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Residual Current Devices Specifications
Electrium
Electrium Sales - Residual Current Devices Specifications
Technical Data Specification
Applications
RCBOs provide both earth fault and overcurrent protection. For
commercial and industrial applications a unit should be employed,
utilising Type C (5–10In) classification of MCB. RCBOs, other MCB
classifications available to order.
Polestar and 2 module Loadstar RCBOs employ an electromechanical
operating principle. Loadstar 1 module RCBOs employ an electronic
operating principleincorporating loss of supply neutral protection
via a functional earth lead.
All RCBOs give a high level of protection to individual circuits
whilst exhibiting improved immunity to response caused by
transients. Two module switched neutral RCBO’s have safety
advantages over single module RCBO’s and are exclusively used in
continental europe.
Advantages of Switched Neutral RCBOs
If a neutral to earth fault occurs in a circuit fed via an RCBO with
a solid neutral which is backed up by an upstream selective RCD, the
selectivity or discrimination will be lost and the main RCD will
also trip as it will still detect the fault which has not been
cleared.
The main requirements of RCD protection are:
- Additional protection against direct contact with live parts
-
Protection against direct connection with live parts
-
Protection against fire in the case of a fault to earth
If a fault occurs between neutral and earth where a solid neutral
RCBO is protecting a circuit, the RCBO will trip. However, as
previously stated, the fault will still be in the circuit within the
rest of the installation.
As the neutral will be common throughout the installation, it is
possible that current could still flow through the fault and lead to
a fire hazard. This would mean that the RCBO would not offer full
protection against fire and therefore does not comply with one of
it’s main protection requirements.
Testing of outgoing circuits is easier with RCBO’s incorporating a
switched neutral as an electrician does not have to disconnect
terminals before testing.
BS7671 requires that the main switch to a TT earthed installation
must have a switched neutral.
Installation Testing – Caution
As Single Module RCBOs employ electronic components they should be
disconnected when carrying out the following tests on the electrical
installation:
(a) Earth fault loop impedance test
The load terminals should be disconnected if it is intended to
parallel-out the unit for test purposes.
It may incur damage if mains potential is maintained on the load
terminals of this unit after the trip mechanism has operated.
(b) Insulation test
Whilst RCBOs can withstand the effects of normal insulation testers
without damage, false readings may be given on the test instrument.
For this reason it is recommended that the device is disconnected
during this test.
IEC Publication 60479 Curves with Crabtree RCD Characteristics
Superimposed
Time/Current Zones of Effects of AC Current (15–100Hz) on Persons
Zone Physiological Effects
1. Usually no reaction effects.
2. Usually no harmful physiological effects.
3. Usually no organic damage to be expected.
Likelihood of muscular contraction and difficulty of breathing,
reversible disturbances of formation and conduction of impulses in
the heart, and transient cardiac arrest without ventricular
fibrillation increases with current magnitude and time.
4. In addition to the effects of zone 3, probability of ventricular
fibrillation increased up to 5% (Curve C2) up to 50%
(Curve C3) and above 50% beyond Curve C3. Increasing with magnitude
and time, pathyphysio-logical effects such as cardiac arrest,
breathing arrest and heavy burns may occur.
Electrium Sales Ltd
Commercial Centre
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Bridgtown
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