Re: 50 Amp MH connected to 30-Amp Service

In article <lgate41sqcr9bh7aoehpqnqoqaue8ldqd6@xxxxxxx>,
Sandy A. Nicolaysen <sandynic@xxxxxxxxxxx> wrote:
On Thu, 9 Oct 2008 16:40:55 -0700, "Bob Hatch" <bobhatch@xxxxxx>
wrote:

"Jenny6833A" <Jenny6833A@xxxxxxx> wrote in message
news:bd7237ff-badd-4fff-ac4d-406db5c31206@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
We're considering converting our 30-amp motorhome to 50-amp. We've
never used a 50-amp motor home.

I want to make sure I understand how this works. Better safe than
sorry!

Assume a motor home wired for 50-amp service in the _standard_
manner. (No Wolf tricks!) Some appliances are wired to Line 1 and
others wired to Line 2. When plugged into 50-amp service, all the
appliances get power.

When plugged into 30-amp service, I think the Line 2 appliances do NOT
get power. Right?

That is, when deciding which appliances to wire to Line 2, one chooses
the appliances (bedroom AC, washer, dryer, ... ) that one can get
along without when only 30-amp service is available. Right?

:-)

Jenny

You've been pointed to the link on my page, but I'll point again.
http://www.bobhatch.com/electricStuff/30to50amp.htm

Your first assumption is correct. 50 amp service is 120/240 volt, and that's
explained in some detail on my link. The conversion can be cheap, meaning
about $500.00 if you have a 120/240 ATS and a 120/240 main breaker panel. If
you don't have either of these things the cost could run up to $1000.00.

Your second assumption is not correct. You will use a 30 amp male to 50 amp
female adapter. The 2 legs of the single hot power supply are jumped inside
the adapter. Because of that fact, both legs will get power, but you'll be
back to 30 amp. See here:
http://www.bobhatch.com/electricStuff/dogBoneAdapter/index.htm

Your last assumption is incorrect, because your second assumption is
incorrect.

The trick is to attempt to balance the loads on each of the 2 hot lines so
that you have approximately the same amp usage on each side. This is
important because of the way the American power grid works, and what happens
with the return current on the neutral line.

Questions, ask me.
Bob: Shouldn't the RV industry have called 50A service 100A service?

yes, The names are 'somewhat' misleading. It isn't _just_ the RV industry,
though. *everybody* does it that way. A house with "100A service" has
100A @ 240V in, and two 100A breakers (one for each hot) in the panel.
similarly, "200A service" has 2 200A breakers. But *old* houses -- ones
built before the 1960s, and never upgraded for air conditioning -- with
'60A service' have 60A @ 120V available -- usually a box with _four_ 15 A
*fuses*.

When I plug into 50A service there is a DOUBLE 50A breaker, i.e. TWO
50A hots plus a neutral.

That's 50A @ 240V. You can't draw any more than 50 A for any _one_ thing,
regardless of whether it runs at 120V or 140v.. But, yes, you can draw up
to 50 A @120 V from each of the 2 sides of the 240V circuit. You're
guaranteed to be able to draw 50A@120V, and _may_ be able to draw twice
that _if_ the two legs are absolutely balanced. In practice, you'll get
a sum of "more than 50A@120V, but less than 100A@120V", because things are
not perfectly balanced.

With 30A service I get one hot plus one
neutral.

Right. 30A @ 120V. You can't draw more than 30 A for any _one_ thing.
*AND* you can't draw more than 30A for everything.

Even with a cheater box on two 30A outlets, I'm really only getting
60A worth of power, right? Please correct me if I'm misguided here.

Correct. the cheater combines 2 30A 120V circuits to give 30 A @240v.
You cannot draw more than 30A for any _one_ thing. But you can draw
'more than 30A, but less than 60A' _total_ for everything. If you go
over the 30A on one side , you'll trip that one breaker at the pedestal,
and only be able to run the stuff connected to the 'other side' of the
240V circuit in the RV.


.

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