Stupid question about breaker boxes and circuit loads.

M

mark1

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Apr 19, 2009
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Yep, you're right, and that's normal (though not all main breakers are 30 amp).

Look at your house's breaker box, and you'll see the same thing. If you add up all the individual breakers (other than the main), you'll end up with
a lot bigger number than the main breaker is rated for. That's fine, since what you really want to do is to prevent the mains coming into your house
from bursting into flames.

And FWIW, it's the same in a car, where you have a big fuse protecting a host of circuits that collectively can draw a LOT more amps than the main
fuse could supply.

The end result is safe - no circuit, including the mains, are going to be overloaded with the properly sized breaker box design. Just because you
COULD turn on everything in the coach at once doesn't mean it was designed to let you do that without popping the main breaker.
--
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
 
> Yep, you're right, and that's normal (though not all main breakers are 30 amp).
>
> Look at your house's breaker box, and you'll see the same thing. If you add up all the individual breakers (other than the main), you'll end up
> with a lot bigger number than the main breaker is rated for. That's fine, since what you really want to do is to prevent the mains coming into your
> house from bursting into flames.
>
> And FWIW, it's the same in a car, where you have a big fuse protecting a host of circuits that collectively can draw a LOT more amps than the main
> fuse could supply.
>
> The end result is safe - no circuit, including the mains, are going to be overloaded with the properly sized breaker box design. Just because you
> COULD turn on everything in the coach at once doesn't mean it was designed to let you do that without popping the main breaker.

Thanks for the explination Mark
--
Rich Mondor,

Brockville, ON

77 Hughes 2600
 
Rich Mondor wrote: "if you combine the A/C and fridge i gather you'd pop the main breaker like this coach will."

Rich, I gather you have a non-GMC finished coach, eg Coachman or the like. But even a little 30 amp main breaker should easily run a roof A/C and a
refrigerator at the same time. Roof A/C takes about 15 amps (except at start-up), and the refer should only take a few amps, whether it's the old
AC/DC Norcold compressor type or the more common Propane/Electric absorbtion type. If you're sure nothing else is pulling power and these two things
are popping your main breaker, I'd check for 1) voltage drop from an undersized extension or shore power cord, or 2) a bad main breaker. (Yes, they
can wear out if tripped many times.)
FWIW, I commonly run my refer, buzz box, and one roof A/C on a 30 amp circuit, via a 100' extension cord to my barn, but it's a big 6AWG cord. I have
also run both roof A/Cs on a 30 amp service until the park manager yelled at me for running up his electric bill. (When does 30 amp service not allow
you 30 amps? At the Royal Gorge KOA!)
I have an AC voltmeter in my coach, and usually shed load if it gets down to 100 volts.
HTH

--
Rick Staples, '75 Eleganza, Johnstown, CO

"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
 
> Rich Mondor wrote: "if you combine the A/C and fridge i gather you'd pop the main breaker like this coach will."
>
> Rich, I gather you have a non-GMC finished coach, eg Coachman or the like. But even a little 30 amp main breaker should easily run a roof A/C and
> a refrigerator at the same time. Roof A/C takes about 15 amps (except at start-up), and the refer should only take a few amps, whether it's the old
> AC/DC Norcold compressor type or the more common Propane/Electric absorbtion type. If you're sure nothing else is pulling power and these two
> things are popping your main breaker, I'd check for 1) voltage drop from an undersized extension or shore power cord, or 2) a bad main breaker.
> (Yes, they can wear out if tripped many times.)
> FWIW, I commonly run my refer, buzz box, and one roof A/C on a 30 amp circuit, via a 100' extension cord to my barn, but it's a big 6AWG cord. I
> have also run both roof A/Cs on a 30 amp service until the park manager yelled at me for running up his electric bill. (When does 30 amp service
> not allow you 30 amps? At the Royal Gorge KOA!)
> I have an AC voltmeter in my coach, and usually shed load if it gets down to 100 volts.
> HTH

You are correct its a Hughes coach.

