BCM magazine typo

[DrivingMissLazy]

Got my copy today and it looks great.

There is a typo in two locations on page 50 and 51 that reads

Each hot leg is rated for 25 Amps

.

This is I believe a typographical error and should be 50 amps, therefore the statement should be

Each hot leg is rated for 50 Amps

. Please revise your copy accordingly.

Richard

Discussion is about 50 amp shorepower service.

[Nick Badame Refrig/ACC]

Hi Richard,

I think the centerfold 102C3 has a typo too..  It's listed as a 1998'  should say "88"

All in all, it's a really good issue along with Jack's detailed latch installation.

Nick-

[DrivingMissLazy]

Hi Richard,

I think the centerfold 102C3 has a typo too..  It's listed as a 1998'  should say "88"

All in all, it's a really good issue along with Jack's detailed latch installation.

Nick-

I agree. One of the best issues I have seen lately.

Richard

[Sam 4106]

Hi Richard,
I think you are being very charitable by attributing the error to a typo. If that wre the only thing wrong with the article I might agree. However, he also states that if both hots in a 50 amp socket are on the same phase you can overload the neutral. I don't see how that could happen. Unless the errors were made in the editing process I think the author has a serious credibility problem.
Thanks, Sam 4106

[Sean]

... However, he also states that if both hots in a 50 amp socket are on the same phase you can overload the neutral. I don't see how that could happen. ...

Well, since I no longer subscribe, I don't have the original copy in front of me.  However, rest assured that if a park mis-wires a 50-amp service so that both hots are on the same phase, you most certainly can overload the neutral.

When two hots are on opposite legs, the current returned on the neutral is the difference between the two hot currents.  In other words, if one hot is pulling 50 amps, and the other is pulling zero, the neutral will carry 50 amps, whereas if both hots are pulling 50 amps, the neutral will carry zero.  If one hot is pulling, say, 40 amps, and the other is pulling 30 amps, the neutral will carry 10 amps -- the difference between 40 and 30.

On the other hand, if bot hots are on the same leg, then the return current will be the sum of both hot currents.  If you pull 50 amps on both hots, there will be 100 amps on the neutral.  If you pull 40 amps on one hot and 30 on the other, there will be 70 amps on the neutral.

Since the neutral wire in your coach is rated at 50 amps (and likely the one in the pedestal is, too), you can easily melt the insulation and start a fire with this setup.

If you read zero volts between hots and 120 from either hot to neutral with your meter, I would advise you to either refrain from using the outlet, or, if you must, then take steps to ensure you do not draw more than 50 amps total on both sides.

-Sean
http://ourodyssey.blogspot.com

[Sam 4106]

Hi Sean,
I understand that in a normal 120/240 volt 50 amp connection the neutral only carries the difference in amperage between the two hots and that with both hot legs supplied by the same phase you could have an overload on the neutral. But in the only situation I have seen at a campground where both hots were on the same leg was where someone had hooked the recepticle to a single pole 50 amp breaker and used a jumper between the two hot sides of the recepticle. In that situation you could not overload the neutral, I can see where if the jumper were placed somewhere else between the transformer and the power post you could overload the neutral. I based my comment on the only situation that I have observed. Please accept my apology.
Thanks, Sam 4106

[DrivingMissLazy]

Sean, here is the error that I noticed as published;

There is a subtle problem with the inphase
mis-wire. Each hot leg is rated for 25
Amps. If you were using 25 Amps from each
hot leg, for 50 Amps total, how much current
is flowing in the neutral leg? If the circuit is
wired properly with out-of-phase hot legs,
then the neutral leg has NO current in it! If the
circuit is mis-wired with in-phase hot wires,
then the neutral wire has to carry 50 Amps!
The neutral wire is probably only rated to
carry 25 Amps since this is the most it would
have to carry in a correct circuit. That happens
if only one hot leg is conducting at 25 Amps.
We've seen power cords that have burned
up the neutral conductor from such mis-wired
50 Amp service. Power cords are available
with a neutral conductor rated for 50 Amps,
but is your internal wiring? For other reasons
discussed later, your internal neutral wire
should be rated for 50 Amps.

and here:

Fifty Amp Wiring
If you wire your motor coach with 50 Amp service there will be two
internal hot circuits representing the two hot wires. Each hot leg is only
rated for 25 Amps.

Richard

[Sean]

.... Please accept my apology.
...

Sam -- no apology required.  I hope I did not offend you with all the emphasis in my post.  But many people read these threads, and it is important, IMO, that they "get" it.  You are, of course, right that if both legs are cross-tied to a single 50-amp single-pole breaker, then that will limit total current to 50 amps.  But, trust me, I've seen installations where the cross-tie was upstream of a double-pole 50-amp breaker.

Richard -- thanks for posting the relevant section.  I would hope that MAK publishes a correction to that in the next issue.  It's a major gaffe.

-Sean
http://ourodyssey.blogspot.com