E/F Realy Setting for Office Building Load

And the definition of the acronym E/F is what, please?

Under British Standard 7671 it would be more common for earth fault devices to be installed at the distribution board for the downstream circuits. It is now common for a TT-system, for example, to have a 500mA earth trip feeding the whole board, which improves the tripping response to earth faults downstream of the board with a much lower fault trip current that the individual breaker setting, with a 30mA setting applied to individual circuits for personal protection against electrocution. Residual-Current-Breaker-Overloads [the acronym is RCBO] used to be the way to go, however under the latest edition of the standard, it is easier and cheaper to fit a 30mA Residual Current Device [the acronym is RCD] upstream of the protected circuits and fit individual overload breakers to the outgoing circuits. It also takes up less space within the distribution board itself.

Many trained electricians can work out the above. For distribution transformer work it is best to refer to national standards applicable to the country of installation and consult a trained and experienced Electrical Engineer locally before proceeding further.

Thanks Guru.

Since the E/F relay will be connected to transformer neutral CT and there is expectation of large unbalance current in the neutral because of majority single / two phase loads, it would always trip due to low setting (500 mA or 30 mA).

Do you say in each consumer unit to fix a RCBO(...mA) for the incomer and a RCD(30mA)for each outgoing including lighting circuits?. What is the recommended mA rating of RCBO?.

As minimum as possible, but at the same time more than the anticipated system unbalance current, due to unequal distribution and/or utilisation of single phase loads across the three phases.

How does the anticipated unbalance current affect any earth leakage trip setting, please?

All Final Distribution Boards must have at least two busbar sections, be arranged so as to provide for at least two zones of Earth Leakage Protection (e.g. 100mA and 30mA) and to avoid complete disconnection of power to the area being served, in the event of an earth fault. This may be achieved by either of the following methods:

(a) Two or more busbar sections, each protected by an RCD;

(b) One busbar section, with individual RCBOs fitted on all Final Circuits;

(c) Two or more FDBs installed together to serve an area, each having one busbar section protected by an RCD of appropriate rating (e.g. one DB with an incomer 100mA RCD for lighting and another DB with incomer 30mA RCD for power circuits)

Residual operating current settings for RCDs and ELP devices

LV main circuit breakers or switchboards --> 300 - 500mA (time-delayed)

NOTE:

l) Final Circuits in a bathroom (including lighting) must be provided with 30 mA RCD protection.

2) Where a circuit supplies more than one type of equipment the lower value must be used for RCD protection (e.g. a circuit supplying bedroom lighting and bathroom lighting must be protected by a 30 mA RCD).

In the Guidance Notes issued some time back I have seen the lighting circuits without RCD. Can you quote the regulation or amendment which recommends a RCD for lighting circuits too?.

1)all Final Circuits must be protected by an RCD of residual current rating 30 mA and complying with BS EN 61008 and BS 4293.

Why should the "Guidance notes" contradict BS?. What is the recommendations by IEC?.

412.5 Additional protection by residual current

devices

531.2 Residual current devices

Clause 412.5 specifies that protection by residual current

devices (RCDs) is to be provided as an additional protection

method against electric shock. The primary protection methods

include insulation of live parts, barriers or enclosures, obstacles,

and placing out of reach.

The rated operating current for the RCDs is not to exceed 30

mA. In the opinion of the U.S. National Code Committee, a

30 mA trip rating is too high to prevent serious physiological

effects other than ventricular fibrillation. These other effects

include inability to let go, interference with breathing, etc.

(according to publication by Biegelmeier, Skuggevig, and

Takahashi, "The Influence of Low-Voltage Network Systems

on the Safety of Electrical Energy Distribution," © 1995,

UL).

For other than horticultural and agricultural buildings, the

IEC 60364 documents specify 30 mA maximum RCDs only

as a method of protection against electric shock. For the above

two types of premises, 705.422 specifies 0.5 A RCDs as

protection against fire.

Even though IEC 60364 documents specify 30 mA RCDs

only for protection against indirect contact, there are indications

that to achieve the disconnecting times in Table 41A of Sec.

Plan of IEC 60364:

E l e c t r i c a l I n s t a l l a t i o n s o f B u i l d i n g s.

Chapters Title

Section 709 Electrical installations in marinas and pleasure craft

Section 710 Medical locations and associated areas

Section 711 Electrical installations in exhibitions, shows, stands, and fun fairs

Section 712 Not allocated

Section 713 Furniture

Section 714 External lighting installations

The guidance notes has divided the busbar in a consumer unit into two sections and shown an RCD for MCBs feeding socket outlets(receptacles) and no RCD for MCBs feeding lighting circuits.

may be its time for you to move into BS or IEC or NEC......