Category: Electrium Sales Residual Current
Devices Specifications
Electrium Sales Residual Current Devices
Specifications Email
Electrium - Crabtree
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.
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