fault between the
pedestal and the coach breaker the 50A will _probably_ open.

Stu

"Heck is where you go if you don't believe in Gosh."
 
It's 50 amps per leg, a 2 pole 50 amp over currant devise. You can call it 100 amps but it's really 50 amps @ 240 volts. If you tried to pull 100 amps
@ 120 volts you'd put twice the amps on the grounded conductor (neutral) that it is rated for. If you had a 2 pole 25 amp breaker, I'd give you the
50 amp total but again the same conditions applying to the neutral.
Hal
--
1977 Royale 101348,

1977 Royale 101586, Diesel powered,

1975 Eleganza II, 101230,

1974 Eagle Bus 45',w/slideout,

Rio Rancho, NM
 
Hal, I will enter the fray here.

The current on the neutral conductor will be the difference of the two hot conductors, not the sum. So if you had 25 amps on each of the hot
conductors, the current on the neutral would be ZERO amps. If you had 25 on one and 20 on the other, then the current on the neutral would be 5
amps.

Respectively,

Ken B.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Very true Ken B. But to be even pickier, GMC upfit coaches usually have a 40A dual pole main breaker at the coach box. When on Onan, the full combined
L1 and L2 is carried by the neutral, but the 50A Onan breaker protects the cord set which was not designed for 80A on the neutral. So they thought it
through
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
You are correct. I thought were were talking feeding the coach with 240 volt shore power vs. 30 amp 120 volt shore power.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
We were. But to truly understand the reasons "why" , you really need a full understanding of the system. I assume he has a TT-30 non GMC upfit system.
So-- if you have an 14-50P to TT-30 adapter at the post, you have the potential of overheating the TT-30 cord set, should a fault occur.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
The fact that GMC only ever shipped coaches with 50 amp cords is not a well known.

Check the parts book.

Dolph

DE AD0LF

Wheeling, West Virginia

1977 26’ ex-PalmBeach
Howell EFI & EBL, Reaction Arms, Manny Transmission

“The Aluminum and Fiberglass Mistress"

>
> We were. But to truly understand the reasons "why" , you really need a full understanding of the system. I assume he has a TT-30 non GMC upfit system.
> So-- if you have an 14-50P to TT-30 adapter at the post, you have the potential of overheating the TT-30 cord set, should a fault occur.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Actually they didn’t. Many people, including you, assume that they have a 50 amp cord but look at your cord and you’ll see that it is marked 40 amps.
The plug is the same as a 50 amp but the 40 amp cord matches the two 20 amp breakers in the box.

Emery Stora
77 Kingsley
Frederick CO

>
> The fact that GMC only ever shipped coaches with 50 amp cords is not a well known.
>
> Check the parts book.
>
>
> Dolph
>
> DE AD0LF
>
> Wheeling, West Virginia
>
> 1977 26’ ex-PalmBeach
> Howell EFI & EBL, Reaction Arms, Manny Transmission
>
> “The Aluminum and Fiberglass Mistress"
>

>>
>> We were. But to truly understand the reasons "why" , you really need a full understanding of the system. I assume he has a TT-30 non GMC upfit system.
>> So-- if you have an 14-50P to TT-30 adapter at the post, you have the potential of overheating the TT-30 cord set, should a fault occur.
>> --
>> John Lebetski
>> Woodstock, IL
>> 77 Eleganza II
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Just for grins 'n giggles, I thought I would throw this little known fact
out. In 1978 only, GM offered a 145 Ampere Delcotron Generator. Part #
1117148. It had different mounting brackets, and a double v-belt sheave.
Not an exact bolt on without those matching brackets, etc.
Jim Hupy
Salem, Oregon

On Wed, Jan 15, 2020, 1:00 PM Emery Stora via Gmclist <

> Actually they didn’t. Many people, including you, assume that they have a
> 50 amp cord but look at your cord and you’ll see that it is marked 40 amps.
> The plug is the same as a 50 amp but the 40 amp cord matches the two 20
> amp breakers in the box.
>
> Emery Stora
> 77 Kingsley
> Frederick CO
>
> > On Jan 15, 2020, at 12:22 PM, Dolph Santorine via Gmclist <

