| 30amp or 50amp [message #361071] |
Mon, 21 December 2020 23:10  |
thigh19
Messages: 92
Registered: July 2019
Location: Vancouver Wa
Karma: 1
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Okay, everything I’ve read and/or researched, my 73 Sequoia is 30amp.
I ran a 30amp shore power line outside my shop. Plugged in my surge protector and everything is good.
Ran a 50’ 30amp extension cord to the motorhome. The plug on the shore power from the gmc is a 4 prong, guessing 50amp style. There is an adapter going from 4 lug to 3 lug, came with the motorhome.
When everything is plugged in, the surge protector says reverse polarity, unplug the motorhome and surge protector says all’s good.
Has my motorhome been converted to 50amp?
I can use a regular plug and everything works, including the A/C, and it’s only a 15amp service.
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| Re: 30amp or 50amp [message #361072 is a reply to message #361071] |
Tue, 22 December 2020 03:48  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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I believe all 73 coaches were 50 amp (240 volt). From the description you gave in your posting, yours is too. The 4 conductor plug is used for 50amp 240 volts. A 30 amp 120 volt plug plug only has 3 wires NOT 4.
I do not have the 1973 GMC diagram and the one on Billy's bdub site just comes down as a blank page, so I could not verify the above statement.
Ken B.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] 30amp or 50amp [message #361076 is a reply to message #361072] |
Tue, 22 December 2020 07:48 |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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Senior Member |
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The 4-conductor plug (and socket) are designed for
split 240 Volt AC (120 Volts either side of the neutral).
However, since the Onan genset output is only 120 Volt,
its output is fed to BOTH conductors of the 50 Amp wiring.
This is no problem when using the Onan to power the
coach since the original wiring from the socket feeds
power to two separate circuits.
It also enables the coach to be fed from a true split 240
Volt source.
If you only have a 120 Volt source at a campground, you
would need an adapter to be able to feed ALL the circuits
in the coach.
If some prior owner has modified the coach, ALL bets are off
as to what you will need to do!
D C "Mac" Macdonald
Amateur Radio K2GKK
Since 30 November '53
USAF and FAA, Retired
Member GMCMI & Classics
Oklahoma City, OK
"The Money Pit"
TZE166V101966
'76 ex-Palm Beach
k2gkk + hotmail dot com
________________________________
From: Gmclist on behalf of Ken Burton via Gmclist
Sent: Tuesday, December 22, 2020 03:48
To: gmclist@list.gmcnet.org
Cc: Ken Burton
Subject: Re: [GMCnet] 30amp or 50amp
I believe all 73 coaches were 50 amp (240 volt). From the description you gave in your posting, yours is too. The 4 conductor plug is used for
50amp 240 volts. A 30 amp 120 volt plug plug only has 3 wires NOT 4.
I do not have the 1973 GMC diagram and the one on Billy's bdub site just comes down as a blank page, so I could not verify the above statement.
Ken B.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: 30amp or 50amp [message #361079 is a reply to message #361071] |
Tue, 22 December 2020 09:47 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Where is this surge protector located? Remember that a 30 to 50 dongle (TT30P to 14-50R) will tie L1 and L2 of the 14-50 together internally and power them from the single TT30 hot conductor. Neutral and Ground remain one for one.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] 30amp or 50amp [message #361082 is a reply to message #361075] |
Tue, 22 December 2020 17:05 |
Dolph Santorine
Messages: 1236
Registered: April 2011
Location: Wheeling, WV
Karma: -41
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I’m going to stir this one up- the plug was 50 amp, but there were two 20 amp breakers, meaning 40 amps.
The cord shown in the Parts Book as listed as a 40 amp cord, and I’ve heard from more than one owner with an original cord set that it is indeed marked 40 amp.
The PO on my coach had one of the RV shops put an easier to handle 30 amp cord in my coach with one rooftop AC.
Dolph
DE AD0LF
Wheeling, West Virginia
1977 26’ ex-PalmBeach
Howell EFI & EBL, Reaction Arms, Manny Transmission
“The Aluminum and Fiberglass Mistress”
|[ ]~~~[][ ][] \
"--OO--[]---O-"
> On Dec 22, 2020, at 8:51 AM, Matt Colie via Gmclist wrote:
>
> Thigh,
>
> I am not tying to up stage Ken B, but in 1973 I was working for Thetford. The engineering group was given a special introduction to the GMC Motorhome
> one day. They made it clear that they expected to be ahead of the motorhome developments.
>
> One of those areas was the 50Amp electric service. They actually thought that the future of RV power demands was such that all campgrounds would be
> 50amp in less than 10 years. (I guesses they missed that one.)
>
> They other area was gray water discharge. At that time, some RVs just had a hose to allow the owner to lead the gray water away from the coach. That
> is why they chose to go with a single tank. Only one tank to dump. (They more or less missed that one too.)
>
> The one they hit more or less right is the single service access door on the left side.
>
> Matt
> --
> Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Near DTW - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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| Re: 30amp or 50amp [message #361083 is a reply to message #361071] |
Tue, 22 December 2020 19:51 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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The cord set is NEMA 14-50P and meant to be safely matched to a 14-50R breakered at 50A 2pole. That protects the cord set to code. The mains GMC breakers are 40A 2 pole. There are 80 Amps total available on board at 125V. I believe the original safety decals mention 40A and stuff about different standards when traveling outside the USA.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: 30amp or 50amp [message #361087 is a reply to message #361071] |
Wed, 23 December 2020 08:53 |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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Just to clarify...
With the 50 Amp cord plugged into a 50 Amp /240 Volt service, the two 40 Amp main breakers will limit you to 40 amps on each 120 volt leg.
- 40 Amps x 120V = 4800 watts per leg x 2 legs = 9600 watts total power
- IF you had some 240V equipment (which I don't know anyone who has added this) you would be limited to 40Amp x 240V = 9600 watts total. You must add in any 120V equipment consumption so the power through either 40Amp breaker does not exceed 40 Amps.
IF you plugged into a 30 Amp 120V service, through an adapter, you would be limited to 30 Amps total on both 120V legs by the 30 Amp service breaker.
- 30 Amps x 120V = 3600 watts total power
IF you are plugged into a 15 or 20 Amp service through an adaptor, you are limited to either 15 or 20 Amps by the service breaker (including other loads which maybe on the circuit)
- 15 Amps x 120V = 1,800 watts total power
- 20 Amps x 120V = 2,400 watts total power
IF you are plugged into the 6Kw Onan generator you have 50Amps at 120V = 6,000 watts max power. You are limited to the maximum of:
- A) 40 Amps on either leg and...
- B) A total of 50 Amps on both main breakers.
On my '77 Palm Beach, the breaker I am most likely to trip is the 20Amp breaker all for the wall outlets. All the wall outlets are on the same breaker, so plugging in the toaster and coffee maker put me at the Max for that breaker. Add the microwave and it will trip.
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
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