ELCB SENSITIVITIES

Well... in North America... we classify them as either life safety or equipment safety devices.

The Canadian code making body is in the process of redefining a GFCI. We used to refer to them as either a "Class A" or "Class B" or as a "Class C" device.

A "Class A" GFCI is considered the life safety device and has a maximum trip point of 6ma. The "Class B" device has a maximum trip point of 20ma. The "Class C" device has a maximum trip point of 30ma or higher.

If you intend to provide a device that offers "life safety" aspects, go with a device with as low a trip point as possible. Remember to keep nuisance trips in mind, or the device might be bypassed.

Hello Guest.

It really depends on the application.

In Hospitals here the general setting is 10mA, which is rather lower than your list of trip currents.

Likewise, in a heavy industrial situation, it is important not to have bothersome trips, and yet maintain a safe workplace.

With all installations using ELCB's, it is important to always use the local Regulations, to maintain safety of personnel, machinery, and avoid all expensive Insurance payouts too.

Kind Regards....

In Europe, at least in my corner of it, the "standard" ELCB for household use is 30mA.

This was chosen based on physiological precept that 30 mA is the brink of deadly current for the average human (or sheep, oddly enough).

We put the units in the switch boards, protecting all household circuits.

In particularily moist areas, such as the area around a Jacuzzi, the circuits are protected with 10mA units.

The 300mA and greater current units are used as a main breaker (after the main CB) as anti-electrocution measure in an installation where no protective ground is effective, such as in a mobile home, or when ground resistance is greater than 20 ohm.

Hello Everyone,

Thanks for the answers but my doubt still persists... I understand the practical applications of Elcb's but not the basis on which their sensitivity is selected....I will reframe the question... According to me, a human can withstand maximum current of 16mA without shock... So, how can an Elcb of 30mA which is used for domestic purposes protect him from Earth Leakage current..... On what basis is this sensitivity of 30mA, 100mA and 300mA selected?....

The Wiring Regulations require you to consider the recommended disconnection times e.g for 0.4 secs portable or 5 secs for fixed electrical appliances, etc to determine the type of overcurrent protective device. Where conditions (e.g poor earthing resistance, etc) cannot meet required disconnection times, then rcd may be used.

A residual current device (rcd & not elcb which is being phased out for poor reliability) used for indirect contact protection must satisfy the relationship : Isens. x Zs <50V. i.e the product of the rcd operating current or sensitivity, Isens. (e.g. 30mA, 100mA, etc) and the circuit earth fault loop impedance, Zs must not exceed 50Volts, which is considered safe allowable voltage limit on exposed conductive parts. Thus, your Zs value must be very low.

As earlier mentioned, 30mA rating is mostly used for most final cct. small power applications such as 13A sockets, etc, but 100mA or 300mA may be used for other upstream sub -distribution boards or where nuisance tripping is being encountered.

Hope this helps. cheers.

You ask:

According to me, a human can withstand maximum current of 16mA without shock... So, how can an Elcb of 30mA which is used for domestic purposes protect him from Earth Leakage current..... On what basis is this sensitivity of 30mA, 100mA and 300mA selected?....

Answer: You are wrong in your assumption that 16mA is deadly. Those powers that be have decided that 30mA is deadly in normal situations where the current flow is likelly to be hand to foot to ground. In areas where the current flow may be shorter, due to bathing, for example, then 10mA is used.

ratings above 30mA are more arbitrary, but set according to the necessities of applications described quite nicely by the other posters.

10mA can be sensed by human being. 30mA for 30msec is deemed as the safe cut-off point to avaoid fatalities. 100mA is used to prevent fires. 300mA with adjustable time delay is used for the upstream device to provide discrimination between devices and to protect plant.

In addition to the above, 100mA is used as the whole-house ELCB on TT distributions systems, mainly found in rural areas, where a higher current value in connection with a poor earth electrode resistance might result in high voltages being generated on the earth conductors around the home. Then, 30mA is used as the individual circuit breaker for:

• kitchen sockets
• cooker feed
• power shower feed
• areas feeding power to outside circuits, such as garden lighting.
• other high-wet-risk areas.

While it is possible to select and install individual breakers onto modern dis-boards, it is more economical to supply the home from a 'split-load' board, where one half of it is fed through a single 30mA breaker and the rest not; it is good practice to place circuits powering freezers on the non-ELCB side of the board.

BS7671 gives details of current UK electrical practice. Note that Part P of the Building Regulations currently applies to all new installations, and a certificate of test will need to be provided to comply with the regulations and thereby close-out the building project to the satisfaction of the Local Authority. Part P doesn't stop DIY installation, nor is it intended to; it just means that the testing service will need to be bought-in after the installation is complete.

Hi,

Please refer this web site. Should be of help.

http://www.schneider-electric.com/documents/technical-publications/en/shared/electrical-engineering/protection-devices-monitoring/low-voltage-minus-1kv/ect114.pdf

Regards,

Swagata