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EFVA, Somes major differences relative to dwellings.

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North American vs. French:




Somes major differences relative to dwellings.

The use of grounding schematics with these millions of installations over decades has put into light the technical evidence.

- Electro-magnetic compatibility:

Given the small residual current (limited by the use of current devices), the TT grounding schematic are performant in faces of these phenomena. In contrast, the TN family are less efficient for the inverse reasons, which can sometimes
make use of electronic detection devices being more delicate.

- Impact on the stability of power supplies:

The differential devices are stable. It is rare that they have phantom tripping. Many facilities have even redone main-breakers with integrated differentials that have not been changed (they are owned by the former state monopoly, Electricité de France) for 20-30 years. These devices still work perfectly.

- Economic impact:

It is minimal relative to the security provided. A main-breaker with a differential associated to an electrical installation of an average home in France costs about $ 120 USD *.

A differential on average between 17€ and 35€ or between USD $24 and USD $ 50 *.

* (Exchange rate of 01-30-2011).

- Electrical fires, safety impact:

· The interest for the use of differentials and the choice of ground schematic relative to fire risks.

The widespread use of differential devices at the head of the installation for almost 50 years has enabled generations of French electricians to understand the absolute usefulness when dealing with insulation faults. These flaws are dangerous because they often produce hotspots generating prime atmospheres conducive for fires. Differentials ( placed in the panel ) are the only devices capable of restricting insulation faults:

· For current devices 0.500 A = 230 V x 0.500 A = 115 watts
· For current devices 0.300 A = 230 V x 0.300 A = 69 watts (1)
· For current devices 0.030 A = 230 V x 0.030 A = 7 watts (2)

During operation, the tripping is done when contact is made to ground independently. As if the circuit was "diverted". It is therefore a very soft and very fast trigger: the differential devices such as GFCIs have a response time generally faster than breakers.

(1) For the electrical installations of buildings open to the public (who are not covered by the same standards as for housing), including those with TT, it is advocated for decades to place 300 mA differential devices in front of lighting circuits to limit insulation faults to 69 Watts and limit the risk of fires. This value is too high but it is a compromise between the continuity of power and security.

(2) Virtually all dwelling circuits are protected by 30 mA.

In contrast, for TN-CS installation, an insulation fault will be solicited by the overload current protection, in 115 Volts: 115 V x 15 A = 1725 Watts

And it is a short circuit which will trigger the overload current protection, creating an arc and thousands of amperes in an already overheated atmosphere where the lack of insulation has been progressive (3), which is generally the case. It is difficult for French electricians to imagine such a thing as they have used differentials for decades to control defects with low values.

(3) Perhaps because of the belief "fires of electrical origin are due to arcs? In France, the mass of people talk about short circuits as the cause of fires, which is also erroneous.

Also for decades, the French electricians often installed differential devices when the Neutral-to-Ground schematic was TN-C-S, (similar to that found in US homes) to make the installation safe and reduce the risk of fire due to parallel arcs (Live to Ground and Neutral to Ground):




1 - Insulation fault (parallel arc) here in the wires.
2 - The PE evacuates to neutral a quantity of current resulting from the insulation fault (parallel arc).
3 - The differential device 0.3 Amp. detetects the difference and cuts off power in an instant, by a value of 230 Volt x 0.03 Ampere = 6,9 Watts.


In comparison, the TT neutral-to-ground schematic therefore seems safer to use than TN neutral-to-ground schematic. Accustomed to control low value faults, the French have also banned the TN neutral-to-ground schematic for some applications.

Concerning the prevention of parallel arcs (Phase to Ground) the TT neutral-to-ground schematic adopted by the French in 1960's years, has revealed for over 50 years the absolute utility of residual current devices placed at the head of the circuits.

Only those devices (such as GFCI) at the circuit's head are able to prevent insulation faults and their consequences in the panels, wiring, receptacles, and even appliances. And significantly reduce the proportion of electrical fires. It is obvious for French electricians and engineers, forged by decades of experience, expertise and controls. But while these devices have greatly increased security, the French also have a large proportion of electrical fires: on both sides of the Atlantic, in electrical installations there is still a "lack of protection" which is responsible for almost all of these fires.



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