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I'm thinking it operates along the lines of a current transformer. There is no neutral load other than the one at the sensing device. It doesn't appear to be manually adjustable to set the normal load current setting.

A neutral makes no difference.
I can't think of a way to detect a symmetrical (balanced) fault.

There is no neutral load at all in the hot tub scenario that spawned this thread.

GFCI is not an OCPD. Even if it were, I can't think of how a GFCI could tell whether the motor is starting or a human grabbed T1 and T2.


[This message has been edited by Dspark (edited 05-09-2001).]

So back to the hot tub installation...

It is imperative to ensure that it is impossible to touch both ungrounded poles in any 240 V installation. GFCI cannot protect against this.

I think this is a bit different from a 120 V installation with GFCI.
In 120 V, I can get a nasty shock between ungrounded and grounded conductors. However, enough current might leak through my feet to the earth and trip the GFCI.

With 240 V, if the amounts leaking to earth from each ungrounded conductor are equal, they cancel each other locally and don't trip the GFCI.

Envision the cable being cut and submerged into a mud puddle.

The 120 V GFCI will probably trip as current follows earth or ground rather than neutral.
The 240 V GFCI possibly won't trip.


[This message has been edited by Dspark (edited 05-09-2001).]

Dspark;
ok, this is assuming a perfect short circuit, short being different than ground fault.

I am not assuming a perfect short circuit at all.

I am assuming a symmetrical ground fault.

Take one ungrounded conductor to a mud puddle on the north side of the building and the other ungrounded conductor to a mud puddle on the south side of the building.
Say that both have a resistance from the main panel to their respective points of 25 ohms.

Energize the circuit.
Current flows indefinitely.
Please don't tell me that this is not a ground fault condition.

(It is a contrived scenario. But clearly a ground fault.)

To put a fine point on things, remember, this is not really a 240v GFCI Circuit Breaker. We should try to find a digram for one of those.

Bill

I think you are the first person in this thread to say "Circuit Breaker".

I was just calling it a (non-specific) 240 V (two-pole) GFCI (variations mentioned in the Hot Tub thread).

The CB wiring should be the same albeit with some components integrated within the CB.

I was looking at the schematic [more like a pictorial, but so what!] with a bit more detail today, when this came to mind:

I kind of thought that the GFCI elements in this type of circuitry would be connected L-L, not L-N!!
I figured this since they are mass produced items for either 240 VAC or 120/240 VAC use, plus some crackpot ideas of mine [loss of one Line or open neutral cannot trip device - told you it's crackpot!! ].

So much for me thinking, huh??

Now, all this talk about being fried from both lines to ground [leakage ground faults] at the same time and of equal intensity has me wondering if this has happened before, and if so, how many times??
It could happen!!
Wouldn't want to be that human conductor [not the ones that ride in cabooses] caught not only between both lines, but also to ground!!
OWWWWW---CCCCHHHH!!!
Meanwhile, the GFCI sensing items are confident that all is OK with the flowing currents, so why trip?!
Again - OWWWWW---CCCCHHH!!!!

On a non-related note , the "Conductor" and "Caboose" thing reminded me of something I say often in the field:

When someone asks if I am an Engineer, I'll say - Yes! I drive the Cannonball from Hooterville to Pettycoat Junction!!
[then after they are completely convinced that I am looney, I'll mention something towards EE].

This is only for fun, not thrown at any clients [unless they have sense of humor, then there's no holding back!!].

Got a lot of strange reactions from that one!!

Time for some meds [joke]

P.S. - what was the original pictorial setup like before Bill edited it?? was it a connection mistake or just difficult to read??

Scott SET - local Cannonball steam locomotive operator on silly 60's sitcoms.

In the upper left the three wires changed from horizontal to vertical at the wrong places, like LN to T1, L1 to T2, L2 to TN, or something like that.

Dspark;
L1 & L2 both to ground would be a 'ground fault'
a human holding both L1 & L2 ( assuming well insulated sandals) would be a 'short'

either situation is suspect, maybe the listing would serve as clarity,


from siemens GFI instructions;

"EL GFCI no protege a las personas contra choque de tension entre fases."

[oops.... wrong side....... ]

"The GFCI will not protect a person against a line to line shock"

makes the noodle look important !





[This message has been edited by sparky (edited 05-10-2001).]