ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Main Switch or Circuit Breaker?

Irish distribution boards all have a main switch and main fuse on the board itself. This has been standard practice going right back to the early days.

This was originally a diazed fuse, now more commonly a minized switch-fuse unit that looks like this:





They carry a standard neozed fuse

There's also a sealed double-pole switch after the meter on more modern installations. (Sealed by the contractor after certification of the system)

The logic being, that on a 230/400V distribution system the end users couldn't realistically expect fault protection from the network side. It would take a pretty serious distribution system fault for the over current protection on a pad mounted transformer to kick in.

C-H,
Are you saying that Type E will trip quicker than either Type B or C curve MCB's?
Reason I ask this is because we use B curve breakers here for standard domestic installations here, C curve is used in places like commercial installations, where there might be a bit of inductive loading or for Submain cables to an out-building.
D-curve is used exclusively for motor protection.
Now any type of E-curve breaker (never having heard of it before and with it being a Selective type also) makes me think that it could be a heavier type, not unlike our Selective RCD's that have a trip level of 300mA.
Your thoughts?.

Mike,

yes that is basically what I'm saying. (Darn, it is near impossible to type on a german kezbaoard which has z and y transposed)

As I understand it, it is supposed to keep the utilitys fuse on the pole from blowing. This saves the utility some work in replacing fuses, I suppose. It also allows the consumer to overload the breaker less than with a type B or C, which I suppose translates into less load on the network. As the main breaker is anyway bigger than the rest of the breakers in the house, it should still be selective towards smaller breakers. (E.g. the main breaker is 63 A and the outlets are on 20A circuits.)

(I am in Switzerland at the moment on a business trip. All outdoor cable here is orange. Not rubber, but something else. I swear that one in every ten vehicles this morning belonged to a sparky and there were guys at work everywhere. Later in the day, lots of party tents with beer halls and shops went up later, explaining where the cables were to go.)

From the Draft for Public Comment for AS3000-
2.5.1.1 Consumers' mains
Overcurrent protection of consumers' mains shall be arranged as follows:
(a) Short circuit protection and overload protection shall be provided at the origin of the
consumers' mains (the point of supply); or
(b) Short circuit protection shall be provided at the origin of the consumers' mains and
overload protection shall be provided at the main switchboard; or
(c) Short circuit protection need not be provided where -
(i) Overload protection is provided at the main switchboard; and
(ii) The consumers' mains are constructed and installed in such a manner as to
minimise the risk of short circuit.
Notes
1. Single core insulated and sheathed cables enclosed in Heavy Duty PVC conduit to
AS/NZS 2053 are deemed to satisfy this provision.
2. Underground wiring or fire rated wiring enclosures may also be used to satisfy this
provision.
3. An electricity distributor's service protective device may provide short circuit protection for
consumers' mains.