Re: [CAD_CAM_EDM_DRO] Re: Delta 3 Phase fault finding

Speaking of earthworms coming out of the ground, I use a
500 amp Lincoln welder with the ends connected about
50 feet apart to earth rods, fire up the welder and come
back a while later, and worms for the pickin.

Steve

----------
From: Ray Henry <rehenry@...>
To: CAD_CAM_EDM_DRO@onelist.com
Subject: [CAD_CAM_EDM_DRO] Re: Delta 3 Phase fault finding
Date: Saturday, March 11, 2000 6:41 AM

From: Ray Henry <rehenry@...>


In the USA we have several possible ways of defining ground (earth) in an
electrical distribution system. The undefined ground system that Bill
spoke of in the mines is a common 440, 460, 480 volt practice for a lot of
industrial sites.

In such a system, once you get past the transformer, one leg can be
connected to earth and nothing will blow. Motor windings can short to the
frame somewhere between two legs and it just drives that frame and all the
metal attached to it to that voltage. You don't notice anything when you
touch it unless you are also connected to some other grounded system.

But get two competing shorts to earth at a distance and things begin to
happen -- all the earthworms jump out of the ground between -- sparks
begin to fly at weak conduit connections -- metal heats up.

Ground fault sensing breakers are worthless in these supply systems. But
the lower voltage 220, 240 that you are likely to encounter at home or in
smaller shops do have a well defined ground. But sometimes these things can
go astray also. I like to check machine frame to concrete voltage. I drop
a chunk of iron into a puddle of salt water on the concrete and read
voltage from this to the machine ground.

More than a couple volts and women will begin to complain. More than five
and men will begin to complain. At our common AC frequencies, 55 volts,
connected right will kill.

Ray

>Message: 16 [CAD_CAM_EDM_DRO] Digest Number 396
> Date: Fri, 10 Mar 2000 12:35:29 EST
> From: wanliker@...
>Subject: Re: SV: Delta 3 Phase fault finding
>
>In a message dated 3/10/00 7:51:08 AM Mountain Standard Time,
>anders.blix@... writes:
>
><< If you ask for 3-phase you get earth allong as wel. But you are not
> allowed to connect something betwen one phase and earth. I think this

have

> something to do wit why it is so easy to get 3-phase installed.
> >>
>We used this system in the copper mines where we worked, the big danger

was

>if one phase became grounded two things happened. The other two phases

went

>to very high voltages with reference to ground, electrical shock hazard,

and

>harder on insulation. But the bigger danger is one phase was shorted to
>ground, at a given location, and another phase shorted to ground at

another

>location, fuses would blow, and equipment would go off line, and sometimes

>damage equipment. One of the things we did was to monitor the phases to
>ground with a series string of light bulbs, from each phase to ground, we
>used three 120 volt lamps in series for a 220 volt circuit, per phase for

a

>total of 9 lamps. If all was well they would just glow dimly, if there was

a

>fault on a phase, one string would go out, and the other two would glow
>brighter. This way we could turn off equipment to isolate the faulty
>equipment, before the problem became a big one, shut off the faulty

equipment

>and the lamps would return to normal. Higher resistance and intermittent
>faults would show clearly as the bulb strings would blink, and again show

you

>that there was a problem. I would highly recommend this kind of status

board

>for any 3 phase Delta equipped shop,
>

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