GFI Breakers

GFI Breakers come with the neutral wire wound into a coil. Does this coiling of the neutral wire affect the operation of the breaker or can the neutral wire be straightened out for neatness of the installation?

The wire is coiled for packaging and neetness. it can be straightened out but must be connected to the neutral buss in order for it to operate correctly.

So induction on the neutral plays no part whatsoever?

I found the answer...

After searching I've found the answer... I'll share it here as a conclusion to this post.
During a ground fault condition there is a load on the GFI's neutral for a short period of time, the time required for the GFI to operate and open the circuit. If the neutral wire is straight, the current on the neutral will rise rapidly until the GFI operates. By coiling the neutral, inductive reactance causes the current to rise more slowly, therefore resulting in a lower peak current before the GFI opens the circuit.

fluoronator said:

After searching I've found the answer... I'll share it here as a conclusion to this post.
The during a ground fault condition there is a load on the GFI's neutral for a short period of time, the time required for the GFI to operate and open the circuit. If the neutral wire is straight, the current on the neutral will rise rapidly until the GFI operates. By coiling the neutral, inductive reactance causes the current to rise more slowly, therefore resulting in a lower peak current before the GFI opens the circuit.

Click to expand...

Good intention. I wonder how many electricians know this. I also wonder how many of them straighten the neutral out, anyway.

With all due respect, I tend to doubt whether this matters. If it did, the GFI breaker manufacturer would have molded the coil with epoxy or something to keep those unknowing of this property from just uncoiling it...

I always figured it was done because it is a fine strained wire and if it were not it would be hard to manage

slightly OT

Do they make 480VAC GFCI breakers? If they do, how high of Amperage do they go?

We have issues in this plant where a ground faulted motor will take out the whole switchgear, thus causing a complete plant outage. Sometimes the fault is on an office air conditioner and the entire plant will suffer 6 hrs downtime to recover.

I've used ground fault detection on switchgear, which usually results in a 'needle in a haystack' search for a bad motor. Is there a better way to narrow down where the fault is?

Okay, I've done further reading on the internal workings of the GFI and am convinced that the above answer is at least partially hogwash, I applogize for posting it prematurally. The GIF's neutral always carries the load, not just in a ground fault condition. If inductive reactance on the neutral plays any part whatsoever, it is VERY trivial. It seems that uncoiling the wire is okay.

cntrlfrk said:

Do they make 480VAC GFCI breakers? If they do, how high of Amperage do they go?

We have issues in this plant where a ground faulted motor will take out the whole switchgear, thus causing a complete plant outage. Sometimes the fault is on an office air conditioner and the entire plant will suffer 6 hrs downtime to recover.

I've used ground fault detection on switchgear, which usually results in a 'needle in a haystack' search for a bad motor. Is there a better way to narrow down where the fault is?

Click to expand...

Many modern electronic motor starters have gound fault detection built in. Upgrading the starters may solve your problem.

This is just a matter of proper protection co-ordination. I've never heard of a GFI being used on a 460V motor. If a ground faulted motor is tripping out your switch gear your fusing is incorrect. You should get in contact with a professional to do a co-ordination study in your plant.

fluoronator said:

After searching I've found the answer... I'll share it here as a conclusion to this post.
During a ground fault condition there is a load on the GFI's neutral for a short period of time, the time required for the GFI to operate and open the circuit. If the neutral wire is straight, the current on the neutral will rise rapidly until the GFI operates. By coiling the neutral, inductive reactance causes the current to rise more slowly, therefore resulting in a lower peak current before the GFI opens the circuit.

Click to expand...

Where did you find this, drivel?? Please stop passing on this type of mis-information.

This "reasoning" makes absolutely no sense at all. It is not part of any manufacturer's instructions. GFCI receptacles work perfectly fine without any inductive coil. There is always a load on the circuit's neutral otherwise the the breaker would not be able to supply 120V as well as 240V circuits.

GFCI devices do not care about rate of rise - they simply measure the current in the "black" wire and the current in the "white" wire and compare them. Any time there is a 5mA difference, the GFCI protective circuit operates.

fluoronator said:

Okay, I've done further reading on the internal workings of the GFI and am convinced that the above answer is at least partially hogwash, I applogize for posting it prematurally. The GIF's neutral always carries the load, not just in a ground fault condition. If inductive reactance on the neutral plays any part whatsoever, it is VERY trivial. It seems that uncoiling the wire is okay.

Click to expand...

Sorry, it appears my timing could have been better.

It is statements like this that make "single" web searches and sites like Wikipidea such a bad source for reference. Someone posts a mis-statement and all of a sudden it is gospel just because it is "on the web".

cntrlfrk said:

Do they make 480VAC GFCI breakers? If they do, how high of Amperage do they go?

Click to expand...

GFCI breakers are intended for personnel safety. Cutler Hammer, Allen Bradley, and I'm sure many others have motor protection systems that are intended for equipment protection. Phase balance and so on are probably more cost effective devices for your purpose. Contact a knowledgeable local distributor.

Jim Dungar said:

This "reasoning" makes absolutely no sense at all.

Click to expand...

Exactly what I was thinking. Who ever wrote this dosen't understand how GFIs work and doesn't understand that counter EMF generated in a coil lags the increase in current.

GFI's contain a small internal torriod thru which both the hot and neutral conductors pass. As long as the current flow in the hot and neutral conductors match exactly then no voltage can be induced into the torroid winding. By Kirchoff's first law, as long as there are no ground faults or incorrect wiring, then these currents will match exactly. As soon as the respective hot/neutral currents differ by even a few millamperes, the voltage on the torroid coil will rise and the interruptor opens the circuit.

Cntrl Freak wrote:

I've used ground fault detection on switchgear, which usually results in a 'needle in a haystack' search for a bad motor. Is there a better way to narrow down where the fault is?

Click to expand...

The ground fault detection switchgear should be only used on final cicuits.
That is to say you don't put them in series protecting each stage of the distibution but have them each protecting final circuits that the protection is required for.

The office conditioner should not of course be on the same circuit as the plant machinery and in no way should in cause a complete plant shutdown.

Put in as many as is practical to feed each section seperately. Making sure that for example a light failing does not trip the other power circuits in the area. Or that a fault in line A does not stop line B (assuming of course that the two lines are independent)

I have seen some "Square D" distribution boards over here (Ireland) and I actually like the idea that each circuit breaker can easily be a ground fault detector also just by wiring in the correct breaker.

In typical boards over here we don't have a neutral wire attached (by the manufacturer) to the breaker which are known here as RCB's (Residual Current Breakers without overload protection) or RCBO's if they also have overload protection.
It is the installer who connects the common neutral to the feed side of the RCB, an RCB out of the box just has 4 terminals (8 for 3 phase power)

Alaric's explanation of the operation of a GFI is correct. Here in Ireland the requirement is that if the difference on a circuit exceeds 30mA then the circuit should trip, 30mA being the current which defibrillation of the heart may occur. (we also have other sizes but the 30mA is the most common).


The current carrying capacity of the breaker is much higher and the voltage isn't really a factor in its use (apart from the designed tolerences for use)