> >
> > The fact that GMC only ever shipped coaches with 50 amp cords is not a
> well known.
> >
> > Check the parts book.
> >
> >
> > Dolph
> >
> > DE AD0LF
> >
> > Wheeling, West Virginia
> >
> > 1977 26’ ex-PalmBeach
> > Howell EFI & EBL, Reaction Arms, Manny Transmission
> >
> > “The Aluminum and Fiberglass Mistress"
> >
> >> On Jan 15, 2020, at 10:50 AM, John R. Lebetski via Gmclist <

> >>
> >> We were. But to truly understand the reasons "why" , you really need a
> full understanding of the system. I assume he has a TT-30 non GMC upfit
> system.
> >> So-- if you have an 14-50P to TT-30 adapter at the post, you have the
> potential of overheating the TT-30 cord set, should a fault occur.
> >> --
> >> John Lebetski
> >> Woodstock, IL
> >> 77 Eleganza II
> >>
> >>
> >> _______________________________________________
> >> GMCnet mailing list
> >> Unsubscribe or Change List Options:
> >> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
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>
 
Emery

No illusions here - my coach has a 30 amp cord (10 gauge) that was installed by the PO

That combined with the 40 amp breakers and the 6 kW generator just didn’t add up.

Bill Helmouth and the parts book confirm that the 50 amp cord was the only thing GM shipped.

Dolph Santorine

DE AD0LF

Wheeling, West Virginia

1977 ex-Palm Beach TZE167V100820
Howell EFI/EBL , Reaction Arms, Manny Transmission

>
> Actually they didn’t. Many people, including you, assume that they have a 50 amp cord but look at your cord and you’ll see that it is marked 40 amps.
> The plug is the same as a 50 amp but the 40 amp cord matches the two 20 amp breakers in the box.
>
> Emery Stora
> 77 Kingsley
> Frederick CO
>

>>
>> The fact that GMC only ever shipped coaches with 50 amp cords is not a well known.
>>
>> Check the parts book.
>>
>>
>> Dolph
>>
>> DE AD0LF
>>
>> Wheeling, West Virginia
>>
>> 1977 26’ ex-PalmBeach
>> Howell EFI & EBL, Reaction Arms, Manny Transmission
>>
>> “The Aluminum and Fiberglass Mistress"
>>

>>>
>>> We were. But to truly understand the reasons "why" , you really need a full understanding of the system. I assume he has a TT-30 non GMC upfit system.
>>> So-- if you have an 14-50P to TT-30 adapter at the post, you have the potential of overheating the TT-30 cord set, should a fault occur.
>>> --
>>> John Lebetski
>>> Woodstock, IL
>>> 77 Eleganza II
>>>
>>>
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Both parts books that I have, as well as the 1975-76 and 77-78 Maintence
manuals all refer to the cord set as 40 AMPERE. I could not find any
reference to a 50 amp cord set in any of my stuff including the idiots
guide. So, it can't be proved beyond a shadow of a doubt by anything that I
have. If you have a 50 amp service in your coach, ONE POSSIBILITY MIGHT BE
that it has been upgraded somewhere during its 40 year existence.
Jim Hupy
Salem, Oregon

On Wed, Jan 15, 2020, 3:26 PM Adolph Santorine via Gmclist <

> Emery
>
> No illusions here - my coach has a 30 amp cord (10 gauge) that was
> installed by the PO
>
> That combined with the 40 amp breakers and the 6 kW generator just didn’t
> add up.
>
> Bill Helmouth and the parts book confirm that the 50 amp cord was the only
> thing GM shipped.
>
> Dolph Santorine
>
> DE AD0LF
>
> Wheeling, West Virginia
>
> 1977 ex-Palm Beach TZE167V100820
> Howell EFI/EBL , Reaction Arms, Manny Transmission
>
>
> > On Jan 15, 2020, at 4:00 PM, Emery Stora via Gmclist <

> >
> > Actually they didn’t. Many people, including you, assume that they have
> a 50 amp cord but look at your cord and you’ll see that it is marked 40
> amps.
> > The plug is the same as a 50 amp but the 40 amp cord matches the two 20
> amp breakers in the box.
> >
> > Emery Stora
> > 77 Kingsley
> > Frederick CO
> >
> >> On Jan 15, 2020, at 12:22 PM, Dolph Santorine via Gmclist <

