No power to whole house after water fell on to cooker???

[telectrix]

last "whole house dead" i was on, L-N 0V, L-E 240V. hence all L and N conductors in the house were "live", nothing worked. I isolated at Main Isolator and called Scottish Power. was a failed N joint where customer's supply was tapped off underground in street. SP started digging at 6pm. supply back on by 8pm.

 

[pc1966]

The 3036 should be selective with the DNO fuse, certainly at a 2:1 sort of ratio (30A and 63A or more BS88) to faults of 0.5kA or so. But I would have doubts if the PFC is very large given the modest break rating of the 3036, and even more fundamentally the possibility that someone has already changed the 30A wire for whatever but of mid-sized copper to hand.

Personally I would always change for the Wylex MCB replacements if a CU change is currently unaffordable, so much less trouble to reset than Joe Public trying to rewire a fuse (often in the dark) and no risk of wrong size replacement wire.

 

[HappyHippyDad]

Well, it was the 100A cutout fuse! New fuse and all back working.

 

[UKMeterman]

If that was the case I would be saying dear Mr Landlord please do a full test ASAP, and ask to see the previous test certificate.

 

[UNG]

Over my 40+ years in the industry I have seen the DNO fuse blow without the local OCPD blowing or tripping a handful of times. The last time was about 7 - 8 years ago an old rubber cable gave up, it shorted took the DNO fuse and caused a fire and left the 3036 30A fuse intact
Most of the times it was a rewireable cut out fuse that blew so the whole service head was changed

 

[pc1966]

Looking at the plots for BS 3036 fuses in the regs (p365 & p366) by time you get to 0.1s the curves are looking like "constant I2t" region (they are sloping down at 2 decades of time per decade of current on the log-log scale) and using the tabulated values for current at 0.1s blowing time I get:

• 20A = 260A * 260A * 0.1s = 6.8kA A2s
• 30A = 20kA
• 45A = 81kA

Looking up one of the data sheets I have for Mersen BS88 LV fuse links they have the pre-arcing I2t for a 100A fuse as 14kA so in fact a 30A rewireable fuse is able to get a 100A HRC fuse beyond the point of no return on an adequately large fault.