Im in the process of changing the shore cable as the wires were a little green from a broken cable/plug head (discovered when i went to change plug)
and will change the breaker as i suspect its original (the last time it popped it didnt feel right when it reset). Once i get these things done i
guess i could grab my amp clamp and check thqe actual load to see whats going on.

Thanks for the info.
--
Rich Mondor,

Brockville, ON

77 Hughes 2600
 
Rich,

This is all much more simple than you might expect.

If you have to, draw a block diagram with breakers and branches noted. Any breaker should protect the smaller wire size attached.

So, If you have a 8-8-6-8 SJO shore power cable, it will be plugging a 14-50 receptacle with a 2*50 breaker. But it is only good for 40 amps, so it
has to end at a 2*40amp breaker.

That 2*40 breaker feeds the buss bars in the box that are probably good for 100amps.

The branch circuits will all be #12 or #14 AWG and therefore should be fed by 20 and 15 amp breakers.

One word of caution if you are going to go into the main box with a vengeance. Be aware that there is a neutral and an safety ground, and they are
not the same as in a dwelling. There should be bars for both and neither should be bonded to the box itself. The real safety ground (Green) should
be be bonded to the either the ground at the generator frame or the shore power source. This is necessary to preclude a "Hot Skin" condition where
the entire coach has a voltage that is above ground. This can be a dangerous condition.

Oh, if you are going to pull in any new 120V circuits, look for marine wire that is like three conductor Rolex, but the conductors are stranded.
While being stranded makes termination more involved, it is much easier to pull it into strange places.

Matt


--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Matt,

Reading your answer "Be aware that there is a neutral and an safety ground, and they are not the same as in a dwelling. There should be bars for both
and neither should be bonded to the box itself. The real safety ground (Green) should be be bonded to the either the ground at the generator frame or
the shore power source. This is necessary to preclude a "Hot Skin" condition where the entire coach has a voltage that is above ground."

Are you saying the ground from the shore cable should be kept electrically isolated from the coach body? That is what I'm reading anyway. The ground
bar in my OEM electrical box is fastened directly to the box while the Neutral bar is isolated from the box and is not connected to the ground bar.
The Neutral and Ground should be connected at the source of power of course. But I believe the ground cable of the shore power should be connected
(bonded) to the coach frame and body. The ground wire should also be connected to the case (box) of every appliance (A/C) and electrical outlet as
well as the outlet box. Otherwise what is going to protect you if a "Hot Skin" condition does occur?

Maybe I just read it wrong?

--
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
 
> Matt,
>
> Reading your answer "Be aware that there is a neutral and an safety ground, and they are not the same as in a dwelling. There should be bars for
> both and neither should be bonded to the box itself. The real safety ground (Green) should be be bonded to the either the ground at the generator
> frame or the shore power source. This is necessary to preclude a "Hot Skin" condition where the entire coach has a voltage that is above ground."
>
> Are you saying the ground from the shore cable should be kept electrically isolated from the coach body? That is what I'm reading anyway. The
> ground bar in my OEM electrical box is fastened directly to the box while the Neutral bar is isolated from the box and is not connected to the
> ground bar. The Neutral and Ground should be connected at the source of power of course. But I believe the ground cable of the shore power should
> be connected (bonded) to the coach frame and body. The ground wire should also be connected to the case (box) of every appliance (A/C) and
> electrical outlet as well as the outlet box. Otherwise what is going to protect you if a "Hot Skin" condition does occur?
>
> Maybe I just read it wrong?

Bruce,

I am glad that you read it and didn't understand.
The way I wrote it was wrong.
The safety ground should get bonded to the coach by way of the box. It is the neutral only that should remain isolated.

Thanks

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Thanks fhe info and the lesson guys....its nice to learn new things :)

Power cord is replaced....going to throw a couple new breakers in there tomorrow and then break out the amp clamp to see whats what.

Next will be new converter and new fuse block.
--
Rich Mondor,

Brockville, ON

77 Hughes 2600
 
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