What is device co-ordination or cascading and how do I use it?
Sizing circuit breakers according to system current and voltage specifications should not be the only criteria considered when selecting the protective devices such as MCCBs. Although important, it is also crucial for system functionality to ensure that the chosen protective devices discriminate with one another and those that are already existing.
For this reason, many electrical specifications may require evidence that an installation has sufficient device co-ordination, both in the installation and to upstream energy supply assets, appropriate co-ordination is usually proven by a protection coordination study, which is a formal document showing the ratings and discrimination settings of all protection devices.
What is discrimination and how do I use it?
AS/NZS 3008:2018 (the Wiring Rules) Clause 2.5.7.2.1 defines discrimination (selectivity) to depend on the operating specifications of two or more protective devices such that the downstream device shall operate for a given fault current whilst the protection device upstream does not. As per the AS/NZS 3000:2018 standard, selectivity is a mandatory requirement in all electrical systems so that nuisance tripping of the protective devices can be minimised.
Can I fit accessories to Hager MCCBs?
Yes, a full range of accessories fit the h3 MCCB range. These include auxiliary, signal, shunt trip and under voltage trip. Each range has specific handles and barriers etc. The accessories can be retrofitted, when the front cover is removed (MCCB trips), no copper/metal parts are exposed.
Each range (x160, x250, X630, h250, h630, H3+ 160, H3+ 250, H3+ 630, h1000 and h1600) has a separate selection of accessories and auxiliaries.
Can I adjust the current ratings / trip settings?
With the exception of the x160(Thermal only) all of the h3 and H3+ MCCBs have incremental thermal / short circuit trip adjustments or a selectable thermal / short characteristic. Please refer to the relevant MCCB user instructions.
What does LSI mean?
This refers to MCCBs with an adjustable electronic trip unit, In comparison with thermal-magnetic trip units, they allow a more precise setting both in terms of trip times as well as in terms of current thresholds in order to meet better the installation requirements. This assists with discrimination and fault loop impedance compliance in switchboard design
(L) Long time delay- setup current and time delay
(S) Short time delay - setup current and time delay
(I) Instantaneous time delay - setup current without delay.
What is the difference between Load Break and Isolator Switches?
Load break switches are intended to close (make) on full load current and open (break) on full load current. The switch contacts open/close rapidly in a wiping motion that cleans contacts.
Isolator switches are intended to operate on no load.
Do I need to consider fault ratings during the design of an installation?
Yes, the load break needs to be able to withstand the forces generated by a fault until a protective device operates. So the peak withstand rating of the switch should be less than or equal to the peak let through level of the largest protection device in series with the switch.
When should I use a load break switch versus isolator?
A Load Break switch is used when isolation is required under load.
An isolator switch is typically used in a domestic application or when loads can be turned off before the isolator is operated.
What does AC22, AC23 mean?
These numbers are the "Utilization category" derived from the IEC 60947 standard.
AC22 - switching of mixed resistive and inductive loads including moderate overloads.
AC23 - switching of motor loads or other highly inductive loads.
