In article , Vernon wrote:
Guys,

I am building a heavy "extension cord" intended to carry 50 amps not
more than 100' from our 200 amp power box to my van. Inside the van
will be a couple of welders and a plasma cutter.

The idea will be to move the van around the yard to where I need to do
welding or cutting so that I don't have to load and unload the
equipment constantly.

I am running AWG #4 four conductor wire. The power supply end of the
cord will plug into a 4 conductor (two hots, ground, and neutral) 50
amp plug protected by a 50 amp breaker located at the main power box.

The cord will terminates at a 100 amp weatherproof box that is screwed
to a 4' piece of 2x12. This "panel board" will be semi-permanently
affixed to the interior of the van - perhaps fastened to the back of
one of the bucket seats.

Make sure that the neutral bus in that panel is *not* bonded (electrically
connected) to the panel chassis or to the ground bus.

Also make sure that the ground bus *is* bonded to the frame of the van.


The panel box only has spaces for three 240v circuits. One of these
three will be a 50 amp plug controlled by a 50 amp breaker inside the
panel box. Another will be a 20 amp 220v circuit for my inverter
welder. It's the same plug configuration as for a 220v air
conditioning unit.

I wish to use the last of the three spaces for 2 pole circuit breaker
energizing a two gang box that will have two duplex 120v receptacles
(i.e. four 120v receptacles).

Rather than put these 120v plugs on 120v single pole breakers I would
prefer to split each leg of the double pole breaker to feed two of the
outlets.

I believe I'm correct that every time you double the voltage you
reduce the amperage by 50%?

Yes.

Does this mean that a 20 amp double pole breaker will give me 40 amps
of 120 volt protection?

Not exactly. It will give you two 20A circuits at 120V. That's 40A total, of
course, but it's on two circuits.

In other words, if I have 4 outlets (two on
each leg) protected by a single 20 amp breaker will each duplex 120v
receptacle be good for 20 amps?

Each *circuit* will be good for 20 amps. Whether the *receptacles* are or not
depends on whether you get 20A receptacles (the standard receps that you get
for 69 cents at Home Depot are 15A, not 20A).

Also, from a code standpoint is it permissible to protect more than
one circuit by the same breaker?

No.

In other words, and by way of
example, is it kosher to run a single 240v plug PLUS two 120v outlets
by simply doubling up the hot wires under the breaker lugs?

No. The problem there, though, isn't mixing 240V and 120V outlets on the same
circuit. The problem is two wires under the breaker lugs.

There's nothing wrong with putting all three receptacles on a three-conductor
cable (which actually has four wires -- black, red, white, and bare) wired
thus:

(In the breaker panel)
- black and red to the two poles of a double-pole breaker
- white to the neutral bus
- bare to the ground bus

(At the 240V receptacle)
- black to the black wire continuing on to the first 120V receptacle *and* to
a black pigtail connecting to one hot terminal on the 240V receptacle
- red to the red wire continuing on to the first 120V receptacle *and* to a
red pigtail connecting to the other hot terminal on the 240V receptacle
- bare to the bare wire continuing on to the first 120V receptacle *and* to a
bare pigtail connecting to the ground terminal on the 240V receptacle
- white to the white wire continuing on the the first 120V receptacle
- white is *not* connected to the 240V receptacle

(At the first 120V receptacle)
- black to the hot terminal
- white to the white wire continuing on to the second 120V receptacle *and* to
a white pigtail connecting to the neutral terminal on first 120V receptacle
- bare to the bare wire continuing on the the second 120V receptable *and* to
a bare pigtail connecting to the ground terminal on the first 120V receptacle
- red is not connected

(At the second 120V receptacle)
- red to the hot terminal
- white to the neutral terminal
- bare to the ground terminal
- black is not connected

Since I work alone it is not gonna happen that I'm using the inverter
welder and any 120v power tool at the same time. I just wanna know if
anybody remembers what the codes say about this and can give me a
title reference.

Remember what the Code says? You bet.
Give you a specific reference? That might take a while, I don't have the
article numbers memorized. :-)

To the extent that it is not inconsistent with good
electrical practice I would prefer to have enough outlets mounted on
the panel board to keep all of the equipment permanently plugged in -
or at least one of the big welders AND the plasma cutter. That would
save me having to crawl in and out plugging and unplugging machines.

Finally, should I ground the truck frame to the box?

Absolutely.