Well, you've all had time to get used to some other peculiarities of British wiring, so I reckon it's time to stir up some more controversy....
In residential panels, there are three types of overcurrent protection in use at the moment: Rewireable fuses, cartridge fuses, and miniature cct-breakers. It's the first of these I'll describe here.
Rewireable fuses consist of a plug-in porcelain carrier with two contacts, between which a short length of fuse wire (about 2 in.) is fastened with screw terminals. Some later types are a plastic carrier with a ceramic insert.
Just about every hardware store still sells cards of fuse wire: 5, 15, and 30A. Replacement means threading a new length of wire through the carrier. Crude? You bet!
The pre-war types generally had carriers all physically the same for any given model of fusebox, so a householder had to be very careful to check what size needed to be used.
The post-war designs for the then-new "consumer units," adopted marked carriers with different pin spaciing so that, for example, a 30A carrier could not be inserted into a 15A position. Manufacturers also adopted a standard color code for carriers: white=5A, blue=15A, red=30A.
All well & good, but of course that doesn't stop people re-fusing a 5A carrier with 30A fuse wire! I understand a common trick with your Edison-base fuses is to bridge them with a penny; bits of wire or opened out paperclips serve the same purpose on these fuses here.
You may think that these things are relics of early installations, but the rewireable fuse was still being installed in new homes until at least the late 1970s. One manufacturer still makes replacement carriers in 4 sizes (20A (yellow) was added in later years).
There are still MANY of these panels in service, although cartridge fuses or C/B are gradually taking over on rewires.
The IEE has suggested a move away ("deprecated" is their favorite word for this) from rewireable fuses since at least the 1955 edition, but still recognizes them as acceptable.
Did you ever have crude fuses like these before the Edison-base type came along?
In Point Pleasant, WV in a hotel called the "Lowe" there are load centers made of the most beautiful wood, with glass doors and copper busses and K&T wiring... And Fuse Wire for the OCPD...Still in use too!
I will get pics of these the next time I'm there... They really are beautiful works of art!
Tom, Max, (and anyone else) have you guys been there?
-Virgil Residential/Commercial Inspector 5 Star Inspections Member IAEI
Re: British overcurrent protection#132694 09/05/0106:18 AM09/05/0106:18 AM
Cartridge fuses or miniature circuit breakers are now the norm for new work, but it's been a long time coming. Our equivalent to your "load centers" are a somewhat different design, in part because of the 240V 2-W service so we only need one hot busbar instead of two.
Cartridge fuses were used in some better residential installations in the past, and many manufacturers had both types available to fit the same panel for many years.
MEM (Midland Electrical Manufacturing) panels seem to have been very popular in this area in the 1950s-1970s period, and they had interchangeable fuse carriers, so some were upgraded in the 1960s/1970s.
Unfortunately, replacements are no longer available, but if I strip out one of these panels and it has cartridge fuses, I keep the plug-in carriers. That way at least I can sometimes upgrade an old MEM panel to cartridge fuses if the owner doesn't want the expense of a new panel.
Circuit breakers have been available for decades, but rarely used on domestic work until the last 15 years or so. When my father rewired an old pre-war house when I was a kid in 1970 he used breakers; it was probably the only house in the street to have them!
Re: British overcurrent protection#132696 09/05/0111:12 AM09/05/0111:12 AM