Ah yes the coloured dots.  The Wylex standard for the open wire fuses to BS 3036.

As beloved for all installations from about 1950 to about 1980. Often could look and see if the bit of card with the spare fuse wire wrapped around it had dropped into the box down the gap at the back where the wall is not flat. Of course quite often the wire size you actually need has run out.

so the following often found.

White = 5A  - replace with single strand from off cut of flex. Light fittings, fans clocks and TV amplifier if house has  TV.

Blue = 15 A    replace with 3 of above twisted.  Immersion heater or circuits to outbuildings. Storage heaters and lone sockets converted from round pin ones.

Yellow = 20A  - as above, 15 and 20 are similar, right ?

Red 30A  - rings of sockets, cookers, anything big really,  replace with unbent paper clip.

Green 40A  - they must have a shower or a two cookers on one line. Must go in the slot near the mains switch. Replace with offcut strand from the earth core of the stranded type of ring main cable that we used before 2.5mm.

I fully agree on the pulling things but checking that the  right circuit goes dead. I watched my father blow up  the ohms range on what had been a rather nice  (and expensive) analogue meter by believing the labeling on the fuse board and not actually isolating the circuit we were fault finding. I learnt two things that day. 

1) it is really important to double check isolation, labels can be wrong, and

2) some new vocabulary for special occasions..

both lessons remain valuable.

Ah yes the coloured dots.  The Wylex standard for the open wire fuses to BS 3036.

As beloved for all installations from about 1950 to about 1980. Often could look and see if the bit of card with the spare fuse wire wrapped around it had dropped into the box down the gap at the back where the wall is not flat. Of course quite often the wire size you actually need has run out.

so the following often found.

White = 5A  - replace with single strand from off cut of flex. Light fittings, fans clocks and TV amplifier if house has  TV.

Blue = 15 A    replace with 3 of above twisted.  Immersion heater or circuits to outbuildings. Storage heaters and lone sockets converted from round pin ones.

Yellow = 20A  - as above, 15 and 20 are similar, right ?

Red 30A  - rings of sockets, cookers, anything big really,  replace with unbent paper clip.

Green 40A  - they must have a shower or a two cookers on one line. Must go in the slot near the mains switch. Replace with offcut strand from the earth core of the stranded type of ring main cable that we used before 2.5mm.

I fully agree on the pulling things but checking that the  right circuit goes dead. I watched my father blow up  the ohms range on what had been a rather nice  (and expensive) analogue meter by believing the labeling on the fuse board and not actually isolating the circuit we were fault finding. I learnt two things that day. 

1) it is really important to double check isolation, labels can be wrong, and

2) some new vocabulary for special occasions..

both lessons remain valuable.