jason1969

Posts: 26
Joined: 09 January 2015
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No, not dense at all...
CU in overheat condition typically melts & disintegrates.
Consider the melting point of a polystyrene tile or consumer unit.
Indirect chance of L-E N-E fault re RCD disconnect...
- Neutral & Earth bars collapse off plastic fixings
- DIN rail fixings plastic fixings give way with heavy assembly
- Live Busbar & heavy DIN components sink to bottom of case
Direct chance of L-E N-E fault re RCD disconnect...
- FTE cables melt, bare CPC contacting L or N
Unfortunately hot busbar & hot tails give little chance of a L-E L-N fault.
Passive solution
CU made out of metal ... does nothing about faulty parts / workmanship.
Active solution
#1 - HEAD END Time Delayed RCD = CAN disconnect installation on L-E N-E fault -> disconnect heat -> stop fire.
#2 - Earth braid in meter tails = Create L-E N-E fault -> disconnect installation -> disconnect heat -> stop fire.
#3 - Metal back CU = Create L-E N-E fault -> disconnect installation -> disconnect heat -> stop fire.
#4 - Double brass screw brass barrel terminals for Main Switch & RCD
#5 - Mandate recall of any CU which fails F/R test, otherwise it WILL keep burning.
Meter tails could also be 16-strand or fine to ease fitting, internal N tail is always fine strand so I see no problem there if sheathed singles. Terminals need to accept fine strand (see brass as above) or simple bootlace ferrule.
It is quite common to use Time Delayed 300mA RCD as installation fire protection. Some timber frame builders have been doing so for years long before FBU woke up to statistical celebrity status.
Some EU countries mandates/are-to-mandate it as head-end install - easy integration into smart meters.
Of course the other issue here is the CU that do not self extinguish.
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