> >>
> >> The fact that GMC only ever shipped coaches with 50 amp cords is not a
> well known.
> >>
> >> Check the parts book.
> >>
> >>
> >> Dolph
> >>
> >> DE AD0LF
> >>
> >> Wheeling, West Virginia
> >>
> >> 1977 26’ ex-PalmBeach
> >> Howell EFI & EBL, Reaction Arms, Manny Transmission
> >>
> >> “The Aluminum and Fiberglass Mistress"
> >>
> >>>> On Jan 15, 2020, at 10:50 AM, John R. Lebetski via Gmclist <

> >>>
> >>> We were. But to truly understand the reasons "why" , you really need a
> full understanding of the system. I assume he has a TT-30 non GMC upfit
> system.
> >>> So-- if you have an 14-50P to TT-30 adapter at the post, you have the
> potential of overheating the TT-30 cord set, should a fault occur.
> >>> --
> >>> John Lebetski
> >>> Woodstock, IL
> >>> 77 Eleganza II
> >>>
> >>>
> >>> _______________________________________________
> >>> GMCnet mailing list
> >>> Unsubscribe or Change List Options:
> >>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >>
> >> _______________________________________________
> >> GMCnet mailing list
> >> Unsubscribe or Change List Options:
> >> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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>
 
I checked the Parts book 78Z and it clearly refers to a 40 amp cord. It doesn’t show a 50 amp cord. I can provide the page number in the parts book if you need it.
It looks like Bill Helmouth (could that have been Bill Helmore) gave you incorrect information.

Since your prior owner replace your cord with a 30 amp you can’t look at the original cord but it clearly is embossed with 40 amp all along the rubber covering of the cord. That is what GM put on all of the factory built motorhomes.

Emery Stora

>
> Emery
>
> No illusions here - my coach has a 30 amp cord (10 gauge) that was installed by the PO
>
> That combined with the 40 amp breakers and the 6 kW generator just didn’t add up.
>
> Bill Helmouth and the parts book confirm that the 50 amp cord was the only thing GM shipped.
>
> Dolph Santorine
>
> DE AD0LF
>
> Wheeling, West Virginia
>
> 1977 ex-Palm Beach TZE167V100820
> Howell EFI/EBL , Reaction Arms, Manny Transmission
>
>

>>
>> Actually they didn’t. Many people, including you, assume that they have a 50 amp cord but look at your cord and you’ll see that it is marked 40 amps.
>> The plug is the same as a 50 amp but the 40 amp cord matches the two 20 amp breakers in the box.
>>
>> Emery Stora
>> 77 Kingsley
>> Frederick CO
>>

>>>
>>> The fact that GMC only ever shipped coaches with 50 amp cords is not a well known.
>>>
>>> Check the parts book.
>>>
>>>
>>> Dolph
>>>
>>> DE AD0LF
>>>
>>> Wheeling, West Virginia
>>>
>>> 1977 26’ ex-PalmBeach
>>> Howell EFI & EBL, Reaction Arms, Manny Transmission
>>>
>>> “The Aluminum and Fiberglass Mistress"
>>>

>>>>
>>>> We were. But to truly understand the reasons "why" , you really need a full understanding of the system. I assume he has a TT-30 non GMC upfit system.
>>>> So-- if you have an 14-50P to TT-30 adapter at the post, you have the potential of overheating the TT-30 cord set, should a fault occur.
>>>> --
>>>> John Lebetski
>>>> Woodstock, IL
>>>> 77 Eleganza II
>>>>
>>>>
>>>> _______________________________________________
>>>> GMCnet mailing list
>>>> Unsubscribe or Change List Options:
>>>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>>
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
> Hal, I will enter the fray here.
>
> The current on the neutral conductor will be the difference of the two hot conductors, not the sum. So if you had 25 amps on each of the hot
> conductors, the current on the neutral would be ZERO amps. If you had 25 on one and 20 on the other, then the current on the neutral would be 5
> amps.
>
> Respectively,
>
> Ken B.

True only if they are on different phases. When people start using 50/30 adapters loads imposed on the neutral can get out of wack depending on how
the rest of the system is wired.
Hal
--
1977 Royale 101348,

1977 Royale 101586, Diesel powered,

1975 Eleganza II, 101230,

1974 Eagle Bus 45',w/slideout,

Rio Rancho, NM
 
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