"tarquinlinbin" wrote
| I;m about to replace my existing metal cased wylex consumer
| unit,the one with the big grey RCD on/off switch which has
| a penchant for nuisance trippage,with a new unit which will
| have an isolator and mcb,s. Do i really need an rcd though ?.

You *must* have RCD protection on:
- a TT (earth rod) installation
- sockets likely to be used for appliances out of doors

In practice, it is usually easier to provide RCD protection to all sockets
as this saves proving by calculation that the MCB alone offers sufficient
protection.

You should NOT use a whole-house 30mA RCD main switch. This is contrary to
the Regulations.

If you have a TT installation then use a 100mA Time-Delay RCD main switch
and 30mA RCD on socket circuits (either a split load CU or RCBOs on
individual circuits).

If you do not have a TT installation then use either a split load CU or
RCBOs on individual circuits.

| My biggest issue is nuisance trippage once or twice a year
| leading to fridge /freezer defrost.

You should try to identify which circuit(s) is tripping the RCD. There may
be a fault such as poor insulation or ingress of damp.

If you use a split load CU, then the freezer can be wired on the non-RCD
side, as should be lighting and smoke alarms.

Owain